characterization of n-polar gan/algan/ gan hemts on
TRANSCRIPT
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Characterization of N-polar GaN/AlGaN/
GaN HEMTs on Sapphire by Metal
Organic Chemical Vapor Deposition
Steve Xu Chen
Faculty advisor: Steven P. DenBaars
Mentor: , David F. Brown, Stacia Keller
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•High cut off frequency
•High break down voltage
•High power density
•Low noise
Signal Amp
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Wireless communication, mobile phone base
station, satellite, radar etc.
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•Epitaxial layer design
•Crystal growth (MOCVD)
•Material Characterization
•Device processing
•Device Characterization
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High Al composition should increase
the electron density in 2DEG
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XRD data shows high quality GaN and AlGaN Epitaxial layer were grown
AlGaN
GaN
X Ray Source GaN
AlGaN
The reflected X-ray have different reflection angle
Simulated
Atom spacing of AlGaN > GaN
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Smooth surface helps to reduce the electron scattering and
increase the electron mobility
rms = 1.28 nm
20 nm 38% Al grade
12.5 X 12.5 12.5 X 12.5 20 nm
0 nm
Well ordered steps were formed on the surface
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rms = 5.77 nm rms = 1.28 nm
High Al composition increases the sheet charge density
Electron mobility drops at high electron density
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Rs = Slope
Low resistance is critical for high frequency performance
Total resistance = 2Rc + Rs
Rc
Rs =Slope of line = rL/dw
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Devices parallel with the surface features show lower sheet
resistance
Direction of TLM pads
Transistors should be fabricated parallel to the
surface features
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Large Gm is obtained and we expect good high frequency performance for this device.
The device pinches off very well and it helps to improve high
frequency performance .
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•Good DC performance is achieved
•Low sheet resistance is reported
• High sheet electron density is obtained for high Al composition
Future work may include:
•Radio frequency measurement
•Capacitance-voltage characteristics
•Surface passivation