Changes in Optical Properties of GaAsN During Annealing
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Changes in Optical Properties of GaAsN During Annealing Ting Liu1, S. Chandril2, E. D. Schires2, N. Wu3, Xinqi Chen4, D. Korakakis1 and T. H. Myers2 1 Lane Department of Computer Science and Electrical Engineering, West Virginia University, Morgantown, West Virginia 26506 2 Department of Physics, West Virginia University, Morgantown, West Virginia 26506 3 Department of Mechanical and Aerospace Engineering, West Virginia University, Morgantown, West Virginia 26506 4 NUANCE Center, Northwestern University, Evanston, IL 60208 ABSTRACT GaAs1-xNx layers and quantum dot-like structures were grown on (100) GaAs substrates by molecular beam epitaxy. The dependence of photoluminescence emission spectra on annealing temperature is consistent with literature at lower temperatures but after annealing at 750 ºC a net red-shift is consistently observed. X-ray photoelectron spectroscopy measurements indicate that for different annealing times and temperatures, the nitrogen and arsenic surface concentrations changed compared to that of as-grown samples, specifically arsenic is lost from the material. Raman measurements are consistent with the trends in photoluminescence and also suggest the loss of arsenic occurs at higher annealing temperatures in both samples capped with GaAs and uncapped samples. INTRODUCTION GaAsN has attracted a lot of interest because of its potential in long wavelength applications in optoelectronic devices. To date, most research on GaAsN is based on quantum well (QW) or thicker bulk-like structures with low nitrogen content, typically 2-3%, and not more than ~14.8% [1,2]. The predicted reduction of band gap in GaAsN alloys due to the band gap bowing has been clearly demonstrated, which is dependent on the N composition [2-5]. Surprisingly, the majority of the quantum dot (QD) studies involving GaAsN have involved InAs QDs with a GaAsN overlay to reduce strain [6,7]. In this work we report on our studies of annealing GaAsN thin layers and QD-like structures. The general trends in photoluminescence (PL) emission spectra reported in the literature for QWs and single layers, for example by Loke et al. [8], are that after low temperature annealing the initial blue-shift is followed by a slight red-shift in the photoluminescence (PL) spectra observed from nitrogen containing layers. However, in their study of thin GaAsN layers [8] they always observed a net blue-shift after the higher temperatures annealing. In the study reported here, a net red-shift was observed after the highest annealing temperatures. Raman and x-ray photoelectron spectroscopy (XPS) measurements suggest a possible mechanism. EXPERIMENTAL SETUP The GaAsN samples for this study were grown at West Virginia University (WVU) using a VG V80H molecular beam epitaxy (MBE) system. An Oxford Applied Research nitrogen source was used for the RF nitrogen plasma, and arsenic species were generated through an EPI cracker cell operating with a cracking temperature of 550oC. The nitrogen partial pressure and power were varied around the 10-7
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