UWBGS_Proposers_Day_presentations_20231005.pdf

Ultra-Wide BandGap Semiconductors (UWBGS)

October 5, 2023

Dr. Thomas Kazior Program Manager, MTO

Proposers Day

Ultra-wide bandgap materials – the next revolution in high performance semiconductor technology

Distribution A: Approved for public release; distribution unlimited.

Part 1

Part 2

Agenda

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Start (EDT) Duration Topic/Speaker

8:30 AM 30 min Check-in

9:00 AM 5 min Welcome – Agenda, reminders Dr. Thomas Kazior, DARPA/MTO Program Manager

9:05 AM 10 min Introduction to MTO Dr. Mark Rosker, DARPA/MTO Director

9:15 AM 30 min Program Overview Dr. Thomas Kazior, DARPA/MTO Program Manager

9:45 AM 30 min Challenges and Approaches for P-type and N-type Doping of AlN Prof. Alan Doolittle, Georgia Institute of Technology

10:15 AM 30 min Doping and Low Resistance Contacts on Diamond and c-BN Prof. Robert Nemanich, Arizona State University

10:45 AM 15 min Break

11:00 AM 20 min NRL IV&V Support Dr. Virginia Wheeler, Materials Research Engineer, Naval Research Laboratory

11:20 AM 30 min Contracting Overview Mr. Lon Wang, DARPA/CMO Contracting Officer

11:50 AM 15 min Security Overview Mr. Joey Gilchrist, DARPA/MTO Program Security Representative

12:05 PM 45 min Q&A/Discussion Dr. Thomas Kazior, DARPA/MTO Program Manager

12:50 PM 70 min Lunch Break

2:00 PM 4 hr One-on-One Sessions (by appointment) Dr. Thomas Kazior, DARPA/MTO Program Manager

6:00 PM --- Adjourn

Part 1

Part 2

UWBG* materials enable new classes of high performance devices

Properties Potential Applications

High breakdown strength

• RF electronics

• Power electronics

• High temperature electronics

Good carrier transport electronic properties

High thermal conductivity

Large optical bandgap Deep ultraviolet optoelectronics

Defect quantum spin Magnetometry

*UWBG = ultra-wide bandgap Si = silicon GaAs = gallium arsenide SiC = silicon carbide GaN = gallium nitride AlN = aluminum nitride c-BN = cubic boron nitride

Distribution A: Approved for public release; distribution unlimited.

Source: Naval Research Laboratory

Poor quality of UWBG materials and electrical contacts limit performance of UWBG devices

Substrates (quality*, size)

Device layers (material quality*, doping, junctions)

Electrical contacts (quality*)

Devices (diodes, transistors, passive components, uniformity, reliability, …)

Circuits

Applications

UWBGS

Foundation for ultra-wide bandgap semiconductor electronics

* quality = uniformity, repeatability, low defect density, low contact resistance

UWBGS Goals

0.2

0.4

0.6

0.8

1.00E+021.00E+031.00E+041.00E+051.00E+06

N or m al ize d

Do pi ng E ffi ci en cy

Material Quality (Defect Density) [cm-2]

Diamond

AlN

*Measured doping efficiency / max theoretical doping efficiency UWBG = ultra-wide bandgap Si = silicon GaAs = gallium arsenide GaN = gallium nitride

Program Goals

• Enable UWBG applications by developing foundational, high-quality materials and electrical contacts necessary for realization of practical electronics:

• High quality substrates and device layers

• High doping efficiency

• Low resistance contacts

Si, GaAs, GaN

105 104 103 102 106

Technical Challenges (TCs)

TC1: Creation of large area device quality UWBG substrates

TC2A: Controlled incorporation of electrically active impurities (dopants) in UWBG materials

TC2B: Creation of low defect and abrupt UWBG homo-and hetero-junctions

TC3: Achieving ultra-low resistance electrical contacts to UWBG materials

UWBGS Technical Challenges

UWBG substrate

UWBG substrates

UWBG device layers

Contacts

UWBG test device (diode)

• Technical Challenge 1:

Creation of large area, device quality UWBG substrates

• UWBGS seeks to scale substrate diameter while maintaining low defect density (point defects and dislocations)

UWGBS Goal

100 mm

10 mm

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Technical Challenge 1: Substrates

• Approaches may include but are not limited to:

• Bulk growth using physical vapor transport (PVT)

• Seed expansion techniques such as epitaxial lateral overgrowth

• Seed tiling

• Homo- or heteroepitaxial growth processes

• Innovations in nucleation layers

• Innovations in defect annihilation techniques/processes

• Innovations in reactor design, substrate holders, and growth processes/chemistry

• Innovations in “wafering” (wafer slicing, chemical-mechanical or plasma assisted polishing)

Hexatech Product Datasheet (AlN-30)

50 mm

Today AlNDiamond

• Technical Challenge 2A: Controlled incorporation of electrically active impurities (dopants) in UWBG materials

• Approaches may include but are not limited to:

• Novel epitaxial growth chemistry and growth processes

• Ion implantation

• Innovations in epitaxial reactor design and substrate holders

• Technical Challenge 2B: Creation of low defect and abrupt UWBG homo- and hetero-junctions

• Approaches may include but are not limited to:

• Layer bonding of dissimilar materials to create novel heterostructures

• Co-doping to compensate for carriers and create steep doping gradients

• Innovations in reactor design, substrate holders, and growth processes/chemistry

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Technical Challenge 2: Device Layers

Source: Shutterstock

DAPRA Heterogeneous Heterostructures (H2) µE North Carolina State University

Near ideal bonded p-n junction

N- P+

• Technical Challenge 3: Achieving ultra-low resistance electrical contacts to UWBG materials

• Approaches may include but are not limited to:

• Novel electrical contact processes to add interface materials between contact metals and UWBG material

• N+ regrown contact layers to reduce barrier to current flow

• Refractory metals to improve contact robustness

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Technical Challenge 3: Electrical Contacts

Al0.75Ga0.25N

Metal contact Al0.06Ga0.94N

Compositional grading of UWBG materials

UWBG Semiconductor

N+ Regrown layer

Regrown layer

Metal contact

UWBGS Program Structure and Schedule

Program Kickoff

BAA

July ’24Oct ’23

Technical Area 1: UWBG substrates Technical Area 2: UWBG device layers and electrical contacts

Phase 1 (24 mo) Phase 2 (12 mo)

FY 2026FY 2024

CY 2026

FY 2025

CY 2024 CY 2025

FY 2027

CY 2027

• Substrate quality; size = 50 mm

• Efficient device layer doping

• Abrupt homo/hetero junctions

• Low resistance electrical contacts

• Diode demonstration

• Scale substrates to 100 mm

• Device layer uniformity

• Low defect junctions

• Robust electrical contacts

• Uniform diode demonstration

IV&V: NRL

CY 2023

Milestones/Deliverables for IV&V

UWBG Material and Contact Development UWBG Material and Contact Scaling

UWBGS TA1 Program Metrics (Substrate)

Metric Units SOA Phase 1 Phase 2

Size (1, 2) mm (1) 50 100

Defect density Dislocation (3) Point defects (3, 4)

/cm2

/cm3 (1) (1)

Thermal conductivity (5) W/m-K X (1) 0.95X 0.95X

Surface roughness (6) nm (1) 0.2 0.2

1. Proposer-defined ultra-wide bandgap material with minimum thermal conductivity of 300 W/m-K, with substrate diameter, defect density, thermal conductivity, and surface roughness based on proposer’s baseline material

2. Substrate must be single crystal, 0.5 mm nominal thickness with proposer defined crystal orientation

3. Characterize using performer defined approach such as cathodoluminescence or x-ray topography

4. Point defects include vacancies, interstitials, and impurity atoms

5. Thermal conductivity in vertical and lateral directions at ≤ 100 °C

6. Average surface roughness (Ra) over a 100 µm scan on epi-ready side

UWBGS TA2 Program Metrics (Device Layer and Contacts)

Metric Units SOA Phase 1 Phase 2 Normalized doping efficiency (1, 2, 3, 4) -- < 0.2 0.6 0.9

Material non-uniformity (5) % 50 10 5

Electrical contact resistance (6, 7) Ω-cm2 2 x 10-3 2 x 10-5 2 x 10-6

Test diode ideality factor (8) -- > 2 < 1.5 < 1.1

Test diode non-uniformity (9) % 50 10 5

Test diode Fco (10) GHz 40 400 1000

1. Normalized doping efficiency: measured doping efficiency / maximum theoretical doping efficiency for proposer selected UWBG material system

2. Doping efficiency: electrically conducting carriers / incorporated dopant atoms

3. n- and p-type dopants; controllable carrier concentration ranges as low as 1016 and up to 1019 cm-3, with minimum room temperature thermal conductivity of 50 W/m-K

4. Device layer point defect density (include vacancies, interstitials, and impurity atoms): < 1 x 1016/cm3

5. Proposer defined; for example, sheet resistivity measured across a minimum of a 25 mm diameter wafer in Phase 1 and a 50 mm diameter wafer in Phase 2; minimum 25 data points per wafer; measured on two or more wafers

6. Contact resistance to both n-type and p-type semiconductors

7. Contact resistance must not degrade (< 5% change in contact resistance) under 1000-hour bias stress test; measured on a minimum of 6 electrical contact test structures;

proposer defined bias conditions; bias conditions must reflect a relevant operational environment in a real-world device

8. Proposer defined homo- or hetero-junction diode with breakdown field strength of 4 MV/cm; diode must exhibit abrupt junctions (< 100 nm) with low junction defect density (<

1012/cm2)

9. Diode electrical characteristics (ideality factor, breakdown voltage, leakage current); measured across minimum 25 mm diameter wafer (Phase 1) and 50 mm diameter wafer

(Phase 2), minimum 25 data points /wafer; measured on two or more wafers

10. Diode figure of merit Fco = 1/2πRonCoff

• Proposers should not propose to more than one Technical Area in a single proposal

• Proposers who wish to propose to both Technical Areas must submit a separate full proposal for each individual Technical Area.

• Proposals for Technical Area 1 must address Technical Challenge 1, and proposals for Technical Area 2 must address Technical Challenges 2A, 2B, and 3

• TA1

• UWBG materials with thermal conductivities less than 300 W/m-K are not within the scope of this solicitation

• TA2

• It is expected that, in Phase 2, TA2 performers will need to procure UWBG substrates that meet or exceed the TA1 substrate metrics

Other Considerations

Reports and updates

• Detailed spend plan at program kickoff and execution of subsequent option awards

• Quarterly technical reports

• Monthly technical status updates

• Monthly financial reports including updated expenditures.

• Briefing materials for program kickoff, periodic technical status reviews and program-wide (PI) reviews

• Test data packages for all hardware deliverables Hardware deliverables:

• TA1

• Interim: Minimum of one substrate every 6 months starting 12 months after kick-off

• End of Phase: Minimum of five UWBG substrates

• TA2

• Interim: Minimum of one wafer with device layers, test structure, and test devices every 6 months starting 12 months after kick-off

• End of Phase: Minimum of two wafers with device layers and material, electrical contact resistance and diode test structures

• End of Phase 1 deliverables should be received by government no less than six weeks before end of phase to allow time for IV&V

Deliverables

TA1 (substrate)

• Metrology techniques may include:

• Defect density: cathodoluminescence or x-ray topography

• Surface roughness: Atomic force microscopy (AFM)

• Thermal conductivity: steady state thermoreflectance (SSTR) or laser flash analysis (LFA)

TA2 (device layer and contacts)

• Test articles include:

• Material test structures

• Electrical contact test structures

• Contact resistance measurement

• 1000-hour bias stress test measured on a minimum of 6 test structures

• Diodes

• Homo- or hetero-junction diode with breakdown field strength of 4 MV/cm

• Measured across minimum 25 mm diameter wafer (Phase 1) and 50 mm diameter wafer (Phase 2)

Independent Verification and Validation (IV&V)

• To ensure consistency in characterization, performers are expected to coordinate with IV&V team to define appropriate test structure and metrology techniques for substrate, device layers, electrical contact, and diode characterization

Metrology and Test Articles

Key UWBGS Dates

• Abstract Due Date: November 1, 2023 4:00 pm (ET)

• FAQ Submission Deadline: December 4, 2023 by 4:00 pm (ET)

• Proposal Due Date: December 15, 2023 4:00 pm (ET)

• Estimated period of performance start: July 2024

Agenda

Distribution A: Approved for public release; distribution unlimited.

Start (EDT) Duration Topic/Speaker

8:30 AM 30 min Check-in

9:00 AM 5 min Welcome – Agenda, reminders Dr. Thomas Kazior, DARPA/MTO Program Manager

9:05 AM 10 min Introduction to MTO Dr. Mark Rosker, DARPA/MTO Director

9:15 AM 30 min Program Overview Dr. Thomas Kazior, DARPA/MTO Program Manager

9:45 AM 30 min Challenges and Approaches for P-type and N-type Doping of AlN Prof. Alan Doolittle, Georgia Institute of Technology

10:15 AM 30 min Doping and Low Resistance Contacts on Diamond and c-BN Prof. Robert Nemanich, Arizona State University

10:45 AM 15 min Break

11:00 AM 20 min NRL IV&V Support Dr. Virginia Wheeler, Materials Research Engineer, Naval Research Laboratory

11:20 AM 30 min Contracting Overview Mr. Lon Wang, DARPA/CMO Contracting Officer

11:50 AM 15 min Security Overview Mr. Joey Gilchrist, DARPA/MTO Program Security Representative

12:05 PM 45 min Q&A/Discussion Dr. Thomas Kazior, DARPA/MTO Program Manager

12:50 PM 70 min Lunch Break

2:00 PM 4 hr One-on-One Sessions (by appointment) Dr. Thomas Kazior, DARPA/MTO Program Manager

6:00 PM --- Adjourn www.darpa.mil

18Distribution A: Approved for public release; distribution unlimited.

MTO Ultra-Wide BandGap Semiconductors (UWBGS) Proposer's Day Introduction brief

Mark Rosker, MTO Director

Briefing prepared for UWBGS Proposer’s Day

05 October 2023

Approved For Public Release; Distribution Unlimited

Our mission

C4ISR: Command, Control, Communications, Computers, Intelligence, Surveillance, and Reconnaissance PNT: Positioning, Navigation, and Timing

High-performance, intelligent microsystems and next-generation components

Electronics Resurgence Initiative (ERI) 2.0 timeline

Original ERI ERI 2.0: Reinventing microsystems manufacturing for a new age

FY27FY26FY25FY24FY23FY22

NGMM: Next-Generation Microelectronics Manufacturing program

NGMM Phase 0 BAA August 2022

ERI Summit 2023 August 22-24 / Seattle, WA

UWBGS enables several MTO thrust areas Electronics Resurgence Initiative (ERI)

3D: Three-dimensional AI: Artificial Intelligence

AC

T Increasing the effectiveness of radiation on target

NA

VI

GA

TE

Embedding accurate positioning and timing

SE

E Gaining an advantage in sensing the physical world

TA

LK Securing communications

SE

CU

RE Overcoming security threats across the entire hardware lifecycle

HA

RD

EN Developing electronics for extreme environments

BU

IL

D Manufacturing complex 3D microsystems

CO

M

PO

SE

Optimizing design and test for complex circuits

CO

M

PU

TE Increasing information processing efficiency at the edge

DE

CI

DE Accelerating innovation in AI hardware https://www.darpa.mil/about-us/offices/mto 4Approved For Public Release; Distribution Unlimited

To date, poor quality of UWBG materials and electrical contacts has limited performance of UWBG devices

Substrates (quality*, size)

Device layers (material quality*, doping, junctions)

Electrical contacts (quality*)

Devices (diodes, transistors, passive components, uniformity, reliability, …)

Circuits

Applications

UWBGS

Foundation for ultra-wide bandgap semiconductor electronics

* quality = uniformity, repeatability, low defect density, low contact resistance

UWBGS: Ultra-wide bandgap semiconductors

We’ve been here before…

Source: DARPA / 2005 CS MANTECH conference

UWBG materials will enable new classes of high performance devices

Properties Potential Applications

High breakdown strength

• RF electronics

• Power electronics

• High temperature electronics

Good carrier transport electronic properties

High thermal conductivity

Large optical bandgap Deep ultraviolet optoelectronics

Defect quantum spin Magnetometry

AlN: Aluminum nitride c-BN: Cubic boron nitride GaAs: Gallium arsenide GaN: Gallium nitride

Source: Naval Research Laboratory

RF: Radio frequency Si: Silicon SiC: Silicon carbide UWBG: Ultra-wide bandgap www.darpa.mil

October 4, 2023 1alan.doolittle@ece.gatech.edu

Challenges and Approaches for p-type and n-type Doping of AlN

W. Alan Doolittle, Habib Ahmad, Christopher M. Matthews, Keisuke Motoki, Zachary Engel, and Sangho Lee

Georgia Institute of Technology

DARPA UWBG Industry Day, October 5th, 2023 Supported by ONR – Lynn Peterson (p-type and contacts)

AFOSR - Dr. Ali Sayir (n-type and characterization) and DARPA – Ben Griffin (AlScN)

Extreme Environments

(radiation and heat)

High Temperature Electronics

High Temperature Sensors (electronic, chemical and acoustic)

High Voltage switching, protection and distribution

High Power RF Deep UV LEDs for sterilization, water purification and biological warfare neutralization.

Deep UV Lasers for lithography, atmospheric communications, cutting.

mailto:alan.doolittle@ece.gatech.edu

October 4, 2023 2alan.doolittle@ece.gatech.edu

W. Alan Doolittle, Christopher M. Matthews, Habib Ahmad, Keisuke Motoki, Sangho Lee, Aheli Ghosh, Emily N. Marshall, Amanda L. Tang, Pratyush Manocha, P. Douglas Yoder, “Prospectives for AlN Electronics and Optoelectronics and the Important Role of Alternative Synthesis”, APL Perspectives, Appl. Phys. Lett. 123, 070501 (2023)

H. Ahmad, Z. Engel, C. M. Matthews, S. Lee, and W. Alan Doolittle, “Realization of homojunction PN AlN diodes”, J. Appl. Phys. 131, 175701 (2022)

H. Ahmad, J. Lindemuth, Z. Engel, C. M. Matthews, K. Motoki, W. Alan Doolittle, “Substantial P-type Conductivity of AlN Achieved via Beryllium Doping,” Advanced Materials 33 (42), 2104497, September 2021.

Primary References

October 4, 2023 3alan.doolittle@ece.gatech.edu

Outline Background on AlN Doping

Dopant Impurities Compensating Defects

Why Low Temperature Growth? Metal Modulated Epitaxy Explained Low Temperature Growth does not mean “low quality” Not just “Shuttered Growth” Replaces Temperature with Barrier Lowering/Rapid Growth to Accomplish Diffusion

Control

New Accomplishments Improved P-type (p=4.4x1018 cm-3, 30 cm2/V-sec, 0.04 ohm-cm*) bulk conducting AlN Improved mobility in N-type (n=3x1018 cm-3 , 509 cm2/V-sec, 0.02 ohm-cm*) bulk conducting AlN Temperature Dependent IV of pin AlN Homojunction diode reveals understanding of defect energies and conduction dominance.

Comments on Contact Issues with AlN

* When contact resistance is high, Van de Pauw anomalies for AlN result in ~10x lower values than this but are suspect.

October 4, 2023 4alan.doolittle@ece.gatech.edu

Material EG (eV)

Vsat (107 cm/s)

Ecrit @ 1016 cm-3

(MV)

Thermal Conductivity

(W/m-K)

Johnson

FOM

(1012 V/S)

~VBreak @ 10 mW cm2 (V)

Available Substrate? N-type? P-type?

Light Emission

Si 1.12 1.0 0.3 145 0.48 100 Yes Yes Yes No

SiC 3.26 3.1 490 3000 Yes Yes Yes No

GaN 3.45 1.4 4.9 253 11 5000 Almost Yes Yes Yes β-Ga2O3 4.8 1.1 10.3 27 18 6000 Yes Yes No No

AlN (Parameter

Rank)

6.1 (#1)

1.3 (#2)

15.4 (#1)

(#2)

(#1)

20,000 (#2)

Yes Yes This

Work!

Yes This

Work!

Yes

Motivation: AlN Ranks in the Top 2 in All Major UWBS Performance Parameters

• In all performance predictors, AlN is either the best or a close second to other semiconductors with a 2” diameter substrate.

• The critical electric field of AlN is:

• ~1.5x Ga2O3 (3x if you consider Ga2O3 can only use Schottky rectifiers)

• ~3x GaN

• ~5x SiC.

• Up to now, the major limitation for AlN PIN diodes was the lack of doping.

We achieved substantial conductivity with p-type AlN:Be films and n-type AlN:Si films grown via metal modulated epitaxy (MME).

Adv. Electron. Mater. 2018, 4, 1600501

October 4, 2023 5alan.doolittle@ece.gatech.edu

Justifying New Investment:

Will it Pay Off in Multiple Applications?

Extreme Environments

(radiation and heat)

High Temperature Electronics

High Temperature Sensors (electronic, chemical and acoustic)

High Voltage switching, protection and distribution

High Power RF

Deep UV LEDs for sterilization, water purification and biological warfare neutralization.

Deep UV Lasers for lithography, atmospheric communications, cutting.

Earth Background Radiation

Solar Background Radiation

Black Body

Atmosphere Filtered

0.

Solar Blind Detection

GaNAlN

Optical Applications

Electrical Applications

October 4, 2023 6alan.doolittle@ece.gatech.edu

Dopant Theory

Experimental Surface / Near Surface

Experimental Bulk

Mg p-type

• 580 meV (Y. Zhang et al. Phys. Rev. B - Condens.

Matter Mater. Phys., vol. 77, p. 035201, 2008 )

• 510 meV (K. Nam et al. Applied Physics Letters, vol.

83, p. 878, 2003).

• 630 meV (Taniyasu et al. Nature, vol. 441, p. 325, 2006)

No prior success No prior success

C p-type

Various • K. Kishimoto, M. Funato, Y.

Kawakami, Applied Physics Express 2020, 13, 015512.

• Large Surface Sheet Charges

No prior success

Be p-type

• 220-262 meV F. Mireles et al. Physical Review B. 58 (7), 3879, 1998.

• 330 meV A. Sedhain et al. Applied Physics Letters, vol. 93, p. 141104, 2008

• 340 meV R. Q. Wu et al. Appl. Phys. Lett., vol. 91, p.

152110 , 2007.

No prior success No prior success

Si n-type

• L. Gordon, J. L. Lyons, A. Janotti, C. G. van de Walle, Physical Review B - Condensed Matter and Materials Physics 2014, 89, 085204

• I. Bryan, et al, Appl. Phys. Lett. 2018, 112, 062102.

• Provides key incite into compensating defect structures: DX center and Al vacancies

• M. H. Breckenridge, et al, Appl.

Phys. Lett. 2020, 116, 172103.

• M. H. Breckenridge, et al, Applied Physics Letters 2021, 118, 112104.

• High doping via ion implantation suggests Si is not the limitation but defect compensation is.

• M. L. Nakarmi, et al, Applied Physics Letters 2004, 85, 3769.

• T. Ive, et al, Applied Physics Letters 2005, 86, 024106.

• N ~ 1015 cm-3 Maximum

O

• G. A. Slack, J. Phys. Chem. Solids. 1973, 34, 321 showed O is an important compensating defect forming a DX center and aggravated by Al vacancies

Key Prior AlN Doping and Defect Work

Here:

p=3.1x1018 cm-3

Here:

n=6.1x1018 cm-3

Update:

p=4.4x1018 cm-3

October 4, 2023 7alan.doolittle@ece.gatech.edu

Pathway for Doping Success:

Takeaway

• Vacancies, lattice expansion (temperature increases) and O impurities lead to compensation of carriers.

• Vacancy concentrations and thus, compensation, is reduced by many orders of magnitude at low temperature!

Use lowest strain element possible (Be).

• Be requires low substrate temperatures to avoid Be runaway.

• Absolutely critical to avoid oxygen

(low temperature).

• Oscillate from N-rich to Metal Rich

• Avoid N-rich to improve crystal quality.

• Prefer N-rich for chemistry

• Avoid vacancies (low temperature).

• Use Al-rich conditions (avoid Al vacancy that complexes with Si)

• Avoid lattice expansion that aggravates Si c-axis bond breakage that forms the compensating DX center low temperature.

• Avoid vacancies (low temperature).

• Low Temperature (low outgassing of O and small lattice expansion) environment is critical.

October 4, 2023 8alan.doolittle@ece.gatech.edu

The Science Behind the Heresy

• Thermal Energy is not required for good epitaxy. Large surface diffusion lengths are!

• MBE of epitaxial Aluminum is performed at 100º C or less

• MBE of epitaxial AlN is performed at 800º C - 1400º C (or more)

• Surface Bond Strength Dominates Over Temperature in Epitaxy

Hopping Rate = 𝜔𝜔e−∅/kT

Exponential Dependence on Temperature

Exponential Dependence Surface Barriers φ

Binding Energy φ

Binding Energy

Replacing the Strong Bonds in Wide Bandgap Semiconductors with Weak Metal Bonds

Increases Diffusion Even at Low Temperatures

Vibration Frequency ~1013 Hz (slightly T dependent)

Surface Diffusivity = 𝑎𝑎2 𝜔𝜔 e−∅/𝑘𝑘𝑘𝑘

Do

Strong Bonds in Wide Bandgap Semiconductors Cause Desorption and Diffusion to be Competitive

October 4, 2023 9alan.doolittle@ece.gatech.edu

The Science Behind the Heresy

• Thermal Energy is not required for good epitaxy. Large surface diffusion lengths are!

• MBE of epitaxial Aluminum is performed at 100º C or less

• MBE of epitaxial AlN is performed at 800º C - 1400º C (or more)

• Surface Bond Strength Dominates Over Temperature in Epitaxy

Hopping Rate = 𝜔𝜔e−∅/kT

Exponential Dependence on Temperature

Exponential Dependence Surface Barriers φ

Binding Energy φ

Binding Energy

Replacing the Strong Bonds in Wide Bandgap Semiconductors with Weak Metal Bonds

Increases Diffusion Even at Low Temperatures

Vibration Frequency ~1013 Hz (slightly T dependent)

Surface Diffusivity = 𝑎𝑎2 𝜔𝜔 e−∅/𝑘𝑘𝑘𝑘

Do

Strong Bonds in Wide Bandgap Semiconductors Cause Desorption and Diffusion to be Competitive

CVD Solution: Go to High Temperatures Byproduct: Enormous vacancy concentrations

Compensation [Vacancies]=[Natomic ]e-E/kT

October 4, 2023 10alan.doolittle@ece.gatech.edu φ based on reported values for GaN in:

J. Neugebauer, T. K. Zywietz, M. Scheffler, J.E. Northrup, H. Chen, and R.M. Feenstra, Phys. Rev. Lett. 90(5), 056101 (2003).

J. Neugebauer, T. K. Zywietz, M. Scheffler, and J. E. Northrup, Appl. Surf. Sci. 159–160, 355–359 (2000).

N-Terminated Al-Polar AlN

Al-Terminated Al-Polar AlN

Al-Bilayer Terminated Al-Polar AlN φ ≈1.4-1.8 eV φ ≈ 𝟎𝟎.𝟕𝟕 eV φ ≈ 𝟎𝟎.𝟏𝟏𝟏𝟏 eV

Comparison of Surface Diffusion Barriers on GaN

Metallic bilayers reduce the diffusion barrier significantly.

Modified Images after: C. D. Lee, Y. Dong, R. M. Feenstra, J. E. Northrup, J. Neugebauer, Phys. Rev. B 68, 205317 (2003)

October 4, 2023 11alan.doolittle@ece.gatech.edu

0.000

0.001

0.010

0.100

1.000

10.000

1E+06

1E+07

1E+08

1E+09

1E+10

1E+11

1E+12

1E+13

0 200 400 600 800 1000 1200

Du ff us io n Le ng th

[µ m

Ho pp in g

Fr eq ue nc y [H z]

Substrate Temperature [C]

0.12 eV N adatom Buried in Ga Bilayer

0.7 eV N adatom on Ga-Rich Surface

1.4-1.8 eV Ga adatom on N-Rich Surface

The Science Behind the Heresy

• Adatom diffusion is orders of magnitude faster for metallic surfaces than semiconductor surfaces.

• Diffusion lengths longer than 1 um obtained.*

• Metallic surfaces have several advantages:

• Adatom diffusion is almost constant with temperature

• Approaching the “mobility regime” where φ/kT ~1

• Leads to improved control of the epitaxy process especially for ternaries.

* Hopping rates assume ω=1013 Hz, and φ based on reported values in:

J. Neugebauer, T. K. Zywietz, M. Scheffler, J.E. Northrup, H. Chen, and R.M. Feenstra, Phys. Rev. Lett. 90(5), 056101 (2003).

J. Neugebauer, T. K. Zywietz, M. Scheffler, and J. E. Northrup, Appl. Surf. Sci. 159–160, 355–359 (2000).

Diffusion lengths assume 1 um/hour growth rates which define the time before overgrowth inhibits diffusion.

October 4, 2023 12alan.doolittle@ece.gatech.edu

Metal Adlayer III-Nitride Film

Group III source

Shutter

Metal Flux N flux

• Extremely metal-rich fluxes (1.3-3x greater than stoichiometric point)

• Tsub ~ 600 °C growth avoids intermediate regime

• Enhanced adlayer mobility from bilayer

• Consumes droplets into film on shutter close

• Growth rate up to 10 µm/hour and beyond!

Metal-Modulated Epitaxy

October 4, 2023 13alan.doolittle@ece.gatech.edu

0.19 nm RMS at 600 °C

Metal Adlayer III-Nitride Film

Group III source

Shutter

Metal Flux N flux

Atomically Smooth Surfaces at Low

Substrate Temperature

Metal-Modulated Epitaxy

October 4, 2023 14alan.doolittle@ece.gatech.edu

RMS Roughness:

0.73 nm

33 34 35 36 37 38 39 In te ns ity

2 Theta - Omega

Tsub = 400 oC

Tsub = 650 oC

Theoretical peak position for Sc0.18Al0.82N

33 34 35 36 37 38 39

In te ns ity

2θ−ω (Degrees)

002 RC FWHM: 250 arcsec

ScAlN 105 RC FWHM: 469 arcsecGaN

ScAlN

GaN

• Proper control of metal buildup allows for the growth of ScAlN under metal rich conditions without loss of phase purity.

• A significant catalytic effect is observed in growth with Sc. A 2-3x increase in growth rate is observed in ScN growth vs AlN.

• Excellent electrical performance is demonstrated, with a sheet charge as high as 5.9x1013 cm-2 and a sheet resistance as low as 152 Ω/□

002 RC FWHM: 229 arcsec

Sheet Resistance Mobility Sheet Charge

20nm ScAlN/GaN

HEMT Structure 152 Ω/□ 700 cm2/vs 5.9x1013 cm-2

State of the Art AlScN/GaN Sheet Resistance and Experiment Matches Theoretical Sheet Charge

October 4, 2023 15alan.doolittle@ece.gatech.edu

𝑵𝑵𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪𝑪 =

𝟎𝟎.𝟏𝟏

𝑪𝑪

𝟑𝟑

1018 1019 1020 1021101710161015

Mechanism: Kinetics of Non-equilibrium Growth Forms Acceptor Impurity Band

Fischer and Doolittle et al. Phys. Status Solidi B, 254 (8), 1600668 (2017)

𝑪𝑪 =

𝟒𝟒𝟒𝟒𝝐𝝐𝑹𝑹𝝐𝝐𝒐𝒐 ħ𝟏𝟏 𝒎𝒎𝒉𝒉 ∗𝒒𝒒𝟏𝟏

CB

CH Γ7

HH Γ9LH Γ7

AlN

Hopping

Impurity BandEA

EV

EC

ND

W. Alan Doolittle, C. M. Matthews, H. Ahmad, K. Motoki, S. Lee, A. Ghosh, E. N.

Marshall, A. L. Tang, P. Manocha, P. D. Yoder, APL Perspectives, Appl. Phys. Lett. 123, 070501 (2023)

October 4, 2023 16alan.doolittle@ece.gatech.edu

CB

CH Γ7

HH Γ9LH Γ7

CB

CH Γ7

HH Γ9LH Γ7

AlN GaN

AlN Has Anomalous Valence Band Structure

• In contrast to GaN, the highest-lying valence band in AlN is the split-off band, which exhibits smaller effective mass.

• Vertical devices (mp*=0.24mo)

• Lateral device (mp*=3.66mo)

• Results: 0.04 ohm-cm p-type AlN

GaN AlN µ∼1-3 cm2/V-sec @ p~4x1018 cm-3 µ=30 cm2/V-sec @ p=4.4x1018 cm-3 m*p ≈ 0.8 mo m*p ≈ 0.24 mo Ncritical ≈

4 × 1019 cm-3 Ncritical ≈

1.2 × 1018 cm-3 W. Alan Doolittle, C. M. Matthews, H. Ahmad, K. Motoki, S. Lee, A. Ghosh, E. N. Marshall, A.

L. Tang, P. Manocha, P. D. Yoder, APL Perspectives, Appl. Phys. Lett. 123, 070501 (2023) mp*=3.66mo mp*=0.24mo

DFT Valence Band Structure (Compliments of Doug Yoder, Ga Tech)

October 4, 2023 17alan.doolittle@ece.gatech.edu

Growth of Homojunction MME AlN PIN Diode

MSES HVPE AlN on sapphire substrate

1 µm MME AlN:Si 8×1018 cm-3 at Tsub=800 °C n-contact

200 nm MME AlN:Be 7×1018 cm-3 at Tsub=700 °C p-contact

200 nm MME AlN:Si 5×1017 cm-3 at Tsub=800 °C

Corresponding electron concentration 5×1017 cm-3

Corresponding hole concentration 1×1018 cm-3

Corresponding electron concentration was unmeasurable by Hall

• The current levels of plasma etched n-type AlN:Si contacts in the PIN diode are lower by 2-3 orders of magnitude than contacts to as grown material.

• Presumably due to difficulty in making contacts to the plasma damaged AlN films.

• Introduces high series resistance into the device.

N-type AlN Planar As-

Grown Film 1x1 cm2 AlN

N-type AlN Etched Device

TLM

~10’s um

October 4, 2023 18alan.doolittle@ece.gatech.edu

First-ever AlN Homojunction Diodes

• ~6-7 orders of magnitude small reverse to large forward rectification is achieved.

• We achieved a nearly ideal turn-on voltage of ~6V for a 6.1 eV semiconductor.

• A high series resistance is also evident by the current density tail on the semilog plot.

• This high series resistance is attributed to the high etched/damaged N-contacts resistance.

• Contacts improvement will further improve the performance of these devices.

H. Ahmad, Z. Engel, C. M. Matthews, S. Lee, and W. Alan Doolittle, J. Appl. Phys. 131, 175701 (2022)

October 4, 2023 19alan.doolittle@ece.gatech.edu

25°C

300°C

Current-Voltage-Temperature Study Shows improved Performance at ~575ºK

• Diodes show improved IV at higher temperature

– Series resistance dominates IV but reduces by 70x

– Exponential IV after turn on

• Current Density is greater than 2.8 A/cm2

0.0

0.5

1.0

1.5

2.0

2.5

3.0

0 4 8 12 16 20 24 28 32 36

Cu rr en t D en si ty [A

/c m

2 ]

Voltage [V]

25 C 50 C 75 C

100 C 125 C 150 C

175 C 200 C 225 C

250 C 275 C 300 C

@577K Rseries=7.8 Ω−cm2

@300K Rseries=2280 Ω−cm2

Origin of this anomalous kink?

October 4, 2023 20alan.doolittle@ece.gatech.edu

Initial Growths: Source of and Solution for Non-Ideal IV

Two-beam <1 -1 0 0>: Highlights edge type dislocations and stacking faults

Two-beam <0 0 0 2>: Highlights screw type dislocations

Zone axis [1 1 -2 0] highlights all defects (edge, screw and stacking faults)

Al-Oxide related contamination result in interfacial stacking faults and edge dislocations lowering crystal quality

October 4, 2023 21alan.doolittle@ece.gatech.edu

Two-beam <1 -1 0 0>: Highlights edge type dislocations and stacking faults

Two-beam <0 0 0 2>: Highlights screw type dislocations

Zone axis [1 1 -2 0] highlights all defects (edge, screw and stacking faults)

Flashing removes all oxygen related stacking faults and results in duplication of the template’s crystal quality

Improved Growths: Solution for Non-Ideal IV

October 4, 2023 22alan.doolittle@ece.gatech.edu

Source of and Solution for Non-Ideal IV

Two-beam <1 -1 0 0>: Highlights edge type dislocations and stacking faults

Two-beam <0 0 0 2>: Highlights screw type dislocations

Zone axis [1 1 -2 0] highlights all defects (edge, screw and stacking faults)

Two-beam <1 -1 0 0>: Highlights edge type dislocations and stacking faults

Two-beam <0 0 0 2>: Highlights screw type dislocations

Zone axis [1 1 -2 0] highlights all defects (edge, screw and stacking faults)

1E-08

0.0000001

0.000001

0.00001

0.0001

0.001

0.01

0.1

0 5 10 15 20 25 30 35

Cu rr en t D en si ty [A

/c m

2 ]

Voltage [V]

Unflashed N4633 Flashed Best Flashed Typical

Flashing removes all oxygen related stacking faults and results in duplication of the template’s crystal quality

Al-Oxide related contamination results in interfacial stacking faults and edge dislocations lowering crystal quality

• Metallic aluminum cleaning drastically reduces defect density.

– Virtually eliminates stacking faults and thus, edge dislocations.

– No increase in screw dislocations

– Improved forward IV

October 4, 2023 23alan.doolittle@ece.gatech.edu

Ln(J) = +0.0816x - 6.0712

Ln(J) = -0.0214/kT - 9.8092

Ln(J) = -0.1453/kT - 4.5098 ln(J) = -0.505/kT + 4.5396

Ln(J) = -0.0148/kT - 10.723

Ln(J) = -0.444/kT + 0.8981 y = -0.3043x + 6.5431

Ln(J) = -0.2245/kT + 1.6496

-12

-10

-8

-6

-4

-2

15 20 25 30 35 40

Ln (J

A/ cm 2 ]

1/kT [1/eV]

@6V

@0.75V

@4.4V

@20V

@6V

@0.75V

@4.4V

@20V

@-10V 1E-11

1E-10

1E-09

1E-08

1E-07

1E-06

1E-05

1E-04

1E-03

1E-02

1E-01

1E+00

1E+01

0 5 10 15 20 25 30

Cu rr en t D en si ty [A

/c m

2 ]

Voltage [V]

25 C 50 C 75 C

100 C 125 C 150 C

175 C 200 C 225 C

250 C 275 C 300 C

Current-Voltage-Temperature Study Shows Improved Performance at ~575ºK

• Dominant current mechanisms:

– Possibly tunneling at low voltage

– Thermionic via defect/impurity character around turn on

• Two separate activation energies below and above 200º C

– Series resistance EA=0.3 eV

October 4, 2023 24alan.doolittle@ece.gatech.edu

1E-04

1E-03

1E-02

1E-01

1E+00

1E+01

1E+02

1E+03

1E+04

1E+05

1E+06

1E+07

1E+08

1E+09

1E+15

1E+16

1E+17

1E+18

1E+19

1E+20

1E+21

1E+22

0 0.5 1 1.5 2 2.5 3

Se co nd ar y io n in te ns ity (c ou nt s/ se c)

C on ce nt ra tio n (A to m s/ cm

3)

Depth (µm)

N4506

Al->

Be jd035i1_N4506

[Be] too High. Polarity Inversion leads to reduced incorporation on N-face (same as for

Slope = d[Be]/dx = 3.5x1021/um

Be Solubility and Abrupt Profile Control

• Be solubility in AlN seems to be ~1020 cm-3

• Be can be accurately placed with no surface accumulation for MME (not true for MBE)

• Similar (slightly higher) values expected for Si (solubility limit not yet reached)

October 4, 2023 25alan.doolittle@ece.gatech.edu φB=0.6 eV

Modeling AlN Contacts: What to Expect

• Planar transistor ohmic contacts are more straight forward than quasi-vertical devices.

• Plasma etched contacts are atrocious and may offer a clue as to what is making the doping work.

• Electron Affinity Model (EAM) is a guide and not always valid.

• Predicts difficulty for n-type AlN since AlN has an electron affinity <2 eV.

• The measured AlN electron affinity has not been measured in doped AlN.

• Surface oxides complicate the known values of the electron affinity.

• Contacts (Ti for example) often introduce a n+ region to facilitate Thermionic-Field Emission

• In practice, Field-Emission is not reached in many wide bandgaps (requires >1020 cm-3 doping).

• Literature reports of UWBG Contact Resistance < 10-6 Ω-cm2 are questionable and can only be possible with non-standard means.

N-type Si P-type Si

Si images after Schroeder

October 4, 2023 26alan.doolittle@ece.gatech.edu φB=0.6 Ev (Si) Proven φB=0.6 eV (GaN) Proven φB=0.6 eV (AlN) Barrier Height predicted by EAM may not be achievable φB= ~2.2 eV (AlN:Ti)

Modeling AlN Contacts: To Achieve DARPA Goals, High Doping and Non-Standard Approaches are

Likely to Be Needed

• Doping and barrier height dominates over other all other material parameters when determining contact resistance.

• As bandgap increases, the EAM suggests DARPA goal is challenging.

• Solutions exist but require non-standard approaches.

October 4, 2023 27alan.doolittle@ece.gatech.edu

Progress Toward an AlN Transistor

• New contact strategies being addressed

• 356 mA/mm for n-type AlN @ 10V

• 37 mA/mm for p-type AlN @ 30V

• Fabrication limited not fundamentally limited

October 4, 2023 28alan.doolittle@ece.gatech.edu

Summary Conclusions

• Low temperatures are a viable option for synthesis of AlN devices

– Less thermal expansion limits DX centers

– Lower outgassing of compensating impurities

– Compatible with dopants that can lower strain and decrease interstitial formation

• Device quality and State-of-the-Art Devices have been produced

• p-type AlN – p=4.4x1018 cm-3!

• First AlN PIN Diodes!

• 6000x improvement in n-type AlN

• n= 1x1015 cm-3 6x1018 cm-3!

• The Electron Affinity Model predicts difficulty for good ohmic contacts to

UWBGS

• But creative solutions exist…

Doping and Low Resistance Contacts on Diamond and c-BN

Robert J. Nemanich, Franz A. Koeck, Terry Alford, Stephen Goodnick, David Smith, Trevor Thornton

Arizona State University

In collaboration with Northrop Grumman Corp.

Cubic Boron Nitride (c-BN)

• sp3 bonded BN

• B - 5e; N – 7e

• Zinc Blende a = 3.62 Å[2]

Diamond Cubic

• sp3 bonded carbon

• C – 6e

• Diamond Cubic a = 3.57 Å

• sp3 bonded Al-N

• Al - 13e; N – 7e

• Wurtzite structure

• a = 3.11 Å

• c = 4.93 Å

G. L. Doll, J. A. Sell, C. A. Taylor II, and R. Clarke, Phys. Rev. B, 43, 6816 (1991).

Wurtzite AlN (BxAl1-xN)

ULTRA Semiconductors

HexaTech 50 mm

Augsburg Univ.

DiamFab

Wide Bandgap Properties

Wide Bandgap Semiconductor Properties

J. Tsao et al., Adv. Electron. Mater. 2017, 1600501. DOI: 10.1002/aelm.201600501

Interface character:

cubic/hexagonal, covalent/ionic, polar/non-polar

N 1.7 eV

B 0.37 eV

P 0.6 eV

Diamond

5.45 eV

Be, Mg, Zn

0.23 eV

Si, S 0.24-

0.30 eV c-BN

6.4 eV

Diamond for High Power Applications pulsed

DC

• 𝐼𝐼𝑀𝑀𝑀𝑀𝑀𝑀 = ~1.35 𝐴𝐴

• 𝐽𝐽𝑀𝑀𝑀𝑀𝑀𝑀 = ~116 𝑘𝑘𝐴𝐴/𝑐𝑐𝑚𝑚2

• 𝐼𝐼𝑂𝑂𝑂𝑂/𝑂𝑂𝑂𝑂𝑂𝑂 = 6 × 1012

• Maximum Power = ~1.9 𝑀𝑀𝑀𝑀/𝑐𝑐𝑚𝑚2

• Minimum 𝑅𝑅𝑂𝑂𝑂𝑂𝑆𝑆 = ~5 × 10−5Ω. 𝑐𝑐𝑚𝑚2

Pseudo-Vertical Diamond SPIND

H. Surdi et al., IEEE Trans. Elect. Dev. 69, 254 (2022)

RF Characterization of Diamond Schottky p-i-n Diodes for Receiver Protector Applications Harshad Surdi, Mohammad Faizan Ahmad, Franz Koeck, Robert J.

Nemanich, Stephen Goodnick , and Trevor J. Thornton IEEE Microwave and Wireless Components Letters 30, 1141 (2020)

Substitutional Doping:

n-type Diamond using Phosphorus

Diamond Doping

*K. Oyama, et al, APL 94, 152109 (2009)

1×1018 cm-3

8×1019 cm-3

1×1018 cm-3

2×1020 cm-3

P-doping nearest neighbor hopping B-doping variable range hopping

N 1.7 eV

B 0.3 eV

P 0.6 eV

Diamond Bandgap 5.45 eV

Hathwar et al., J. Appl. Phys. 119, 225703 (2016) 8

H. Kato et al., Diam Relat Mater. 27, 19 (2012) Hathwar et al., J. Appl. Phys. 119, 225703 (2016)

P-doping nearest neighbor hopping B-doping variable range hopping

N 1.7 eV

B 0.3 eV

P 0.6 eV

Materials Enabled by Plasma Enhanced Chemical Vapor Deposition (PECVD)

Substrate

Reactants

H2, CH4

Diamond Film

Plasma H2 microwave 2H

CH4 + H CH3 + H2

thermal

½ inch

Semiconductor Diamond Devices through Doped Diamond

Microwave plasma enhanced CVD for n-type, phosphorus doped diamond

Temperature controlled Mo block

Mo disk Diamond plate

Mo holderPlasma Growth Challenges:

• Separate control of temperature and plasma power (sample holder design*)

• Control the active species at the surface

(in situ RGA)

• Reduce impurities (compensation)

• Surface morphology:

Starting surface Step flow growth (off axis sample)

Approach:

In situ RGA, pyrometer, and OES Ex situ SIMS, optical microscopy, TEM

*Koeck, Franz A., and Robert J. Nemanich. "Sample stage/holder for improved thermal and gas flow control at elevated growth temperatures." U.S. Patent 10,704,160, issued July 7, 2020.

½ inch Separate plasma power and substrate temperature (Tn).

T1 T2<T1

Materials Enabled by Plasma Enhanced Chemical Vapor Deposition (PECVD)

Establishing impurity background levels (N) Fast response (~second) for time resolved characterization of growth species ↔ comparison with OES

Important for controlling the doping gradient /profile

Start End

Phosphorus Doping

In situ characterization for PECVD

Stability

PH

RGA at ~10-5 Torr

OES /

Optical Emission Spectroscopy

(OES)

Epitaxy of P-Doped Diamond

S. Ohmagari et al. / Journal of Crystal Growth 479 (2017) 52–58

Desorption of P-admolecules:

lifetime of P-admolecules (τ) is shorter than time required for terrace overgrowth (tcover)

Incorporation of P-admolecules:

(τ) is longer than tcover (= w/Rlateral)

Controlled P-Doping with Plasma Enhanced CVD

Optical microscopy identifies a step-flow growth mode.

Substrate: IIa CVD (111) plate Phosphorus doping source:

200ppm trimethylphosphine (TMP) in H2

Correlation of the phosphorus doping concentration to the growth temperature (Pyrometer) doping species (PH)

How do surface properties affect the phosphorus incorporation?

What phenomena drive a step-flow growth mode?

Phosphorus doped diamond growth was characterized In situ by pyrometer for growth temperature RGA (OES) for gas chemistry characterization (PH) and SIMS was performed to evaluate the phosphorus doping concentration.

Electrical Contacts to P-doped Diamond

Low work function contacts to n-type UWBS is complicated

Electron Contacts to UWBS

Surface states (or CNL) on diamond and AlN (and c-BN) can pin the interface Fermi level providing a large Schottky barrier that limits electron injection.

*K. Oyama, et al, APL 94, 152109 (2009)

1×1018 cm-3

8×1019 cm-3

1×1018 cm-3

2×1020 cm-3

P-doping nearest neighbor hopping B-doping variable range hopping

N 1.7 eV

B 0.3 eV

P 0.6 eV

Hathwar et al., J. Appl. Phys. 119, 225703 (2016) 17

Diamond Contacts

N 1.7 eV

B 0.3 eV

P 0.6 eV

Diamond Bandgap 5.45 eV

T. Matsumoto, Ch 4.2 Schottky and ohmic contacts on diamond, Power Electronics Device Applications of Diamond Semiconductors, (2018). 18

Electron Contacts to UWBS

UWBS surface

N-type Interlayer

UWBS surface

Metal Layer Metal Layer

SBUWBS surface

Metal Layer

N-type Tunneling Surface

Electron Contacts to UWBS

Diamond surface

N-doped Nano-carbon

Interlayer

AlN surface

Metal Layer Metal Layer

SBUWBS surface

Metal Layer

N-type AlGaN

Nanostructured carbon (nanoC) layer Dedicated PECVD

Parameter Growth Hydrogen [sccm] 5 Methane [sccm] 20 Nitrogen [sccm] 100 Argon [sccm] 10 µ-wave [W] 900 Pressure [torr] 20 Pyrometer [°C] 900 Time [min] 20

Argon chemistry for re-nucleation process.

Significant nitrogen addition.

Growth Parameters

SIMS

TLM

SEM

Film Morphology

Nanostructured Carbon Contact Layers

Contact Strategy

Nitrogen incorporation (SIMS) >3x1020 cm-3

Nanostructured carbon layer with a thickness of ~200nm.

TLM characterization to derive contact resistance for Ti/Pt/Au metallurgy

Contact resistivity of ~10-3 Ω cm2 suitable for devices.

Electron Contacts to UWBS

Diamond surface

N-doped Nano-carbon

Interlayer

Metal Layer

Electron Contacts to UWBS

SIMS profile showing phosphorus concentration in diamond film.

Comparing the specific contact resistivity for moderately P-doped diamond films

[5] Teraji et al, JJAP L1096 (1999) [20] Teraji et al, APL 1303 (2000) [21] Teraji et al, JJAP L882 (2003) [21] Takemasa et al, ECS Trans, 491 (2014)

Plasma Enhanced CVD of c-BN

Density (gm/cm3)- 3.48 3.47 2.2 2.26 Bonding sp3 sp3 sp2 sp2

Boron Nitride Crystalline Phases

N. Izyumskaya et al., Adv. Electron. Mater. 3, 1600485 (2017) c-BN Growth

BBBB

N N

H

N

H H

NNNN

B B

F

B

F F

H F H F

N*

• H or F proposed for abstraction of H from N surface sites.

• H or F plus impinging ions proposed to abstract F from B surface sites.

Nucleation of Epitaxial c-BN

Ratio of H2 to BF3 is critical to the deposition of c-BN or h-BN

J. Brown, et al., J. Appl. Phys 133, 215303 (2023)

Hydrogen defects h-BN

Precursors Plasma Surface c-BN / w-BN – Diamond (111)

BN film thickness ~ 160 nm c-BN / w-BN – Diamond (111)

EELS at BN – Diamond Interface c-BN – Diamond PIN n-type c-BN p++ Diamond p- Diamond

C-B

D. Zhao, et al, RSC Adv. 9, 8435-8443 (2019). DOI:10.1039/c9ra00784a 30

Summary and Status

• Substitutional doping and hopping conduction enables PiN diodes.

• In situ characterization for real time control of n-type doping in diamond.

• Contact strategy including doping and nano carbon interlayer.

• Synthesis of c-BN epitaxy through control of gas phase precursors and plasma conditions.

• Synthesis of both cubic and hexagonal BN (control of precursors).

• P-i-N diode proposed with p-diamond and n-type c-BN.

Funding Acknowledgment

• Department of Energy through the ULTRA Energy Frontier Research

Center (ULTRA EFRC)

• DARPA – through Northrop Grumman seedling project

• NSF/DARPA – Electrons in Diamond project

NRL IV&V Capabilities

Ginger Wheeler

Eric Jin, James Champlain, Andrew Lang, Brian Downey, David Meyer

UWBG Proposer Day

Oct. 5th, 2023

Evaluation for UWBG Program Overview of Capabilities:

• X-ray diffraction to determine substrate orientation and offcut

• Chemical etching to determine dislocation density

• X-ray topography to determine extended defect/dislocation density and resulting strain fields

• Photoluminescence to identify the presence and density of point defects

• Raman spectroscopy to identify the presence of subsurface damage and uniformity of strain

• Transmission electron microscopy to identify extended and point defects, lattice constants, and chemical information from EELS/EDX

• X-ray photoelectron spectroscopy detect any surface impurities, stoichiometry of layers, band offsets, etc.

• Atomic force microscopy to determine surface roughness and topography

• Wafer curvature measurements to determine substrate bow

• Steady-state thermoreflectance and/or laser flash analysis to determine thermal conductivity

• Contactless sheet resistance measurements to determine electrical resistivity

• C-V, I-V, Hall electrical measurements to measure sheet resistance, carrier concentrations/dopant efficiency, interface trap densities, breakdown voltage, etc.

• Small signal RF measurements to measure diode figure of merits

Material Structure-Property Characterization

Rigaku 9 kW monochromated SmartLab Diffractometer with rotating copper anode

• High resolution rocking curve measurements (12 arcsec resolution)

• Rocking curve X/Y wafer maps

• Offcut and offcut maps

• Wafer scale measurements

Thermal Fischer DXR Raman System

• 532 and 455 nm lasers

• High resolution stage mapping – ideal spatial resolution 0.5um

• Confocal depth resolution 1.7um

Vendor 1 Vendor 2 Vendor 3

Coherent Deep UV photoluminescence system

• 192 nm lower resolution achieved via 4th harmonic

• Identify band edge and mid gap defects in UWBG materials

• Quantification can be done but must careful calibrate and run system

• Can use CL for comparison and different depth of defects

High resolution X-ray topography measurements (N. Mahadik)

• Transmission geometry using Mo Kα radiation

• Reflection geometry using Cu Kα radiation – pentration depth 15μm

• Lattice curvature and dislocations can be mapped

Nion UltraSTEM 200X

• Aberration-corrected dedicated STEM w/

<100 pm resolution

• Single atom composition - EDS

• Plasmon and core-shell spectroscopy -

EELS

• Merlin EELS detector w/ 4x sensitivity

• in situ experiments – heating, electrical biasing, wet cell, electrochemical

• Dark-field atomic image simulations

JEOL 2200FS

• 4D-STEM – 2D diffraction × XY raster w/ strain & shear

• OneView 4k × 4k camera at 25 Hz imaging

• 3D electron tomography at ~1 nm3 voxels

• EDS and EELS spectroscopy

Si

SiO2

NbOx

Pt

100 nm

Strain XY

Shear XX

Two Custom In-house Surface Science Chambers

• XPS, UPS, IPE , SEES, LEED, AES

• Electron affinity, band offsets

• Simultaneous chemical and structural analysis hemispherical analyzer

LEED /

AES

light sourceRGA

Multiple XPS Systems – Nexsa and Theta Probe

• Up to 4” wafer capability

• Angle-resolve without tilt for mapping

• Monoatomic and cluster ion sources for depth profiling

• UPS capabilities

Maier, F, et al. Surf. Sci. 443(3) 177-185 (1999) 6

Bruker Dimension AFM with both Icon and FastScan Heads

• Tapping and contact modes available

• Upto 90 μm2 scans over 150 mm wafer scale

• Local I-V and piezoelectric measurements possible kSA MOS UltraScan wafer curvature mapping

• 1”-8” wafer size capability

• 1 µm XY stage resolution

• 4 × 10-5 m-1 curvature resolution and 2 m to 50 km radius of curvature range

• 0.32 MPa stress accuracy/resolution

• Can compare with white light profilometry (Zygo measurements)

Nikon Optical Microscopy

• Differential interference contrast imaging possible

• Polarization options included

• Fluorescence filter for color center detection

Diamond substrates

Physical Properties Measurement System (PPMS)

Quantum Design DynaCool PPMS

• Cryogen-free, 9 T magnet, temperature range 1.8-400 K

• AC and DC resistance capabilities; van der Pauw Hall transport; angle-dependent B field measurements

• Measure quantum materials, exotic low-temperature effects

• Working to upgrade for RF measurements

GaAs 2DEG (Palmstrom group, UCSB) STO (UCSB, S.Mack NRL)

Electrical Characterization – wafer scale

LEI Contactless Measurement System

• Up to 6” wafer mapping

• Fast, Non-destructive sheet resistance measurements

MDC 802B-150 Mercury CV Probe

• Up to 6” wafers and partial wafers

• Schottky and MOS C-V characterization for epilayer diagnostics such as carrier concentration, HEMT evaluation, thickness, and dielectric constants

• 100Hz to 1 MHz

Electrical Characterization/Diode Qualification

400 °C DC IV/CV Probe Station w/ Light Enclosure

On-Wafer Hall Effect

• Room temperature carrier density and mobility measurement

Keithley 4200A-SCS Parameter Analyzer • 4 IV SMUs

• CV up to 10 MHz

• UV light

• Dual-tip Kelvin probes for removal of probe resistance

Capabilities

Evaluation

• Contact and sheet resistance extraction (TLM/CTLM)

• Diode ideality factor extraction

• Built-in potential, diode series resistance estimation

• Geometric analysis of IV behavior

J. G. Champlain, R. Magno, D. Park, H. S. Newman, and J. B.

Boos, “High-Frequency, 6.2 Å pN Heterojunction Diodes,” Solid-

State Electronics, vol 67, pp. 105-108 (2012)

Electrical Characterization/Diode Qualification Multiple Small-Signal RF Characterization Systems

• S-parameter measurement

• W-band (75-110 GHz) frequency extenders

• Keysight ADS circuit modeling

Capabilities

• Small-signal model extraction

– Series resistance (RS), junction resistance (Rj) and capacitance (Cj)

• RC-cutoff frequency (fRC) calculation and analysis

J. G. Champlain, R. Magno, D. Park, H. S. Newman, and J. B. Boos, “High-Frequency, 6.2 Å pN Heterojunction Diodes,” Solid-State Electronics, vol 67, pp. 105-108 (2012)

Diode Small-Signal Model

• Lots of fundamental material and electrical characterization capabilities – many are wafer scale or can be mapped

• Significant experience in characterizing WBG and UWBG materials and devices

• Happy to discuss additional characterization techniques as needed or short loop characterization

Virginia (Ginger) Wheeler…