Study of high quality AIN layers grown on Si(111) substrates by plasma-assisted molecular beam epitaxy
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Internet Journal o f
Nitride S emiconductor Research
Volume 2, Article 33
Study of high quality AlN layers grown on Si(111) substrates by plasma-assisted molecular beam epitaxy M. A. Sánchez-García, E. Calleja, E. Monroy, F. J. Sánchez, F. Calle, E. Muñoz Dpt. Ingeniería Electrónica, E.T.S.I. Telecomunicación, Politécnica, Ciudad Universitaria A.Sanz. Hervas, C. Villar, M. Aguilar Dpto Tecn. Electronica, ETSIT. Univ, Politecnica Madrid This article was received on June 11, 1997 and accepted on September 15, 1997.
Abstract High quality AlN layers with full widths at half maximum values of 10 arcmin and average surface roughness (rms) of 48Å were grown by molecular beam epitaxy on Si(111) substrates. A systematic study and optimization of the growth conditions was performed in order to use these AlN layers as buffers in the growth of GaN films. Atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques were employed to determine the surface and structural quality of the layers. Best AlN films were obtained at high substrate temperatures (Tsubs>900°C) and III/V ratios close to stoichiometry. Growth conditions with III/V ratios beyond stoichiometry (Al-rich) did not further improve the crystal quality. In these cases a higher substrate temperature is needed to prevent condensation of Al on the surface. GaN films with full width at half maximum of 10 arcmin and improved optical properties were grown on top of optimized AlN buffer layers.
1. Introduction Growth of group III nitrides has received a great deal of attention during the last few years because of their potential as materials for optoelectronic devices in the blue to ultraviolet spectral range. Room-temperature continuous-wave operation of InGaN multi-quantum-well laser diodes have already been reported on sapphire substrates by metal organic chemical vapor deposition (MOCVD) techniques [1]. However, silicon-based nitride epitaxy offers the potential for cointegration of wide band-gap optoelectronics devices with large scale circuits employing silicon-based technology. A common approach in the growth of GaN films is the use of buffer layers to improve the quality of the material [2] [3]. It is important to obtain very smooth and low defect density buffers on which to grow high quality GaN [4]. In this work we present a systematic study of the growth conditions of AlN on Si(111) by plasma assisted molecular beam epitaxy (MBE). Atomic force microscopy (AFM) and X-ray diffraction (XRD) techniques enable the assesment of the material quality. Optimization of the growth conditions leads to high quality AlN layers which are then used as buffer layers in the growth of GaN films.
2. Experimental AlN films were grown by MBE on Si(111) substrates which had been previously cleaned following a modified Shiraki procedure. Substrates were heated at 930°C for 20 minutes in the growth chamber until a 1x1 reconstruction appeared. When lowering the substrate temperature to 780°C, a 7x7 reconstruction with prominent Kikuchi lines appeared, indicating a high qualit
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