Direct observation of subband structures in (110) PMOSFETs under high magnetic field: Impact of energy split between bands and effective masses on hole mobility

The band structures and carrier transport in (110) pFETs are thoroughly studied over a wide temperature range under high magnetic fields. In (110) pFETs, the degenerate hole bands in bulk Si are separated into the higher energy band (H band) and the lower energy band (L band). The energy difference between these bands is experimentally evaluated. The effective masses of each band are directly obtained from the Shubnikov-de Haas (SdH) oscillation analysis. It is demonstrated that mobility in the higher energy band is worse than that in the lower energy band, resulting in sharp mobility drop at higher surface carrier concentrations (N_s) and a clear hump in I_d-V_g characteristics at low temperatures of less than 20 K. In order to further enhance mobility in (110) pFETs, the increase in the energy split between H and L bands is important.