Annealing studies of AlN capped, MOCVD grown GaN films

An AlN annealing cap has been developed for GaN films grown on sapphire substrates that enables them to be annealed at temperatures as high as 1300°C for times as long as 30 min or times as long as 120 min at a temperature of 1150°C without creating a significant number of electrically active N vacancies or new thermal etch pits due to the preferential evaporation of N. However, the pits in the as-grown sample became larger and their sidewalls became steeper, and the flat areas of the film became a little rougher when the annealing time and/or temperature was larger. The films became more relaxed as indicated by a >10% reduction in the X-ray rocking curve peak widths and the creation of a more uniform convex bow. Both the net carrier concentration and electron mobility were reduced by the anneal suggesting that compensating point defects had been created. One possible explanation is that more C in these metal organic chemical vapor deposition (MOCVD) grown films occupied N sites where it is believed to be a deep acceptor.