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