We report on the development of GaN-based violet laser diodes (LDs) for the high-capacity optical storage application and blue LDs for the laser projection display application. InGaN LDs with emission wavelength of ~405 nm are already being adopted for next-generation optical-storage systems. We present results on >400 mW single-mode output power under pulsed operation which can be employed in 100 Gbyte multi-layer BD systems. We designed LD layer structures to exhibit high level of catastrophic optical damage (COD) and small beam divergence. In addition, GaN-based blue LDs with emission wavelength of ~450 nm have also been developed for the application to the blue light sources of laser display systems. We demonstrate single-mode blue InGaN LDs with >100 mW CW output power. Interestingly, we observed anomalous temperature characteristics from the blue InGaN LDs, which has shown highly-stable temperature dependence of output power or even negative characteristic temperature (T<sub>0</sub>) in a certain operation temperature range. This unusual temperature characteristic is attributed to originate from unique carrier transport properties of InGaN QWs with high In composition, which is deduced from the simulation of carrier density and optical gain.
The enhanced output power with improved lifetime is required for the GaN-based blue-violet laser diode (LD) as a light source for Blu-ray Disc or HD-DVD. In this paper, the output power levels and aging behaviors in GaN-based LDs grown on sapphire substrates were compared in epi-up and epi-down bonding. At low current level, the two bondings
show little differences in L-I characteristics. At high current level, however, the epi-up bonding shows a rapidly decreased slope efficiency in L-I characteristics with increasing current injection. On the contrary, the slope efficiency in epi-down bonding is not so much deteriorating as that in epi-up bonding. The differences in junction temperature between epi-up and epi-down bonding are large at higher current levels. The junction temperature of epi-up bonding is
about two times higher than that of epi-down bonding, implying efficient heat dissipation in epi-down bonding. At aging test, the epi-down bonding LD shows lower degradation rate at the aging slope than that of epi-up bonding LD. The degradation rate is accelerated by poor heat dissipation in epi-up bonding. Thus, for the higher power and longer lifetime, it is necessary to employ efficient heat dissipation structures such as epi-down bonding for the GaN-based LD
on sapphire substrate.