To prevent the cracking of GaN thick films grown on a sapphire substrate by hydride vapor phase epitaxy (HVPE), a novel technique without complex processes is developed. By adding a temperature ramping step in the HVPE GaN epitaxy process, more than 300-μm-thick high-quality crack-free GaN thick films on sapphire substrate can be obtained by this technique. After separation by a conventional laser-induced lift-off process, a 1.5 in. 300 μm freestanding GaN wafer with a dislocation density of approximately 1 × 107 cm-2 could be fabricated without any cracks. No additional designed-patterned or stress-reduced structures were applied in these samples to reduce the dislocation density and thermal stress.
- Freestanding GaN