Structural, Optical and Electrical Properties of InGaN Sputtered Thin Films
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Structural, Optical and Electrical Properties of InGaN Sputtered Thin Films Mohammad A. Ebdah, Daniel R. Hoy, Martin E. Kordesch. Department of Physics and Astronomy, Ohio University, Athens, OH 45701, USA. ABSTRACT InGaN films were successfully fabricated using radio frequency (RF) magnetron sputtering technique with a sputtering target of pure In and Ga metal alloys under a flow of nitrogen. Films were deposited on quartz substrates, with the ratio of In to Ga varied from 0.46 to 0.85 in the alloys. The structures and compositions have been studied using X-ray diffraction (XRD) and energy dispersive x-ray spectroscopy (EDX), respectively. Multiple crystallographic phases have been observed indicating phase segregation and inhomogeneous distribution of the metal compositions in the films. The existence of wurtzite structures has been observed in all samples, with the In percentage (y) in a crystalline phase calculated from the XRD being less than the total In percentage (x) in each film as determined by the EDX spectroscopy. The (0002) orientation has been observed in all films, and the (10-11) orientation has been observed for x = 0.46 and 0.70 only. The optical transmission and absorbance of the films were studied by the spectrophotometry technique, which indicate that the dominant phases in all samples are amorphous. Consequently, the corresponding optical bandgaps have been characterized. Hall Effect measurements were made in 0.55 T magnetic field at room temperature to characterize the electrical conductivity, free carrier concentration, and mobility. INTRODUCTION The band gap of ternary III-nitride semiconductor, InGaN, extends from 0.8 to 3.4 eV covering the entire visible range. The incorporation of InGaN in device applications has been well established such as in blue and green light emitting diodes (LEDs)[1-3]. InGaN has been extensively grown at temperatures higher than 600 oC by organometallic vapor phase epitaxy (OMVPE) [4-6], molecular beam epitaxy (MBE) [7], and metal organic chemical vapor deposition (MOCVD) [8]. The growth conditions influence the compositional, structural, and electronic properties of InGaN films. The most challenging problems are the phase separation and composition inhomogeneity. Amorphous InGaN grown by magnetron sputtering has not yet been explored. Therefore, in the present study, we grow InGaN on fused silica by RF-magnetron sputtering at room temperature (RT) and (-40 oC). We investigate the obtained structures and compositions. The optical transmission, optical bandgap, and Hall Effect measurements have been also included. EXPERIMENT InGaN alloys were grown by RF-magnetron sputtering technique with a sputtering target of pure In and Ga metals under a flow of Nitrogen. Films were deposited on fused silica substrates, with the ratio of In to Ga varied from 0.46 to .85 in the alloys. Five samples have been grown; samples #(1-4) were grown at room temperature, while sample #5 was grown on a cooled substrate at -40 oC temperature using dry ice. The base pressure o
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