A. Maassdorf

Buried DFB gratings floating in AlGaAs with low oxygen contamination enable high power and efficiency DFB lasers

We report a novel design and fabrication technique for buried overgrown DFB gratings floating in AlGaAs. In-situ etching enables low oxygen contamination and results in >; 60% efficient and 10W reliable high power DFB lasers.

Efficiency-optimized 973nm high power broad area DFB lasers with overgrown aluminium-free gratings for peak power conversion of 63%

970–980nm broad area (BA) diode lasers with 90–100µm stripe widths are commercially important as pump source for solid state and fiber lasers, as well as for direct applications. Although BA lasers demonstrate high continuous wave (CW) power conversion efficiency η<inf>c</inf> > 60% and high reliable powers, P<inf>rel</inf> > 7W, the emission spectrum is too broad (∼ 4nm) and varies too quickly with temperature (∼ 0.4nm/K) for many applications [1]. Introduction of a uniform overgrown distributed feedback (DFB) grating leads to narrow (FWHM &#60; 1nm), temperature stable spectra, but this typically causes additional losses in the BA laser, leading to η<inf>c</inf> &#60; 60% and P<inf>rel</inf> &#60; 5W [2].

11W broad area 976nm DFB lasers with 58% efficiency

Optimized 976 nm DFB lasers have peak power conversion efficiency of 58%, peak power of 11 W, linewidth of ~0.4 nm and vertical far-field FWHM 28°. A comparison with Fabry-Pérot lasers to the same design is presented.

Investigation of breakdown and DC behavior in HBTs with (Al,Ga)As collector layer

We report on the realization of an InGaP-GaAs-based double heterojunction bipolar transistor with high breakdown voltages of up to 85 V using an Al/sub 0.2/Ga/sub 0.8/As collector. These results were achieved with devices with a 2.8 /spl mu/m collector doped to 6/spl times/10/sup 15/ cm/sup -3/ (with an emitter area of 60/spl times/60 /spl mu/m/sup 2/). They agree well with calculated data from a semi-analytical breakdown model. A /spl beta//R/sub SBI/ (intrinsic base sheet resistance) ratio of more than 0.5 by introducing a 150-nm-thick graded Al-content region at the base-collector heterojunction was achieved. This layer is needed to efficiently suppress current blocking, which is otherwise caused by the conduction band offset from GaAs to Al/sub 0.2/Ga/sub 0.8/As. The thickness of this region was determined by two-dimensional numerical device simulations that are in good agreement with the measured device properties.