Design optimization of optically pumped terahertz lasers in stepped quantum wells

Asymmetric stepped quantum wells (QWs) have been used in many optoelectronic devices. This paper proposes a modulation doping position at the edge of the stepped well to minimize the potential distortion caused by the doping. As a result, parasitic potential wells are eliminated, and the sensitivity of the energy levels to dopant concentrations is substantially reduced. We also Suggest a stacked design to juxtapose two QW slabs in order to improve the waveguide mode overlap in optically pumped terahertz lasers using, the structure. The percentage of overlap between the active QWs layers and the laser mode increases from 9.8% for a thinned substrate single slab scheme to 68.4% for the stacked double slabs, respectively, with two highly doped layers acting as plasma waveguide. A diffraction integral model is established to Simulate the laser cavity tolerance to possible misalignment in the stacked design. Our modelling result shows that the diffraction loss due to small (few micrometre) misalignment or difference in slab length is negligible compared to other losses in the laser system.