The impact of pressure and temperature on growth rate and layer uniformity in the sublimation growth of AlN crystals

Abstract

a b s t r a c tTo effectively design a large furnace for producing large-size AlN crystals, a fully coupled compressible flow solver was developed to study the sublimation and mass transport processes in AlN crystal growth. Compressible effect, buoyancy effects, flow coupling between aluminum gas and nitrogen gas, and Stefan effect are included. Two sets of experimental data were used to validate the present solver. Simulation results showed that the distributions of Al and N 2 partial pressures are opposite along the axial direction due to constant total pressure and Stefan effect, with the Al and nitrogen partial pressures being highest at the source and seed crystals positions, respectively. The distributions of species inside the growth chamber are obviously two-dimensional, which can curve a flat crystal surface. Simulation results also showed that AlN crystal growth rate can be increased by reducing total pressure or by increasing seed temperature or by increasing source-seed temperature difference. High nitrogen pressure causes decrease in growth rate, but it is beneficial for obtaining uniform growth rate in the radial direction. Results of simulation also showed that there is an optimized temperature difference (40 1C) in the present furnace for obtaining good homogeneity of growth rate.

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

“…In this work, only two species (Al and N 2 ) in the growth chamber were considered, while impurities such as Al 2 O were neglected due to their low concentrations [10][11][12][13][14][15][16]. The powder source charged at the crucible bottom was considered a porous medium.…”

“…In Mode II, both heaters were used, and the bottom center of the powder source (T bc ) and seed center (T sc ) were chosen as the TCPs. Due to the presence of Knudsen layers at the source and seed surfaces [14][15][16], the vapor flux at the sublimation and deposition surfaces could be precisely determined by solving the Hertz-Knudsen equation. The deposition or sublimation molar flux is given by…”

“…Wu et al [11][12][13] evaluated the effects of growth conditions on the crystal growth rate by mass transport modeling and simulation. Gao et al [14] analyzed the influence of growth parameters on the growth rate using a mass transport model. Wang et al [15] developed a mass transport model to study the rate limiting step in the crystal growth process, and the results showed the relationship between the Al partial pressure gradient and growth rate under different thermal fields.…”

Simulation and Experiment for Growth of High-Quality and Large-Size AlN Seed Crystals by Spontaneous Nucleation

“…At present, the physical vapor transport (PVT) method, also called the sublimation–recondensation method, has been proven to be the most successful approach for bulk AlN single crystal seed growth [ 12 , 13 , 14 , 15 , 16 ]. In a nitrogen atmosphere, the AlN powder sublimates into gaseous Al and N 2 at the higher-temperature source zone and the vapor species transport to the lower-temperature crystalline zone, promoting the growth of AlN crystals at the substrate [ 17 , 18 , 19 ]. However, it is still challenging to grow large-size and high-quality AlN seeds by PVT due to the harsh growth conditions.…”

Homogenization of Radial Temperature by a Tungsten Sink in Sublimation Growth of 45 mm AlN Single Crystal

“…Liu [7] and Wu [8] formulated an integrated model that considered induction heating, thermal system design, mass transport and growth kinetics. Gao et al [9] established a fully coupled compressible flow model to study the sublimation and mass transport processes in AlN crystal growth. Wang et al [10] studied the distribution and evolution of the total resolved shear stress in AlN single crystals.…”