Gain in quantum cascade lasers and superlattices: A quantum transport theory

Gain in current-driven semiconductor heterostructure devices is calculated within the theory of nonequilibrium Green functions. In order to treat the nonequilibrium distribution self-consistently the full two-time structure of the theory is employed without relying on any sort of Kadanoff-Baym Ansatz. The results are independent of the choice of the electromagnetic field if the variation of the self-energy is taken into account. Excellent quantitative agreement is obtained with the experimental gain spectrum of a quantum cascade laser. Calculations for semiconductor superlattices show that the simple 2-time miniband transport model gives reliable results for large miniband widths at room temperatureComment: 8 Pages, 4 Figures directly included, to appear in Physical Review

Structural properties of epitaxial YSZ and doped CeO2 films on different substrates prepared by liquid sources MOCVD (LSMOCVD)

With LSMOCVD it is possible to deposit reproducibly oxide films without need for high vacuum systems. On in-plane aligned oxide and metallic substrates epitaxial film growth takes place. Film morphology, interface layers and surface roughness can be controlled by choice of deposition parameters like temperature, gas phase composition and mass flow. The layers were characterized by SEM, AFM and texture analysis. Yttria-stabilized zirconia (YSZ), ceria and ceria doped with Gadolinium are prepared and the dependence of film properties on deposition parameters is investigated. The suitability of these films for the use of buffer layers in YBCO-deposition is discussed