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This paper describes the successful stacking of multilayered InAs quantum dots (QD) on a GaAs substrate up to 12 layers. The laser oscillated from the ground state under the condition of mirror loss at less than 7 -8 cm À1 . The extremely low threshold current density per QD-layer of 7 A/cm 2 /layer was obtained with a lasing wavelength of 1.21 mm at room temperature, which is the lowest value for any known semiconductor laser.

The study of next generation high energy accelerators based on 16 T dipoles has emphasized the need for higher performance, cost-effective Nb3Sn superconducting wires. A Conductor Development Program aiming to reach a non-copper critical current density (Jc) of 1500 A/mm 2 at 16 T and 4.2 K has been launched by CERN, with the involvement of industry and laboratories worldwide. In this article, the targets and strategy of the program are presented, with an overview of the wire layouts and development activities being pursued by each partner, and the latest characterization results are reported. Three of the four participating manufacturers have successfully reached the first stage Jc milestone, but a significant advance is still needed to achieve the final target. The next steps are briefly discussed, as the program focuses increasingly on novel alloys and methods to maximize Jc.

A model of carrier leakage lifetime is presented taking into account the density of states for quantum-wells and band nonparabolicity. Rate equations are also proposed including leakage of both types of carriers and carrier loss in both sides of optical confinement layers. The carrier loss coefficients extracted by adopting this model on the measured modulation bandwidth of 1.5 µm-wavelength multiquantum-well lasers coincided with reported values within their distributions. Measured temperature sensitivity of threshold current and that of K factor were also well explained with the improved model using those extracted carrier loss coefficients. The dominant causes of low characteristic temperature T 0 of present compressive-strained multiquantum-well lasers were quantitatively considered and found to be attributed to 1) Auger carrier loss and 2) thermionic carrier leakage and diffusion delay effect. T 0 over 150 K is expected by reducing the effect of those two factors. Possibilities of finding an actual method to reduce the effect of the above two factors are discussed.