C.B. Thomas

Photoluminescence study of MBE-grown films on ZnS

Polycrystalline films of ZnS with a slight excess of S have been grown on (100) Si by congruent sublimation from a single Knudsen cell. Intense blue emission is observed at 460 nm from room-temperature photoluminescence studies, and is ascribed to S-Zn vacancies acting as self-activated (SA) centres. The emission is quenched by the addition of Zn from a second Knudsen cell, which also causes the growth of a luminescent peak centred on 678 nm. No reduction in the SA luminescence is seen when co-sublimating ZnS and AgS, implying that it is not possible to remove the S-vacancy completely. Quenching of the blue emission occurs when Mn, instead of Zn, is added to the ZnS films, providing direct evidence of Mn incorporation into Zn vacancies. At the optimum Mn concentration, the intensity of the Mn emission at 580 nm is comparable to the blue emission (460 nm) from the undoped ZnS films.

Growth and dielectric characterization of yttrium oxide thin films deposited on Si by r.f.-magnetron sputtering

Thin films of Y2O3 have been deposited by r.f.-magnetron sputtering onto 100 mm diameter n-type single crystal Si wafers. The growth conditions are discussed including an optical interferometric technique for in-situ thickness monitoring. The dielectric properties of films deposited at 60 °C, 100 °C and 190 °C are measured, with optimum values of the relative dielectric constant and breakdown strength determined as ϵr = 16 and Ebd = 3.85 MVcm-1 respectively. Deposition was uniform with respect to film thickness over 50 cm2 (±5%), and the refractive index of the Y2O3 was determined as n = 1.911

Characterization of heterojunction devices constructed by amorphous diamondlike films on silicon

The electronic properties of amorphous diamondlike carbon (DLC) films on silicon were examined for their capability for application to electronic devices. Metal-insulator-semiconductor (MIS) diodes and p-n heterojunction devices were created and characterized. The films used were grown using rf plasma assisted CVD of methane. They were grown on n-type silicon (100) wafers. Their structural composition was identified by Raman spectroscopy, ellipsometry, and x rays. They showed an insulating behavior and they were suitable for the creation of MIS devices. They showed extremely low internal conductivity due to defect currents. This conductivity showed a behavior of the form I∼T1/4. Then the density of trapping states at the silicon/carbon interface was measured using the conductance technique. The aim of investigating the nature and behavior of these states was to determine the magnitude of the density of states and try to find a way to reduce it. Thus optimization of the DLC/silicon interface could be made,...

Characterisation of the Interface States between Amorphous Diamond‐Like Carbon Films and (100) Silicon

Amorphous diamond-like carbon films were grown onto (100) Si substrates using rf plasma CVD of methane. Then the interface states were examined using the conductance technique. Metal-insulator-semiconductor (MIS) devices were made and proper modeling was used. The statistical model was used to fit the experimental data and calculate the density of interface states. The technique revealed a density of interface states between 10 11 and 10 12 eV -1 cm -2 . Subsequent thermal annealing reduced this density.

Effect of deposition process on the thin‐film ZnS/p‐Si interface

Thin films of ZnS have been deposited on p‐Si by evaporation, radio‐frequency sputtering, and magnetron sputtering to form metal‐insulator‐semiconductor structures. The 1 MHz admittance‐voltage characteristics of each have been compared for a qualitative study of the ZnS/p‐Si interface. It is shown that radio‐frequency sputtering results in Fermi‐level pinning, which is ascribed to the presence of silicon dangling bonds caused by radiation damage. It is argued that this damage is advantageous for ZnS/p‐Si electroluminescent diodes.

High efficiency ZnS:Mn ac thin film electroluminescent device structure

A method for improving the luminous efficiency of a ZnS:Mn ac thin film electroluminescent device by modifying the structure to include thin, 100 A, barrier layers of a Y2O3 is presented, with experimental comparisons of devices showing a fourfold increase in efficiency. The results are discussed in terms of electron tunneling and field redistribution as the mechanisms responsible for the enhancement of efficiency.

A study of the luminescent and electrical characteristics of films of ZnS doped with Mn

Abstract The preparation of films of ZnS by radio-frequency sputtering and also the doping with manganese by either co-sputtering or ion-beam implantation has been described. The brightness of ZnS: Mn films doped by both techniques have been compared. Also concentration quenching has been examined. In addition the conditions for preparing ZnS films on I.T.O. substrates which are free of pin-holes have been given. Space-charge limited currents, defined by thickness dependence, have been observed prior to the onset of electroluminescence. A brief description is presented also of the behaviour of d.c. pulsed devices of I.T.O./ZnS: Mn/Al devices during electroluminescent operation.

The relative contributions of recombination and tunnelling at interface states to the a.c. conductance of metal-insulator-semiconductor diodes

Abstract The effect on the a.c. conductivity of MIS structures of localized states at the interface between the insulator and semiconductor has been described previously by either Shockley-Read recombination or tunnelling effects. Both of these models are examined here using MIS diodes fabricated from films of semi-insulating silicon doped with oxygen (SIPOS) on p -type Si. The tunnelling model as presently understood does not explain the frequency dispersion seen in the conductance but the inclusion of an extra Shockley-Read term corrects this. Nevertheless we conclude that, although the “extended” tunnelling model provides a better physical understanding of the a.c. conductance, it is more convenient for computational purposes to use the statistical model.

Preparation and characterization of thin films of NbO2

Abstract Thin films of NbO 2 , with thicknesses ranging from 1000 to 20 000 A, were prepared by r.f. sputtering powder targets of NbO 2 in a reducing atmosphere of 90vol.%Ar–10vol.%H. Transmission electron microscopy and X-ray diffraction studies of self-supported films indicate that the as-deposited material was amorphous. Compositional analysis, derived from interpretation of Rutherford back-scattering spectra and neutron activation analysis of films deposited onto vitreous carbon substrates, indicates a high degree of stoichiometry. The variation in the electrical conductivity with the rate of deposition is reported, and also a comparison is made between the electrical conductivity of the amorphous and crystalline phases of films of NbO 2 .

The contribution of bulk states to the ac conductance of metal‐insulator‐semiconductor diodes

Measurements of the density of interface states in metal‐insulator‐semiconductor diodes by conductance techniques have revealed two resonances in the equivalent parallel conductance. Interface states are responsible for one, but the other is due to bulk states in the silicon crossing the Fermi energy in the depletion region. This latter contribution is found to resonate at a fixed frequency independent of the bias applied to the diode, unlike the interface state response which varies in the normal way. From the maximum in the equivalent parallel conductance we have calculated the density of bulk states to be 1014 cm−3 and identified sodium as the likely impurity responsible.