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Design and technology developments targeted at increasing both power conversion efficiency and optical output power of GaAs-based diode lasers are under intense study worldwide, driven by the demands of commercial laser systems. The conversion efficiency at the operation point is known to be limited by electrical and optical losses in the p-side waveguide. In this paper an ‘extreme, double asymmetric’ design to mitigate the impact of the p-side waveguide is studied and compared with a more conventional design. An increase of the efficiency at the highest power is demonstrated, but it is less than expected from simulations.

AlxGa1−xAs grown on GaAs is known to be almost perfectly lattice matched with a maximum lattice mismatch of 0.14% at room temperature and even less at temperatures of 700 °C–800 °C. However, as layer structures for edge-emitting diode lasers exhibit an increasing overall thickness of several microns of AlxGa1−xAs, e.g., diode lasers comprising a super-large optical cavity, the accumulated elastic strain energy increases as well. Depending on the growth temperature the formation energy of dislocations can be reached, which is limiting the pseudomorphic growth. In this regard, the thermal expansion coefficient difference between layer and substrate is an important parameter. We utilize in situ curvature measurements during growth of AlxGa1−xAs by metal-organic vapour phase epitaxy to determine the thermal expansion coefficient α. The curvature change with increasing layer thickness, as well as with wafer temperature at constant layer thickness is used to assess α. This is compared to ex situ temperature dependent X-ray diffraction measurements to obtain α. All determined values for α are in good agreement, yielding αAlAs=4.1×10−6 K−1 for a given GaAs linear thermal expansion coefficient of αGaAs=5.73×10−6 K−1.

High-power broad-area diode lasers are the most efficient light sources, with 90-μm stripe GaAs-based 940-980 nm single emitters delivering > 10 W optical output at a power conversion efficiency ηE(10 W) > 65%. A review of efforts to increase ηE is presented here and we show that for well-optimized structures, the residual losses are dominated by the p -side waveguide and nonideal internal quantum efficiency ηi . The challenge in measuring efficiency to sufficient precision is also discussed. We show that ηE can most directly be improved using low heat sink temperature THS with ηE(10 W) reaching > 70% at THS = -50 °C. In contrast, increases in ηE at THS = 25 °C require improvements in both material quality and design, with growth studies targeting increased ηi and reduced threshold current and design studies seeking to mitigate the impact of the p-side waveguide. “Extreme, double asymmetric” (EDAS) designs are shown to substantially reduce p-side losses, at the penalty of increased threshold current. The benefit of EDAS designs is shown here using diode lasers with 30-μm stripes, (in development as high beam quality sources for material processing). Efficiency increases of ~ 10% relative to conventional designs are demonstrated at high powers.

We report optical nanostructuring technology, developed for distributed feedback gratings, broadly useable for many applications. The nanostructure is pre-structured into aluminum-free layers on top of AlGaAs then etched inside the epitaxy reactor and overgrown with AlGaAs. Oxygen contamination at the grating-interface is ∼3 × 1011 cm−2. These gratings introduce no extra internal optical loss and series resistance in broad-area lasers. Distributed feedback broad-area lasers using this technology achieve optical power >12 W, peak efficiency >60%, wide spectral locking range in current and heatsink temperature (over at least ∼30 °C) and operate at 10 W for >5000 h in a preliminary reliability test.

A report is presented on how distributed feedback (DFB) lasers can achieve high optical power and power conversion efficiency together with a narrow vertical emission angle. Recently developed 976 nm DFB lasers emit 11 W, have a maximum power conversion efficiency of 58%, a spectral linewidth of ∼0.4 nm FWHM and a narrow vertical far field of 28° FWHM. This considerable enhancement was obtained with an improved epitaxy design and optimised grating fabrication process. These are DFB lasers that achieve power, efficiency and emission angle values comparable to conventional Fabry-Perot lasers, but with spectral stabilisation. Accordingly, these lasers are particularly well suited for pumping fibre and solid-state lasers.