Abstract
High-quality thick GaN layers were directly grown by hydride vapor phase epitaxy on sapphire substrates preliminary processed by a laser beam focused within the substrate. The critical thickness for crack generation was improved drastically from 10–20 µm for regular substrates to 220–250 µm by using the laser processed sapphire substrates. Layers of 200 µm thickness grown on the laser processed sapphire substrates exhibited a crack-free surface over the entire 2-in. area and a threading dislocation density as low as 1×107 cm-2, which is one order of magnitude lower than that achievable with a regular sapphire substrate.