Study of Optical Gain in Thick GaN Epilayers by Variable Stripe Length Technique

Abstract

AbstractWe report on the gain study in high-quality thick GaN layers using the Variable Stripe Length (VSL) technique. The layers were grown by Migration Enhanced Metal Organic Chemical Vapor Deposition (MEMOCVDTM). The amplification of light was investigated for the propagation directions along the layer surface (perpendicular to the c-axis of the crystal) and perpendicular to the layer (along the c-axis) for the layers with thicknesses up to 11 νm. By fitting the experimental stripe length dependence of the edge luminescence with one-dimensional description of light amplification in medium with positive gain, peak gain coefficients of up to 7300 cm-1 were estimated in GaN at the excitation power density of 2 MW/cm2. We discuss limitations of the VSL technique due to the assumption of one-dimensional light propagation and strong influence of gain saturation in a high-gain medium. The contribution of new gain modes after saturation of the highest-gain modes was observed. The optical gains in GaN samples with different carrier lifetimes (obtained using time-resolved photoluminescence and light-induced transient grating techniques) were compared.