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 Nₛ of 1.4×{}10¹² and 3.8×{}10¹² cm^-2 for InAs (acceptor concentration NA=1×{}10¹⁷ cm^-3) and InP (NA=1.7×{}10¹⁶ cm^-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 Nₛ values, defect scattering due to the out-diffusion of group-V atoms at intermediate Nₛ values, and surface roughness scattering at high Nₛ 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.