Optimization of a stagnation point flow reactor design for metalorganic chemical vapor deposition by flow visualization

Abstract

Various design parameters of a stagnation point flow reactor such as mixing chamber, gas distributor and reactor shape are optimized by a technique of flow visualization. A dense smoke of TiO 2 particles generated in the mixing cup with the help of unidirectional tangential jets of TiCl 4, H 2O and helium is used to show the flow patterns. A sheet of laser (5 mW He-Ne) light formed with the help of a cylindrical lens is used to illuminate the trajectory of smoke particles. The flow patterns are recorded photographically. Rapid and uniform mixing of a number of gas streams is achieved by tangential jets. A “capillary plug” as an ideal gas distributor, incorporated in the inlet, removes the swirl due to tangential jets completely and develops an axially uniform gas velocity profile across the inlet. Various reactor shapes such as cylindrical, triangular, diffuser and modified diffuser (a diffuser with reduced height) are studied for their performance. The modified diffuser with capillary plug as a gas distributor in the inlet is the only appropriate metalorganic chemical vapor deposition (MOCVD) reactor configuration that can develop and sustain a smooth, laminar and vortex free flow at room temperature as well as at 773 K in absence of substrate rotation and /or application of vacuum.