InGaN/GaN/AlGaN-based laser diodes grown on free-standing GaN substrates

The InGaN multi-quantum-well (MQW)-structure laser diode (LD) was grown on an epitaxially laterally overgrown GaN on sapphire. The lowest threshold current densities between 1.2 and 2.8 kA cm−2 were obtained when the number of InGaN well layer was 2. The LDs showed an output power as high as 420 mW per facet under room-temperature (RT) continuous-wave (CW) operation. The lifetime of the LDs at a constant output power of 30 mW was 250 h under CW operation at an ambient temperature of 50°C. Another InGaN MQW LD was grown on a free-standing GaN substrate that was obtained by removing the sapphire substrate. The LDs on free-standing GaN substrate with cleaved mirror facets showed an output power as high as 30 mW under RT-CW operation. The stable fundamental transverse mode was observed by reducing the ridge width to as small as 2 μm. The lifetime of the LDs on free-standing GaN substrate at a constant output power of 5 mW was about 160 h under CW operation at an ambient temperature of 50°C, due to a high threshold current density of 6 kA cm−2.