SURFACE-STATE STUDIES OF NONPARABOLIC BAND SEMICONDUCTORS USING MIS STRUCTURES

Capacitance (C-V) and capacitance derivative (C′-V) measurements have been taken on MIS Hg0.8Cd0.2Te-ZnS devices. The surface-state distributions are determined from a digital simulation program describing the characteristics of an MIS structure with a semiconductor having a nonparabolic conduction band and a parabolic valence band. A combination of a nonuniform acceptor surface-state distribution centered at the conduction band edge and a nonuniform donor surface-state distribution centered at the valence band edge is necessary to fit the experimental C-V and C′-V data. From flat-band voltage versus insulator thickness plots, the work function for Hg0.8Cd0.02Te is 4.23±0.67 eV. The immobile trapped charge density in the samples studied has an average value of 1.66×1012 cm-2.