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 μm 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 transmittance of the 200 μm thick freestanding AlN substrate is as high as 66% at 265 nm. This performance aligns perfectly with the demands of AlGaN-based deep ultraviolet optoelectronic devices.