6. Summary

There has been significant progress in the field of III-nitride material growth driven by the impetus of device application. Over the last decade, AlGaN has been grown with much improved quality and reasonably good control of conductivity, with Al mole fraction covering the whole range between the two binary extremes, i.e. GaN and AlN. Yet, due to the lack of native substrates and the associated high defect density inherent to foreign substrates, the growth technology of nitride semiconductors at large, and of AlGaN in particular, is far from being fully mastered. It can be expected, however, with the surging of research activities in this field, high quality AlGaN material will be available for application in the near future.