Pros and cons of green InGaN laser on c-plane GaN

The challenges of green InGaN lasers are discussed concerning material quality as a function of InGaN composition, quantum well design and piezoelectrical fields. Investigations of polar quantum well designs and comparison with simulated nonpolar structures demonstrate that the quality of the indium rich layers is more important than the influence of interface charges. A high risk of dark spots at high In concentrations of 26-33% is observed. Small changes of about 2% of In significant reduce or increase the quantity and size of dark luminescence areas. Polar designs are a trade-off between low indium concentrations of 4 nm wide quantum wells and high overlap of electrons and holes in 2 nm narrow designs. Furthermore, our single quantum wells have less non-radiative defects than indium rich multi-quantum well structures. Optimized active layer designs and the material qualities enable us to get green InGaN lasers on c-plane substrates for cw operation at 515-524 nm and wall plug efficiencies of 3.9-2.3%. Slope efficiency of 0.3-0.4 W/A allows up to now highest optical output power of 50 mW. (C) 2011 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim