Post on 11-Jan-2016
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High Electron Mobility Transistor (HEMT)
Flament Benjamin
PLAN
•Presentation
•Fabrication
Presentation
• 1980 at Fujitsu
• TEGFET, MODFET, HFET
• Goal->transportation in a doped material
• Heterojunction: 2 layers
– Highly doped layer with grand gap
– Non-doped layer with small gap
Presentation
Source
Gate
Drain
CAP small doped gap CAP small doped gap
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
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 :
x=1, 3, 5 stands for the various oxides of arsenic
• Ga oxide is removed by:
)2
1(2 4222 AsAsOxHxHOAs x
OHOGaHOGa 2232 24
Fabrication
• Becomes volatile at 200°C so we choose a
temperature of 400°C
OGa2
Fabrication
• We grow the different layer by molecular beam epitaxy (MBE)
30 periods of AlGaAs/GaAs superlattice buffer 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
Photoresist
Wafer and others layers
Mask
Fabrication
photoresist
Mask
Fabrication
metal
metal GaAs metal
GaAs photoresist GaAs
Layers
Source Drain
CAP small doped gap CAP small doped gap
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
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