Mechanism of yellow luminescence in GaN at room temperature

Abstract

We investigated the excitation intensity (Φ) dependent photoluminescence (PL), at room temperature (RT), from GaN-based metal-insulator-semiconductor structures under gate bias (VG) from accumulation to deep depletion resulting in variations of the space charge region width. We found that depending on VG, different Φ-dependencies of the YL band energy position (blueshift or redshift), shape (band enlargement or narrowing) and intensity (signal saturation) can be obtained. In order to explain such an unusual YL behavior, we developed a phenomenological PL model, which is based on the solution of the three-dimensional Poisson's equation, current continuity equations and rate equations, and which takes into account the grain structure of GaN layers and the contribution of interface regions into recombination processes. Our model reproduced well the experimental Φ-dependencies of the YL band intensity. It also predicts that YL arises from the donor-acceptor pair (DAP) recombination in very limited areas (width of several nanometers) inside the depletion regions related to grain/grain interfaces and external crystal surfaces. On this basis, we showed that VG-controlled Φ-dependencies of the YL peak position and shape, can be well explained if we assume that YL is due to DAP-type transitions, in which the final state consists of the Coulomb interaction and strong interaction between the dipole moment of ionized DAP and the depletion region electric field. This recombination mechanism can play a significant role at RT, but should be negligible at low temperatures, where one can expect the significant reduction of interface barriers under illumination.