Abstract
Metal–organic chemical vapor deposition (MOCVD)-grown GaN on sapphire substrate was etched by hot phosphoric acids. Pyramid structures were obtained in the N-polar face of the MOCVD–GaN. Details of the formation process and morphology of the structures were discussed. The crystallographic plane index of the pyramid facet was calculated dependent on the symmetry of the wurtzite crystal structure and the tilt angle. The substrates with pyramid structures were utilized in subsequent hydride vapor phase epitaxy (HVPE) growth of GaN. Free-standing crystals were obtained, while HVPE-grown GaN achieved a certain thickness. Raman spectroscopy was employed to obtain the stress conditions of the HVPE–GaN without and with sapphire substrate. The mechanism of the self-separation process was discussed. This facile wet etching method may provide a simple way to acquire free-standing GaN by HVPE growth.
Highlights
In the last decade, many studies have been carried out in growing GaN for its advanced performance as a semiconductor material of optical and electrical devices, such as light-emitting diodes (LEDs) [1,2], laser diodes (LD) [3,4], UV detectors [5], and high-power, high-frequency electronic devices [6]
We report a facile method to acquire free-standing GaN by hydride vapor phase epitaxy (HVPE) on the etched metal–organic chemical vapor deposition (MOCVD)–GaN/sapphire substrate
The substrates used in the HVPE process were 3–5 μm GaN layers fabricated by MOCVD on 2 in c-plane sapphire substrates
Summary
Many studies have been carried out in growing GaN for its advanced performance as a semiconductor material of optical and electrical devices, such as light-emitting diodes (LEDs) [1,2], laser diodes (LD) [3,4], UV detectors [5], and high-power, high-frequency electronic devices [6]. [9,10] To reduce the dislocation density, the in situ etched metal–organic chemical vapor deposition (MOCVD)-grown GaN template [11] or etched in molten salts template [12]. The most effective way to reduce stress and dislocation is homoepitaxy on free-standing GaN substrate. Removing the substrate of heteroepitaxy-grown GaN layer with laser lift-off technology is the most common method [13]. A TiN nanonet structure was used to fabricate a free-standing GaN layer by HVPE with a void-assisted separation process [14]. Williams and co-workers obtained free-standing GaN substrates after cooling through a natural separation process mechanism caused by the difference of thermal expansion coefficients between GaN and the sapphire substrate [15]. Arrays of GaN nanorods with side-walls coated with silicon dioxide (SiO2 ) were arranged randomly on the sapphire substrate as a growth
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