Wafer-scale crack-free AlGaN on GaN through two-step selective-area growth for optically pumped stimulated emission

• Vertical growth mode of GaN and lateral growh mode of AlGaN was discussed.
• We obtained crack-free Al0.2Ga0.8N template of 2-in. wafer by using 2-step SAG.
• We demonstrated AlGaN with low dislocation density of ~7.6×108 /cm2.
• Optically pumped stimulated emission at 355.5 nm was obtained from GaN/AlGaN MQW grown on crack-free AlGaN template.

Crack-free AlGaN template has been successfully grown over entire 2-in. wafer by using 2-step selective-area growth (SAG). The GaN truncated structure was obtained by vertical growth mode with low growth temperature. AlGaN of second step was grown under lateral growth mode. Low pressure enhanced the relative ratio of lateral to vertical growth rate as well as absolute overall growth rate. High V/III ratio was favorable for lateral growth mode. Crack-free planar AlGaN was obtained under low pressure of 30 Torr and high V/III ratio of 4400. The AlGaN was crack-free over entire 2-in. wafer and had quite uniform Al-mole fraction. The dislocation density of the AlGaN with 20% Al-composition was as low as ~7.6×108 /cm2, measured by cathodoluminescence. GaN/AlGaN multi-quantum well (MQW) with cladding and waveguide layers were grown on the crack-free AlGaN template with low dislocation density. It was confirmed that the MQW on the AlGaN template emitted the stimulated emission at 355.5 nm through optical pumping experiment. The AlGaN obtained by 2-step SAG would provide high crystal quality for highly-efficient optoelectronic devices as well as the ultraviolet laser diode.