Time-Resolved Studies of InGaN/GaN Quantum Dots

Abstract

We report on structural and optical properties of InGaN inclusions in a GaN matrix. High-resolution transmission electron microscopy (HRTEM) studies and HRTEM image processing indicate the spontaneous formation of ultra-dense arrays of InGaN disc-like nano-inclusions. Non-resonant pulsed excitation results in a broad photoluminescence (PL) peak, which shifts towards longer wavelengths with time, demonstrating also an increase in decay time at the peak maximum. In contrast to that, resonant excitation into the non-resonant PL maximum results in an evolution of a sharp resonant PL peak, having a spectral shape defined by the excitation laser pulse and a radiative decay time close to that revealed for PL under non-resonant excitation. No spectral diffusion or PL peak energy shift caused by reduced piezoelectric screening at lower overall concentrations of non-equilibrium carriers was found. These observations give a clear proof of the quantum dot nature of PL in our InGaN/GaN samples.