Pressure Behaviours of N and NNi Traps in Gap

It has been well known that localized electronic states in semiconductors are closely related to the electronic band structure. In fact, exploration of the interrelation between localized electronic states and the band structure represents a basic aspect of the electronic theory of semiconductors. The photoluminescence under high pressure provide an important means for investigating this interrelation. The pressure behaviors of N and NNi traps as well as some other shallow states in GaP have been investigated. We find at both room temperature and 77 K, when the pressure is lower than 3.3 GPa, the single nitrogen traps dominate the luminescence while above 3.3 GPa the free exciton becomes important, we observe nonlinear behaviors associated with the binding of an exciton bound to N and NNi traps. This work shows that the pressure behaviors of whole series of exciton bund to N and NNi in GaP can be quantitatively explained on the basis of the band Green's function taking account of pressure-dependent effective masses. This further confirmed by a Green's function treatment based upon a proper pseudo band structure.