Thermodynamic and Experimental Study of High‐Purity Aluminum Nitride Formation from Aluminum Chloride by Chemical Vapor Deposition

Thermodynamic calculations in the systems Al-Cl, Al-Cl-N, and H-Al-Cl-N were used to assess the capabilities of AlCl3 or mixtures of AlCl3 with Al to produce AlN by chemical vapor deposition (CVD) techniques. Direct nitridation (N2 as reaction agent) is possible only at high temperatures (≥1500 K), using AlCl3–Al mixtures. Reaction with NH3 at equilibrium gives low yields but the suppression of NH3 dissociation yields near 100%, which makes the method suitable for powder production, coating, and single-crystal growth. AlN with less than 1 wt% oxygen was obtained from technical grade AlCl3 by this process. The formation of both amorphous AlN powder and crystalline AlN coatings was observed. It is assumed that the formation of AlCl3·xNH3 adducts by mixing of Al-Cl vapor and NH3 at temperatures ≤1273 K prevents NH3 dissociation and favors the production of amorphous AlN.