A systematic study has been performed to investigate the flow and thermal patterns of vertical rotating Thomas Swan MOCVD reactor at low pressure, using 2-D dynamic modeling. By varying and calculating the several important process parameters of the reactor, the optimized conditions of the uniform distributions of velocity and temperature profiles in steady state have been obtained. Then, time-dependent models with the step response perturbation of the total gas rate can help identify the visual transient behavior inside the reactor and analyze the mechanism of delay time, relaxation oscillation and pulsative oscillation. These results are beneficial to the process parameter optimization and geometrical configuration design of the MOCVD reactor. heteroepitaxy, MOCVD reactor, transport process, flow fields and thermal Citation: Zhong S Q, Ren X M, Huang Y Q, et al. Numerical studies on flow and thermal fields in MOCVD reactor. The metalorganic chemical vapor deposition (MOCVD) equipment was invented by Manasevit et al. [1] in 1968. Nowadays, this equipment has been extensively used for the large-scale production of microelectronic and optoelectronic devices with compound semiconductor materials in highspeed optical communication, 3G mobile communication, broad band satellite communication, high-efficiency solar cell and so on [2−6].During MOCVD growth, a mixture of precursor vapors containing the source elements to be incorporated in the very thin film is diluted in a carrier gas and flows over a heated substrate, resulting in epitaxial growth of a very thin solid film. To grow heterojunction semiconductor materials and devices, precursors are turned on and off periodically into a steady flow of the carrier gas. This periodic switching creates many transient processes in the reactant supply to the substrate. To achieve abrupt interfaces during heterostructure growth, the component transients should ideally be shorter than the time needed to grow one atomic layer. Especially in recent years, the transient problem was been getting more and more important for the fabrication of quantum dots (QDs), quantum wires (QWs) and multiquantum wells (MQWs) to grow the advanced nanometer scale materials and devices. So, we not only focus on the time required for the entire reactor to reach a new steady state, but also are interested in the duration of transients above the substrate. Solving this problem will provide an efficient growth of the semiconductor materials with desirable physical properties that are often inaccessible by conventional approach.Since the 1980s, the study on transport phenomena in MOCVD reactor has become one of the most important and extensive subjects. The researchers have utilized hydraulic experiments, optical measurements [7−9] and advanced computational fluid dynamics (CFD) [10−21] to study the extremely complicated mass transportation in the reactor and lots of progress has been achieved. However, all previous work concentrates on the side of steady state flow, and particularly emphasizes the inno...