Electron subbands and transport properties in inversion layers of InAs and InP

Subband structures and electron transport are systematically investigated in the two-dimensional inversion layers on InAs and InP metal-insulator-semiconductor field-effect transistors. Hybrid quantum oscillations of conductivity under a strong magnetic field reveal that the two-subband conduction state is realized above an electron concentration $N_s$ of 1.4×${10}^{12}$ and 3.8×${10}^{12}$ ${\mathrm{cm}}^{\mathrm{-}2}$ for InAs (acceptor concentration $N_A$=1×${10}^{17}$ ${\mathrm{cm}}^{\mathrm{-}3}$) and InP ($N_A$=1.7×${10}^{16}$ ${\mathrm{cm}}^{\mathrm{-}3}$), respectively. Field-effect mobility is observed to decrease abruptly at the onset of the two-subband conduction state at low temperatures. This remarkable effect is due to intersubband scattering. Electron mobility in inversion layers on these III-V compounds is also found to be limited mainly by three scattering mechanisms: screened Coulomb scattering due to the charged interface states at low $N_s$ values, defect scattering due to the out-diffusion of group-V atoms at intermediate $N_s$ values, and surface roughness scattering at high $N_s$ values. Additionally, negative magnetoresistance is observed due to the weak localization effect in the two-dimensional systems. Positive magnetoresistance is also observed in InAs, due to the spin-orbit interaction with a large absolute value of an effective g factor. Finally, intersubband scattering is found to give rise to a remarkable effect on the weak localization.