HRTEM study of strain energy distribution on the self-organized in-rich quantum dots of the InGaN/GaN quantum wells

Abstract

Summary form only given. The formation of quantum-dot structures will induce strain energy in the quantum well layer, optical measurements of photoluminescence (PL) spectral peak and microstructure analyses with high-resolution transmission electron microscopy (HRTEM) showed the strong dependency on quantum well (QW) width in InGaN/GaN QW structures. Quantum-dot-like structures are formed because of the large lattice mismatch between InN and GaN, which will result in potential fluctuations and hence the effect of carrier localization (CL). Due to the strain energy, quantum dot structures will also be built during the growth of InGaN QW layers. Therefore, the designated QW width becomes a crucial factor in cluster formation and the consequent photon emission characteristics. In this study, we had done our first time to calculate the strain energy distribution around the QDs. Due to the higher strain energy built in the QW layer, the QDs structures are clearly observed on 4 nm well widths (w40) sample. High strain energy is expected in w40, due to the higher strain energy might be relaxed through the formation of thread dislocations or local lattice distortions in the QW layers, and they also led to quite poor photon emission efficiency. PL spectral peak variations with temperature of the three samples under various thermal annealing conditions. After thermal annealing, the S-shape variation of PL peak is maintained in each case. Thermal annealing results in blue shifts of PL peak in w20 and red shifts in w30 and w40. At 3 nm well widths, more gathering of indium structures appear in barriers and again affected the distribution of strain energy and the atomic-scale HRTEM images of sample. However, especially at 4 nm well widths, because the larger well width leads to larger strain energy, spinoidal decomposition becomes less effective. In this situation, the strain energy might be relaxed through the formation of more stacking faults or local lattice distortions. Stacking faults and local distortions were easily observed in atomic-scale HRTEM images of the sample. In conclusion, we have shown different level distribution of strain energy observed in each sample of different QW widths.