Hughes Aircraft Company

Julius Hyman, Jr

Lawrence Everett Anderson

Juan F Lam

Jesse N Matossian

Robert W Schumacher

John Robert Beattie

Owen K Wu

Joseph Santoru

Robin J Harvey

Dan M Goebel

Robert L Poeschel

A molecular beam epitaxy (MBE) growth method and apparatus is disclosed which achieves a significantly improved sticking coefficient for materials like Hg upon a substrate, and thus a higher efficiency. A highly ionized, low pressure plasma is formed consisting of a mixture of ions of one substance of a compound to be epitaxially grown, neutral particles of the substance and electrons, and also preferably both ionization and excitation radiation. The plasma is directed onto a substrate together with a flux of the other substance in the compound; the flux can be in the form of either a vapor, or a second plasma. Radiation assisted epitaxial growth for Hg compounds in which ionization and excitation radiation are formed from Hg vapor and used to assist epitaxial growth with neutral Hg particles is also described. The plasma is formed in a special discharge chamber having a hollow cathode with an emissive-mix-free cathode insert. The source is preferably a refractory metal such as rolled tantalum foil, which is substantially emissive-material-free and does not contaminate the plasma. Good results are obtained by allowing the plasma to simply diffuse out through an exit port in the discharge chamber, without special extraction assemblies required by prior ion thrusters. Hg sticking coefficients have been improved by a factor of 40 or more.

Plasma/radiation assisted molecular beam epitaxy method

A diverging magnetic field is established between the cathode and control electrode of a hollow cathode plasma switch to expand the plasma at a passageway through the control electrode, thus significantly increasing the switch's current handling capability. Preferred ranges of magnetic field strength, gas pressure, spacing between the hollow cathode and control electrode, and the mesh aperture size for the control grid are described.

Hollow cathode plasma switch with magnetic field

Plasma/radiation assisted molecular beam epitaxy method and apparatus

A high-power microwave/mm-wave oscillator is filled with an ionizable gas at a pressure of about 1-20 mTorr, into which an electron beam is injected at a high current density of at least about 1 amp/cm.sup.2, but typically 50-100 A/cm.sup.2. A plasma is formed which inhibits space-charge blowup of the beam, thereby eliminating the prior requirement of a magnet system to control the beam. The system functions as a slow-wave tube to produce narrow-band microwaves for a gas pressure of about 1-5 mTorr, and as a plasma wave tube to produce broadband microwave/mm-wave radiation for a gas pressure of about 10-20 mTorr. A new high output, hollow-cathode-plasma electron gun is employed in which a metal oxide layer is formed on the inner surface to enhance the secondary electron yield; a cathode, grid, and extraction anode have respective sets of multiple apertures which are mutually aligned to yield a high perveance beam; the cathode, grid, and anode are curved to geometrically focus the beam, and a beam with a circular cross-section is generated.

Plasma-assisted high-power microwave generator

Ion chamber 20 receives electrons from cathode 28 and produces ions by electron bombardment in discharge plasma chamber 20. Ions are extracted through ion optics including screen 22 and accelerator electrode 24. Higher ion densities in the center of the discharge chamber are reduced by spoiler 42 which is operated at a potential between cathode and anode potential. This reduces double ionization and central peaking to provide a more uniform ion beam through the optics. By employing laterally positioned spoiler elements beam steering can be accomplished. The ion source is useful wherever a uniform beam profile is desirable as in ion implantation. Controlling the direction of beam density is useful in ion machining and in ion thrusters for space application.

Ion beam profile control apparatus and method

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Los Angeles, CA, United States of America

Julius Hyman, Jr