Opto-electronic modulation spectroscopy (OEMS)

Abstract

A technique is described which combines wavelength modulated monochromatic illumination with impedance measurements to discriminate the responses of bulk and surface states in the depletion regions of electronic devices. The method reveals the inherent ambiguity in conventional capacitance vs voltage and conductance vs voltage (C-V and G-V) measurements of state densities. The opto-electronic modulation spectroscopy (OEMS) spectra peak energies provide the state to band transition energies directly and these can be indexed onto an energy diagram to give the spatial positions of the responding states as well as the band with which they communicate. Measurements made on an SiO₂/n-GaAs device show an absence of surface state related peaks and suggest that surface potential pinning under positive bias may be related to bulk states emerging at the surface.