Growth and Electronic Properties of InN and N-rich Alloys

This project will study the growth and characterisation of a new optoelectronic semiconductor material, namely indium nitride (InN). Starting from the deposition of the first few atoms that make up a single atomic layer of the material, the growth will be observed using scanning tunnelling microscopy (STM), through to the development of complete monolayers, and all the way to the growth of thin films (i.e. several microns thick). This material is important technologically because up until late 2002, it was thought that InN had a band-gap energy of 1.9 eV. However, in 2002, high quality InN thin films were grown for the first time and this material was found to have a band-gap energy of 0.7 eV (i.e. in the infra-red). This discovery has meant that it is important to re-assess all of the fundamental properties (i.e. structural, optical and electronic properties) of this material and its alloys. The technologically important reason for this is that now, with this lower band-gap energy, InN can be combined with the wide-gap material GaN (band gap of 3.4 eV / i.e. in the ultra-violet) to form InGaN. It will therefore be possible to make a whole range of new devices, including a range of high efficiency solar cells spanning the entire solar spectrum, and high frequency devices that operate in the THz band, without having to combine several different semiconductor materials, with all the problems that go with that complex process. Because of a range of inherent properties associated with pure InN (surface electron accumulation and difficulty with p-type doping) which we have previously discovered, we will develop a range of novel alloys of this material with both gallium (Ga) and arsenic (As). We will do this by carefully examining how these materials grow (quite literally atomic layer-by-atomic layer) and what fundamental properties of the thin films improve, as a function of Ga and As content, enabling a whole range of new optical and electronic device applications.