HEMT(高电子迁移率晶体管)介绍

HEMT" redirects here. For the military truck, see Heavy Expanded Mobility Tactical Truck.

HEMT stands for High Electron Mobility Transistor, and is also called heterostructure FET

(HFET) or modulation-doped FET (MODFET). A HEMT is a field effect transistor incorporatin

g a junction between two materials with different band gaps (i.e., a heterojunction) as the channel i

nstead of a doped region, as is generally the case for MOSFETs. A commonly used material combi

nation is GaAs with AlGaAs, though there is wide variation, dependent on the application of the d

evice. Devices incorporating more indium generally show better high-frequency performance, whi

le in recent years, gallium nitride HEMTs have seen a massive increase in research effort, due to th

mart device to resolve this seemingly inherent unsolvable contradiction.

HEMT accomplishes this by use of high mobility electrons generated using the heterojunction of a

highly-doped wide-bandgap n-type donor-supply layer (AlGaAs in our example) and a non-doped

narrow-bandgap channel layer with no dopant impurities (GaAs in this case). The electrons genera

ted in the n-type AlGaAs thin layer drop completely into the GaAs layer to form a depleted AlGaA

s layer, because the heterojunction created by different band-gap materials forms a quantum well

(a steep canyon) in the conduction band on the GaAs side where the electrons can move quickly w

ithout colliding with any impurities because the GaAs layer is undoped, and from which they cann

ot escape. The effect of this is to create a very thin layer of highly mobile conducting electrons wit

h very high concentration, giving the channel very low resistivity (or to put it another way, "high e