UGaN growth on laser patterned sapphire substrate: quality feature

Abstract

AbstractLaser patterning technique as a flexible tool to grow high quality undoped gallium nitride (uGaN) on sapphire wafers is presented. A series of stripes were formed on sapphire wafer surface using Nd:YAG laser (100 kHz, 266 nm, 30 ps pulse) with variable pulse power (40‐670 mW), laser spot velocity over the wafer (1‐46 mm/s) and distance between the stripes (4‐15 μm). Stripes width was ∼2‐5 μm. After laser patterning sapphire wafers were cleaned using aqua regia and etched using sulphuric and phosphoric acid solution. SEM images after wet chemical etching show less surface roughness and open sapphire crystalline planes compared to surfaces treated with laser. Undoped GaN was grown by metal‐organic chemical vapour deposition (MOCVD). Used III/IV ratio: 2400, reactor pressure: 150 mBar, temperature: 1065 °C. SEM and AFM results show reduction of dislocation density in grown gallium nitride layer. The growing of this layer was performed using epitaxial lateral overgrowth (ELO) method on laser patterned sapphire substrates. Our observation revealed that the optimal laser power for sapphire substrate patterning for ELO GaN growth is 70‐300 mW. Moreover, we demonstrated intermediate GaN lateral growth states. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)