Effect of Flux Rate Variation at Fixed V/III Ratio on Semi-Polar (112¯2) GaN: Crystal Quality and Surface Morphology Study

We report on the crystal improvement of semi-polar (112¯2) gallium nitride epitaxy layer on m-plane (101¯0) sapphire substrate by changing the flux rate at a fixed V/III ratio. The high-resolution X-ray diffraction (HR-XRD) analysis showed that lower flux rate enhanced the crystal quality of GaN epitaxy with the lowest FWHM values of 394 and 1173 arc seconds at [11¯23] and [11¯00] planes, respectively. In addition, Raman spectroscopy showed that flux rate did not affect the stress state of the GaN crystal. However, atomic force microscopy (AFM) micrograph depicted an anomalous trend where the lowest flux rate produces roughest surface with RMS roughness of 40.41 nm. Further analysis of AFM results on the undulation period length along [11¯23] and [11¯00] directions is carried out. It shows that as the growth rate decreases, the average undulation period along [11¯23] and [11¯00] directions increases from 2.59 µm and 1.90 µm to 3.52 µm and 3.52 µm, respectively. The mechanism for the surface roughening at the lower flux rate is then explained by using the adatom surface diffusion relation L ~ Dτ.