Real-time optical monitoring of gas phase dynamics for the growth of InN at elevated pressures
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Real-time optical monitoring of gas phase dynamics for the growth of InN at elevated pressures N. Dietz* , H. Born, M. Strassburg and V. Woods Department of Physics & Astronomy, Georgia State University, Atlanta GA 30303 * [email protected]
ABSTRACT The request for increased performance in high-power / high-frequency optoelectronic devices requires new methods for the fabrication of high quality III nitride alloys that exhibit large thermal decomposition pressure such as InN and related materials. To extend the process and growth window towards elevated pressures, a high-pressure CVD system with integrated real time optical characterization techniques has been constructed. The built-in real-time monitoring techniques allow the characterization of gas flow dynamics, precursor decomposition kinetics, as well as the monitoring of the crucial steps of nucleation and film formation. The gas flow dynamics has been characterized and the process parameter are obtained under which the thin film growth process can be maintained under laminar flow condition. Laser light scattering (LLS) has been proven as the most robust optical tool to characterize the onset of turbulence. INTRODUCTION InN is a semiconductor material that is intensively considered for applications in optical devices based on AlN-GaN-InN alloys and heterostructures, since this material system may provide active optoelectronic devices in the blue and ultraviolet spectral regions capable of operating at high power levels, high temperatures and in harsh environments. High quality Garich epilayers of Gax In1-xN can be fabricated successfully[1-3] by traditional low pressure chemical vapor deposition (CVD) methods where the influence of flow dynamics on growth conditions are minimal. However, low-pressure deposition processes are limited to a regime where the partial pressures of the constituents do not differ vastly and the decomposition process can be countered by off-equilibrium process conditions. Off-equilibrium conditions such as employed in MBE and organometallic CVD growth of InN require low growth temperature to overcome the thermal decomposition pressures, which limits the quality of InN and In rich GaxIn1-xN epilayers[4-6]. Due to the low growth temperatures, extremely high V-III ratios have to be applied to prevent the formation of metal droplets on the surface. New approaches for the growth of In-rich Ga xIn1-xN have to be explored, in order to obtain more accurate structural and optical properties of InN[7] and related alloys. The approach taken here is to utilize a CVD growth process at elevated pressure in order to stabilize the surface of InN at optimal processing temperatures. A high background pressure of nitrogen has been shown to stabilize the surface of InN at elevated temperatures[8] but has not yet been incorporated into a CVD growth scheme. Expanding the processing window for the growth of InN towards higher pressures (1 - 100 bar)
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may allow the growth at higher temperatures, leading to an improved crystalline quality an
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