Crack-Free, Highly Conducting GaN Layers on Si Substrates by Ge Doping

GaN based epitaxy on silicon usually requires strain-engineering methods to avoid tensile stress after cooling from growth temperature. Silicon doping of GaN induces additional tensile stress during growth originating from edge dislocation climb. Especially in the GaN-on-Si case high tensile stresses for highly Si-doped layers limit the freedom in device design and performance. We show that germanium doping does not influence strain evolution and enables the growth of thick highly n-type doped crack-free layers on silicon. It is concluded that dislocation climb in the case of silicon doping does not originate from surface roughening but from silicon-nitride induced dislocation masking.