Pressure studies of defects and impurities in nitrides

A review of the selected results concerning the role of hydrostatic pressur e in studies of impurity and defect centers in III-V nitrides, and in InGaA sN with small amount of N is presented. Firstly, the shallow to deep impuri ty state transition for basic donors, i.e. Si and O in GaN and AlGaN and th eir DX-Iike center behavior is discussed. It corresponds to the localized s tate of the appropriate donor (resonant with the conduction band at low pre ssures) which enters the band gap of GaN or AlxGa1-xN at sufficiently high pressure and/or x value. Next, the concept of pressure application to prove the effective mass character of Mg acceptor in GaN is demonstrated. We als o present results of an anomalous decrease of the pressure coefficient with increasing amount of In in InyGa1-yN for photoluminescence and electrolumi nescence. It is compared with the pressure induced changes of the photocurr ent spectrum in green Nichia diodes which we consider as corresponding to t he variation of the InxGa1-yN band gap with pressure. Finally studies of th e peculiarities of the conduction band structure and related transport prop erties as a function of pressure in InGaAsN are presented.