Thermodynamic Analysis and Growth Characterization of thick GaN films grown by Chloride VPE using GaCl₃/N₂ and NH₃/N₂

Abstract

Thermodynamic calculations were carried out on chloride transport vapor phase epitaxy of GaN using GaCl₃/N₂ and NH₃/N₂. At typical growth temperature and gas flow rates, both GaN formation and gas phase etching reactions of GaN are thermodynamically favored. Under thermodynamic equilibrium, most ammonia should decompose to nitrogen and hydrogen gases and gas phase etching of GaN occurs by HCl. From experimental measurements, less than 10% of the incoming ammonia decomposes and under this condition, GaN formation from GaCl₃/N₂ and NH₃/N₂ is thermodynamically favored. Higher V/III ratios give a larger driving force for GaN fromation. These calculations match our experimental results. Experimentally, we have optimized the growth conditions of GaN. High crystalline quality thick GaN films (10 ~ l5µm) were grown on c-Al₂O₃. The GaN films show band edge emission dominated PL at both room temperature and 77 K. Only one set of diffraction peaks from $\left( {10\bar 12} \right)$ planes with 60° spacing in the ϕ-scan of X-ray diffraction are observed. This indicates that the GaN films grown on c-Al₂O₃ are single crystalline. Typical growth rates were about 10 ~ l5µm/hr and typical Hall mobility values of GaN films were in the range of 3 to 40 cm²/Vsec.