Stephen D. Russell

Photoluminescent thin-film porous silicon on sapphire

Results from the chemical stain etch fabrication and analysis of thin-film photoluminescent porous silicon on sapphire substrates are presented. The transparent sapphire substrate allows the excitation and collection of the luminescence at either the front or back of the wafer. Morphological differences found using scanning electron microscopy between porous SOS and porous bulk silicon are attributed to preferential etching of threading dislocations. This is confirmed by an observed stress relaxation in the Raman spectra. Also, it is shown for the first time that photoluminescent porous silicon (n-type) can be produced by photoinitiation of the chemical stain etch.

Voltage-induced broad-spectrum reflectivity change with surface-plasmon waves

Voltage-induced broad-spectrum reflectivity change with surface-plasmon waves is reported. When white light is incident at a metal/electro-optical material interface, surface-plasmon waves can be excited under phase match conditions. This surface-plasmon resonance depends on the dielectric constants of both the metal and the electro-optical material. Photons in the surface-plasmon resonance wavelength range are absorbed by the interface. Since metals have large imaginary parts of their dielectric constants, the surface-plasmon resonances are broad and may cover all visible wavelengths. Applying voltage to the electro-optical material to change its dielectric constant can result in a change in the reflectivity at the interface. Experimental results showed a reflectivity change from almost 0% to about 40% under an applied voltage using a liquid-crystal and nickel film structure, and the results had good agreement with theoretical calculations. The theoretical calculations also predicted a 90% reflectivity r...

Demonstration of Y1Ba2Cu3O7−δ and complementary metal‐oxide‐semiconductor device fabrication on the same sapphire substrate

We report the first fabrication of active semiconductor and high‐temperature superconducting devices on the same substrate. Test structures of complementary metal‐oxide‐semiconductor transistors were fabricated on the same sapphire substrate as test structures of Y1Ba2Cu3O7−δ flux‐flow transistors, and separately, Y1Ba2Cu3O7−δ superconducting quantum interference devices utilizing both biepitaxial and step‐edge Josephson junctions. Both semiconductor and superconductor devices were operated at 77 K. The cofabrication of devices using these disparate yet complementary electronic technologies on the same substrate opens the door for the fabrication of true semiconductive/superconductive hybrid integrated circuits capable of exploiting the best features of each of these technologies.

Surface plasmon tunable filter and spectrometer-on-a-chip

The surface plasmon tunable filter (SPTF) is a new technology invented at the Jet Propulsion Laboratory. When white light is incident on a metal/air/metal structure, under appropriate conditions, surface plasmon waves are excited at one metal/air material interface. Those photons in the surface plasmon resonance wavelength range will be converted into the energy of free electrons in the metal, then coupled into the other metal film which re-radiates light at the identical resonant wavelength. This surface plasmon resonance depends on the dielectric constant of the metal and the thickness of the air gap. When the thickness of the air gap changes, the surface plasmon resonance spectrum shifts from one wavelength to another, and the device functions as a tunable filter. The SPTF is a light weight, low power device, which can be integrated with a solid state image sensor to form a spectrometer-on-a-chip. Theoretical calculation has shown that this image spectrometer can also work in IR range up to at least 10 micrometers .

The effects of microcrystalline structure on the photoluminescence of porous silicon‐on‐sapphire

Silicon‐on‐sapphire was fabricated in as‐deposited, improved, and bonded wafer forms. Each of the fabrication techniques imparts characteristic microcrystalline defects in the silicon layer. Microstructural defects such as microtwins and threading dislocations in the starting material have no observed effect on the light emitting properties of porous silicon‐on‐sapphire. Vacancies imparted by ion implantation damage, however, can amorphize the material resulting in a quenching of the photoluminescence (PL). An apparent increase in the density of light emitting structures leading to enhanced PL can also be obtained by limited ion damage of the material prior to the fabrication of the porous layer.

Electronically tunable mirror with surface plasmons

Surface plasmon tunable filter is a new technology under development at the Jet Propulsion Laboratory. This technology can also be used to build an electronically tunable mirror. When white light is incident on a metal/electro-optic material interface under certain conditions, surface plasmon waves can be excited at the interface. Photons in the wavelength range of the surface plasmon resonance will be converted into the energy of free electrons in the metal. When using nickel or a rhodium/aluminum bilayer as the metal, the bandwidth of the surface plasmon resonance can cover all of the visible spectrum. This surface plasmon resonance depends on the dielectric constants of both the metal and the electro-optic materials Therefore, application of a voltage to the electro optic material to change its dielectric constant can theoretically result in a change in the reflectivity of the interface from less than 0.5 percent to over 80 percent. The experimental results show a contrast ratio of 50:1 and a maximum reflection of 50 percent.

Nanophotonic applications for silicon-on-insulator (SOI)

Silicon-on-insulator is a proven technology for very large scale integration of microelectronic devices. The technology also offers the potential for development of nanophotonic devices and the ability to interface such devices to the macroscopic world. This paper will report on fabrication techniques used to form nano-structured silicon wires on an insulating structure that is amenable to interfacing nanostructured sensors with high-performance microelectronic circuitry for practical implementation. Nanostructures formed on silicon-on-sapphire can also exploit the transparent substrate for novel device geometries. This research harnesses the unique properties of a high-quality single crystal film of silicon on sapphire and uses the film thickness as one of the confinement dimensions. Lateral arrays of silicon nanowires were fabricated in the thin (5 to 20 nm) silicon layer and studied. This technique offers simplified contact to individual wires and provides wire surfaces that are more readily accessible for controlled alteration and device designs.

Porous SOS, BESOS and SOQ for flat panel emissive displays

The motivation for this research was to develop an efficient photonic source compatible with silicon VLSI technology for flat panel emissive displays, optical interconnections and optoelectronic applications. Recent research has shown that porous silicon layers can be formed on transparent substrates and offers unique device geometries due to the ability to observe the photoemission through the substrate rather than relying on semitransparent (Au) or transparent (ITO) electrodes. This report details the fabrication of porous silicon layers on transparent sapphire (SOS), quartz (SOQ) and bonded SOS (BESOS) and their corresponding emission spectra.

Demonstration of monolithic Co-fabrication of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-/spl delta// and CMOS devices on the same sapphire substrate

Abstract : This paper reports the first fabrication of active semiconductor and high temperature superconducting (HTS) devices on the same substrate. Complementary Metal-Oxide-Semiconductor (CMOS) transistors were fabricated on the same sapphire substrate as either YBCO flux-flow transistors (FFTs) or YBCO superconducting quantum interference devices (SQUIDs). All devices functioned as expected at 77 K without degradation, demonstrating that a compatible process has been found to monolithically integrate adjacent CMOS and HTS devices.

Advanced AE Technology for High-Power Microwave Radar Tubes

Acoustic emission (AE) and micro-seismic activity are naturally occurring phenomena. Almost all materials emit sound or acoustic emission when they are sufficiently stressed. Wood and rock produce AE signals in audible frequency ranges when stressed. It was also believed that AE signal generation could exist in the ultrasonic frequency range during deformation of materials, but it was not until 1950 when Joseph Kaiser reported the first comprehensive investigations on acoustic emission phenomenon in conventional engineering materials using electronic equipment and tensile testing machines. Kaiser also observed that AE activity was irreversible. Acoustic emissions are not generated during the reloading of a material until the stress level has exceeded its previous highest value. This AE irreversible phenomenon is now known as the Kaiser Effect. He also proposed a distinction between burst and continuous AE activity. The use of piezoelectric sensors and electronic amplifiers to observe high-frequency AE activity gradually led to the definition of acoustic emission. According to the ASNT Handbook (1987), acoustic emission refers to the generation of transient elastic stress (strain) waves due to the rapid release of energy from a localized source within a material undergoing some kind of deformation. The kind of stress applied to materials under testing could be tensile, compressive or shear. The transient elastic stress waves of AE have frequencies ranging from 20 kHz (kilohertz) to 1 MHz (megahertz). Green (1980) has listed many mechanisms that produce acoustic emission activity in materials. Among them, the principal mechanisms are mechanical deformation, fracture, crack propagation, dislocation motion and multiplication, twin formation, phase transformation, corrosion, friction and internal magnetic processes. Mechanical loading is not the only way to generate AE activity (phonon signals). Thermal shock loading and electrical sparking are also known to cause AE activity. Generation of AE activity during chemical reactions has also been observed. It was realized quite earlier that AE activity appears in two types, burst signals and continuous signals.