Photoluminescence and Raman Spectra of Flux Processed Bulk Single Crystal GaN
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Photoluminescence and Raman Spectra of Flux Processed Bulk Single Crystal GaN Chae Ryong Cho1, Sang Eon Park1,2, Yong Chan Cho1,2 and Se-Young Jeong2 1 COMTECS Ltd, Advanced Materials Research Laboratory, Taegu, 704-702, KOREA 2 Department of Physics, Pusan National University, Pusan, 609-735, KOREA ABSTRACT Bulk wurtzite-GaN crystal was obtained with a size more than 3 mm along the length of the and 100 bar for 24 hrs in the flux crystal and with a thickness 200 ~ 300 µm at around 750 growth method. The structural and compositional property of the GaN bulk single crystal was also studied by X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) techniques. Photoluminescence, cathodoluminescence and micro-Raman measurements at room temperature are investigated for bulk single crystals of wurtzite GaN. The cathodoluminescence peak of near band-to-band transition at 365.5 nm and the E2(high energy, 568 cm-1) and A1(LO, 737 cm-1) Raman phonon modes were obtained according to the different position of the (0001) surface of GaN grown by flux method. Sharp line shape for the strain-sensitive E2 (high) mode is considered to be due to the high crystalline quality of the crystal. INTRODUCTION GaN has been known to be one of most promising wide band gap semiconductor material for their application in light-emitting diodes (LEDs) and laser diodes (LDs) [1,2]. One of the main problems in fabricating high-quality GaN layers is the large lattice mis-match between GaN film and substrates [3]. Hence, bulk GaN single crystals are the most suitable substrates for homoepitaxial growth for high-quality nitride-based laser diodes and devices. But, it is very difficult to grow bulk GaN by standard methods used for most other semiconductors, such as Czochralski or Bridgeman growth. GaN crystals must be grown by other methods that utilize lower temperatures [4]. Presently, bulk GaN crystals have been prepared by high-pressure using nitrogen over high-temperature technique [5]. The various techniques have been attempted to grow GaN like vapor phase [6,7], sublimation method [8], free-standing hydride-vapor-phaseepitaxy [9], and high-pressure process [10]. It was reported that bulk GaN crystals using Na flux and a pressures of ~100 bar with sizes of about 1 mm were grown at a temperature of ~800 for 100 hrs [11,12]. The studies on the surface properties and optical quality for bulk GaN crystal grown by the flux method have not yet been carried out in detail. In the present study, we report and 100 the growth of bulk wurtzite-GaN crystal with a size more than 3mm at around 750 bar for 24 hrs in the flux growth method. Crystal morphology was investigated by using scanning electron microscopy (SEM), while structural characteristics were evaluated using x-ray diffraction. The optical properties including photoluminescence (PL), cathodoluminescence (CL) and micro-Raman spectroscopy techniques of GaN were also discussed. Surface chemical bonding states of the bulk GaN crystal were measured and characterized by X-ray photoelectron spect
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