Pressure studies of band structure, defects and impurities in group III nitrides

This paper reviews high pressure investigations of the physical properties of group III nitrides. After presenting the most important results of high pressure research in this field, we focus on the problem of donors and acce pters in GaN and AlGaN with the special emphasis on the highly localized el ectronic states. Oxygen and silicon donors and their resonant localized sta tes are discussed in detail. Finally the anomaly of the pressure coefficien t of the energy gap of InGaN, will be considered in the relation to the pec uliarities of these mixed crystals band structure.