Strain relaxation dependent island nucleation rates during the Stranski-Krastanow growth of GaN on AlN by molecular beam epitaxy

This study reports on the correlation between strain relaxation and nucleation kinetics during the Stranski-Krastanow growth of GaN on (0001)AlN by plasma-assisted molecular beam epitaxy. Using reflection high-energy electron diffraction and real-time desorption mass spectrometry, the strain-related Ga adatom detachment and desorption rates were determined, giving information about the average GaN island nucleation rate. Two different regimes were found: one at low-temperature growth (690 < T-S < 720 degrees C), where strain relaxation occurred slowly, yielding impeded island nucleation rates and small island sizes (diameter similar to 8-12 nm and height similar to 2.3-2.7 nm). In the other, i.e., high-temperature growth regime (T-S>720 degrees C), islands showed an abrupt relaxation mode, accompanied by a fast nucleation rate toward island sizes twice as large.