Surface Energy Discrepancy between Ga- and N -Polar GaN: An Enhanced Thermodynamic Study

Abstract

This study addresses critical limitations in conventional thermodynamic models for GaN growth with hydride vapor phase epitaxy method by incorporating thermal decomposition kinetics and surface energy effects. The revised model integrates HCl/GaCl conversion rates and NH3 decomposition submodels, aligning theoretical driving forces with experimental growth rate at elevated temperatures. By combining experimental data from halide vapor phase epitaxy (HVPE) growth experiments conducted near the ceiling temperature on N-polar and Ga-polar GaN crystals with the enhanced model, we quantitatively differentiate their surface energies. The results indicate that the Ga-polar surface exhibits higher energy (approximately 0.057 eV/Å2) than the N-polar surface. Furthermore, the model extends applicability to nonstandard atmospheric pressures, offering a comprehensive framework for optimizing HVPE growth conditions near the thermodynamic limit. This work introduces a new way to experimentally determine surface energy discrepancy across crystallographic planes in GaN, which may also be applicable to other III-nitride materials, such as InN, AlN, and BN. Additionally, the enhanced model improves predictive accuracy for GaN crystallization processes, supporting the development of high-quality free-standing substrates for advanced power and optoelectronic devices.