Effects of Pressure and Gas Feed Rate on Growth Rate Profile of GaN Thin Film in Vertical MOCVD Reactor

The effects of pressure and flow rate of gas in a CVD reactor are studied on the GaN epitaxial thin film preparation by a metalorganic chemical vapor deposition (MOCVD) method using trimethylgallium (TMG) and ammonia as the source gases. The thickness profiles of GaN films are measured for those grown on a substrate heated at 1373 K in a single-substrate, vertical, cold-wall reactor. A model to describe the gas-phase chemical reactions leading to the formation of adducts and polymers from TMG and ammonia is introduced to simulate the GaN film preparation process. The growth rate profile of GaN films is then predicted by numerically calculating the distributions of flow velocity, temperature and concentration of species in the reactor. The calculated results reproduce well the measured change in growth rate with a total pressure change from the atmospheric to its 1/8, and a flattening of growth rate profile at an increased flow rate and a reduced pressure. It is concluded from the simulation that the changes of growth rate profile are caused by the influence of recirculating flow in the reactor on the GaN precursor concentration distribution above the substrate.