InP-basierte Diodenlaser hoher Brillanz bei 14xx nm (English shop)

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Within the scope of this work, InGaAsP tapered lasers epitaxially grown by solid-source MBE emitting at 14xx nm could be demonstrated for the first time. The first part of the work dealt with the design of the vertical structure. For the modelling, a passive calculation of the mode profile in the fast-axis direction was used. Two approaches to dimensioning the epitaxial layers were pursued: on the one hand, the LOC concept, well established for GaAs high-power lasers, was transferred to InGaAsP in order to realise structures with low optical losses. The other approach comprised a structure with thin waveguide layers, which enables a higher modal gain and provided more design freedom for further development. Various LOC structures and one vertical structure with a narrow waveguide were realised experimentally and characterised in pulsed operation using rapid-process emitters. It was shown that a spacer layer on both sides of the active zone increased the internal quantum efficiency of the device by about 15% and thus contributes to a lower laser threshold. A variation of the number of quantum wells in the LOC-based structures allowed the extraction of the material gain and the transparency current density, which entered the BPM simulation of the tapered lasers as parameters. Furthermore, a prediction for an optimised active zone specifically for the tapered laser could be derived from this: with four QWs (LOC structure) or three QWs (narrow waveguide), a minimisation of the threshold current was to be expected. Of all the vertical structures investigated, the structure variant with a narrow waveguide exhibited the best electro-optical properties, which could be attributed to a better carrier capture in the active zone and to the higher modal gain. A variation of the doping profile showed that the lower limit of the internal losses lies at about 7 cm−1, since at a lower p-doping the internal quantum efficiency deteriorates dramatically. Here again, the advantage of the LOC concept was confirmed, with which internal losses between 2.0 and 3.3 cm−1 could be realised. These values are in the range of the best values published for InGaAsP lasers at this wavelength.