Reduced radiative emission for wide nonpolar III-nitride quantum wells

The radiative rate of GaInN/GaN quantum well structures on nonpolar substrates is investigated for different quantum well widths, showing a significant decrease of the radiative emission towards larger well widths. This effect can be explained by the strict selection rules that apply for radiative transitions in nonpolar structures without any polarization fields in the direction of quantization. The selection rule Delta n = 0 reduces the number of possible radiative transitions that involve higher quantized hole states. These states will get occupied towards room temperature for wider quantum wells due to the decrease in quantization energies. Since the effective masses are strongly different in the conduction and valence bands, the thermal population of higher states is imbalanced between electrons and holes. Applying a simple model in a nondegenerate limit, we can well describe the width dependence of the experimentally determined radiative rates. At room temperature, the decrease amounts to a factor of 2-4 for nonpolar quantum wells of 8 nm thickness.