2020, Elatta, M., Brox, O., Della Casa, P., Maaßdorf, A., Martin, D., Wenzel, H., Knigge, A., Crump, P.

Broad-area diode lasers with increased brightness and efficiency are presented, which are fabricated using an enhanced self-aligned lateral structure by means of a two-step epitaxial growth process with an intermediate etching step. In this structure, current-blocking layers in the device edges ensure current confinement under the central stripe, which can limit the detrimental effects of current spreading and lateral carrier accumulation on beam quality. It also minimizes losses at stripe edges, thus lowering the lasing threshold and increasing conversion efficiency, while maintaining high polarization purity. In the first realization of this structure, the current block is integrated within an extreme-triple-asymmetric epitaxial design with a thin p-doped side, meaning that the distance between the current block and the active zone can be minimized without added process complexity. Using this configuration, enhanced self-aligned structure devices with 90 µm stripe width and 4 mm resonator length show up to 20% lower threshold current, 21% narrower beam waist, and slightly higher (1.03 ) peak efficiency in comparison to reference devices with the same dimensions, while slope, divergence angle and polarization purity remain almost unchanged. These results correspond to an increase in brightness by up to 25%, and measurement results of devices with varying stripe widths follow the same trend. © 2020 The Author(s). Published by IOP Publishing Ltd.

2020, Boni, A., Wünsche, H.J., Wenzel, H., Crump, P.

Electrons and holes injected into a semiconductor heterostructure containing quantum wells are captured with a finite time. We show theoretically that this very fact can cause a considerable excess contribution to the series resistivity and this is one of the main limiting factors to higher efficiency for GaAs based high-power lasers. The theory combines a standard microscopic-based model for the capture-escape processes in the quantum well with a drift-diffusion description of current flow outside the quantum well. Simulations of five GaAs-based devices differing in their Al-content reveal the root-cause of the unexpected and until now unexplained increase of the series resistance with decreasing heat sink temperature measured recently. The finite capture time results in resistances in excess of the bulk layer resistances (decreasing with increasing temperature) from 1 mΩ up to 30 mΩ in good agreement with the experiment. © 2020 The Author(s). Published by IOP Publishing Ltd.