The growth of high-quality and self-separation GaN thick-films by hydride vapor phase epitaxy

About 1.2 mm thick GaN bulk crystals were obtained by combining a pulsed NH3-flow modulation (PFM) method and a self-separation method of short-shutting NH3 flow when using hydride vapor phase epitaxy (HVPE). High crystal quality of bulk GaN was evaluated by X-ray rocking curves (XRC) and the full width at half maximum (FWHM) values were 110, 72 and 83 arcsec for (002), (102) and (100) reflection planes, respectively. The PFM method is proved to be effective in reducing cracks and keeping the surface smooth. And the method of short-shutting NH3 flow can lead to GaN thick layer separate from sapphire substrate when cooling from the high growth temperature. Growth and separation mechanisms were investigated. Two states were found in PFM method. With PFM method modulating between high quality state and low stress state, 300 μm thick GaN layers without cracks were obtained. Study of spontaneous separation mechanism revealed that the separation attributed to formation of voids inside the GaN layer.

► High quality state and low stress state exist in the growth of GaN by HVPE method.
► NH3-flow modulation (PFM) method is modulated between the two states.
► 300 μμm thick GaN layers without cracks were obtained by PFM method.
► High quality bulk GaN crystals of thickness ∼1.2 mm were obtained.
► Self-separation is attributed to formation of voids layer inside the GaN film.