Dislocation Reduction and Structural Properties of GaN layers Grown on N + -implanted AlN/Si (111) Substrates
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Dislocation Reduction and Structural Properties of GaN layers Grown on N+-implanted AlN/Si (111) Substrates. M. Jamil, J. R. Grandusky, V. Jindal, N. Tripathi and F. Shahedipour-Sandvik* College of Nanoscale Science and Engineering, University at Albany-State University of New York, 255 Fuller Rd, Albany, NY 12203, U.S.A. ABSTRACT An alternative scheme to the growth of crack free, dislocation reduced III-Nitride layers on Silicon substrate has been previously introduced that relies on formation of an ion implanted defective layer in the substrate with implantation taking place in the presence of AlN buffer layer. Here, the effects of N+ ion implantation of AlN/Si (111) substrate on the structural and optical properties of the overgrown GaN epilayers have been investigated. Temperature dependent photoluminescence has been used to investigate the impact of the implantation conditions (energy and dose) on optical and structural quality of the GaN overgrown layers. A correlation between PL and high resolution x-ray diffraction (XRD) of the overgrown GaN layers show that the lowest FWHM of bandedge, the highest bandedge to deep defect blue luminescence band ratio, and the lowest symmetric rocking curve FWHM are achieved for the optimized implantation conditions. This correlates well with the results of etch pit density measurement showing an order of magnitude reduction in threading dislocation defect density. INTRODUCTION The epitaxy of GaN on Silicon has attracted much attention and offers considerable cost benefits compared with the growth on sapphire or SiC. The potential integration of GaN based optoelectronic devices with Si based electronics is another driver behind highly pursued GaN/Si heteroepitaxy [1]. Si, with well characterized electrical and thermal properties can also meet the requirements for large diameter and high quality substrate availability. However large thermal expansion coefficient (116%) and lattice mismatch (~17%) between GaN and Si substrate poses serious problems such as cracks and high dislocation density and hinder the rapid development of GaN devices based on silicon. Various approaches [2, 3, 4, 5, 6, 7, 8, 9, 10] and buffer schemes [11, 12, 13, 14, 15, 16] have been undertaken to overcome the issues posed by the strain and achieve better quality films, with varying degrees of successes. We have developed a scheme of substrate engineering by which dislocations can be reduced significantly, simultaneously achieving nearly crack free films within a single set of experimental conditions [17, 18]. In this article, we are reporting further study and effects of ion implanted defective layer in the substrate on the optical quality of overgrown GaN epilayers. Temperature dependant behavior of band edge and defect related luminescence bands have been investigated for GaN films grown on both non-implanted and implanted AlN/Si substrates. Films grown on engineered substrates show improved crystal quality and significant reduction in dislocations for optimized
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