The effect of a temperature-varying sandwich buffer layer structure on GaN epitaxial layer grown on Si substrate

A special HT-/LT-/HT-AlN sandwich buffer layer was used to diminish the strain between its upper or overlying GaN and underlying Si substrate. It is found that, by simply inserting a LT-AlN layer, one can get an almost crack free GaN layer on Si substrate. SEM images gave a clear observation of the effect of LT-AlN insertion layer on surface morphology. Further analysis of the residual stress in overlaying GaN layer also confirms the function of LT-AlN layer. After comparing the pit densities from AFM images and calculating the dislocations from XRD measurement for all samples, a proper growth temperature for the intermediate layer was found to improve the crystalline quality. On inserting 720 °C LT-AlN, the tensile stress could be reduced to only 0.36 GPa and an almost crack-free surface could be achieved.

► We use a special HT-/LT-/HT-AlN sandwich buffer layer to diminish the strain.
► Proper growth temperature for insertion layer can improve the crystalline quality.
► The tensile stress could be reduced to only 0.36 GPa with inserting LT-AlN.
► We could achieve an almost crack-free surface.