The optimum value for the In content in InGaN has yet to be determined, for the moment we are concentrating on samples with a fixed In content, but we will look in the future at other In/Ga compositions. The InGaN samples have to be grown at relatively low temperature and this may result in less than optimum quality of the resulting material. To further improve the quality of the InGaN, we will look at alternative growth techniques such as migration enhanced epitaxy [25], which is known to improve the properties of films grown at low temperature. One of the key problems with all nitride semiconductor structures is the high density of defects. It is well known that this can be improved significantly by growth on bulk substrates, which are now available commercially. One future possibility, therefore, is to consider growth of InGaN-based IBSC structures on bulk GaN substrates.
Finally, Mn is the first possible dopant considered for IBSCs based on InGaN [8]; however, other dopants need to be considered and investigated experimentally. Other possibilities include carbon (C), which is known to be a deep level in GaN and can be incorporated in large quantities into GaN.
