Structural Characterisation of Improved GaN Epilayers Grown on a Ge(111) Substrate

Despite the large lattice mismatch between GaN and Ge of 20.1%, the successful growth of GaN on Ge(111) using plasma-assisted molecular beam epitaxy (PA-MBE) has been achieved. Recent work has shown that the crystal quality of GaN can be improved using either a miscut substrate or a higher growth temperature (above 800 °C), to enhance the step-flow growth. This paper reports the structural characterisation of these improved GaN epilayers grown on Ge. The threading dislocation density has been measured using cross-sectional transmission electron microscopy (TEM) imaging. The polarity of the epilayers is determined using convergent beam electron diffraction (CBED).