Fabrication of a freestanding AlN substrate via HVPE homoepitaxy on a PVT-AlN substrate

Hydride vapor phase epitaxy (HVPE) is employed for the homoepitaxial development of AlN thick films on AlN substrates grown via physical vapor transport (PVT). A freestanding AlN substrate with a 200 mu m thickness is then obtained by mechanically grinding away the PVT-AlN substrate. The as-grown HVPE AlN layer has a smooth surface with long parallel atomic steps. The freestanding HVPE-AlN substrate is crack-free and stress-free. In comparison to PVT-AlN substrate, HVPE-AlN substrate not only has better crystal quality but also substantially lower C, O, and Si impurity concentrations. The deep ultraviolet (DUV) transmittance of the 200 mu m thick freestanding AlN substrate is as high as 66% at 265 nm. This performance aligns perfectly with the demands of AlGaN-based DUV optoelectronic devices.