Current-injection operation of quantum-wire lasers and verification of low threshold currents

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We achieved single-mode lasing in two-types of T-shaped-quantum-wire (T-wire) lasers using current-injection via perpendicular and parallel p-and n-doping layers. These lasers had cavity length of 0.5 mm and cavity mirror facets coated by high-reflectivity Au/SiO2 thin films. The T-wire lasers are formed by the cleaved-edge overgrowth method, and laser optical waveguide is located at a corner on each wafer, for which we cannot use conventional photo-lithography technique. In addition, singular p-n junction geometry of T-wire lasers with non-plainer structures cannot be designed with conventional one-dimensional Poisson equation tools. Therefore, we designed perpendicular and parallel doping profiles in T-wire lasers by try-and-errors, developed manual semiconductor processing methods, and devised our homemade optical characterization tools.In a T-wire laser with 15-array of T-wires and perpendicular p-and n-doping layers, we observed single-mode lasing in a wide temperature range of 5- … More 110K, which is the highest lasing temperature in current-injection T-wire lasers. Laser performance becomes optimum at 100 K, where we obtained threshold current of 2.1mA and differential quantum efficiency of 0.9%. In a T-wire laser with 20-array of T-wires and parallel p-and n-doping layers, on the other hand, we observed single-mode lasing in a temperature range of 30-70K. Laser performance becomes optimum at 30 K, where we obtained the lowest threshold current of 0.27 mA and high differential quantum efficiency of 12%. This threshold current value of 0.27 mA corresponds to 14 μ A per single T-wire. A theoretical value estimated by Yariv's analysis method and wire length of 0.5 mm, temperature of 30 K, and carrier lifetime of 0.4 ns is about 10 μ A per single T-wire. Our present result is very close to this estimation, and in principle confirms the predicted low threshold current in quantum wire lasers. Further detailed characterizations of luminescence and lasing spectra, current-voltage characteristics, current-light-output characteristics, threshold currents, differential quantum efficiencies as well as their temperature dependences have been achieved on our current-injection T-wire lasers. Less