Selectively delta - doped Al sub x Ga sub 1-x As/GaAs Heterostructures with High Two-Dimensional Electron-Gsup 12 cm sup(-2) for Heterostructure Transistors.

The delta - doping concept is applied to selectively doped heterostructures in the Al sub x Ga sub 1-x As/GaAs material system. High two-dimensional electron-gas concentrations >= 1.5 x 10 sup 12 cm sup(-2) are obtained at T = 300K in such selectively delta - doped heterostructures (S DELTA DH) due to (i) size quantization in the Al sub x Ga sub (1-x) As and (ii) localization of donor-impurities within one atomic monolayer. Shubnikov-de Haas measurements yield n sub 2DEG = 1.1 x 10 sub 12 cm sup(-2) at 300mK and a spacer thickness of 25angstroms. Selectively delta - doped heterostructure transistor (S DELTA DHT) are fabricated and have excellent characteristics due to the enhanced electron-gas concentrations achieved. A very high transconductance of g sub m =~ 350 mS/mm at a gate-length of 1.2microns is obtained in depletion-mode S DELTA DHTs at T=300K.