Effect of different abrasive grain sizes of the diamond grinding wheel on the surface characteristics of GaN

Gallium nitride (GaN) substrates were ground in two different grinding wheel abrasive sizes of 270 and 800-mesh, and the change in surface morphologies of the substrates and the depth of subsurface damage (SSD) were observed. With the 800-mesh grinding wheel, the surface roughness (SR) and the depth of SSD of the sample tended to decrease, which was not the case with the 270-mesh grinding wheel. In the X-ray rocking curve, the sample exhibited some compressive stress with the 270-mesh grinding wheel, but with the 800-mesh grinding wheel, it demonstrated the occurrence of tensile stresses in the sample and a decrease in full width at half maximum (FWHM), which confirms an improvement in the crystallinity. In the Raman spectra, the compressive stress of the 270-mesh grinding wheel and the tensile stress of the 800-mesh grinding wheel were confirmed through peak shifts. Photoluminescence (PL) spectra confirmed that the intensity ratio of the yellow luminescence increased at the 800-mesh grinding wheel, and a blue shift occurred further. These results indicate that the SR and the depth of SSD were proportional to the abrasive grain size of the grinding wheel. At the same time, the increase in PL intensity at specific peak positions indicates that the stress stemming from the grinding process was concentrated at the crystal surface. The above mechanism is illustrated in a schematic diagram, which confirms the possibility of improving the grinding efficiency and subsequent polishing processes in future applications.