Influences of Powder Source Porosity on Mass Transport during AlN Crystal Growth Using Physical Vapor Transport Method

Abstract

We developed a two-dimensional (2D) transport model to investigate mass transport during bulk AlN crystal growth via the physical vapor transport (PVT) process using the finite element method (FEM), taking the powder source porosity, buoyancy, and vapor diffusion into account. The porosity effects of the powder source on mass transport under various growth conditions were investigated in detail. The simulation results show that the porosity of the powder source significantly affects the mass transport process during AlN sublimation growth. When the porosity of the powder source decreases, the growth rate becomes more uniform along the seed deposition surface, although the sublimation rate and crystal growth rate decrease, which can be attributed to the reduced specific surface area of the powder source and the reduced flow rate of Al vapor in the powder source. A flat growth interface can be achieved at a porosity of 0.2 under our specific growth conditions, which in turn facilitate the growth of high-quality AlN crystals and better yield. The decomposition of the powder source and the transport of Al vapor in the growth chamber can be suppressed by increasing the pressure. In addition, the AlN growth rate variation along the deposition surface can be attributed to the Al vapor pressure gradient caused by the temperature difference in the growth chamber.

Homoepitaxial growth of 3-inch single crystalline AlN boules by the physical vapor transport process

“…Accordingly, thermal gradient calibration near the crystal growth interface should be deliberately conducted to balance the axial and radial thermal gradients for lateral diameter expansion as well as to prohibit parasitic growth and cracking. Accordingly, a proprietary growth system was designed and optimized using FEMAG software and self-developed finite element method (FEM) codes, including impurity transport (Fu et al, 2020), mass transfer Fu et al, 2021), anisotropic 3D stress (Wang et al, 2018;Wang et al, 2019c;Zhao et al, 2021), and supersaturation and growth rate prediction modules (Zhang et al, 2022). Particular attention was paid to the redesigning of a crucible system enabling a convex thermal field for parasitic-free growth with lateral diameter expansion by these FEM modules.…”

Toward Φ56 mm Al-Polar AlN Single Crystals Grown by the Homoepitaxial PVT Method

“…A sufficiently high radial temperature gradient (ΔT r ) around the seed surface is necessary for reasonable crystal diameter expansion, although a large ΔT r can lead to additional defects, such as low-angle grain boundaries (LAGBs) or basal plane dislocations (BPDs). 29−31 Considering the abovementioned, we designed a proprietary hotzone setup and crucible system and optimized it using FEMAG software and a series of in-house finite element codes, including a mass transfer module, 28,32 an impurity transport module, 27 an anisotropic 3D stress module, 33−35 and a growth rate and supersaturation prediction module. 36 In particular, a seed holder that can sustain positive supersaturation only at the seed deposition surface was designed to prevent any parasitic nucleation adjacent to the growing AlN seed and therefore to completely eliminate parasitic polycrystalline growth on the periphery of AlN boules.…”

Optimization of the process parameters for the AlN crystal growth in the PVT method through an improved numerical simulation considering partial pressure of gas phases

“…Subsequently, they developed a two-dimensional multiphase flow model, considering diffusion, buoyancy, and the Stefan flow, and simulated the effect of porosity on mass transport under different growth conditions. 27 Based on this model, Fu et al 28 developed a two-dimensional transport model considering powder source porosity, buoyancy, and vapor diffusion, to simulate and study mass transport during AlN crystal growth.…”