Diffusion Analysis of Charge Carriers in InGaN/GaN Heterostructures by Microphotoluminescence

Lateral ambipolar diffusion in an InGaN/GaN single quantum well (SQW) structure grown on bulk GaN is studied by microphotoluminescence (mu PL) investigations. The analysis is done via pinhole scans, that is, by decoupling the excitation area from the detection area and scanning the latter one. Knowing the size of the excited region, conclusions about the carrier transport in the in-plane layer of the QW can be drawn. In this study, a diffusion length Ld up to 12 mu m is observed at room temperature. Furthermore, the energy of the spectral peak is analyzed as a function of distance, showing a pronounced blueshift at the excitation center. An increase in distance to the injection region is accompanied by a redshift. The indication of peak energy is used to relate the drop of PL intensity with increasing radius to actual diffusion of charge carriers. In addition, temperature-dependent studies of the diffusion behavior are done, covering the range between 10 K and room temperature. No significant change of diffusion length can be seen with temperature, indicating that temperature dependencies of carrier lifetime and of mobility compensate each other.