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High-power blue-violet laser diodes with aspect ratio as low as 2.3 and threshold current down to 33 mA have been realized. The relationship between threshold current and optical confinement factor was investigated in order to minimize the beam divergence angle perpendicular to the junction plane (θ⊥). θ⊥ was found to decrease with reduction of the optical confinement factor, whereas threshold current density increased. A new layer structure, in which a p-typed cladding layer was located next to an AlGaN electron blocking layer, and a GaInN guiding layer was inserted between the active and the AlGaN electron blocking layer, was effective for obtaining small θ⊥ while maintaining low threshold current.

Degradation experiments for AlGaInN-based laser diodes were conducted for the purpose of constructing a possible model of the degradation mechanism. Lasers in this experiment were aged under 30 mW continuous-wave operation at 60 °C, and the lifetime was defined as the time at which the operating current increased by 20%. The lifetime was found to be dependent on the dislocation density of the basal ELOGaN layer, with the degradation rate being almost proportional to the square root of aging time. A model of degradation in which degradation is governed by a diffusion process is proposed based on these results. Although the model describes the experimental findings well, further investigation is considered necessary before the degradation mechanism in AlGaInN lasers can be fully understood.

PACS 42.55.Px, 42.60.Lh, 78.66.Fd, 81.05.Ea, 81.15Gh GaN-based blue-violet lasers with a kink-free output power of higher than 150 mW have been successfully realized by adopting a new ridge structure and appropriately designing the beam divergence. The new ridge structure is a narrow 1.4 µm ridge covered with a stacked layer of Si on SiO 2 and the beam divergence half-angles parallel and perpendicular to the junction plane are set at 8° and 21°, respectively. These lasers have been operating stably for more than 500 h under 130-mW pulsed operation at 60 °C. The empirical activation energy of device lifetime under 30-mW continuous-wave operation is 0.32 eV.Introduction GaN-based high-power blue-violet laser diodes (BV-LDs) operating in the 400-410 nm wavelength band are promising light sources for large-capacity optical storage systems. The characteristics of BV-LDs have been improved remarkably since Nakamura et al. reported the first roomtemperature continuous-wave (CW) operation in 1996 [1]. Reliable BV-LDs with estimated lifetimes exceeding 10,000 h under 30-mW CW operation at 60 °C have been realized in recent years [2][3][4]. Although these devices can be readily used in high-density digital video recording systems [5], reliable BV-LDs capable of much higher output power will be required in the near future as the technology for optical disk systems extends to multi-layer disks and higher data transfer rates to facilitate higher densities and higher recording speeds.In designing a high-power laser suitable for use in optical disk systems, it is essential to maintain both a high kink level and a high catastrophic optical damage (COD) level of output power. These two levels are closely related to the optical confinement in the stripe of the laser structure, and hence to the beam divergence angles. The lifetime of BV-LDs is also governed by the density of dislocations within the stripe [6]. The stripes of current lasers typically contain significantly less than 100 dislocations, reduced from previously much higher numbers through the use of dislocation-reduction techniques such as epitaxial lateral overgrowth (ELO) [7,8], and lifetimes of over 1,000 h at 60 °C have already been achieved. However, even one dislocation in a stripe causes rapid degradation in other III-V laser diodes such as AlGaAs, GaInAsP and AlGaInP lasers. The remarkably long lifetimes and resilient nature of GaN-based lasers is therefore apparently associated with the inherent rigidity of this material system.In this paper, the kink and COD levels of a laser structure optimized for obtaining high output powers of more than 100 mW are described with reference to the most important device parameters. The dependence of the lifetime of these high-power lasers on the ambient temperature and output power are also reported.

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