Shallow Electron Trap Research Articles

Investigation of Radiation Damage in Mosfets Using Bias-Temperature Treatments

Radiation damage in thermally-grown p-channel enhancement mode MOS devices irradiated with 1.5 MeV electrons at various doses and gate potentials was investigated by applying bias-temperature (B-T) treatments. It was found that at negative and small positive gate biases applied during irradiation, electrons are trapped in weakly bound states in the oxide. These trapped electrons may readily be removed from the oxide by B-T treatment. The ratio of electrons trapped in the oxide to the radiation-induced net positive charge has a maximum at about -3V bombardment bias. This region of gate bias also corresponds to the minimum of radiation damage commonly observed in this type of device. At zero bombardment bias a saturation of shallow electron trapping is observed at a dose of 3 - 6 × 1013 e/cm2.

Optical Quenching of Photoconductivity in Single-Crystal Stannic Oxide

The optical quenching of photoconductivity in single-crystal specimens of stannic oxide has been investigated as a function of extrinsic wavelength and of temperature in the region where sensitization occurs. Quenching is found in a single band extending from the fundamental optical gap at 4.0 eV down to a cutoff indicative of a 1.3-eV activation energy for the sensitizing centers. The discrepancy between this value and the 0.33-eV value obtained earlier from thermal-quenching measurements suggests that the sensitizing states themselves do not play an active role in the process of thermal quenching, but rather that the thermal quenching arises through the action of the shallow electron trapping states.

ELectron traps in silver chloride crystals

The photoelectret state has been examined for AgCl crystals after treatment with heat and light; it is found that there are shallow electron trapping levels, whose ionization energy ɛ1 is about 0.2 eV and whose concentration n1 is about 1017 cm−3. These appear to be due to inherent defects in the lattice of AgCl.

Luminescence and Photoconductivity in Silver Halides

Pulsed and steady-state luminescence and photoconductivity were measured in AgCl and AgBr at low temperatures using x-ray and uv excitation. The luminescence efficiency and electron range (Schubweg) are found to be competitive forms of response as functions of temperature. In AgCl at 4.2\ifmmode^\circ\else\textdegree\fi{}K electron-hole pairs are captured (or formed) at a luminescence center in about ${10}^{\ensuremath{-}8}$ sec, thus accounting for the large decrease of electron range observed at low temperatures. A model is proposed in which an intrinsic luminescence center is represented by a shallow (0.05-eV) electron trap with a characteristic lifetime for radiative recombination after electron capture of about 25 \ensuremath{\mu}sec. Similarity to the intrinsic luminescence of alkali halides is noted. Large dark currents of the order of mA and electroluminescence were observed in some crystals after pre-irradiation at 4.2\ifmmode^\circ\else\textdegree\fi{}K.

Nonuniformly Excited Photoconductivity in Sensitive Photoconductors

An analysis of the photocurrents produced by nonuniform illumination of a sensitive photoconductor is given. It is shown that for sensitive photoconductors in the steady state, the current density is a constant throughout the bulk of the photoconductor, under all conditions of excitation. The expression for the photocurrent density as a function of illumination and applied field is then obtained through an integration of Poisson’s equation, with a model of the photoconductor as a thin, flat slab and illumination incident perpendicular to one face. The boundary conditions take into account the existence of secondary photocurrents drawn in from the electrodes by space charge resulting from the primary excitation. It is found that large secondary photocurrents can be obtained under nonuniform excitation if the shallow electron trap density is low and electron capture cross section of hole-containing centers is low. Experimental results are reported for photocurrents in sensitive evaporated films of CdS:Ag, which satisfy the geometry requirements of the analysis.

Photochemical Effects and the Effect of Oxygen on Photoconducting Cadmium Sulphide Crystals

ABSTRACT Single crystals of cadmium sulphide can be activated to give high photo-conductive sensitivity in a variety of ways. Experiment shows that crystals containing a non-stoichiometric excess of cadmium in the form of sulphur vacancies are inherently unstable. Their photoconductivity decays under illumination and on exposure to an ambient atmosphere containing oxygen. This instability can be eliminated by using an activation treatment which does not produce sulphur vacancies. The photochemical effects and the effects of heat treatment in oxygen on a number of differently activated crystals have been investigated with particular reference to the shallow electron trapping effects produced. Further support has been obtained for the ideas advanced in an earlier paper (Woods and Wright 1058) in which an attempt was made to identify the defects responsible for the well-defined peaks in the thermally stimulated, current curve. These ideas are extended in the present paper to account for some aspects of the p...