Transcript High Electron Mobility Transistor (HEMT)

High Electron Mobility
Transistor (HEMT)
Flament Benjamin
PLAN
•Presentation
•Fabrication
Presentation
• 1980 at Fujitsu
• TEGFET, MODFET, HFET
• Goal->transportation in a doped material
Presentation
• Heterojunction: 2 layers
– Highly doped layer with grand gap
– Non-doped layer with small gap
Gate
Source
CAP
Drain
small doped gap
CAP
Schottky contact
grand gap non doped
Carrier donor layer
grand gap doped
Spacer
grand gap non doped
Canal
small gap non doped
Buffer
grand gap non doped
Substrat
small doped gap
PLAN
•Presentation
•Fabrication
Plan
•Cleaning
•Deposition, MBE
•Ohmic contacts
Fabrication
• Cleaning of the wafer
– GaAs wafer->more complicated than Si wafer
– Difficulties to remove the oxide of Ga and As
– We use the electron cyclotron resonance
(ECR)
Fabrication
• As oxide is removed by heating and :
1
As 2 O x  2 xH  xH 2 O  As 2 ( As 4 )
2
x=1, 3, 5 stands for the various oxides of arsenic
• Ga oxide is removed by:
Ga2O3  4H  Ga2O  2H 2O
Fabrication
• Ga2O Becomes volatile at 200°C so we choose a
temperature of 400°C
Fabrication
• We grow the different layer by molecular beam
epitaxy (MBE)
Buffer
30 periods of AlGaAs/GaAs
superlattice
buffer
grand gap non
doped
Substrat
30 periods of AlGaAs/GaAs superlattice buffer
Canal
small gap non doped
Buffer
grand gap non doped
Substrat
120 Å of In(0.2)Ga(0.8)As
Spacer
grand gap non doped
Canal
small gap non doped
Buffer
grand gap non doped
Substrat
35 Å of Al(0.23)Ga(0.77)As
Carrier donor layer
grand gap doped
Spacer
grand gap non doped
Canal
small gap non doped
Buffer
grand gap non doped
Substrat
Schottky contact
grand gap non doped
Carrier donor layer
grand gap doped
Spacer
grand gap non doped
Canal
small gap non doped
Buffer
grand gap non doped
Substrat
250 Å of Al(0.23)Ga(0.77)As
Fabrication
photoresist
Wafer and others layers
Fabrication
Mask
Photoresist
Wafer and others layers
Fabrication
Mask
photoresist
Fabrication
metal
metal
GaAs
metal
GaAs
photoresist
GaAs
Layers
Source
CAP
Drain
small doped gap
CAP
Schottky contact
grand gap non doped
Carrier donor layer
grand gap doped
Spacer
grand gap non doped
Canal
small gap non doped
Buffer
grand gap non doped
Substrat
small doped gap
Fabrication
• 3 layers:
– PPMA for the bottom layer
– PMIPK for the middle layer
– PPMA for the top layer
• PPMA(polypropylmethacrylate)
• PMIPK(polymethylisopropenylketone)
Fabrication
• Using deep UV lithography
Research
• Lattice matching