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

PHOTOLUMINESCENCE AND ESR STUDIES OF LOCALIZED STATES IN AMORPHOUS PHOSPHORUS

Photoluminescence and electron spin resonance measurements have been performed in bulk a-red P. We observe a photoluminescence band at 1.40 eV which exhibits a sensitivity to the excitation energy employed. Specifically, the peak of this band progresses to lower energies for higher energy excitation. Electron spin resonance measurements indicate ~1017 spins/cm3 for "cold dark" and optically induced (6328Å) conditions. In contrast to similar measurements in bulk a-As, thermally generated paramagnetism is not apparent in bulk a-red P up to 300K. These results are compared with various defect models proposed for the pnictides

COMPARISON OF OPTICALLY INDUCED LOCALIZED STATES IN CHALCOGENIDE GLASSES AND THEIR CRYSTALLINE COUNTERPARTS

The below-gap peaks observed in the PLE spectra for deep PL bands in the minerals orpiment and realgar are attributed to strong impurity absorption bands, possibly associated with the high concentrations of 3d transition metals (e.g. Mn and Fe) detected by ESR. It is suggested that the weak below-gap tails in the PLE spectra of chalcogenide glasses and synthetic arsenic chalcogenide crystals have the same origin, but that impurity concentrations are much lower in these materials. Optically induced ESR spectra observed in crystalline arsenic chalcogenides are ascribed to paramagnetic Cu2+ ions rather than to the optically induced paramagnetic intrinsic defects associated with major constituent atoms as observed in chalcogenide glasses

OPTICAL PROPERTIES OF GaAs/AlGaAs MULTIPLE QUANTUM WELLS GROWN IN THE [111] CRYSTALLOGRAPHIC DIRECTION

Photoreflectance measurements have been performed on high quality GaAs/AlGaAs multiple quantum wells grown along the [111] crystallographic direction. These measurements indicate that the heavy and light hole masses are 0.8 and 0.08, respectively, in the [111] direction of bulk GaAs. These values are in good agreement with the Luttinger parameters for GaAs. In addition, this investigation indicates that the band alignments of GaAs and AlGaAs are not very sensitive to crystallographic orientation

FAR INFRARED MAGNETO-ABSORPTION STUDY OF BARRIER IMPURITIES AND SCREENING IN GaAs/AlGaAs MULTIPLE QUANTUM WELLS

Far infrared magneto-absorption experiments have been performed at 4.2K on MBE-grown GaAs/AlGaAs MQW heterostructures that were selectively doped with Si donors in the centers of the quantum wells and barrier layers. Data were obtained for several values of dopant concentration in the barriers in order to study in detail the binding of electrons in the quantum wells to positively charged ions in the barriers and the effects of the screening of the Coulomb interaction by free carriers. The results are compared with recent calculations