Abstract
We carried out a kinetic analysis of metallorganic vapor phase epitaxy (MOVPE) of GaN to investigate the dependence of the growth rate on the process conditions as a function of residence time of the precursors in the reactor. The wafer was not rotated during growth, allowing us to analyze the thickness profile of the film in the direction of gas flow, and hence the dependence of the growth rate on the residence time. The growth rate is determined mainly by the concentration of the growth species and mass transfer of the growth species to the wafer surface. The growth rate peaked in the flow direction, and the position of this peak could, in most cases, be explained by considering a combination of the linear gas velocity and the time constant for vertical diffusion of trimethylgallium (TMGa) and/or growth species across the NH3 feed stream to the wafer surface. In some cases this was not possible, indicating that more complex effects were significant. This work is expected to contribute to understanding of the reaction pathways for GaN-MOVPE, and the growth rate data reported here are expected to provide useful benchmarks for growth simulations that combine computational fluid dynamics and reaction models.
Highlights
With Gallium nitride (GaN)-Metalorganic vapor phase epitaxy (MOVPE), the reactor configuration and process conditions are usually designed to minimize the residence time of the precursors in the the reactor to suppress the above-mentioned parasitic reactions
To determine the growth rate precisely, without being influenced by the initial nucleation behavior on the sapphire substrate,[50,51,52] GaN layers of a fixed thickness were grown using our standard recipe with a rotating wafer, which were used as a template for the subsequent growth of a target GaN layer that was used for analysis of the growth kinetics
The growth rate at the upstream area increased with position in the flow direction in all cases, which is consistent with a discussion of the reaction mechanisms of GaN MOVPE, whereby GaN grows via gas-phase intermediate species generated from TMGa
Summary
GaN growth was carried out using a 2 sapphire wafer in a horizontal MOVPE reactor as shown in Fig. 2 (AIXTRON AIX 200RF-S).[47,48,49] To determine the growth rate precisely, without being influenced by the initial nucleation behavior on the sapphire substrate,[50,51,52] GaN layers of a fixed thickness were grown using our standard recipe with a rotating wafer, which were used as a template for the subsequent growth of a target GaN layer that was used for analysis of the growth kinetics This target GaN layer was grown without rotating the wafer, which allowed us to investigate the growth rate profile in the direction of the flow of precursors, providing information on the dependence of the growth rate on the residence time of the precursors in the reactor.[37,38,53] The growth conditions for the target GaN layer were systematically varied to analyze the dependence of the growth rate profile on the deposition conditions. Reflectivity measurements were employed to monitor the film thickness at the center of the wafer in situ during the growth of the target GaN layer. The surface morphology of the films was observed using Nomarski microscopy (Nikon, Eclipse ME600)
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