HEMTHigh Electron Mobility Transsitor

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HEMT-High Electron Mobility Transsitor
Making a heterojunction
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2-D electron gas
Schroedinger Equation
Solution
Poisson Equation in GaAs
2D sheet density
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Finding density of 2D Gas
Fermi level
2D density of states
Poisson Equation in AlGaAs
Charge equality
Spacer Potential
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2D electron-gas density at finite temperature
T0K
Tgt0K
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HEMT with the gate
Schottky barrier
Poisson Eq. In AlGaAs
zA
Potential drop across the depletion layer
EquateFermi levels difference with the gate
voltage
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Threshold voltage
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I-V characteristics
In MOSFET saturation takes place when VDVG-VT
but in HEMT velocity saturates first
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Velocity saturation
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Saturation
Velocity saturation
Mostly Pinch-off
Mostly Velocity saturation
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Saturation current
Mostly Velocity saturation
Transconductance gmCgWvsat
Speed
Mostly Pinch-off
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AlGaAs HFET
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HFET RF Mixers
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MESFET
Depletion layer thickness
eVB- eVGeV(x) eVdep?-?eNDAd2/2??-?
Contact potential
eVCeVB-(?-?)
Current density
Total current
Integrate
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Pinch-off in MESFET
g0e?nNDAW/L
Pinch-off (depletion) voltage
VPOeNDA2/2?
x
Ad(VD,sat)A i.e. VD,satVC-VG eNDA2/2?VPO
Pinch-off occurs when
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Transconductance of MESFET
Triode region
Saturation region
Capacitance
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Speed of MESFET
VD,satVC-VGVPO
g0e?nNDAW/L
VPOeNDA2/2?
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Nonvolatile Memories
0 state
1 state
Gauss law
Cox,i?I/di
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Threshold
E1- depletion field at the interface
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Graphic solution
QG1 QG2Vox,1 Cox,1 , QG2 Vox,2 Cox,2 Vox
Vox,1 Vox,2 QG2/ Cox,1 QG1/ Cox,1 QG2/
Cox,2 (QG1 QG2)(Cox,1 1 Cox,2 1)- QG1/
Cox,2 (QG1 QG2)/ Cox - QG1/ Cox,2