Analysis of energy states of two-dimensional electron gas in pseudomorphically strained InSb high-electron-mobility transistors taking into account the nonparabolicity of the conduction band

Abstract

We propose a high electron mobility transistor with a pseudomorphically strained InSb channel (InSb-PHEMT) having an InSb composite channel layer in which the AlyIn1−ySb sub-channel layer is inserted between the InSb channel and the AlxIn1−xSb barrier layers to increase the conduction-band offset (ΔEC) at the heterointerface between the InSb channel and the AlxIn1−xSb barrier layers. The energy states for the proposed InSb-PHEMTs are calculated using our analytical method, taking account of the nonparabolicity of the conduction band. For the proposed InSb-PHEMTs, putting the sub-channel layers into the channel is found to be effective for obtaining a sufficiently large ΔEC (∼0.563 eV) to restrain electrons in the channel and increase the sheet concentration of two-dimensional electron gas to as high as 2.5 × 1012 cm−2, which is comparable to that of InAs-PHEMTs. This also leads to a large transconductance of PHEMTs. In the proposed InSb-PHEMTs, electrons are strongly bound to the channel layer compared with InAs-PHEMTs, despite the effective mass at the conduction band (0.0139 m0) of InSb being smaller than that of InAs and ΔEC for the InSb-PHEMTs being 25% smaller than that for the InAs-PHEMTs. This is because the bandgap energy of InSb is about one-half that of InAs, and hence, the nonparabolicity parameter of InSb is about twice as large as that of InAs.