Accurate vapor pressure equation for trimethylindium in OMVPE

Abstract

From the vapor pressure equation of a metalorganic precursor, its partial pressure is calculated. The accuracy of that vapor pressure equation is therefore important when calculating the deposition efficiency of a precursor. Knowing the exact value of the vapor pressure is even more important to accurately plot the solid composition versus gas phase composition in the case of an alloy. For indium-containing Organo-Metallic Vapor Phase Epitaxy (OMVPE), trimethylindium (TMI) has been the preferred precursor. However, the four established vapor pressure equations reported in the literature for TMI have been found to differ significantly. These equations offer overestimated vapor pressure of TMI, often by as much as 20–40%. Not knowing the accurate vapor pressure has been a concern to growers. In this study, we report the comparative evaluation of these four established equations by using accurate measurements of actual consumptions of TMI from its depletion studies, coupled with gas phase concentration studies with Epison III ultrasonic monitor. Our studies conclude that the vapor pressure equation, log P (Torr)=10.98–3204/T (K), provides the most accurate vapor pressures of TMI within a wide range of growth conditions currently used in OMVPE. Also reported are the cylinder design aspects and Uni-Flo™ II cylinder design that lead to stable depletion of TMI under high throughput conditions of temperature, flow and pressure employed industrially.