Stoichiometry Optimization in InGaN Epitaxy Towards Stimulated Emission in Near Infrared with Minimum Threshold

The results of studies of stimulated emission and spontaneous photoluminescence from InGaN layers with an In content of ~60-100%, obtained on sapphire substrates with GaN/AIN buffer layers by molecular-beam epitaxy with nitrogen plasma activation, are presented. It is shown that at growth temperatures of 470 °C, the optimal ratio of metal fluxes to activated nitrogen (III/V), decreases with increasing Ga content in InGaN from III/V~0.8 for InGaN layers with In >80% to III/V ~0.7 for InGaN layers with In~70%. Such a decrease in the optimal ratio of flows is explained by the improvement in the crystal quality due to the suppression of the processes of phase separation and thermal decomposition in the InGaN layer. A further increase in the Ga content leads to the absence of stimulated emission in InGaN layers with an In content of ~60%, despite the intense spontaneous photoluminescence signal and the high overall crystalline quality of the layers. A possible reason for the sharp increase in the threshold of stimulated emission in InGaN layers with an In content of ~60% is an increase in optical losses due to an increase in the surface roughness of the InGaN layer with a reduction in the III/V ratio.