By analyzing energy barriers for electrons at interfaces of Ge, GaAs, and In0.15Ga0.85As with insulating high-permittivity oxides (HfO2, ZrO2) using the spectroscopy of internal photoemission, we found that the insertion of a nanometer-thin interlayer of a dissimilar semiconductor, i.e., Si on Ge or Ge on GaAs, has no measurable influence on the interface band alignment. This result indicates the absence of any substantial interface dipoles across the stack composed of a semiconductor heterojunction and an insulating oxide and suggests the validity of the transitivity rule previously inferred on the basis of bulk–density–of–states arguments in the case of nanometer-sized multilayer structures.
Low barriers for electrons are found to be the reason for significant charge instability at interfaces of (100)InP and (100)In0.53Ga0.47As with atomic-layer deposited TaSiOx insulators. The formation of these reduced barriers is associated with the growth of a narrow-bandgap interlayer between the semiconductor and TaSiOx, which enables electron tunneling at low electric fields and subsequent trapping in the insulator. A wide-gap passivation layer may be required to improve the performance of TaSiOx as gate insulator.
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