The spatial distribution and formation mechanism of nanopipes defects in <i>β</i>-Ga2O3

Abstract

Similar to micropipes in SiC, nanopipes in β-Ga2O3 are also killer defects. In this work, the spatial distribution was built to explore the formation mechanism of nanopipes in β-Ga2O3 substrates. Contrary to previous reports, suggesting that nanopipes orientation aligns with the growth direction, the nanopipes were found independent of growth method and growth direction. Additionally, the evolution of nanopipe etch pit morphology was observed. Under alkaline etching conditions, nanopipe etch pits exhibit four exposed surfaces. Atomic structure analysis reveals that the center of the nanopipes is located in a three-dimensional space without chemical bonds, extending along the [010] direction. During crystal growth, bubbles trapped at the solid-liquid interface preferentially occupy this three-dimensional space, disrupting the surrounding lattice integrity. The synergistic effect between the [010]-elongated geometry of this space and the growth rate anisotropy of β-Ga2O3 drives the formation of [010]-oriented nanopipes. Furthermore, nanopipe-dense regions in (010) cross sections of the bulk crystal induce X-ray rocking curve broadening, with their morphological characteristics exhibiting axial position-dependent variations. This study suggests that vertical devices on the (010) plane may exhibit leakage risks and further demonstrates that controlling bubble formation and distribution during crystal growth is the key to suppressing nanopipes defects.