Recent progress in blue/green InGaN laser diodes

For blue light emission the direct output of InGaN based lasers is used, while for the green the light emission of GaAs based lasers must be converted by a nonlinear crystal. Due to the inherent difficulties and bigger size of such a light source there is an increased interest to use the direct output of an InGaN based laser diode with emission in the green range. Performance of laser diodes with emission wavelength of around 440 nm that are suitable for such projectors is improving and these diodes show good efficiencies. Recent work to increase the operation wavelength demonstrated lasing up to around 475 nm by using a double quantum well design. Continuous improvements in the quality of the InGaN quantum wells with high Indium content and in the same time reduction of the negative influence of the piezoelectric fields on the carrier injection make it possible to achieve lasing up to a wavelength of 498 nm. A lasing wavelength temperature coefficient of 0.04 nm/K and a To coefficient of ~200 K were calculated. By increasing the temperature to around 80circdegC the 500 nm lasing could be achieved.