A new Fourier transform photo‐modulation spectroscopic technique for narrow band‐gap materials in the mid‐ to far‐infra‐red

Abstract

AbstractThere is a large number of technologically important semiconducting optoelectronic materials with narrow band‐gaps in the “finger‐print” region of the infra‐red (IR) spectrum. However, in many instances their band‐structures have not been very well characterised, making it difficult to engineer their properties. Part of the reason is that the key non‐destructive optical characterisation tool, modulation spectroscopy, becomes increasingly difficult as one attempts to look further out into the IR. To date, conventional diffraction‐grating‐based modulation spectroscopy has been applied predominantly below ∼4 µm. We have developed a new photo‐modulation system, based on a Fourier transform spectrometer, that permits such measurements out to much longer wavelengths. We discuss the advantages and technical difficulties of implementing such a system, and give the results obtained so far for narrower‐gap materials, including bulk‐like GaSb, InAs and InSb, comparing these with what can be obtained with conventional modulation spectroscopy arrangements. We apply our new technique to measure the bandgap in dilute‐N InSbN, achieving what we believe are the first modulation spectroscopy measurements in the mid‐IR beyond ∼6 µm. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)