Stabilization of sputtered AlN/sapphire templates during high temperature annealing

In this work we investigated annealing of 350 nm and 450 nm thick sputtered (SP) AlN on sapphire in the temperature range from 1650 degrees C to 1730 degrees C. The most distinct decrease in the threading dislocation density (TDD), from initially 3 x 10(10) cm(-2) to 4 x 10(8) cm(-2), was achieved for 450 nm AlN at an annealing temperature of 1680 degrees C. Unfortunately, for temperatures >= 1680 degrees C the reaction between AlN and sapphire partially disturbs the AlN layer by formation of polycrystalline AlON at the AlN/sapphire interface. In addition, we found epitaxially oriented (1 1 1) AlON on top of the AlN layers that hinders further epitaxial growth. This problem can be prevented by lower annealing temperatures (<= 1680 degrees C) and thick SP AlN layers. The importance of an appropriate AlN sputtered layer thickness and of a precise temperature control during high temperature annealing are shown in this paper to ultimately achieve a balance between low TDD and suppression of excessive AlON formation.