Gives a critical review of idealised two-phase geometrical models. These treatments derive expressions for the resistivity and Hall coefficient of a composite material in terms of the properties of its constituents. The authors show that these models can be applied to the interpretation of transport measurements in polycrystalline films and powder layers. Important distinctions are made depending on whether the depletion layers extend completely or partially through the grains, whether the Debye length is greater or less than the grain size and whether the mean free path is greater or less than the grain size. The authors discuss the theoretical treatment of the Hall effect in percolative systems, as geometrical models neglect percolation. The modulation of Hall coefficient and conductivity by illumination and the adsorption and desorption of ambient gases are also considered.

https://iopscience.iop.org/article/10.1088/0034-4885/43/11/001/pdf

The Hall effect in polycrystalline and powdered semiconductors

We have characterized the electrical transport properties of neutron‐transmutation‐doped polycrystalline silicon. Zero‐bias measurements of resistance have been made as a function of temperature on both bulk specimens and individual grain boundaries in this material. Below a doping level of ∼2×1015 phosphorus/cm3, the bulk resistance has a nearly Arrhenius behavior with an activation energy of ∼0.55 eV; above this donor concentration the resistivity is markedly curved on an Arrhenius plot with values of slope which decrease with decreasing temperature. Potential probe measurements show that a large spread in grain‐boundary impedances exist in these higher‐doped specimens. We compare our data to theoretical expressions for current flow across grain‐boundary potential barriers and good agreement is observed; these comparisons indicate that the largest grain‐boundary state densities observed in our samples consist of ∼6×1011 available single‐electron‐states/cm2 located within ∼0.2 eV from the center of the f...

Zero‐bias resistance of grain boundaries in neutron‐transmutation‐doped polycrystalline silicon

Zero-bias resistance of grain boundaries in neutron transmutation doped polycrystalline silicon

A detector (110) for optically detecting at least one object (112) is proposed. The detector (110) comprises at least one optical sensor (114). The optical sensor (114) has at least one sensor region (116). The optical sensor (114) is designed to generate at least one sensor signal in a manner dependent on an illumination of the sensor region (116). The sensor signal, given the same total power of the illumination, is dependent on a geometry of the illumination, in particular on a beam cross section of the illumination on the sensor area (118). The detector (110) furthermore has at least one evaluation device (122). The evaluation device (122) is designed to generate at least one item of geometrical information from the sensor signal, in particular at least one item of geometrical information about the illumination and/or the object (112).

Detector for optically detecting at least one object

Synthesis and photoluminescent properties of ZnS nanocrystals doped with copper and halogen

Consideration of simple variations of a basic resistive‐network model for an inhomogeneous material shows that a wide variety of experimentally observed effects can be described with respect to equilibrium or steady‐state Hall and thermoelectric measurements. The correlation between these macroscopic Hall and thermoelectric measurements and the microscopic electrical and geometrical properties of the material is derived. A suitable combination of both Hall and thermoelectric measurements on the same sample makes it possible to determine the dominant average microscopic and geometric parameters of the system. Although developed under the stimulus of research into the photoconductivity mechanism in chemically deposited lead sulfide layers, the results of the consideration may have a wider application.

Interpretation of Equilibrium and Steady-State Hall and Thermoelectric Effects in Inhomogeneous Materials

Annealing in zinc or sulfur vapor introduces major changes in the photoelectronic properties of ZnS single crystals. Insulating insensitive crystals of ZnS were annealed for various periods of time from 20 min to 6 days at 891°C in a saturated zinc vapor. Annealing increases the dark conductivity by at least eight orders of magnitude, the photosensitivity by over three orders of magnitude, and markedly affects photoluminescence emission. The effects of annealing in zinc are reversible by subsequent annealing in sulfur vapor. Optical quenching data show that the high photosensitivity in the zinc‐annealed crystals is associated with sensitizing centers lying 1.2 eV above the valence band with an electron‐capture cross section of about 10−21 cm2. The photosensitivity decreases rapidly with decreasing temperature below 200°K, whether excitation is by intrinsic ultraviolet or extrinsic infrared, because of the effects of a high density of shallow electron traps. The principle effect of annealing appears to be in the variation of the Fermi‐level position in the crystal.

Effects of Annealing on the Photoelectronic Properties of ZnS Crystals

Overcoatings of Al2O3, As2S3, CdTe, MgF2, SiO, and SiO2 were vacuum deposited on thin‐film PbS photodetectors. Overcoating thicknesses were approximately those required to optimize antireflection properties. None of the overcoatings seriously degraded detector properties, although production yields were low with Al2O3, MgF2, and CdTe. The low yields are apparently due to physical incompatibilities of the overcoating and PbS film. Improved detector properties were obtained with As2S3 through a reduction of 1/f noise and passivation to hostile environments. The 1/f noise component is assessed by a comparison of the changes in detector performance parameters upon ’’flashing’’ with the changes theoretically expected for G‐R noise‐dominated detector.

George H. Blount

Papers

Interpretation of Equilibrium and Steady-State Hall and Thermoelectric Effects in Inhomogeneous Materials

Effects of Annealing on the Photoelectronic Properties of ZnS Crystals

Photoconductive properties of chemically deposited PbS with dielectric overcoatings

Ohmic Electrical Contacts to High‐Resistivity ZnS Crystals

Self‐Diffusion of Sulfur in ZnS