High‐power GaN‐based semiconductor lasers

Abstract

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.

Examination of thermal properties and degradation of InGaN - based diode lasers by thermoreflectance spectroscopy and focused ion beam etching

“…The threshold of COMD was determined to be around 40-57MW/cm 2 for InGaN laser diodes. 14,15 These values are an order of magnitude higher than for GaAs counterparts. The mechanism of COMD was (and still is) intensively studied for GaAs based devices but in case of GaN based devices it has not been extensively investigated and has not been confirmed experimentally.…”

High-power laser structures grown on bulk GaN crystals

“…Catastrophic Optical Damage (COD) was not observed for this devices. Already published value for COD of 57 MW/cm 2 for similar mirrors [5] allow for use asymmetric high-reflecting coatings what should result in further increase in the optical power emitted from one cavity mirror. Despite the huge heating effect what resulted in the observed lasing wavelength shift by 3 nm towards the longer wavelength and reduction in differential efficiency to 0.2 W/A, our broad stripe LDs are capable of handling very high power.…”

Thermoreflectance spectroscopy—Analysis of thermal processes in semiconductor lasers

“…Typical degradation mechanisms known from arsenide based devices (like COMD or DLD) are not responsible for failure of GaN based diodes. The threshold of COMD was determined to be around 40-57 MW cm −2 for InGaN laser diodes [144,145]-an order of magnitude higher than for GaAs counterparts.…”