The micro-photoconductivity spectroscopy with the spectral capability extended to mid-infrared

A microphotoconductivity (μPC) spectroscopy is developed with an ordinary monochromator and halogen and SiN globar lamps. The instrument may cover a wide spectral range from visible to mid-infrared. For the μ-PC instrumentation, the improvement of signal-to-noise ratio is a crucial issue. We demonstrate that the employment of the Wheatstone bridge provides an effective solution. The instrument has been successfully applied to the narrow bandgap semiconductors InGaAs and HgCdTe, which show the optical band edges at the wavelengths of 2.35 µm and 5.0 µm at 82 K, respectively. The minimization of the light spot is influenced by the intensity of the light source, and the 45 W globar allows the performance of μPC with a light spot of 30 µm diameter for the spectral range of 2.0-3.5 µm, whereas the light spot of 60 µm diameter is necessarily used for the spectral range around 5.0 µm.