Fundamental study on surface recombination process and its effects on emission efficiency in nitride semiconductors

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Surface recombination in GaN and ZnO crystals was comparatively investigated usingsteady-state and time-resolved photoluminescence (PL) measurements. The measurementswere performed for various surface orientations (+c,-c, and m-plane surfaces), and themeasured PL intensity and lifetime showed distinct dependence on the surface orientation.The dependence clearly indicates that the surface recombination rate is modified by theeffects of surface band bending. The results were also verified by numerical analysisusing a rate equation model considering the diffusion of photoexcited carriers and theirrecombination processes on the surface and inside the crystal.