Tab 4 SOW Posting.pdf

National Aeronautics and Space Administration (NASA), Headquarter, 300 E.

Street, SW, Washington, DC 20546-0001

Contract Center: NASA Marshall Space Flight Center, Huntsville, AL 35812

Project Title: Investigate point defects, line defects and performance of pure and doped crystals grown on earth and microgravity using luminescence, Raman and morphological characteristics.

Proposal to: September 2023

Organization:

Program Officer &Technical PM:

Performing Organization:

Business Manager

Research Team Members:

NASA Marshall Space Flight Center Huntsville, AL 35812

University of Maryland, Baltimore County, 1000 Hilltop Circle, Baltimore, MD 21250

University of Maryland, Baltimore County (UMBC), 1000 Hilltop Circle, Baltimore, MD 21250

State University

SEM for morphology Cryo container Fluorimeter for luminescence measurement

Investigate point and line defects and performance of doped crystals grown on earth and microgravity using luminescence, Raman and morphological characteristics.

1. OBJECTIVES AND REQUIREMENTS

The overall objectives of this project are to understand point and line defects and recombination generated defects due to transition metal doping, substitution and growth conditions of the ZnSe crystals grown on earth and microgravity. This study will provide information to correlate the point defect distribution with growth information to enhance understanding of defect generation processes. These data will provide information to improve the level and process for doping and growth parameters. This finding will generate data for the researchers of NASA Marshall Space

Flight Center. They will be able to adjust parameters for the growth process.

These crystals doped with transition metal impurities are of great importance for space applications and industrial applications to generate mid-infrared wavelength based lasers. The major focus will be to develop nondestructive methods to characterize defects by studying two samples provided by the NASA Marshall Space Flight Center. Based on the discussion NASA may provide other

ZnSe sample also.

The focus will be to design and develop innovative nondestructive approaches in which least post processing such as cutting, polishing or other etching can be used to characterize the sample. In addition, we will explore and prepare parallel surfaces of sample which will save resources and will not introduce further defects.

We will perform nondestructive methods to evaluate defects in pure and doped crystals.

1. Design holder and instruments for NASA supplied samples of ZnSe samples to study at room temperature and at cryogenic temperatures.

2. Calibrate fluorimeter for measurements of luminescence.

3. Determine luminescence spectra for the supplied ZnSe crystals and compare with at least two transition metal impurities.

4. Investigate Raman spectra to determine difference in LO and TO characteristics due to defects caused by processes and doping.

5. Determine morphology by SEM (and evaluate EDX if it shows compositional variation) and correlate with the PL data.

6. The other major objective of this program is also to train graduate and undergraduate students for the materials related multidisciplinary research needed for future needs of the work force of NASA and the United States of America.

2. BACKGROUND, SCOPE AND APPROACH

The proposed materials are of great importance due to following characteristics.

Large transparency

Extremely low absorption

Multiple applications in industries

Flexibility of growing bulk, thin film and nanocrystals

Applications of materials as doped and in quasi phase matched configurations.

Suitability of applications of material in space and on ground devices and systems Because of these NASA Marshall Flight Center has pioneered the crystal growth [1-4] to control convection which plays very important role in producing high quality ZnS and ZnSe large crystals.

The researchers have performed theoretical and experimental investigation to demonstrate that the low gravity plays important roles .The low gravity enables the control of the convection and diffusion during the crystal growth process . Science required documents have been developed to show important parameters for growth, impurity distribution and hence homogeneity of the crystals. These factors are more important multinary materials and in solid solutions where there is a significant density differences between constituent components. Furthermore, the doping to enhance optical and electrical properties significantly change the fluid flow and interface morphology and hence the crystal quality.

With increasing thrust to avoid high cost of rare earth doping studies using transition metal dopants have shown [1-6] growth and importance of selenide crystals. Their publications have described the process and parameters for achieving very large crystals [5-7]. Since these materials have huge impact on electronic and optical technologies, there is a great demand to improve quality by growing in low gravity environments. In addition, these materials have been used as components for antireflection coatings and as dome materials.

Bulk, thin film and nanomaterials and engineered quasi phase matched materials have attracted attention for near IR to long wave infrared wavelength region for high power lasers due to extremely low absorption in a large transparency region. These materials have great flexibility since one can dope with variety of elements including rare earth and transition metals to enhance emission which is another approach to design lasers in desired wavelength region. ZnSe in which an unfilled d shell is present, are doped with dopant, the 3d and 4p electron wave functions are mixed at non-centrosymmetric sites. As a result, transitions among the d levels occur and absorption in MWIR radiation occurs. To avoid costly option of rare earth, they have used a variety of transition metals such as Fe, Cr, Co, and various other dopants in ZnSe crystals.

2.1 Scope: The overall scope of the program is to develop nondestructive all optical methods to evaluate effect of dopant, and convector-diffusive forces induced crystal defects which affect the overall quality of crystals. The understanding of these defects due to doping and convective forces are very important especially when large crystals are required. Several aspects of the tasks to cover the scopes have been published by Su et al [6-10] and some processes have been described.

2.2 Sample holder and maintaining cryogenic temperature: We have designed a sample holder for the measurements. The samples are clamped into the solid state sample holder. Indium wire is used as a thermal conductor between the two plates to maintain thermodynamic transmission between plates for a more uniform temperature across the sample. The sample will be placed in the Oxford Instruments Optistat DN cryostat attachment for the Edinburgh Instruments fluorometer.

Since the light depends on the orientation of the crystal, we will orientation the sample properly before clamping into place to ensure that the sample would allow the 90 degree collection of light off the sample taking care to avoid saturation from specular reflection. The sample chamber will be sealed, and a vacuum drawn via diffusion pump which is monitored using a pirani/cold cathode gauge. Once the vacuum reaches around 10^-9 mbar in the sample chamber the vacuum valve is closed. Liquid nitrogen is poured into the loader on the top of the crysostat slowly to begin the temperature decrease. The temperature is monitored using the oxford temperature reader connected to the top of the cryostat. Liquid nitrogen is then poured in portions until the temperature reaches around 77K. The cryostat is placed in the fluorometer with the windows aligned for a 90 degree collection.

23 Large area coverage of crystal: Since the goal is to determine the defects in the crystals, we are increasing the coverage area by using large area beam of the excitation beam. To achieve this goal, we recently replaced the flash lamp. Eric Bowman a graduate student refocused it and trying to optimize the conditions for the experiments. However, he has achieved conditions so that the spot size should be defined by the slit. The Figure shows a 5mm slit light and image is shown in the figure. In the figure the height is about 5mm, and the width is dependent on whatever setting the slits are set to.

Figure 1. Image of the beam showing a 5mm slit coverage. The width can be easily adjusted to cover the large area of crystals.

2.4 Measurement of luminescence: The photoluminescence includes two concurrent processes, fluorescence and phosphorescence. The need for the traceable characterization of fluorescence instruments is focusing on spectral fluorescence standards for the determination of the wavelength-and polarization-dependent relative spectral responsivity and relative spectral irradiance of fluorescence measuring systems, respectively. The PL quantum yield presents a direct measure for the efficiency of conversion of the absorbed photons into emitted photons. This is one of the spectroscopic key parameters of functional fluorophores. This determines suitability of materials for its applications in optical devices and systems.

For fluorescence instruments equipped with a reference detector, which accounts for fluctuations of the excitation light intensity incident radiant power P( ex)], the linearity of this detection system is important. The range of linearity of the reference detection system can only be determined for instruments with emission and reference detector signals that can be read out separately, typically high-end research-grade fluorometers. Even though ratio-only instruments are typically designed to reduce such effects, it is generally recommended that fluorescence measurements be collected at signal levels far from detector saturation to minimize contributions from nonlinearities of the detection system to the overall uncertainty of spectral correction and fluorescence measurements. If such effects cannot be excluded, as, for instance, in certain cases of quantitative fluorometry with unknown analyte concentrations or for compounds with unknown fluorescence quantum yields, classical N-point calibration procedures have to be additionally performed, thereby considering the eventually reached maximum fluorescence intensity.

(a) (b)

Figure. 2(a) Design of sample holder and (b) cryogenic container

2.4 Data Collection for luminescence: We will use the FS920 spectrofluorimeter which measures the steady state luminescence spectral in the ultraviolet-near infrared wavelength region. This spectrofluorimeter is also capable of measuring excitation and emission scans in both visible and near infrared, steady state fluorescence anisotropy, kinetic measurements, synchronous scans, excitation-emission maps, temperature variation, steady state singlet oxygen emission and phosphorescence data. The Action SpectraPro 500i will be involved also this study. The laser

HeNe (35 mW) will be used as an excitation source. The aquation time will be approximately 1 second, The number of accumulation spectra will be in the range of 10 repetition.

Figure 2. Computer aided fluorimeter for measurements.

2.5 Microstructural studies: The morphology of both crystals were determined by scanning electron microscope model NOVA NANOSEM 450. Although we used a range of 2 to 20 KeV energy range, the data shown here are for the 10KeV.

2.6 Compositional studies: NASA Marshall Space Flight center has carefully doped and grown crystals by Physical Vapor transport method. However, during polishing and cleaning the surfaces with acetone or other organic solvents there is always possibility of presence of carbon on the surfaces. Because of this reason we will perform EDX studies also to evaluate the estimation of materials contamination.

3. TASK ELEMENTS

To understand the effect of convection on point defects and hence performance of this class of semiconductors following tasks will be performed:

The University of Maryland, Baltimore County (UMBC) will perform studies to determine the point defect distribution of the crystals grown on Earth and in low-gravity environment by the.

Two NASA MSFC TM doped ZnSe semiconductor crystals. UMBC will carry out the following tasks pertaining to the project:

Task 1: Sample preparation and stability tests: Preparation of as supplied crystals for the microscopic, electrical and optical characterization. We will design a holder for LCR meter for parallel plate type measurements so that exact thickness can be used for computation of properties.

Materials long term stability will be determined for the electrode materials.

Task 2- Microstructural characteristics and correlation with optical data: Characterization techniques, such as high resolution Scanning Electron Microscope (SEM) and Energy Dispersive studies will be used for determining morphology and properties. The detailed approach is to demine morphology with optical microscope and by using an inhouse scanning electron microscope NOVA NANOSEM 450. Typically, we used 3-5 KeV energy. For the deeper thickness we used a range up to 20KeV energy for the data collection. To compare optical data with morphologies high magnification SEM studies will be performed and compare the segregation induced defects and changes in properties.

Task 3- Design and setup suitable sample holder and luminescence measurements: Based on the crystal size we will design sample holder so that laser properly illuminates it. If size and holder is not suitable, it can fall in the cryocooler. Also, the biggest challenge which requires great attention is to put sample without any mechanical stress in the holder. There are sone indications that mechanical stress can change stress induced effect. Figure 2(a) and (b) shows the existing system which are suitable for the measurements. However, we will fabricate sample holder based on the diameter of the crystal. For the measurements the sample will be clamped into the sample holder and placed in the Oxford Instruments in a very precise orientation to ensure that the sample would allow the 90 degree collection of light off the sample to avoid saturation from specular reflection. Once the vacuum reaches around 10-9 mbar in the sample chamber the vacuum valve will be closed. Liquid nitrogen is poured into the loader on the top of the cryostat slowly to begin the temperature decrease until the temperature reaches around 77K. The cryostat is placed in the fluorometer with the windows aligned for a 90 degree collection. We will use the Action

SpectraPro 500i for this study. We will use He-Ne (35 mW) laser as an excitation source. The aquation time will be approximately 1 second. , The number of accumulation spectra will be 10.

Task 4- Raman Studies: In order to highlight the effects of the lattice defects, impurities, and free carriers in a sample detailed Raman studies will be performed. As it is well known that the incident laser beam used in Raman studies interacts to produce photons with a shifted frequency from the incident light. For the ZnSe crystals, two optical and one acoustic phonon are observed .

For doped crystals both TO and LO modes will be significantly affected by the impurities and defects in the crystals.

Task 5- Student’s training. Undergraduate and graduate students will be trained to learn multidisciplinary tasks involving materials growth, optical characterization such as transmission, SEM, and PL measurements which will be used this project. Since the PM of NASA is a renowned researchers periodic technical discussion with MSFC PI to correlate the point defect distribution with growth information to enhance understanding of defect generation processes.

Task 6- Final report: A final report summarizing the results of the analyses will be generated.

Periodic discussions will also take place with MSFC to correlate the point defect distribution with growth information to enhance understanding of defect generation processes. The data will be published in scientific proceedings and journals with approval of PM and NASA.

4. PLACE OF PERFORMANCE

The work will be performed at the University of Maryland Baltimore County, Baltimore, Maryland. Facilities located in the Department of Chemistry and Biochemistry, and Department of Computer Science and Electrical Engineering (Technology Research Center) will be used to complete the program tasks.

4.1 Facilities in Place; The University of Maryland Baltimore County (UMBC) is very well equipped for executing this program. The required facilities to execute this program are already in place. Figure 3 shows some of the general existing facilities which will be used in this program.

Following major equipment are also in place for materials evaluation and processing of the process:

In addition to the above facilities, we have following in-house facilities for the characterization:

Two independently controlled zone transparent glass furnaces

Ball miller to prepare uniform particles.

Etcher to prepare surfaces.

Photoluminescence spectrometers

LCR meter

Scanning electron microscope (SEM)

Wire saw cutting facility.

Pad based polishing facility where we can use chemo-mechanical polishing.

Two FTIRs

Raman spectrometers

Several vacuum systems to deposit electrodes.

Two DENTON evaporators suitable for PVD of metals and other compounds

Figure 3.General facilities in place

4.2 Specific characterization facilities and their applications for this project:

This provides valuable information about the effects of defects caused by purity, growth process variation, and thermal and solutal stresses

Polishing facilities and Electrical characterization: We have developed process for

ZnSe polishing using a slurry. In addition, we have LCR meter for electrical resistance and capacitance measurements at several bias and frequencies. These data are significantly affected by presence of doping and resulting defects.

Thin Film, coating, nano crystal

Crystal and device characterization

Optical, SEM microscope e Probe facilities for materials and device

Bulk synthesis and crystal growth

Solution crystallizer

High temperature

Blue M furnace for high temp h i Flux growth furnace

Custom CZ growth furnace

Bridgman growth furnace

Three zone CVD growth furnace

Multizone vertical furnace

Nanoline

Bridgman growth gold furnace

D Low temperature Bridgman f

DENTON DENTON

E-Beam

Wide bandgap materials Polytype identification: This technique is employed first as a simple and non-destructive method for polytype determination. This method has been used in case of Ga2O3, heavy metal selenides, Si and SiC wafers.

SEM, AFM and Optical Microscopy: Optical and electron microscopy (SEM) is employed to study as-grown surface morphology as well as structural defects (after polishing and etching) such as voids, precipitates, dislocations, low angle grain boundaries, and cracks. Atomic force microscopy (AFM) and scanning capacitance microscopy (SCM) will provide ex-situ techniques to study the material structure on the nanometer scale and the local impurity (dopant) segregation on the as-grown surface.

Cutting, polishing, and chemical etching: Once the non-destructive characterization is completed, crystals are sliced along a pre-determined orientation and polished. Using the etching technique, with etching temperature and duration varying from 200 to 300°C and from 10 secs to 30 min, will be employed to delineate the crystalline structural defects in the wafers, including micropipes.

Optical absorption: The optical absorption at low temperature will be measured for several crystals. The shape of the absorption edge is characteristic of indirect transitions, in which excitons will be created and the exciton energy gaps for polytypes characterization. Low temperature IR absorption measurements can also be used to detect the impurity absorption in the crystal.

The Principal Investigator is working very closely with several faculty members of Electrical

Engineering and Physics. Some other facilities are available if needed.

5. PERIOD OF PERFORMANCE

The tasks of the program will be performed in the period of October 1st, 2023, through

September 30th, 2024.

6. Contact Information

Address: University of Maryland, Baltimore County (UMBC)

1000 Hilltop Circle, Baltimore, MD 21250