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

Abstract

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<TS<720 °C), where strain relaxation occurred slowly, yielding impeded island nucleation rates and small island sizes (diameter ∼8–12 nm and height ∼2.3–2.7 nm). In the other, i.e., high-temperature growth regime (TS>720 °C), islands showed an abrupt relaxation mode, accompanied by a fast nucleation rate toward island sizes twice as large.