Deep electronic gap levels induced by isovalent P and As impurities in GaN

The electronic and atomic structure of isovalent substitutional P and As impurities in GaN is studied theoretically using a self-consistent plane-wave pseudopotential method. In contrast with the conventional isovalent III-V systems, Ga (N) under bar:P and Ga (N) under bar:As are shown to exhibit deep gap levels. The calculated donor energies are epsilon(+/0)=epsilon(upsilon)+0.22 and epsilon(upsilon)+0.41 eV, respectively, and the double donor energies are epsilon(++/+)=epsilon(upsilon)+0.09 and epsilon(upsilon)+0.24 eV, respectively. The p-like gap wave function is found to be strongly localized on the impurity site. Outward atomic relaxations of similar to 13% and similar to 15% are calculated for the nearest-neighbor Ga atoms surrounding neutral Ga (N) under bar:P-0 and Ga (N) over bar:As-0, respectively. The relaxation increases by similar to l% for the positively charged impurities. The impurity-bound exciton binding energy is calculated at E-b=0.22 and E-b=0.41 eV for Ga (N) under bar:P and Ga (N) under bar:As. The former is in good agreement with the experimental data (E-b=0.232 eV) whereas the latter is offered as a prediction. No clear Jahn-Teller symmetry lowering (T-d-->C-3 upsilon) distortion, suggested by the one-electron configuration, is found for Ga (N) under bar:P+ and Ga (N) under bar:As+. [S0163-1829(98)04727-4].