Photostimulated emission of GaN layers and devices

Photostimulated emission (PSE) of epitaxial GaN layers is readily obtained at photoexcitation densities of order MW cm−2 at temperatures up to room temperature. We report surprising spectral differences between PSE obtained using surface and edge emission geometries for a particular sample. While the peak energy of PSE from the surface of this sample is downshifted from the GaN band edge by only a small amount, the photon energy of the edge-emitted light is reduced by ∼100 meV. Exactly the same downshift is observed in the edge emission spectrum of a commercial Nichia light emitting diode. The origin of the anomalous PSE peaks revealed in these measurements is discussed with reference to recent literature.