Cleavage and anisotropy dependence of material removal behavior of monocrystalline β-Ga2O3 in abrasive machining

Abstract

Beta-phase gallium oxide (β-Ga2O3) is recognized as a promising next-generation semiconductor material with an ultra-wide bandgap and broad application prospects. However, its pronounced cleavage and anisotropy presents great challenges in precision abrasive machining, hindering the advancements in related device manufacturing. In this work, systematic nanoscratching and nanogrinding tests, combined with characterization methods such as SEM, TEM, and Raman spectroscopy, as well as stress field theory were performed to explore the effects of easy-cleavable and anisotropy properties on material removal behaviors, specifically the machining directions parallel and perpendicular to the cleavage planes. The results indicate that when the direction is parallel to the cleavage plane, the scratch morphology is dominated by oriented cracks and bulk fractures, and cleavage cracks and stacking faults extending into the matrix cause more severe subsurface damage; when the direction is perpendicular to the cleavage plane, the scratch morphology is mainly induced by free damaged groove, with the subsurface comprising a mixed phase of nanocrystals and amorphous, and a few stacking faults, resulting in a much shallower damage layer. These results were further validated through nanogrinding tests, which showed that when the direction is parallel to the cleavage plane, the ground surface is dominated by cleavage facets, and both surface roughness and subsurface damage are much worse compared to the direction perpendicular to the cleavage plane. A mechanistic model was established, depicting that cracking on the cleavage plane and slip plane, coupled with crack deflection under stress fields, primarily leads to anisotropy in of material removal during abrasive machining. These results enhanced the understanding of the cleavage and anisotropy dependence in the machining process and provided insights for controlling the surface/subsurface damage in precision abrasive machining of β-Ga2O3.