Steady-state Photoconductivity Measurements Method for the Determination of Effective Excess Carrier Lifetime in GaSb Semiconductor

Abstract

In this study, the photo-response of gallium antimonide (GaSb) epitaxial films is investigated by measuring the spectral as well as injection level dependence of the steady-state photoconductivity. First, the conditions for the determination of optimum photo-signals is established by varying the load resistance connected to the sample during photoconductivity measurements. Then, the spectral dependence of the effective excess carrier lifetimes is described using the various photo-response and galvanometric measurements. The measured and theoretical effective excess carrier lifetimes were fitted using a three-layer model described using Ohm’s law by considering the generationrecombination mechanisms in the deep bulk and the two under surface depleted near-surface regions on either sides of the semiconductor films. The results of the measurements revealed that the main contribution to the low injection level entire bulk photo-response mainly come from the near-surface regions, where the band to-band radiative and Auger recombination mechanisms are very low. From the simulation of the results of the excess carrier lifetime, some of the near-surface characteristics, such as the position of the surface Fermi-level, the band bending at the surface, widths of the under surface depletion layer and the surface recombination velocity, could be determined. The room temperature surface Fermi-level was found to be pinned below the mid-gap irrespective of the doping density in p-type GaSb epilayers.