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A new interpretation of the anisotropy of the conductivity in thin films of a-Ge, and a-Si is presented. The interpretation is based on a transition, previously proposed by the other author, from percolation conduction to Miller and Abrahams conduction at small film thickness. A simple theory together with experimental data is presented. The comparison between them is found to be good. (Modified author abstract), Prepared in cooperation with the Bell Telephone Labs., Murray Hill, N.J.

A new interpretation of the anisotropy of the conductivity in thin films of a-Ge, and a-Si, reported by one of use (J.J.H.) is presented. The interpretation is based on a transition, previously proposed by the other author, from percolation conduction to Miller and Abrahams conduction at small film thickness. A simple theory together with experimental data is presented. The comparison between them is found to be good. (Author), Prepared in cooperation with Bell Telephone Labs., Murray Hill, N.J.

Photoemission has been measured in the 1.8 - 11.8 eV spectral range for cleaved single crystal Ge and amorphous Ge films. Cesium was used to lower the photoelectric threshold and extend the measurements for photon energies less than 5 eV for both phases. Similar measurements were made in the 5 - 11.8 eV spectral range on films grown at room temperature (i.e., amorphous films) and then annealed at temperatures below and above the amorphous-crystalline transition temperature. The optical properties for amorphous films have been determined in the 0.1 - 25.0 eV spectral range from a Kramers-Kronig analysis of reflectance data and in the infrared and absorption edge region for films grown on substrates held at temperatures just below the amorphous-crystalline transition temperature. (Author)

A continuing effort is being made to maintain a closely knit experimental and theoretical program. Theoretical work on the use of Hermite functions to computer Hilbert (Kramer Kronig) transforms is completed and has been successfully tested on several systems and applied to the analysis of optical data on single crystalline and amorphous thin films of Sb2Se3. A satisfactory method of preparing thin amorphous films of controlled composition by coevaporation has been developed and improved upon in the past six months. Mossbauer studies have yielded important information on the short range order of amorphous films and on the structural chemistry of mixed chalcogenide systems. In the optical studies of thin amorphous films, one of the more significant findings has been the close correspondence between the energy band gaps in the crystalline and amorphous form of Sb2Se3 and the apparent lack of band tailing. Several different approaches to modulated reflectivity (and modulated absorption) are under development., See also Semi-annual technical rept. no. 1, AD0714029. Sponsored in part by DARPA.

Transport mechanisms in amorphous films of transition metal oxides and polycrystalline films of CoO, CoO(Li), Nb2O5, and TiO2 are of the Poole-Frenkel or Poole Effect type. In NiO and NiO(Li) films the transport mechanism is explained by the small-polaron conduction. Dielectric dispersion is due to the non-adiabatic hopping of charge carriers at low frequencies and adiabatic hopping at high frequencies. A novel type of switching is observed with switching, delay and recovery times of less than 3 nsec in Nb-Nb2O5-Nb with sputtered Nb counterelectrodes.

Amorphous films of neodymium ultraphosphate and neodymium lanthanum ultrophosphate have been deposited by r.f. sputtering. Optical waveguide structures were fabricated and scattering losses were measured to be less than one dB/cm. Fluorescence lifetime measurements of Nd sup (3 tau) are presented. Data on growth of single crystal films of gallium nitride and tungsten trioxide by reactive sputtering is given. Reduced scattering losses in optical waveguide structures of zinc oxide grown on sapphire have been effected by reduction of secondary electron bombardment of the substrate during film growth. Data is presented on the effect of magnetic field configuration on suppressing secondary electron bombardment and its effect on film uniformity., Sponsored in part by DARPA. See also report dated Oct 1973, AD0769972.

Research and development was continued on mate rials and techniques suitable for the formation of molecular circuits. Material research concerned semiconductive films of silicon carbide, boron, and cadmium selenide and dielectric films of neodymium oxide. Chemical vapor depositions were successful in producing various types of crystallites and crystalline aggregates of silicon carbide; experiments aimed at obtaining uniform films were continued. Amorphous boron films, deposited by means of electron beam evaporation, proved useful in the study of electron transmission through thin films. This research indicates that amorphous films may possess valuable properties quite distinct from those representative of the crystalline state. An operating clipping circuit based on conduction through a boron film was devised. Investigations of dielectric films were concerned with the characterization of neodymium oxide. Deposition procedures were carefully investigated, and electrical properties evaluated over a wide temperature range. This material shows excellent capabilities for use as a high temperature dielectric. Work on field effect devices continued. Cadmium selenide remains the preferred material for the semiconductor film. The application of a field effect device in a current limiter circuit was studied.

Pyrolytic aluminum nitride has been deposited on refractory electrical conductors using AlCl3.NH3 as the source material. Effects which pressure, temperature and rate of deposition have on electrical and other properties of deposits have been determined. Density of deposited coatings approach that of the calculated value. However, they still contain residual chlorine, causing electrical properties to fall short of what is expected of dense high purity AlN. Pyrolytic silicon nitride has been prepared from gaseous mixtures of silane and ammonia under varying conditions of temperature and pressure. Adherent, relatively soft, amorphous films have been deposited on substrates heated in the 700 to 800 C range while hard crystalline coatings of Alpha-Si3N4 have been obtained in the vicinity of 1250C. Coatings, which are both hard and amorphous, have been deposited at 1000C and have been characterized by a number of techniques. High temperature dielectric property tests of aluminum and silicon nitrides have indicated good high temperature resistivities with some samples, but considerable variability existed among samples. Measurements on aluminum nitride in particular, have indicated the presence of impurity conduction. Silicon nitride coatings seem to demonstrate more consistently high resistivities which make this material a potentially useful dielectric at 800 to 1000C at low voltages.

Research on Sb2Sn3 is reviewed covering spectroscopic studies of electron states of crystalline and amorphous forms, reflectivity and transmission measurements, photoemission, preparation and characterization of thin amorphous films, and thermopower and photothermopower measurements. Photoconductivity in antimony oxides is also discussed along with the Mossbauer effect of amorphous semiconductors and glasses., See also AD0753903.

Amorphous films were prepared by vapor quenching in ultra-high vacuum. n- and p-type silicon crystals were used as substrates and vapor source. The measurements (performed on clean and cesium covered surfaces) included photoelectric yield, energy distributions of photoelectrons, surface photovoltage, secondary emission with emphasis on elastic reflections, plasmon excitations, and Auger spectra. Information about densities of states, optical transitions, and position of Fermi level was obtained by direct comparison of photoelectric emission from the amorphous film, a silicon crystal, and a metal measured simultaneously. The results were found to depend on the mode of preparation and annealing of disordered films. (Author Modified Abstract), See also AD-719 562.

The report contains some new measurements on the thermal stability of As2Se3-As2Te3 glasses in which multiple crystallization processes have been found by differential scanning calorimetry. Discussion is given of the structure of As2Se3 films by comparing intensity and rdf curves obtained experimentally with theoretical curves derived from a microcrystallite model. The data strongly indicates that a glassy network model is more in accord with the experimental rdf than a microcrystalline model. Continuation of the work on the interaction between As2Se3 and Cu support grids is indicative of the formation of Cu(2-x)Se upon heat treatment. Finally a review article on electron diffraction rdfs of amorphous films prepared for the Physics of Thin Films is included.

Research on Sb2Se3 is reviewed covering spectroscopic studies of electron states of crystalline and amorphous forms, reflectivity and transmission measurements, photoemission, resistivity vs. temperature studies, preparation and characterization of thin amorphous films, and thermopower and photothermopower measurements. Photoconductivity in antimony oxides is also discussed along with the Mossbauer effect of amorphous semiconductors and glasses., See also AD0744698. Sponsored in part by DARPA.

A very significant finding was that the standard method of preparing the amorphous forms of the Group V-VI compounds by vacuum evaporation from the compound is very unreliable from the compositional viewpoint. It appears probable that no data has ever been reported on truly 'Sb2Se3' amorphous films, despite considerable literature on the subject. Several approaches have been taken, or are under development, which have yielded amorphous Sb2Se3 films. Initial Mossbauer studies have shown that the Sb atoms in amorphous SbxSey (x 2, y 3) films differ in environment from the single crystal form and therefore appear to be amorphous rather than microcrystalline. Kramers-Kronig analysis of optical reflectivity data has been used extensively to analyze optical reflectivity data on single crystals and thin films. Highlights in the optical studies to date are: the band gap in Sb2Se3 appears to be due to a direct transition; plasma resonance frequencies can be accurately determined by thermoreflectance data; photon counter techniques show great promise in determining the critical points in band structure.

To meet requirements for temperature-stable components, an investigation into the temperature-dependence of capacitor dielectrics was undertaken. A review is given of the Gevers-du Pre theory of amorphous dielectrics, and its findings are examined for applicability to amorphous films of silicon monoxide (SiO). Films of SiO were deposited onto borosilicate glass substrates at rates ranging from 54 to 133 A/min. The values of the TCC showed a strong dependence upon the deposition rate; both negative and positive values were obtained--the former for the slower rates of deposition. All the TCC data agreed qualitatively with the Gevers-du Pre theory, which suggests that the negative TCC's are due to large expansion coefficients and low film densities obtained at slow deposition rates. The results of the present study also suggest that zero TCC's are possible and should occur at a rate near 68 A/min. (Author)

The specific heat and heat of crystallization of vapor- and electro-deposited amorphous germanium were measured with a differential scanning calorimeter. The excess specific heat of the amorphous germanium over that of crystalline phase increased linearly with temperature over the temperature range from 215 to 460K. The heat of crystallization of the amorphous films was found to be about 2.75 k cal/gm-atom. The interpretation of the results in terms of the structure is discussed. The specific heat of crystalline germanium was also measured for the temperature range from 215 to 700K. (Author)

V2O3 and V2O4 films have been sputtered by a radio-frequency technique onto relatively cold substrates. The films were amorphous according to x-ray diffraction. Their electrical resistivities at-100C corresponded to that of the respective high temperature phases of the crystals. However, unlike the crystalline solids, the amorphous films did not exhibit the so-called semiconductor-metal transition. At 25C, because of the absence of this transition, the conductivity of amorphous V2O4 is almost four orders of magnitude greater than that of the crystal. (Author)

Aluminum nitride has been deposited on molybdenum, tungsten, and graphite by passing vapors of the AlCl3 NH3 complex over the hot substrates. Microstructure and density measurements indicate that the deposited material has a porosity of 20%. This and the presence of residual amounts of chlorine probably account for the high temperature electrical properties of the coating being poorer than expected of high purity aluminum nitride. Molybdenum substrates, when completely covered with these coatings are protected for oxidation by air at least up to 700 C. Pyrolytic silicon nitride has been prepared using SiF4 2NH3, SiCl4+NH3 and SiH4+NH3 as source materials. The gaseous mixture of silane and ammonia has been the most thoroughly studied and appears to be the most promising. Very adherent, relatively soft, amorphous films have been deposited on substrates heated in the 750 to 800 C range. Very hard crystalline coatings of Si3N4 were obtained in the 1100-1200 C range. These films have high spectral emissivity and provide oxidation protection for molybdenum substrates.

The design and construction of a sputtering system for the deposition of barium titanate thin films is described. The growth and structure of barium titanate films deposited on a variety of substrates including amorphous carbon fi1ms, potassium bromide single crystals, and polycrystalline gold films has been studied. Films deposited on all substrates at room temperature were amorphous. Polycrystalline titanate films were formed on polycrystalline and amorphous substrates at temperatures above 450°C while films with a pronounced texture could be expitaxially deposited on single crystal potassium bromide above a temperature of only 200°C. Results of dielectric measurements made on the films are reported. Amorphous films were highly insulating (resistivities ~1014 ohm.cm with dielectric constants of between 10 and 20.

The design and construction of a sputtering system for the deposition of barium titanate thin films is described. The growth and structure of barium titanate films deposited on a variety of substrates including amorphous carbon fi1ms, potassium bromide single crystals, and polycrystalline gold films has been studied. Films deposited on all substrates at room temperature were amorphous. Polycrystalline titanate films were formed on polycrystalline and amorphous substrates at temperatures above 450°C while films with a pronounced texture could be expitaxially deposited on single crystal potassium bromide above a temperature of only 200°C. Results of dielectric measurements made on the films are reported. Amorphous films were highly insulating (resistivities ~1014 ohm.cm with dielectric constants of between 10 and 20.

The design and construction of a sputtering system for the deposition of barium titanate thin films is described. The growth and structure of barium titanate films deposited on a variety of substrates including amorphous carbon fi1ms, potassium bromide single crystals, and polycrystalline gold films has been studied. Films deposited on all substrates at room temperature were amorphous. Polycrystalline titanate films were formed on polycrystalline and amorphous substrates at temperatures above 450°C while films with a pronounced texture could be expitaxially deposited on single crystal potassium bromide above a temperature of only 200°C. Results of dielectric measurements made on the films are reported. Amorphous films were highly insulating (resistivities ~1014 ohm.cm with dielectric constants of between 10 and 20.