Apriori Process-Property Relationships of GaN Epitaxial Growth in Ga/N/H/C/O Systems
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Apriori Process-Property Relationships of GaN Epitaxial Growth in Ga/N/H/C/O Systems Constantine Loukeris, Shumaila Khan and Christos G. Takoudis Department of Chemical Engineering, Advanced Materials Research Laboratory University of Illinois at Chicago, Chicago, Illinois 60607, USA ABSTRACT A comprehensive thermodynamic analysis has been performed for the Ga/N/H/C/O system. Apriori process-property relationships of the metal organic chemical vapor deposition (MOCVD) of Gallium Nitride (GaN) are thus obtained. The parameter space for pure GaN growth is studied for system water vapor levels of 0.1 ppb – 10 ppm, system pressure between 10-6 - 106 Torr, N/Ga feed ratios of 1 - 100,000, C/Ga feed ratios of 0 – 100, and H2/Ga feed ratios of 100 – 10,000. Higher growth temperatures for pure GaN are predicted at high operating pressures (for pressures greater than 0.1 Torr), low C/Ga feed ratios, high carrier gas flow rates, and mostly at low N/Ga feed ratios. Because relative C/Ga, N/Ga and H2/Ga feed ratios have been considered, the predictions in this study are applicable to any multiple and single precursor systems. Such analyses can be easily extended to the molecular beam epitaxy of GaN, when the feed ratio C/Ga = 0. Experimental data reported on the growth of GaN are found to be in good agreement with our theoretical predictions, for many systems that have included different source species. INTRODUCTION Gallium nitride is a promising wide band-gap semiconductor because of its potential applications to optoelectronics and high temperature, high power microelectronic devices resistant to radiation damage. High quality gallium nitride can be grown by metalorganic chemical vapor deposition (MOCVD) [e.g.,1-9], molecular beam epitaxy (MBE) [e.g.,10], and pulsed laser deposition [11]. Studies involving the characterization of the GaN crystals have also included the thermodynamic properties of GaN at high pressures [12]. Previous studies on the thermodynamic analysis of the epitaxial growth of GaN have either focused on a specific reaction system or considered a small number of chemical reactions [e.g., 13-15]; the latter approach may, therefore, yield results of very limited value. All previous GaN thermodynamic studies have considered ideally clean systems only. A primary objective of this study is to predict the operating parameter space within which epitaxial films of pure GaN can grow in the Ga/N/H/C/O system; these studies would include, for example, the maximum (or minimum) temperature required to grow GaN without carbon codeposition. Operating conditions in which carbon species are predicted to co-deposit with GaN are also presented. Further, the effects of the system water vapor level, the C/Ga feed ratio, the N/Ga feed ratio, the H2/Ga feed ratio, and the system pressure on the CVD of pure GaN are presented. In contrast with previous analyses of GaN growth, this study (i) considers water vapor impurity levels on the conditions suitable to GaN epitaxial growth, (ii) is applicable to any multiple or single precurso
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