Surface band-bending assessment by photocurrent techniques. Application to III-V semiconductors

In epitaxial layers with a large area to thickness ratio, surface and interface space charge regions behave as transverse resistance-capacitance systems modulating the effective volume that takes part in the electrical conductivity. In this work it is shown that in photoconductivity spectroscopy experiments these surface and interface photovoltaic effects can become dominant, therefore giving information about the sample surface and interface band-bending. In photoconductivity spectroscopy, procedures to identify the signatures of such band bending are described. The present technique to assess surface bending is first applied to gated and ungated GaAs samples, to validate the present model. N-type AlGaAs and undoped InGaAs strained buffer layers, with various degrees of strain and surface roughness, are also characterized by this technique.