Temperature and excitation power behaviour of the emission from low dimensional structures can provide important information about localisation effects, strain and electric field distribution. Usually it is difficult to separate the contribution of the particular effect on the observed photoluminescence. In order to understand the influence of those effects photoluminescence measurements in the temperature range 4.2-300K on GaN/AlGaN quantum wells (QW) of different width were performed.
The investigated structures consisted of several GaN QWs of nominal width: 1nm, 1.5nm, 2.5nm, 4nm and 6nm embedded in Al0.15Ga0.85N barriers. Energy positions of the emission observed for QW wells with different width vary from 3.14eV (for 6nm QW) up to 3.52eV (for 1nm QW) as the result of strong built-in electric fields. The increase of the excitation power results in the blue shift of the widest well and the red shift of the narrowest well emission. The magnitude and direction of the energy shift depends on the temperature.
Moreover, the temperature behavior of the QWs emission is entirely different from that observed for unstrained bulk GaN. The particular effect depends on the well width. The observed emission energies exhibit so-called S-shape like temperature behavior. Such dependence is usually interpreted as due to localization of excitons in the QW caused by well thickness fluctuations and/or structural disorder.
The observed results can be understand assuming that not only potential fluctuation but also built-in electric field and strain effects must be taken into account. The role of the particular mechanisms is discussed.