Comparative Study of GaN Growth Process by MOVPE
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In this study, we studied the MOVPE of GaN-based materials by employing an alternative modeling strategy. Since trimethylgallium (TMG) is very dilute in the NH 3 : H 2 mixture, the gas phase reactions have almost no affect on the thermal fluid flow behaviors. However, the growth chemistry pathways are significantly determined by the thermal flow conditions, and can lead to deleterious pre-deposition reactions for GaN growth. Therefore, we performed, without any gas and surface reactions involved, a comparative study of the thermal flow behavior within two different reactors that can grow device quality GaN-based materials. We identified some common features of thermal flow inside these two different reactors. Based on these thermal flow features, we are further studying the growth chemistry in a step-wise fashion, with an increasing chemical complexity in the gas phase at each step, in an effort to discover how these observed common thermal flow features determine the growth pathways. Compared to a typical growth chemistry study, this step-wise growth chemistry investigation provides significant insight into the primary reactions in the GaN MOVPE processes. Based on combined modeling and experimental effort, we aim at providing a general model of GaN growth. In this paper, we will address our study on thermal flow behaviors inside GaN reactors. Unlike the typical 111-V reactor, the GaN reactor involves much higher growth temperature and more extensive predeposition gas phase reactions, therefore the primary focus of this investigation are the flow velocity distribution, temperature profile and residence time. REACTORS & EXPERIMENT Schematic diagrams of the two reactors used in this study are shown in Fig. 1 and Fig.2. The first reactor we studied is a working vertical reactor, the second one is the two-flow reactor invented by Nakamura [2]. We have detailed operating conditions for the vertical reactor, while our simulation study of the two-flow reactor is based on the incomplete TMG NH3 + H2 experimental data distributed in several Dublications and patents by + H2 Nakamura [2][3][4]. Radiation
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our detailed study on the vertical reactor. V...... The simulation of the •cNA1. , R AT TUB I THERMOMETEI two-flow reactor is cooled used as a comparison STAINLESS STEEL Susceptor to verify the features CHAMBER' H 2 +NH3 +3MG present in the vertical ,QUARTZ reactor. For the Figure 1. Diagram of NOZZLE vertical reactor, the vertical reactor trimethylgallium VACUUM (TMG), in a hydrogen EXHAST carrier gas, is supplied through the inner tube while ammonia and hydrogen are supplied in the outer tube. The outer wall of the reactor is watercooled. The graphite susceptor is inductively Figure 2. Diagram of the two-flow reactor ([2] 1) heated. The inner diameter of the reactor is 85 mm and the outer diameters of the two inlet tubes are 6.4 mm and 25.4 mm respectively. The opening of the inner tube is widened at the end above the susceptor, which is 70 mm in diameter. This reactor is operated at a pre
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