The Ge-ZnSe heterojunction has been prepared by vacuum evaporation of the ZnSe onto single-crystal p-type germanium substrates.' The growth conditions have been studied in terms of epitaxial growth on different crystallographic orientations in degrees of vacuum down to the ultra-highvacuum region. Measurements have also been made of the electrical characteristics, capacitance properties, and photoelectric response of the diode. From these measurements a realistic band model has emerged involving intrinsic and extrinsic defects present in the bulk and interfacial region of the zinc selenide. The results of this investigation are compared with those from devices grown by vapour phase epitaxy283 and the data presented suggests that a Mott-type barrier4 rather than a Schottky barrier is present at the germanium-zinc-selenide interface. Techniques have been developed for the removal of this Mott barrier and the resulting change in the physical properties and band structure will be given. Possible applications of heterojunctions with this particular band structure will be discussed. 295, 1968. ', N.M. Schottky-barrier diodes of chromium on n-type epitaxial gallium arsenide phosphide (GaAsP) were studied from 25" to 440°C. The diodes showed significant rectification properties up to a temperature of 440°C. At high temperature the reverse leakage current was 1.15 milliamperes at 25 volts with a diode area of 1.14 X 10-3 cm2 as compared with 0.25 microampere at room temperature.The chromium was evaporated from a tungsten filament in a vac-ion system at a pressure of less than 10-8 Torr. Silver was alloyed into the GaAs substrate to provide a good ohmic contact over the entire temperature range. The epitaxial layer was 200 Hm thick.The slope of the In current versus voltage curves was l.lkT/q. The barrier height for the chromium contact was 1.15 eV from the capacitancevoltage measurements and 1.05 eV from the current-voltage measurements.From the plot of ln(JJT2) versus 1/T, where J, is current density and T is temperature, the effective Richardson constant for these diodes is approximately 2.5 A/crnz/'KZ. The calculated value of carrier concentration from the capacitance-voltage curves was 8 X 1015/cm3. The reversebreakdown voltage of the diodes was in excess of BO volts a t room temperature. 146

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Ferroelectric thin films of BaTiO3 have been successfully deposited on n-type silicon substrates at temperatures above 500 °C by rf sputtering in an O2/Ar atmosphere. Analysis by x-ray diffraction patterns show that films deposited at room temperature are amorphous. At temperatures above 500 °C, crystalline BaTiO3 films with a tetragonal structure are obtained. The polarization-electric field (P-E) hysteresis loops and a broad peak in the dielectric constant versus temperature curve at Curie point indicate that the rf sputtered BaTiO3 films are ferroelectric. An anomalous photovoltaic effect is observed in these thin films which is related to the remanent polarization of the material. The results on open-circuit and short-circuit measurements provide an important basis for a better understanding of the role of photovoltaic field, photovoltaic current, and the pyroelectric properties in photoferroelectric domain switching.

A novel design of a thermionic generator for use on re-entry vehicles is analyzed analytically and experimentally. Equations are derived for prediction of the output current, output power, and conditions of maximum power for the device. The electrical power output potential of a typical re-entry vehicle is obtained by solving the temperature history of a thin-walled emitter. Given the wall temperature and the work function, the saturated Richardson current is easily obtained. Other parameters needed for predicting output power are obtained from curves in the literature. To simulate re-entry conditions, a test model was built and inserted in either a nitrogen or argon plasma jet. Graphite, thoriated tungsten, tungsten and molybdenum were used for the emitter and collector. Of the materials tested, graphite was the only material that met, to some degree, the qualifications needed for operation of the hypersonic plasma thermionic generator

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