Growth and Characterization of AlN and GaN Thin Films Deposited on Si(111) Substrates Containing a Very Thin Al Layer
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Growth and Characterization of AlN and GaN Thin Films Deposited on Si(111) Substrates Containing a Very Thin Al Layer Zachary J. Reitmeier and Robert F. Davis Materials Science and Engineering North Carolina State University Raleigh, NC 27695-7919, U.S.A. ABSTRACT AlN films and GaN films with AlN buffer layers were deposited via metalorganic vapor phase epitaxy on Si(111) substrates previously exposed to trimethylaluminum for increasing times. Atomic force microscopy (AFM) was used to determine the influence of Al pre-flow time on the nucleation and surface morphology of the AlN and GaN films. When preceded by a 10 second Al pre-flow, AlN films feature an increased and more uniform nucleation density as compared to films deposited without Al pre-flows. Ten second Al pre-flows were also found to result in a reduction of the RMS roughness for 100 nm thick AlN films from 3.6 nm to 1.0 nm. AFM of 0.5 µm thick GaN films deposited on AlN buffers with varying pre-flow times showed reduced roughness and decreased pit density when using Al pre-flows of 10 or 20 seconds. High resolution x-ray diffraction of the GaN films showed a reduction in the average full-width halfmaximum (FWHM) of the GaN (00.2) reflection from 1076 arcsec to 914 arcsec when the AlN buffer layer was initiated with a 10 second Al pre-flow. Increasing the pre-flow time to 20 seconds and 30 seconds resulted in average (00.2) FWHM values of 925 arcsec and 928 arcsec, respectively. Similar behavior of the peak widths was observed for the (30.2) and (10.3) reflections when the pre-flow times were varied from 0 to 30 seconds. INRODUCTION Silicon (111) represents an attractive alternative to sapphire and silicon carbide for IIInitride heteroepitaxy due to its low cost, nearly defect free microstructure over large areas, wide range of available resistivities, and the possibility for integration of III-nitride based devices with Si-based devices on one chip. Due to the meltback etching of Si by Ga, it is necessary to employ a buffer layer of another material for deposition of GaN [1]. Some materials which have been employed as buffer layers include GaAs [2], oxidized AlAs [3], , 3C-SiC [4], and AlN [5,6]. This work will focus on the use of an AlN buffer layer since the lattice mismatch induces a compressive stress in the GaN, which can partially compensate for the thermally induced tensile stress [7] between GaN and Si, and is easily deposited in a conventional III-nitride metalorganic vapor phase epitaxy system (MOVPE) system. In using AlN as a buffer layer, numerous researchers have reported the formation of an amorphous 1-4 nm thick SixNy layer at the Si/AlN interface [5,8,9,10], purportedly due to the thermal nitridation of the Si surface in an ammonia atmosphere. This amorphous layer is reported to be discontinuous or of varying thickness across the interface. Indeed, in studying the nitridation of Si(111) in various nitriding agents, Wang et. al. observed SixNy forming at temperatures above 800°C and saturating at a thickness of 2 nm [11]. It is t
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