Effect of growth temperature on point defect density of unintentionally doped GaN grown by metalorganic chemical vapor deposition and hydride vapor phase epitaxy

We report on the investigation of the effect of growth temperature on point defect density of unintentionally doped GaN grown by atmospheric pressure metalorganic chemical vapor deposition and hydride vapor phase epitaxy. A c orrelation between photoluminescence (PL) spectra and the concentration of donors and acceptors in unintentionally doped GaN is presented. The effects of oxygen and native acceptors on the electrical and optical properties of GaN epitaxial layers are discussed and a classification of PL data is pres ented. On this basis we show that oxygen creates a shallow donor in GaN wit h an activation energy of about 23.5+/-1 meV. We determine that the concent ration of native acceptors in GaN increases with an increase in growth temp erature. These native acceptors, probably gallium antisites (Ga-N) and/or g allium vacancies (V-Ga), are nonradiative defects. We show that a second do nor level in GaN has an activation energy of about 52.5+/-2.5 meV and produ ces a PL peak with an energy of about 3.45 eV at low temperatures. From Hal l investigations we show that a third donor in GaN has an activation energy of 110+/-10 meV. (C) 1999 American Institute of Physics. [S0021-8979(99)05 405-5].