We pushed direct green laser diodes towards longer wavelengths at 524–532 nm based on improvements of epitaxial design and material quality on c-plane GaN substrate. Mounted ridge laser diodes show significant performance improvement in cw operation. For 524 nm laser, wall plug efficiency up to 2.3% at 50 mW optical output power is achieved. In pulse mode operation we demonstrate broad-area test lasers with an emission wavelength of 531.7 nm. Nonpolar and polar substrates are compared with respect to indium content in InGaN quantum wells. The limiting factors for achieving longer wavelengths and better performance of green lasers are discussed from this viewpoint.

The recombination kinetics of the electron-hole plasma in strongly excited, intrinsic GaAs is investigated at room temperature by time-resolved photoluminescence using a line-shape analysis of transient spectra. Special structuring of the samples prevents stimulated emission and diffusion. Population of higher energetic subsidiary conduction-band valleys must be taken into account for densities bigger than 1.5 x 10high19 cmhighminus3. A significant influence of Auger recombination is detected for densities bigger than 2.5 x 10high19 cmhighminus3. The bimolecular recombination coefficient and an effective Auger coefficient are found to be B is equal to (1.7 plusminus 0.2) x 10highminus10 cmhigh3 shighminus1 and Csubeff is equal to (7 plusminus 4) x 10highminus30 cmhigh6 shighminus1, respectively

Based on recent improvements of growth of In-rich InGaN quantum wells with low defect density, we demonstrate current driven InGaN laser diodes at wavelengths as long as 500 nm. The laser structures are grown on c-plane GaN substrate and are processed as broad oxide-insulated stripe laser diodes. We discuss the impact of the piezoelectric field on the emission energy of long wavelength laser diodes for this growth orientation. The combination of low threshold current density of 8.2 kA/cm2 with high slope efficiency of 650 mW/A enables high output powers up to several tens of milliwatts.

We demonstrate direct green laser operation from InGaN based diodes at wavelengths as long as 515.9 nm with 50 mW output power in pulse operation. A factor of ∼10 defect reduction for the In-rich InGaN quantum wells based on improvements of the epitaxial growth process and design of the active layers on c-plane GaN-substrates makes it possible to demonstrate laser operation at room temperature. Micrometer-scale photoluminescence mappings and electro-optical measurements confirm the reduction of nonradiative defects in the emitting layers. The 11 μm broad-area gain-guided laser structures were driven in pulse operation to minimize thermal effects and to accurately measure the laser temperature dependence. The threshold current density was ∼9 kA/cm2 and the fitted slope efficiency had a value of ∼130 mW/A for an optical output up to 50 mW.

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In this paper we investigate the waveguiding (WG) of direct green InGaN laser diodes grown on c-planeGaNsubstrates. The problem of parasitic modes emerges due to the reduced refractive index difference between the GaN waveguide and AlGaN cladding layers for green compared to blue emitting laser diodes. We discuss several approaches to avoid substrate modes. We investigate different materials and designs for optimized WG of green InGaN laser diodes using a 1D transfer matrix simulation tool

Experimental gain spectra of 450 and 490 nm laser diodes on c-plane GaN are analyzed by detailed comparison with the results of a fully microscopic theory. The gain calculation shows the importance of electron LO-phonon coupling. The whole spectral gain shape, not only the low energy tail, is strongly influenced by the LO-phonon contribution. The inhomogeneous broadening parameter increases by a factor of about two for the cyan laser diode in comparison with the blue laser structure. This indicates an increase in alloy and thickness fluctuations for the longer wavelength material

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 multiquantum 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.