Pseudo-potential calculations of the electronic and optical properties of GaxAlyIn1–x–yAs
A method for calculating the electronic structure of the quaternary alloy GaAlInAs is presented with zinc blende structure. We have used the empirical pseudo-potential method coupled with the virtual crystal approximation (VCA). The electronic structures are studied for GaAlInAs (x = 0.24, y = 0.24) and GaAlInAs lattice matched to InP as well GaAs. In addition a method for calculating the refractive index is presented, which we used the Sellmeir model. The composition dependence of the refractive index is discussed, the results indicate that refractive index decrease with alloying composition of the quaternary alloy GaAlInAs lattice matched to InP and GaAs.
AlInGaAs 0.8-/spl mu/m high-power semiconductor lasers with delta-doped resonant tunneling quantum wells
In this paper, we describe a new structure design for producing low-threshold high-efficiency and high-brightness 0.807-/spl mu/m lasers. In this structure, we incorporate a self-discriminating weak optical confinement asymmetrical waveguide, and an active region based on single or double AlInGaAs quantum well (QW) with Te n-type /spl delta/-doping. Optimized coupling between the /spl delta/-doping layer and the double QW, along with waveguide and doping profile optimization, yields J/sub th/=140 A/cm/sup -2/ per QW, a far-field angle of /spl sim/24/spl deg/, and M/sup 2/ close to one.
Increasing pulp yield in kraft cooking of softwoods by high initial effective alkali concentration (HIEAC) during impregnation leading to decreasing secondary peeling of cellulose
Abstract Pulp yield can be improved by a more homogeneous delignification of the chips, achieved by improved impregnation prior to the cooking stage. Complete and efficient impregnation is obtained by increasing the diffusion rate by means of an impregnation liquor with a high initial effective alkali concentration (HIEAC). In the present study, the effect of HIEAC in the impregnation was evaluated and compared to a reference impregnation procedure and a prolonged impregnation. After the various impregnation scenarios, the alkali concentration was always adjusted to the same level in the beginning of the cooking stage. Impregnation with a HIEAC resulted in yield improvements by 1–1.5% units, due to a higher cellulose yield and possibly also to higher yield of glucomannan. The HIEAC with an even alkali distribution within the chips prior to the cooking stage resulted in a more uniform delignification carbohydrate degradation. Yield increase obtained by uniform delignification is due to both decreased shives content as well as less secondary peeling.