Long-wavelength photovoltage spectroscopy using an electrolyte/ semiconductor contact for semiconductor bandgap profiling

In this paper we demonstrate, for the first time, that photovoltage spectroscopy (PVS) with an aqueous electrolyte/semoconductor contact can be extended to the wavelength range of 1-2 µm by using an optical fibre which comes directly into contact with the semiconductor, thus avoiding the strong absorption by the electrolyte which occurs in this spectral range. This technique is illustrated for lattice-matched In_1-xGa_xAs grown on lnP having a bandgap of 0.74 eV corresponding to ?_g=1.67 µm. Thus carrier and composition depth profiling can be carried out on ternary and quaternary alloys used for 1.3 µm and 1.5 µm optoelectronic devices.