GaAs/AlGaAs double heterostructure high electron mobility transistors

A selectively doped high electron mobility transistor (HEMT) with 1 µm gate length has been fabricated on AlGaAs/GaAs/AlGaAs double heterostructure material grown by MBE. The sheet carrier density of the two-dimensional electron gas (2-DEG) measured at 77K was 1.9 × 10¹²cm^-2, which is about two times that of a conventional HEMT. Depletion-mode devices of the double heterojunction HEMT can be operated between negative pinch-off voltage and forward-biased gate voltage without any transconductance degradation, which is in contrast to the transconductance degradation observed in the conventional HEMT operated at high positive gate bias. The measured peak extrinsic transconductance for devices with 1 µm gate length at room temperature was 300 mS/mm and 360 mS/mm for depletion- and enhancement-mode devices, respectively. Because of the confinement of electrons by the heterojunctions, the short channel effect is greatly reduced in double heterojunction HEMTs.