Dislocations in undoped GaN moved in response to the in-plane tensile stress present during film growth. Dislocation movement during growth relieves tensile stress, produced arrays of a-type dislocations and reduced the overall dislocation density, with preferential reduction of (a+c)-type dislocations. However, Si-doping limits dislocation movement, limiting the relief of the tensile stress that developed during growth and limiting dislocation reduction, probably due to the formation of Si impurity atmospheres at dislocations. Consequently, Si-doped films were under relatively greater tensile stress compared to undoped GaN films grown under similar conditions. Alternative dopants could be chosen to reduce tensile stress development, such as Ge.

The Effects of Si Doping on Dislocation Movement and Tensile Stress in GaN Films. M.A.Moram, M.J.Kappers, F.Massabuau, R.A.Oliver, C.J.Humphreys: Journal of Applied Physics, 2011, 109[7], 073509