The ladder method for solving the linearized Boltzmann equation is developed to deal with a non-parabolic conduction band. This is applied to find the low field Hall mobility of electrons in bulk GaNxAs1-x using the band-anticrossing (BAC) model, which predicts highly non-parabolic energy dispersion relations. Polar optical, acoustic phonon, piezoelectric, ionized impurity, neutral impurity and nitrogen scattering are incorporated. In finding an exact solution to the linearized Boltzmann equation, we avoid the unrealistic assumption of a relaxation time for inelastic scattering via polar optical phonons. Nitrogen scattering is found to limit the electron mobility to values of the order 1000 cm2V-1s-1, in accordance with relaxation time approximation calculations but still an order of magnitude higher than measured values for dilute nitrides. We conclude that the non-parabolicity of the conduction band alone can not account for these low mobilities.
Many of the schemes under study for Quantum Information Processing technology based on photon states involve active and passive optical components as well as detectors. In order to able to establish fidelity levels for these schemes, the performance of the optical components and the quantum efficiency (q.e.) of the detectors require careful and accurate characterization. Correlated photons produced from spontaneous parametric downconversion, which are also the basis of entangled photon states, conveniently offer a direct means of measuring detector q.e. in the photon counting regime, while stimulated parametric downconversion can be used to measure source radiance. Detector and source calibration using correlated photon techniques therefore address some of the key issues critical to the development of QIP technology and the development of correlated/entangled photon metrology. This paper reports work being undertaken at NPL to establish the accuracy limitations of these correlated photon techniques. Significant sources of uncertainty are the need to measure losses due to any optical components used and the requirement to obtain and maintain good geometrical and spectral alignment.