Optimization of GaAsP-QWs for high power diode lasers at 800 nm

Tensile-strained GaAsP quantum wells (QWs) embedded in AlGaAs waveguide and cladding layers are an alternative approach for the wavelength range 700-500 nm. We will present a detailed experimental and theoretical study of the dependence of the threshold current on the thickness and the strain of the QW for 800 nm. The optimum thickness of the GaAsP QW for a minimum threshold current density is about 14 nm and is thus much larger than for compressively strained QWs. Higher characteristic temperatures To can be obtained with even thicker QWs. In order to achieve high optical output powers and good fiber coupling efficiencies, we used broad waveguides with weak optical confinement and small far field divergence. Pile prepared two structures with 1 mu m thick Al0.65Ga0.35As (structure A) and 2 mu m thick Al0.45Ga0.55As (structure B) waveguides, respectively. For structure B, the thickness of the Al0.70Ga0.30As cladding layers must be carefully optimized in order to suppress higher-order transverse modes. Whereas structure B yields a higher maximum cw output power of AR/HR coated broad-area devices, structure A shows a better high-temperature behavior. Aging tests performed at 2 W (100 pm stripe width) and 25 degrees C suggest a very good reliability of these devices.