In-plane misfits' localization in GaN via graphene-ELOG technology

Abstract

Due to the lack of native GaN substrate, GaN-based devices are heteroepitaxially grown on foreign substrates. Heteroepitaxial GaN has high defect densities due to the lattice mismatch of GaN and substrate. Epitaxial lateral overgrowth (ELOG) technology is an effective way to reduce the defects. However, the reduction of threading dislocations (TDs) to ∼10⁶ cm⁻² remains a challenge. Herein, we have demonstrated the fabrication of TD-free GaN microrods on 4° off-axis SiC by ELOG technology, using graphene as a mask and revealed the evolution mechanism of defects. The microstructural properties were investigated by scanning electron microscopy (SEM), cathodeluminescence (CL), and transmission electron microscopy (TEM). I₁-type basal plane stacking faults (BSFs) were the predominant defects in GaN. ELOG of GaN localized the defects at the interface by formation of “self-limited” SFs (SLSFs), which led to dramatic reduction of defects and TD-free at the surface of GaN microrods. This evolution mechanism of defects was different from that of traditional ELOG technology, and it opens up a guiding principle towards ultralow-threading-dislocation-density GaN films.