Abstract

Indium compositional fluctuations in InGaN are crucially important for efficient light emission in such compounds. It was claimed that the quantum-dot-like InGaN aggregations trapped carriers for radiative recombination before they were trapped by defects for non-radiative recombination. This argument explained the efficient light emission in a compound of high defect density. In this paper, we report the results of photoluminescence (PL), stimulated emission (SE), X-ray diffraction, and high-resolution tunneling electron microscopy in the studies on InGaN/GaN quantum well structures grown with MOCVD. In material analyses, we observed clear indium aggregation and phase separation structures. With a higher nominal indium content, the indium composition fluctuation becomes more prominent. In optical measurements, we observed the S-shape PL peak variation as a function of temperature. The turning points of the S-shape variation relies on the nominal indium content. Meanwhile, we observed a two-peak feature in the SE spectra. The short- and long-wavelength peaks correspond to the carrier recombination of free-carrier states and localized states. Figure 1 shows the integrated PL intensity and the PL peak wavelength as functions of temperature of a five-quantum-well InGaN/GaN sample with 25 % nominal indium content. We can clearly see the S-shape variation of the PL peak wavelength. Meanwhile, the relatively slower decay of the integrated PL intensity, compared with other samples of lower nominal indium contents (not shown in the figure), indicates the more prominent indium compositional fluctuations in this sample. Figure 2 shows the SE spectrum at several temperatures. We can see that peak A (corresponding to localized states) drops with increasing temperature. However, its peak position is not changed. Meanwhile, peak B (corresponding to free-carrier states) level increases with temperature and its position red-shifts with temperature. All these observations will be explained in this presentation.

© 2000 IEEE