Subbands in inversion layers on NGS for Egap to 0

Abstract

Subband states in n-inversion layers on HgCdTe are resonances due to the coupling to the bulk valence-band continuum. The width of the resonances increases with decreasing gap energy. Thus the existence of subband states is questionable if the gap energy is zero. The authors study the subband problem for MIS structures on narrow-gap semiconductors starting from Kane's k.p Hamiltonian. The analytical approach with no specified surface potential shows that for Egap=0 the free-electron term, which is usually neglected for narrow-gap systems, becomes crucial, because it changes the order of the subband differential equation. The authors also solve the subband probe for an analytical surface potential and calculate the density of states. The results demonstrate the existence of a subband resonance even for vanishing gap energy provided that the free-electron term is not neglected.