P-P and As-As isovalent impurity pairs in GaN: Interaction of deept2levels

Abstract

The electronic and atomic structure of substitutional {ital n}th neighbor (1{le}n{le}6) P-P and As-As impurity pairs in zinc blende GaN is investigated using self-consistent plane-wave pseudopotential and empirical pseudopotential methods. A single impurity introduces a deep t{sub 2} gap level; we show that the interaction between the t{sub 2} defect orbitals of the impurity pairs leads to an interesting pattern of single-particle level splitting, being largest for the first (n=1) and fourth (n=4) neighbor pairs, both exhibiting a C{sub 2v} symmetry. The total energy of the {ital n}th order pair {Delta}E{sup (n)} relative to isolated (n{r_arrow}{infinity}) impurities indicates pairing tendency for n=1 and n=2 ({Delta}E{sup (1,2)}{lt}0) while n=4 pairs are unstable ({Delta}E{sup (4)}{gt}0). We explain this behavior of {Delta}E{sup (n)} vs {ital n} as a consequence of the interplay between two effects: an {open_quotes}elastic contribution{close_quotes} representing the interaction between the elastic strain fields of the two impurities and an {open_quotes}electronic contribution{close_quotes} describing the interaction of the defect orbitals of the two impurity atoms. The binding energies of the impurity-pair bound excitons are calculated for the n=1 As-As and P-P pairs and are found to be significantly larger than for the corresponding isolated impurities. The probabilities for electronic transitions between themore » defect levels and conduction band are calculated. The results predict existence of a rich series of spectroscopic features distinct from single impurities. {copyright} {ital 1999} {ital The American Physical Society}« less