Jiandong Meng Yogesh Jaluria Hon. Mem. ASME e-mail: jaluria@iov8.rutgers.edu Department of Mechanical and Aerospace Engineering, Rutgers, The State University of New Jersey, Piscataway, NJ 08854 Numerical Simulation of GaN Growth in a Metalorganic Chemical Vapor Deposition Process A detailed mathematical model for the growth of gallium nitride in a vertical impinging metalorganic chemical vapor deposition (MOCVD) reactor is developed first, and the complete chemical mechanisms are introduced. Then, one validation study is conducted to ensure its accuracy. After that, the flow, temperature and concentration profiles are predicted by numerical modeling. The dependence of the growth rate and uniformity of the deposited layers on operating conditions, such as reactor operating pressure, suscep- tor temperature, inlet velocity and concentration ratio of the precursors, is investigated to gain greater insight into the reactor performance and characteristics. Based on the simulation results, discussion is presented in this paper to offer the possibility of better control of the GaN film growth process and to ultimately lead to an optimization of the process, with respect to production rate and film quality. [DOI: 10.1115/1.4025781] 1 Introduction Gallium nitride (GaN) is one of the most important semicon- ductor materials, with wide band-gap and high breakdown field properties, which has been shown to have tremendous potential in electronic and optoelectronic devices. The mixture of GaN with In (InGaN) or Al (AlGaN), with a band gap dependent on ratio of In or Al to GaN, makes it suitable for manufacturing green, blue, ultraviolet (UV), and eventually white light emitting diodes (LEDs) [1], which have important advantages over traditional in- candescent or fluorescent light. As a starting point for the application of GaN, the film growth of GaN provides a base for improving the technology. In the liter- ature, GaN thin films have been successfully deposited onto sev- eral substrates made of sapphire and silicon carbide [2], by using the metalorganic chemical vapor deposition (MOCVD) and mo- lecular beam epitaxy (MBE) techniques [3,4]. While the latter involves a very simple process, and the growth process can be monitored as the film is built up one atomic layer at a time, it has limitations for commercial application. First, the need for ultrahigh-vacuum conditions makes it expensive and even unaf- fordable. Second, frequent shutdowns and opening of the UHV apparatus need considerable preparation time, before returning to the film growth process, which leads to waste of valuable produc- tion time. Compared with MBE, MOCVD has several major attractions such as versatility and capability for large-scale pro- duction. MOCVD is considered as one of the most versatile and economical techniques, because it is suitable for producing virtu- ally all V/III semiconductor compounds and alloys, and devices requiring large areas, such as LEDs and solar cells [5]. At present, the preferred industrial method for GaN film growth is MOCVD using trimethylgallium (TMGa) and ammonia (NH3) as precursors [6], and hydrogen (H2) or nitrogen (N2) as the carrier gas. Computational fluid dynamics (CFD) simulation is considered as a significant approach to predict the GaN film growth rate and to examine the dependence on various critical parameters. A great deal of effort has been devoted to the numerical simulation under- lying the GaN MOCVD process, and some primary featiu^es of the transport processes involved in the MOCVD process have been obtained [7-10]. However, with simple horizontal and vertical reactors, or a few specific commercial CVD systems, these simu- lations mostly focus on the effects of one or two parameters. There is no an all-inclusive study about the effects of all the pri- mary operational parameters on GaN growth rate and film uni- formity, which will offer the possibility of an in-depth study of high-quality film growth, reactor design and optimization. In this paper, a 2D vertical CVD reactor is considered, and a mathematical description for GaN MOCVD growth process is developed. This consists of mass and momentum balance, and energy and species conservation equations. A detailed chemistry model is employed to model complex gas and surface reactions. Then, the effects of critical design and operating parameters on the GaN growth rate and thin film uniformity are examined. Dis- cussions about the choice of these parameters are also given. 2 Numerical Approach 2.1 Governing Equations. CFD simulations, considering gas-phase and surface chemical reactions, were carried out using the commercial software CFD-ACE+, based on a finite-volume approach [11]. The governing equations of the compressible steady state transport phenomena in a GaN MOCVD process can be mathematically described by a group of conservation equations [12,13] as: Mass conservation equation (Continuity equation): V • (pV) = 0 Momentum force balance equation: V • (pVV) = -Vp + V -x pg (1) (2) Energy conservation equation: V • {p\h) = V • Ns Manuscript received April 11, 2013; final manuscript received October 17. 2013; ' published online November 18. 2013. Assoc. Editor; Yung Shin. Journal of Manufacturing Science and Engineering Copyright © 2013 by ASME (3) DECEMBER2013, Vol. 135 / 061013-1