Preferred orientation of AlN plates prepared by chemical vapour deposition of AlCl3 + NH3 system

Aluminium nitride (AlN) plates about 1 mm thick (maximum) were prepared by chemical vapour deposition (CVD) at the maximum deposition rate of 430 nm s^–1 using AlCl₃, NH₃ and H₂ gases at deposition temperatures,T_dep, of 873–1473 K. The effects of deposition conditions on the preferred orientation, morphology and micro-structure were investigated. WhenT_dep was less than 1073 K, the resulting CVD AlN plates contained some impurity chlorine and the aluminium content exceed the nitrogen content. WhenT_dep exceeded 1173 K, no chlorine was detected, and the Al/N atomic ratio matched the stoichiometric value. The lattice parameters (a=0.311 nm,c=0.4979 nm) and density (3.26×10³ kgm^–3) were in agreement with values reported previously. The crystal planes oriented parallel to the substrates changed from (1 1 ¯2 0) to (1 0 ¯1 0) to (0001) with increasing total gas pressure (P_tot) and decreasingT_dep. This tendency is discussed thermodynamically and is explained by the change of supersaturation in the gas phase.