Abstract
Numerical simulations are a valuable tool for the design and optimization of crystal growth processes because experimental investigations are expensive and access to internal parameters is limited. These technical limitations are particularly large for ammonothermal growth of bulk GaN, an important semiconductor material. This review presents an overview of the literature on simulations targeting ammonothermal growth of GaN. Approaches for validation are also reviewed, and an overview of available methods and data is given. Fluid flow is likely in the transitional range between laminar and turbulent; however, the time-averaged flow patterns likely tend to be stable. Thermal boundary conditions both in experimental and numerical research deserve more detailed evaluation, especially when designing numerical or physical models of the ammonothermal growth system. A key source of uncertainty for calculations is fluid properties under the specific conditions. This originates from their importance not only in numerical simulations but also in designing similar physical model systems and in guiding the selection of the flow model. Due to the various sources of uncertainty, a closer integration of numerical modeling, physical modeling, and the use of measurements under ammonothermal process conditions appear to be necessary for developing numerical models of defined accuracy.
Highlights
Recent progress in ammonothermal GaN growth includes a demonstration of scalability to pilot production for simultaneous growth of likely about 100 boules in one reactor [6], a masking technique for circumventing issues related to growth on different facets [18], growth of nearly bowfree crystals at pressures as low as 100 to 120 MPa [19], and growth of nearly 4-inch size crystals while keeping off-angle distributions as small as ±0.006◦ along both a-axis and m-axis [20]
Besides its use for the growth of bulk GaN, the ammonothermal technique is increasingly being utilized for exploratory syntheses of various binary, ternary, and multinary nitride and oxynitride materials [21,22,23], including nitride semiconductors composed of earth-abundant elements [24]
The LVEL model constitutes a zero-equation low Reynolds number turbulence model, which is valid over the laminar, transitional, and turbulent flow regimes and is well-suited for fluid domains cluttered with solids [68], facilitating the study of the complete ammonothermal growth setup in a computationally affordable way
Summary
Publisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations. Starting from 1995 [2], the ammonothermal process has been increasingly researched as a method for the growth of GaN bulk crystals [3,4,5,6,7,8]. A number of research groups have conducted numerical studies of temperature and flow field [25,26,27,28], partially including further aspects such as the concentration of metastable intermediates [29] and growth rates [29,30]. The accuracy of such numerical results remains unclear, preventing simulations from delivering their full potential impact on further development and use of the ammonothermal method for bulk crystal growth.
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