The warpage of the GaN template grown by HVPE with gallium droplet treatment was 13.8μm; which was reduced by 80.3% of the warpage for GaN templates grown by conventional MOCVD and 43% of the warpage for GaN templates grown by HVPE without gallium droplet treatment. The treatment of gallium droplets on sapphire was achieved by using a thermal evaporator at room temperature. The E2 high peak of a GaN template with gallium droplet treatment appeared at 566.5/cm, whereas the E2 high peak of a GaN template prepared by MOCVD was at 569.5/cm in the Raman scattering spectra. According to the frequency shifts of the E2 high peak position for each template, of around 3/cm, a release of compressive stress in GaN templates grown by HVPE with gallium droplet treatment was demonstrated. Using FE-SEM and glow discharge spectroscopy, voids and depleted zones of gallium and aluminium in the counter direction were formed at the interface between GaN epilayers and sapphire substrates during GaN growth by HVPE. It was expected that the decrease in warpage and stress for GaN templates with gallium droplet treatment was caused by the formation of voids and depleted zones of gallium and aluminium. The etch-pit densities of GaN templates with gallium droplet treatment was around 8.5 x 107/cm2.

Reducing the Warpage and Dislocation Density of GaN Template Grown by HVPE with Gallium Droplet Treatment. Y.J.Choi, H.K.Oh, J.G.Kim, H.H.Hwang, H.Y.Lee, W.J.Lee, B.C.Shin, J.Hwang: Physica Status Solidi C, 2010, 7[7-8], 1770–4