GaN-based violet laser diodes

Three kinds of substrates were used for violet InGaN multi-quantum-well/GaN/AlGaN separate-confinement-heterostructure laser diodes (LDs). One of substrates is epitaxially laterally overgrown GaN (ELOG) substrate. Another is 'free-standing GaN' substrate. In order to obtain it, thick GaN was grown on 'ELOG', and then, sapphire and 'ELOG' were removed. Third one is 'ELOG grown on thick GaN' substrate. The threading dislocation (TD) densities of 'ELOG', 'free-standing GaN' and 'ELOG grown on thick GaN' were 1x10(6) /cm(2), 5x10(7) /cm(2) and 7x10(5) /cm(2), respectively. LDs were fabricated with the structure of epi side up. The estimated lifetime of ID grown on 'ELOG grown on thick GaN' was 15000 h under condition of continuous-wave operation, case temperature of 60 degreesC and output power of 30mW. And those of grown on 'ELOG' and 'free-standing GaN' were 1500 h and 300 h, respectively. Because the sapphire is attached, heat dissipation is bad for LD grown on 'ELOG', considering the heat dissipation of the LD chip. However, the lifetime of LD grown on 'ELOG' was much longer than that of grown on Tree-standing GaN'. This indicates that the heat dissipation to heat sink is not dominant for the lifetime of LDs. The lifetime of LDs strongly depends on the TD density as understood from the comparison between 'ELOG' and 'ELOG grown on thick GaN'. Being forecasted from these results are (1) 'free-standing GaN' is not necessarily needed, (2) dislocation density only has to be low.