Surface emission of In_xGa_1-xN epilayers under strong optical excitation

Effects of strong optical excitation on the properties of surface emission from an InGaN/GaN heterostructure grown by metal-organic chemical-vapor deposition have been investigated. An intriguing feature observed was that as the excitation intensity increased the surface emission spectrum evolved abruptly from a single dominating band to two dominating bands at a critical intensity. This phenomenon has a sharp phase transition or a switching character and can be accounted for by (i) the formation of an electron-hole plasma state in the InGaN vertical cavity under strong optical excitation, (ii) the photoreflectance effect (variation of index of refraction with excitation intensity), and (c) the Fabry-Pérot interference effect in the InGaN vertical cavity. These findings are expected to have impact on the design of the laser structures, in particular on the design of the vertical-cavity surface-emitting laser diodes based on III-nitride wide-band-gap semiconductors.