gan crystal growth & tem sample preparation · gan crystal growth & tem sample preparation...
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![Page 1: GaN Crystal Growth & TEM Sample Preparation · GaN Crystal Growth & TEM Sample Preparation Mentors: Feng Wu & Jan Lofvander Faculty Advisor: ... Comparison of GaN Crystal Growth Methods](https://reader033.vdocument.in/reader033/viewer/2022053017/5f1c62f126e72261cb5b2a6b/html5/thumbnails/1.jpg)
GaN Crystal Growth & TEM Sample Preparation
Mentors:Feng Wu & Jan Lofvander
Faculty Advisor: Jim Speck
Lab Group Funding:DARPA & ONR
Special Thanks to:Ben Haskell & Patrick Waltereit
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Project Focus
• First 3 weeks: – TEM Manual Sample Preparation
• Last 3 weeks: – Automated Sample Preparation (FIB) & – GaN Crystal Growth
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Gallium Nitride
• Blue Light Emitting Diodes (LEDs) & Lasers– Wide Band Gap (3.4 ev)
• Transistors– Electrical Properties– Stability
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3 Methods to Grow GaN
• HVPE– Hydride Vapor Phase Epitaxy
• MOCVD– Metal Organic Chemical Vapor Deposition
• MBE– Molecular Beam Epitaxy
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Comparison of GaN Crystal Growth Methods
highestlowestFilm Quality
lowestmediumhighestGrowth Rate
lowest700 °C
medium1000 °C
highest1050 °C
TempMBEMOCVDHVPE
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Crystal Defect Structures
• Caused by slight incompatibility between GaN & Substrate– Lattice Structure– Thermal Properties– Other
• Examples:– Point Defect 0-D– Dislocation 1-D– Stacking Fault 2-D
http://www.tf.uni-kiel.de/matwis/amat/def_en/kap_5/backbone/r5_2_2.html
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Structural Characterization Tools• X-Ray Diffraction• Atomic Force
Microscope (AFM)• Optical Microscope• Scanning Electron
Microscope (SEM)• Transmission
Electron Microscope (TEM)
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TEM Image Stacking Fault
Plan View
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TEM imageDislocation
Plan View
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TEM Sample Preparation
• Manual Polishing– 1 day – 2 weeks
• Automated Polishing– 2-4 hours– Focused Ion Beam (FIB)
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TEM Sample• Thin film (GaN)• Substrate (Sapphire or Silicon Carbide)
GaN film
Plan ViewGaN film
Substrate
Side View
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Manual Polishing1. Cut & Glue the Sample
GaN film
Substrate
Silicon Silicon
Side View
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Manual Polishing2. Attach sample to Pyrex holder3. Insert Pyrex holder into Tripod
Sample
SampleTripodPyrex Holder
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Manual Polishing
4. Polish 1st side of Sample on Diamond Lapping Film until smooth
5. Glue Sample onto Copper Grid
6. Polish 2nd side of Sample until 10 µm thick
7. Ion Milling until 100 nm thick
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TEM imageDislocation
Plan View
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TEM imageDefects?
Cross Section
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FIB Focused Ion Beam
• No Sample Preparation
• 2 Beams– Electron– Ion
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FIB Procedures
1. Locate Site of Interest2. Mill a trench on either side3. Thin the wall4. Cut it out
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TEM imageDislocation
Cross Section
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Reflections…• Research Lessons:
– TEM Sample Preparation • Time-Consuming• Delicate• Easy to Make Mistakes
– TEM images give most detailed info– Other forms of Microscopy used as a gage
• Classroom Applications:– Interviewing experts key– Learning about other components made it more
interesting/meaningful