Akira Hirako

Modeling of Reaction Pathways of GaN Growth by Metalorganic Vapor-Phase Epitaxy Using TMGa/NH3/H2 System: A Computational Fluid Dynamics Simulation Study

A model of reaction pathways of GaN growth by metalorganic vapor-phase epitaxy was studied by computational fluid dynamics simulations. We included the formation of polymers such as [Ga–N]n and [MMGaNH]n (n=2–6) in the reaction model in a TMGa/NH3/H2 system for the first time. The simulations using this reaction modeling successfully explained experimental growth rates at various temperatures, and clarified the main reaction pathway of GaN growth. The change in gas-phase chemistry due to temperature in the range of 300–1400 K was investigated. It was found that the type of reactive molecule changes with temperature, followed by the formation of different polymers in a certain temperature range, that is, [MMGaNH]n at 600–750 K and [Ga–N]n at higher temperatures.

Band-Edge Energies and Photoelectrochemical Properties of n-Type Al x Ga1 − x N and In y Ga1 − y N Alloys

We studied photoelectrochemical properties of Al x Ga 1-x N for the first time, and compared with those of In y Ga 1-y N. The conduction band-edge energy of n-type Al x Ga 1-x N decreased with Al composition, however the valence band-edge energy did not significantly change. Saturated photocurrent obtained from dynamic photocurrent-voltage measurements under illumination also decreased with increasing Al composition. Greater Al composition also shifted the onset voltage to more negative direction. These phenomena can be explained by the changes of bandgap and band-edge energies with Al composition.

Decomposition and Uniformity of Material Gases in GaN MOVPE

The characteristics of metalorganic vapor-phase epitaxy (MOVPE)-grown GaN layers have been compared with the chemical features of the gaseous phase during growth. The chemical features were evaluated by growth simulation. Two- and three-flow methods were used for GaN MOVPE. It was found both by growth and by simulation that the two-flow is superior to the three-flow method as regards uniformity and quality of the GaN layers.

Investigation of Growth Mechanism for InGaN by Metal?Organic Vapor Phase Epitaxy Using Computational Fluid Simulation

We investigated the mechanism of metal–organic vapor phase epitaxy (MOVPE) growth for InGaN by comparing experimental and simulation results. The simulation results showed a similar trend to the experimental results. Therefore, the simulation system can be used to speculate on physical and chemical phenomena through the behavior of precursors. InGaN growth is largely affected by the amounts of both trimethylindium (TMIn) and NH3 supplied. This is because InN growth is dependent on the amount of NH2 physisorbed on a surface, which is generated by NH3. Moreover, the decomposition of crystallized InN and the desorption of these decomposed precursors of InN during growth cannot be ignored.