Selectively δ-doped AlxGa1−xAs/GaAs heterostructures with high two-dimensional electron-gas concentrations n2DEG≥1.5×1012 cm−2 for field-effect transistors

The δ-doping concept is applied to selectively doped heterostructures in the AlxGa1−xAs/GaAs material system. High two-dimensional electron-gas concentrations ≥1.5×1012 cm−2 are obtained at T=300 K in such selectively δ-doped heterostructures due to (i) size quantization in the AlxGa1−xAs and (ii) localization of donor impurities within one atomic monolayer. Shubnikov–de Haas measurements yield n2DEG =1.1×1012 cm−2 at 300 mK and at a spacer thickness of 25 Å. Selectively δ-doped heterostructure transistors (SΔDHT’s) are fabricated and have excellent characteristics due to the enhanced electron-gas concentrations achieved. A very high transconductance of gm ≂360 mS/mm at a gate length of 1.2 μm is obtained in depletion-mode SΔDHT’s at T=300 K.