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Coupled multi quantum well 650-nm emitting GaInP laser diodes

650nm emitting lasers are required for a number of applications including DVD. A combination of requirements, such as narrow far-field divergence, low temperature dependence of threshold current and low absolute operating current make device design difficult. We have adopted the approach of using coupled multiple quantum wells to minimise quasi-Fermi level separation and hence carrier leakage while using a simple low optical confinement structure, with small refractive index step between waveguide core and cladding, to optimise far-field divergence. The samples studied consist of either 3, 4 or 5 coupled quantum wells set in a waveguide core of (AlxGa1-x)0.5In0.5P (0.520.7Ga0.3)0.5In0.5P. The lasing wavelength was between 650 and 655nm with a threshold current density of between 1267Acm-2 and 1417Acm-2 for a 450μm long device with a maximum T0 of 105K (20-70°C). The measured far-field divergence of 27 ±1 degrees (FWHM) was similar for all three structures. We have performed an in-depth analysis using a single pass, multi-section method to deduce modal gain and loss, spontaneous current and efficiency. This demonstrates that the extra wells provide a smaller than expected improvement in gain at room temperature and negligible improvement in gain-current performance at 220K and we attribute this to imperfect carrier distribution amongst the wells. The measured values of the internal optical mode loss of 9-20cm-1 and approximately 50% for the internal efficiency provide room for improvement in laser performance.