Remote hydrogen plasma processing of ZnO single crystal surfaces

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Abstract
We have studied the effects of remote hydrogen plasma treatment on the defectcharacteristics in single crystalZnO. Temperature-dependent (9–300 K) and excitation intensity-dependent photoluminescence spectra reveal that H-plasma exposure of ZnO effectively suppresses the free-exciton transition and redistributes intensities in the bound-exciton line set and two-electron satellites with their phonon replicas. The resultant spectra after hydrogenation exhibit a relative increase in intensity of the I 4 (3.363 eV) peak, thought to be related to a neutral donor bound exciton, and a peak feature at 3.366 eV with a distinctly small thermal activation energy. Hydrogenation also produces a violet 100 meV wide peak centered at ∼3.15 eV . Remote plasma hydrogenation yields similar changes in room-temperature depth-dependent cathodoluminescence spectra: the emission intensity increases with hydrogenation mostly in the violet and near-ultraviolet range. Subsequent annealing at 450 ° C within the same plasma environment completely restores both the photoluminescence and cathodoluminescence spectra in the subband gap range. The appearance of another bound-exciton feature at 3.366 eV and a relative intensity increase of the donor-bound exciton at line I 4 with H-plasma exposure, and the reversibility with annealing of the spectral changes, indicate a direct link between hydrogen indiffusion and appearance of a shallow donor.