We studied the development of V-shaped defects in GaInN±GaN quantum well superlattices. We observed that these defects could not be suppressed by varying growth parameters like strain, In content, GaInN growth temperature etc. However, perfect superlattices without such defects could be grown by cycling the temperature between low (for the GaInN wells) and high temperatures (for the GaN barriers). Although a large hydrogen/nitrogen ratio in the carrier gas seems to hinder the defect formation in GaN±AlGaN superlattices, it was not possible to suppress the defect formation in a GaInN±GaN superlattice by decreasing the total nitrogen flow.

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Abstract:We designed and studied two sample groups: first, GaInN/AlGaN/GaN quantum wells with asymmetric barrier structure and secondly, GaInN/GaN quantum wells with asymmetrically doped barriers. Time-resolved measurements on the asymmetric structure reveal an enhanced oscillator strength when the AlGaN barrier is on top of the GaInN quantum well, indicating a better carrier confinement in such a structure. The photoluminescence emission energy of the GaInN/GaN quantum well with doped GaN barriers shifts towards higher energy than that of undoped samples due to screening, but only when the GaN barrier layer below the quantum well is doped. In contrast, the sample where only a GaN cap layer above the quantum well is doped, shows no blue-shift. These results, showing asymmetries in GaInN/GaN quantum wells, provide confirming evidence of the piezoelectric field effect and allow us to determine the sign of the piezoelectric field, which points towards the substrate in a compressively strained quantum well. Furthermore, we performed model calculations of the global band bending and the screening effect, which consistently explain our experimental findings.

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