Abstract
Optical characteristics of hexagonal GaN (h-GaN) and cubic GaN (c-GaN) self-assembled quantum dots (QDs) were investigated by means of photoluminescence (PL), PL excitation, cathodoluminescence (CL), and time-resolved PL experiments. We observed a Stokes-like shift between PL excitation absorption edge and PL emission from the h-GaN QDs as well as Al(Ga)N base layer. With increasing temperature, the PL intensity of Al(Ga)N base layer or GaN quantum wells was dramatically decreased while that of GaN QDs was not changed much. We also observed wavelength-resolved CL images reflecting strong carrier localization in the QD confinement. From the time-resolved PL experiments, we found that the measured lifetime of the h-GaN QDs emission increased with decreasing emission energy (i.e., increasing QD size), while that of the c-GaN QDs kept almost constant. Therefore, we conclude that the h-GaN QD emissions are strongly influenced by built-in interal electric field as well as carrier localization in the QDs.
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