HIGH ELECTRON MOBILITY TRANSISTOR (HEMT)

Why HEMT?

• Electron mobility in MESFET channel with typical donor concentration of about 10¹⁷ /cm³ ranges from 4000 to 5000 cm²/V-s at room temperature.

• The mobility in the channel of MESFET at 77 K is not too much higher than at room temperature because of ionized impurity scattering.

• In undoped GaAs , however electron mobility of 2 to 3 x 10⁵ cm²/V-s has been achieved at 77 K

• The electron mobility was found to increase through modulation doping techniques as in GaAs-AlGaAs superlattice.

• a high electron mobility transistor (HEMT) based on modulation doped GaAs –AlGaAs single hetrojunction.  

Advantage of HEMT

• HEMT amplifier can be used upto 70 Ghz
• Lower noise figure
• Higher gain
• Shorter gate length
• Reduce gate and source contact resistances
• Optimizing doping profile

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