Bruno Acklin

Highly reliable 40-W cw InGaAlAs/GaAs 808-nm laser bars

The fundamental question whether aluminum-free semiconductor lasers in the 808 nm band are significantly more reliable than Al-containing lasers is still open. We have fabricated and tested high-power InGaAlAs/GaAs-lasers which show excellent reliability data at and above 40 W cw. The laser structure consists of an InGaAlAs-double-quantum well (DQW) as active layer embedded in a large optical cavity (LOC) waveguide structure. The layers were grown in a low pressure MOVPE (LP- MOVPE) reactor using high quality precursors. Asymmetrically coated bars with a width of 1 cm containing 25 groups of 200 micrometer wide emitters were mounted junction down on actively cooled heatsinks. At a heatsink temperature of 18 degrees Celsius the slope-efficiency is 1.1 - 1.2 W/A. Due to the low series-resistance of 2.2 m(Omega) and the low internal losses in the range of 1.7 cm-1 the overall efficiency at 40 W cw reaches 50%. Lifetime studies over 33 0000 h accumulated device hours show that the laser bars with a resonator length of 900 micrometer can be operated at 40 W with high reliability. The mean degradation rate is -0.11%/kh. This result emphasizes that Al-containing lasers can also have a very high reliability usually claimed for Al-free lasers. As a consequence of these encouraging results we will start further lifetime tests at 50 to 60 W.

High-power AlGaInAs/GaAs microstack laser bars

The maximum useful optical power of laser bars is limited due to thermal and lifetime constraints to typical values of 50 W/cm cw or 120 W/cm qcw. A promising new approach is the so-called microstack laser in which several laseractive areas are integrated vertically in the same monolithic structure. In order to drive these structures in series with high efficiency low-resistance tunnel-junctions have to be realized. By optimizing the MOVPE growth process tunnel- junctions with a specific differential resistivity of 2.5 X 10-4 (Omega) cm2 could be obtained, which are suitable for the monolithic inter-connection of laser structures.

High-power laser bars for 70-W cw (808 nm): a comparison between SQW and DQW

We have investigated the degradation behavior of high power diode-laser bars at 80 nm with single quantum and double quantum well structures in continuous wave operation. The 1 cm bars have a fill factor of 50%. Laser diodes with different resonator lengths from 300 micrometers to 2000 micrometers have been investigated. Different bars were mounted on actively cooled submounts and operated at comparable current densities and heat load.