InN growth by high-pressures chemical vapor deposition: Real-time optical growth characterization

Growth techniques that utilize elevated reactor pressures offer a pathway to overcome limitations in the epitaxy of high quality group III-nitride compounds such as InN or related materials, which exhibit large thermal decomposition pressures. We introduce the growth of InN by a unique high-pressure chemical vapor deposition (HPCVD) system, demonstrating that HPCVD is a valuable method for achieving stoichiometric single-phase surface compositions at optimal processing temperatures. The development and utilization of real-time optical diagnostics for the monitoring of gas-phase and surface chemistry during the heteroepitaxial nucleation and growth is critical for controlling the chemical vapor deposition process. Using real-time optical ultraviolet absorption spectroscopy (UVAS), we have studied the flow and decomposition kinetics of the gas-phase precursors as functions of flow, pressure and temperature. A pulsed-injection technique for the delivery of the chemical precursors is used, enabling the analysis and control of the decomposition kinetics of trimethylindium (TMI) and ammonia as well as the study of the initial stages of InN nucleation and subsequent overgrowth on sapphire substrates. The nucleation and steady state growth of InN is probed with sub-monolayer resolution by principal angle reflectance (PAR) spectroscopy. These real-time optical monitoring techniques demonstrate their utility in the optimization and engineering of the growth process, as well as providing crucial insights into gas phase decomposition dynamics and surface chemistry processes under HPCVD conditions. The resulting InN material exhibits an optical absorption edge that varies from 0.83 to 1.34 eV, strongly dependent upon the precursor flow ratios employed during growth. Structural analysis performed by XRD reveals high quality InN.