Optical properties of InN and related alloys
On the other hand, much less effort has been devoted to InN and In-rich alloys. Earlier InN samples were synthesized using radio-frequency sputtering [7.3]. In most cases, this or similar methods produced polycrystalline samples with high electron concentrations [7.4] and significant oxygen contamination [7.5]. Such materials typically showed relatively low electron mobilities in the range of 10100 cm2/Vs. The optical absorption measured in these samples showed a strong absorption band in the infrared and an absorption edge at about 1.9 eV [7.6]. The value of 1.9 eV was thus widely quoted as the band gap of intrinsic InN [7.7]. One of the unexplained characteristics of this early synthesized InN was the lack of any light emission at or near the purported band edge. This was in stark contrast to GaN and Ga-rich InGaN, which show a strong luminescence despite the very large concentrations of point and extended defects typical for these materials.