Real-time optical monitoring of ammonia flow and decomposition kinetics under high-pressure chemical vapor deposition conditions

Abstract

Understanding the gas phase decomposition kinetics of the chemical precursors involved in the nucleation and thin-film growth processes is crucial for controlling the surface kinetics and the growth process. The growth of emerging materials such as InN and related alloys requires deposition methods operating at elevated vapor densities due to the high thermal decomposition pressure of these materials. High nitrogen overpressure has been demonstrated to suppress the thermal decomposition of InN, but has so far not been explored in chemical vapor deposition experiments. In this contribution we present research results on the decomposition kinetics of ammonia in the laminar flow regime of a high-pressure flow channel reactor. Ultraviolet absorption spectroscopy is applied to analyze absorption features of ammonia with respect to the ammonia flow rate during continuous flow and pulsed ammonia injection. Pulsed ammonia injection has been used to analyze the average gas flow velocity in the high-pressure chemical vapor deposition system as a function of the total gas flow rate and the reactor pressure. The onset of the kinetics related to the decomposition of ammonia was found to start above 900K and showed a marked decrease for higher reactor pressures, thus decreasing the discrepancy of trimethylindium and ammonia decomposition temperatures.