Effect of Growth Conditions on Defect-related Photoluminescence in ZnO Thin Films Grown by Plasma Assisted MBE
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1035-L09-02
Effect of Growth Conditions on Defect-related Photoluminescence in ZnO Thin Films Grown by Plasma Assisted MBE Vitaliy Avrutin1, Mikhail A. Reshchikov2, Natalia Izyumskaya1, Ryoko Shimada1, and Hadis Morkoç1 1 Electrical Engineering, Virginia Commonwealth University, 601 West Main St., Richmond, VA, 23284 2 Physics, Virginia Commonwealth University, 1020 West Main St., Richmond, VA, 23284 ABSTRACT The effect of growth conditions on the luminescence properties of ZnO films grown on aAl2O3/GaN(0001)/c-Al2O3 templates by plasma-assisted molecular beam epitaxy has been investigated. We observed that the deflecting of the ions produced by the RF oxygen plasma away from substrate results in improved excitonic emission and modification of the defect-related PL spectrum. The intensity of the near-band-edge lines in photoluminescence spectra from the layers grown with the ion deflector deflection was found to increase as compared to the controls grown without the ion deflector. The yellow-green spectral range was dominated by different defect bands in the films grown with and without ion deflection. The effect of RF power on peak positions of the defect band was studied for the films grown without ion deflection. INTRODUCTION ZnO has attracted considerable interest owing to its outstanding optical properties. Therefore, it comes as no surprise that a great number of articles have been dedicated to investigation of photoluminescence (PL) in this material. In addition to numerous sharp lines due to recombination of excitons, a typical low-temperature PL spectrum from undoped ZnO contains broad, defect-related bands in the red and yellow-green parts of the spectrum [1]. Most studies focus on the excitonic spectral range, whereas much less attention has been given to defect-related luminescence from ZnO. It is expected that investigation of defect-related emission bands and understanding of their relation to growth conditions can shed some light on the nature of defects responsible for these bands and pave the way for controlling the defect composition of ZnO that is believed to be a key to successful p-type doping. One of the most popular approaches for growing high quality ZnO thin films is plasma-assisted molecular beam epitaxy (MBE). Irradiation of a layer during growth with low-energy ions generated by plasma source, inherent to plasma-assisted MBE, has been reported to affect crystal structure and optical properties of GaNAs [2] and GaPN [3]. Despite the fact that ZnO is believed to be a radiation hard material [4], ion-induced plasma damage of ZnO films can give rise to the formation of defects contributing to the PL spectra. In this contribution, we report on the effect of plasma-induced damage on the PL spectra of ZnO films grown by plasma-assisted MBE with a special attention paid to the defect-related broad bands in the yellow-green spectral range.
EXPERIMENTAL DETAILS
Emission intensity (arb. units)
ZnO layers were grown by plasma-assisted molecular-beam epitaxy on a-plane sapphire and GaN(0001)/c-sa
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