Abstract
We have investigated the relation between the exciton photoluminescence intensity and distortion of the crystal plane in a ZnO wafer. The present investigation utilizes the following two characterization methods that complement the result of the photoluminescence measurement: a circular polariscopic measurement and a θ-2θ x-ray diffraction measurement. The circular polariscopic map clarifies the distribution of the strain exists in the ZnO wafer. The strain found in the circular polariscopic analysis indicates the existence of the crystal-plane distortion, which is confirmed from the appearance of the forbidden reflection line in the x-ray diffraction pattern. The photoluminescence measurements at different positions sensitive to the crystal-plane distortion were performed on the basis of the above-mentioned complementary information. It is found that the crystal-plane distortion causes the enhancement of the exciton photoluminescence intensity. The responsible factor is attributed to the suppression of the exciton diffusion caused by the crystal-plane distortion. This is in contrast to the usual interpretation that the lowering of the crystalline quality leads to the reduction of the exciton photoluminescence intensity; namely, the aid of complementary information is essential to precisely interpret the photoluminescence intensity.
Highlights
Photoluminescence measurements are widely utilized as a method for the characterization of various semiconductors because they have the ability of providing a large amount of information on the properties of semiconductor samples
We demonstrate that the exciton photoluminescence intensity is enhanced by the distortion of the crystal plane in a ZnO wafer
We have systematically investigated the exciton photoluminescence intensity in the ZnO wafer with use of the following complementary characterization methods: the circular polariscopic measurement and θ -2θ x-ray diffraction measurement
Summary
Photoluminescence measurements are widely utilized as a method for the characterization of various semiconductors because they have the ability of providing a large amount of information on the properties of semiconductor samples. We demonstrate that the exciton photoluminescence intensity is enhanced by the distortion of the crystal plane in a ZnO wafer. Taking account of the fact that the presence of the crystal-plane distortion corresponds to the lowering of the crystalline quality, the present finding indicates that the above-mentioned common sense is not always validated. In order to reveal the effect of the internal strain on the crystal plane, we show the θ -2θ x-ray diffraction patterns of the characteristic regions in the circular polariscopic map: one dark region being free from the strain and two bright regions containing the relatively large strain. We plot the exciton photoluminescence peak intensity as a function of distance along a given direction From this plot, it is found that the exciton photoluminescence peak intensity is increased by the internal strain causing the crystal-plane distortion.
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