In order to facilitate the development of next-generation display devices or modern solar cells, material performance is critically important. A combination of high transparency in the optical spectral range and high electrical conductivity under ambient conditions is attractive, if not crucial, for many applications. While the doping-induced presence of free electrons in the conduction bands of CdO can increase the conductivity up to values desired for technological applications, it is, however, expected to impact the optical properties at the same time. More specifically, variations of the band gap, effective electron mass, and optical-absorption onset have been reported. In this work recent results from modern theoretical spectroscopy techniques are compared to experimental values for the optical band gap in order to discuss the different effects that are relevant for an accurate understanding of the absorption edge in the presence of free electrons with different concentrations.
The addition of small amounts of nitrogen to III-V semiconductors leads to a large degree of band-gap bowing, giving rise to band-gaps smaller than in the associated binary materials. The addition of a small percentage of nitrogen to GaSb or InSb is predicted to move their response wavelengths into the long or even very long wavelength IR ranges. We report the growth of GaNxSb1-x by MBE, using an r.f. plasma nitrogen source, examining the influence of plasma power, substrate temperature and growth rate. We demonstrate high structural quality, as determined by x-ray diffraction, and show a reduction in band-gap by over 300meV, compared with GaSb, based on FTIR transmission spectroscopy. We also report initial experiments on the growth of InNxSb1-x and Ga1-yInyNxSb1-x, with a view to extending the response into the long and very long wavelength IR ranges.
InSb and related ternary alloys have many potential applications in addition to the conventional one of infrared detection provided that near ambient temperature operation can be achieved. The growth by MBE of n-type and p-type InSb has been established using silicon and beryllium dopants respectively. Multilayer diode structures have been studied up to 300K in order to determine carrier generation mechanisms and examine concepts for ambient temperature operation.