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

Abstract

Seed crystals are the prerequisite for the growth of high quality and large size aluminum nitride (AlN) single crystal boules. The physical vapor transport (PVT) method is adopted to grow AlN seed crystal. However, this method is not available in nature. Herein, the temperature field distribution in the PVT furnace was simulated using the numerical analysis method to obtain free-standing and large-size seeds. The theoretical studies indicate that the temperature distribution in the crucible is related to the crucible height. According to the theory of growth dynamics and growth surface dynamics, the optimal thermal distribution was achieved through the design of a specific crucible structure, which is determined by the ratio of top-heater power to main-heater power. Moreover, in our experiment, a sole AlN single crystal seed with a length of 12 mm was obtained on the tungsten (W) substrate. The low axial temperature gradient between material source and substrate can decrease the nucleation rate and growth rate, and the high radial temperature gradient of the substrate can promote the expansion of crystal size. Additionally, the crystallinity of the crystals grown under different thermal field conditions are analyzed and compared. The Raman results manifest the superiority of the thermal inversion method in the growth of high quality AlN single crystal.

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

“…In contrast, convective heat transfer has a limited effect on the temperature field and can often be neglected during calculations. 17,30 In this study, the finite element method (FEM) is utilized to analyze the model. The simulation steps can be summarized as follows: first, heat transfer models for solids considering heat conduction and heat radiation are developed separately.…”

“…In designs A and B, tungsten flakes with 4 mm thickness are used to cover the seed diameter and the outer diameter of the crucible, respectively. In designs D and E, a tungsten ring 17 with a right-angle trapezoidal cross-section is applied on the base of designs A and B, respectively. Design C features only one tungsten ring placed in the crucible lid.…”

“…Consequently, numerical simulation tools have become indispensable for optimizing the process conditions of AlN single crystal growth. [17][18][19] Significant progress has already been made in the simulation of AlN crystal growth processes by the PVT method using finite element software-aided design. Segal and Karpov et al 20 proposed an earlier model considering gas diffusion, convective transport, and kinetic limitations of N adsorption/desorption on the AlN surface.…”

Structural Design Optimization of Physical Vapor Transport Furnace for Aluminum Nitride Crystal Growth via Modeling and Simulation

“…Wang et al 20 investigated the effect of different temperature distribution on the growth of AlN by PVT and argued that the axial and radial temperature gradient were chief factor for the crystal growth rate and expanding the diameter, respectively. Qin et al 21 studied the thermal field of the PVT AlN crystal growth furnace numerically and experimentally. They applied a thermal inversion method, maintaining a low axial temperature gradient to suppress the nucleation and growth rate and a high radial temperature gradient to promote the expansion of the crystal size.…”

Influence of Different Heater Structures on the Temperature Field of AlN Crystal Growth by Resistance Heating

“…on the thermal field were simulated. Z. Y. Qin et al investigated the relationship between the hot zone structure and the temperature distribution of the growth chamber [ 18 ]. The simulation results showed that the thickness of the crucible, the size of the induction heating furnace, and the number of tungsten heat shields have a great influence on the temperature gradient.…”