Donor states in modulation-doped Si/SiGe heterostructures

We present a unified approach for calculating the properties of shallow donors inside or outside heterostructure quantum wells. The method allows us to obtain not only the binding energies of all localized states of any symmetry, but also the energy width of the resonant states which may appear when a localized state becomes degenerate with the continuous quantum well subbands. The approach is non-variational, and we are therefore also able to evaluate the wave functions. This is used to calculate the optical absorption spectrum, which is strongly non-isotropic due to the selection rules. The results obtained from calculations for Si/Si$_{1-x}$Ge$_x$ quantum wells allow us to present the general behavior of the impurity states, as the donor position is varied from the center of the well to deep inside the barrier. The influence on the donor ground state from both the central-cell effect and the strain arising from the lattice mismatch is carefully considered.Comment: 17 pages, 10 figure

Electrical and deep-level characterization of GaP xNx grown by gas-source molecular beam epitaxy

We have investigated electrical properties and deep levels of n-GaP1−xNx (x=0%−0.62%) grown on (100) n-GaP substrates by gas source molecular beam epitaxy. The x-ray photoelectron spectroscopy results showed no significant effects on the chemical bonding status of the host Ga-P matrix by the incorporation of small amounts of N atoms. In the Raman spectra, the zone-edge GaP-like vibration was observed at 387 cm−1, originating from alloy disorder or local distortion of the GaP1−xNx lattice. The electrical properties of the GaP1−xNx surfaces were characterized using a Schottky contact structure. An ideality factor of 1.10–1.15 and a Schottky barrier height of 1.1 eV were obtained from the current-voltage characteristics of Ni/GaP1−xNx diodes, indicating good interface quality. The thermal admittance spectroscopy clearly detected the Si donor level with an activation energy of 84±4 meV in GaP and GaP1−xNx. For the GaP1−xNx samples, we observed deep levels probably associated with N-induced defects such as N-N pairs, N clusters, and an N-containing complexes. ©2007 American Institute of Physic

The Monte Carlo method applied to carrier transport in Si/SiGe quantum wells

We present a complete Monte Carlo simulation of the transport properties of a Si/SiGe quantum well. The scattering mechanisms, viz. intervalley phonons, acoustic phonons, interface roughness and impurity scattering (including resonant scattering), are considered in detail, and we derive analytic expressions for the scattering rates, in each case properly taking the quantized electron wave functions into account. The numerically obtained distribution function is used to discuss the influence of each scattering mechanism for different electric fields applied parallel to the interfaces and also different temperatures