Photoluminescence study of InGaN/GaN multiple-quantum-wells nanopillars

Abstract

In this thesis, the carrier localization effect, the quantum confinement Stark effect (QCSE) and nonlinear optical properties of the as-grown InGaN/GaN multiple-quantum-wells (MQWs) structure and nanopillars with diameters of 100 nm and 160 nm and height of 700 nm have been investigated with linear and nonlinear photoluminescence (PL) techniques, \n \nIn order to investigate the carrier localization effect and QCSE, “S-shaped” temperature dependent PL peak positions of the samples are quantitatively simulated and analyzed with the localized-state ensemble luminescence model. It is found that after nanotexturing both the carrier localization effect and QCSE become weakened. Moreover, the smaller the pillars the weaker the two effects will be. In addition, the nanotexturing introduced the new radiative recombination pathways of carriers are confirmed on the sidewalls of the nanopillars with cathodoluminescence (CL) spectrum and panchromatic CL image. \n \nTwo-photon absorption (TPA) induced PL spectra of the three samples are measured to investigate the nonlinear optical properties. A peculiar excitation-power dependence, say I~P1.53, of the PL intensity is revealed. It was proposed that a mixed excitation mechanism, namely two-step successive one-photon absorption occurring in the InGaN well layers and one-step two-photon absorption mainly taking place in the GaN barrier and buffer layers, to interpret the observed phenomenon. Besides, the steady-state energetic distribution of carriers excited via this mixed excitation mechanism is very different from that of carriers via one-step one-photon excitation. In contrast with the case of one-photon PL in the samples, the influence of carrier localization effect becomes weaker in the TPA PL of the two nanopillars.