The crack-free AlGaN template has been successfully grown by using selective area growth with triangular GaN facet. The triangular GaN stripe structure was obtained by vertical growth rate enhanced mode with low growth temperature of 950°C and high growth pressure of 500 torr. The lateral growth rate enhanced mode of AlGaN for crack-free and flat surface was also investigated. Low pressure of 30 torr and high V/III ratio of 4400 were favorable for lateral growth of AlGaN. It was confirmed that the 4 μm -thick Al_0.2Ga_0.8N was crack-free over entire 2-inch wafer. The dislocation density of Al_0.2Ga_0.8N was as low as ~7.6 × 10⁸ /cm² measured by cathodoluminescence. Based on the high quality AlGaN with low dislocation density, the ultraviolet laser diode epitaxy with cladding, waveguide and GaN/AlGaN multiple quantum well (MQW) was grown by metalorganic chemical vapor deposition. The stimulated emission at 349 nm with full width at half maximum of 1.8 nm from the MQW was observed through optical pumping experiment with 193 nm KrF laser. We also have fabricated the deep ridge type ultraviolet laser diode (UV-LD) with 5 μm-wide and 700 μm-long cavity for electrical properties. The turn on voltage was below 5 V and the resistance was ~55 Ω at applied voltage of 10 V. The amplified spontaneous emission spectrum of UV-LD was also observed from pulsed current injection.

Keywords: Crack-free AlGaN, Dislocation density, Selective area growth, Stimulated emission, Ultraviolet laser diode, Amplified spontaneous emission