Abstract

Increased optical output power P_opt from single broad area GaAs-based diode lasers is demanded for material processing, with higher P_opt and cost reduction in €/W enabled by using devices with ever-wider apertures [1]. Device structures suitable for single emitters with very large footprints (> 4 mm²) that sustain high Popt and conversion efficiency ηE without exciting unwanted optical modes (e.g. ring oscillations) are also of interest as an enabling technology for high power photonic crystal surface emitting lasers [2]. We report here progress in broad area diode lasers with resonator length L = 4 mm and emitting aperture of W = 1200 µm with wavelength λ = 915 nm. An η_E-optimized highly vertically asymmetric epitaxial design was used, taken from [3,4,5], and grown using metal organic vapor phase epitaxy (MOVPE). To suppress lateral (e.g. ring) oscillations, following [6], the lateral current path was patterned periodically, with 9 µm current blocking stripes on a 29 µm period. Here, the lateral pattern was realised with a buried-regrown-implant-structure, BRIS, following [3,4,5], see schematic in Fig. 1a. After the first growth the p-side cladding and waveguide layers of the laser are implanted with O⁺ ions to block current flow, periodically within the stripe, and broadly outside the stripe, then the wafer is regrown to complete the structure. In contrast to approaches based on etched p-n junctions [7], the wafer is still planar, minimizing growth defects, and lateral refractive index steps are minimized. Thick (800 nm) highly-doped p-type material was regrown after implantation. The residual thickness is d_res ~ 600 nm (offset between current blocking and active region), sufficient to suppress 70…80% of lateral current spreading at the device edges [7]. After regrowth, single emitters lasers were fabricated using standard techniques, facet passivated (ZnSe) then coated for front and rear facet reflectivity of R_F = 1.8% and R_R = 98%. The devices were mounted with AuSn in a miniaturised (6 × 8 × 3.2 mm) CuW-sandwich package. Fig. 1b presents electro-optic characteristics at 25°C heatsink temperature, P_opt is measured with a calibrated thermoelectric detector, in-pulse-power with a fast photodetector, voltage U in 4-terminal configuration and far field with a goniometer. In quasi-continuous wave QCW test (10 Hz, 500 µs), peak ηE = P_opt / IU = 69% (current, I) at P_opt = 68 W and ηE = 52% at P_opt = 200 W are seen.

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