Modulation doping of InAs/AlSb quantum wells using remote InAs donor layers

Sheet carrier concentrations in quantum wells of InAs clad by AlSb were enhanced by modulation doping with very thin (9–12 Å) remote InAs(Si) donor layers. The growth temperature of the donor layers was a key parameter, with relatively low temperatures required to minimize Si segregation into the AlSb. Sheet carrier concentrations as high as ${\text{3.2×10}}^{12}/{\mathrm{cm}}^{\mathrm{2}}$ and ${\text{5.6×10}}^{12}/{\mathrm{cm}}^{\mathrm{2}}$ were achieved by single- and double-sided modulation doping, respectively. High electron mobility transistors fabricated using the modulation doped structure exhibited a unity current gain cut-off frequency of 60 GHz for a 0.5 μm gate length at a source-drain voltage of 0.5 V.