Epitaxial design of 475 nm InGaN laser diodes with reduced wavelength shift



We have analyzed the quantum well stability of blue-green emitting laser diodes grown on c -plane GaN substrates. Different parameters such as the material composition of the surrounding layers of the quantum well and the number of quantum wells were varied. We observed a strong influence of the barrier material composition (AlGaN, GaN, InGaN) on the quality of In rich quantum wells. Our preferred barrier material is GaN. In contrast InGaN barriers result in a higher defect density of 9.6 × 106 cm–2 in the quantum well whereas GaN barriers show a defect density of 1.8 × 106 cm–2. High indium content quantum wells with good crystalline quality were grown by improving the structure of the complete active region. Further enhancement could be achieved by using a double quantum well structure instead of a single quantum well structure. This offers the advantage that the wavelength shift is strongly reduced as a result of the lower current density in each quantum well. With our improvements we could realize laser diodes emitting at 475 nm with threshold current densities of 12 kA/cm2 and a slope efficiency of 500 mW/A. (© 2009 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)