High-speed tunnel injection quantum well and quantum dot lasers

To circumvent the numerous performance-limiting effects of hot-carrier phenomena in semiconductor quantum-well lasers, we have demonstrated the innovative approach of directly injecting carriers into the lasing subband by tunneling. These lasers, made with a variety of material systems, have shown evidence of reduced hot-carrier effects. Specifically, measured small-signal modulation bandwidth of similar to 50 GHz and maximum intrinsic bandwidth of 110 GHz have been achieved with 0.9 mu m lasers, These are the highest measured modulation bandwidths in any laser. Auger recombination has been virtually eliminated in 1.55 mu m lasers and reduced chirp and temperature dependence are also demonstrated. Significant reduction of hot-carrier and carrier leakage effects have also been recently demonstrated in small-area vertical-cavity surface-emitting lasers. These experimental results are supported by recent simulations that identify gain suppression in high speed lasers to be caused by a coupling between the electron temperature and the quasi Fermi level. Lasers with quantum dots as gain media promise high differential gain, very low threshold current, temperature-insensitive operation and high modulation bandwidth. We have investigated room-temperature single-mode ridge-waveguide quantum box lasers in which the quantum box gain regions are realized by self-organized growth and carrier injection is achieved by conventional means over hetero-barriers and by tunneling. The tunneling injection quantum dot lasers show improvements in both differential gain (6 x 10(-14)cm(2)) and modulation bandwidth. These results will be presented and discussed.