Control of stress and threading dislocation density in the thick GaN/AlN buffer layers grown on Si (111) substrates by low- temperature MBE

We report on successful growth by plasma-assisted molecular beam epitaxy on a Si(111) substrate crack-free GaN/AlN buffer layers with a thickness more than 1 μm. The layers fabricated at relatively low growth temperature of 780°C have at room temperature the residual compressive stress of -97 MPa. Intrinsic stress evolution during the GaN growth was monitored in situ with a multi-beam optical system. Strong dependence of a stress relaxation ratio in the growing layer vs growth temperature was observed. The best-quality crack-free layers with TDs density of ~109 cm-2 and roughly zero bowing were obtained in the sample with sharp 2D-GaN/2D-AlN interface.