Morphology and microstructural evolution in the early stages of hydride vapor phase epitaxy of GaN on sapphire

The early stages of hydride vapor phase epitaxy (HVPE) of GaN on sapphire were studied using atomic force microscopy, field-emission scanning electron microscopy, cross-sectional transmission electron microscopy, and x-ray diffraction rocking curves. At the high growth rate used (∼33 nm/s), the films appear to be fully coalesced for growth periods as short as 1 s. A distinct surface and subsequent bulk transformation were observed, resulting in significantly smoother film surfaces and improved bulk morphology. The growth of thick (i.e., 300 μm) GaN films using HVPE offers a promising technique for the deposition of high-quality substrates for GaN homoepitaxy.