Internal Quantum Efficiency of InGaN quantum dots : Polar vs. Semipolar

Polar (0001) and semipolar (11-22) InGaN quantum dots (QDs) were grown simultaneously by plasma-assisted MBE. Photoluminescence measurements confirm the superior internal quantum efficiency of these QD structures compared to polar InGaN quantum wells (QWs), as a result of the 3D carrier confinement. In the present study, for the synthesis of the InGaN QDs, two growth methods were considered, namely high-temperature growth (substrate in the 650-510°C range, where In desorption is active) and low-temperature growth (substrate in the 460-440°C range, where In desorption is negligible). Polar QDs grown at high temperature showed better thermal stability of their luminescence than that of the semipolar QDs, due to the higher density of structural defects in the semipolar heterostructure. In contrast, at low temperature growth conditions, the only emission from polar QDs is a broad band located around 630 nm wavelength, which corresponds to the spectral location of the yellow band in cubic GaN. At this temperature range, semipolar QDs showed a significant enhancement in the internal quantum efficiency, particularly for samples emitting at longer wavelengths. Therefore, by adequate tuning of the growth parameters, we demonstrate the synthesis of semipolar InGaN/GaN QDs emitting in the 380-700 nm spectral range.