California Institute of Technology

The United States of America As Represented by the Administrator of the

Other

The United States of America As Represented by the Administrator

Joseph Maserjian

Albert W Overhauser

James C Fletcher

Robert J Lang

Li-Jen Cheng Cheng

Udo Lieneweg

Michael Gregg Spencer

Shy Shiun Chern

Margaret A Frerking

Seung P Li

Shy-Shiun Chern

A submillimeter wave-generating integrated circuit includes an array of N photoconductive switches biased across a common voltage source and an optical path difference from a common optical pulse of repetition rate f.sub.0 providing a different optical delay to each of the switches. In one embodiment, each incoming pulse is applied to successive ones of the N switches with successive delays. The N switches are spaced apart with a suitable switch-to-switch spacing so as to generate at the output load or antenna radiation of a submillimeter wave frequency f on the order of Nf.sub.0. Preferably, the optical pulse has a repetition rate of at least 10 GHz and N is of the order of 100, so that the circuit generates radiation of frequency of the order of or greater than 1 Terahertz.

Optically-switched submillimeter-wave oscillator and radiator having a

A time-multiplexed, optically-addressed, crossbar switch (38) is provided using a two-dimensional, optically-addressed, reflective spatial light modulator (O-SLM) (20). Since the optical addressing is time-multiplexed, only N addressing lines are required for an N.times.N crossbar, rather than the N.sup.2 lines needed in the prior art. This reduction in addressing lines makes possible the development of enormous crossbar switches, such as 100.times.100, for the first time. In addition, since data paths remain entirely in the optics domain, data speeds can reach the multi-gigabit level. In the switch, a row (40) of N inputs (42) at the 'read' wavelength is spread over one axis of the O-SLM. The light is refocused along the other axis to an output array (48) of detectors (50), so that each input has the potential to talk to any one output. The O-SLM is normally off, i.e., non-reflective, so that the output is, in the absence of an input signal, zero. A one-dimensional array (52) of lasers (54) at the 'write' wavelength is imaged onto the O-SLM. Each laser scans across an entire row of the O-SLM; where the laser is on, it turns on a portion of the O-SLM and establishes a connection between a particular input and a particular output. A full row is scanned in a time much shorter than the response time of the O-SLM, so that state of the O-SLM is capacitively stored and dynamically refreshed. The scanning is accomplished by tuning the wavelength of the laser and passing it through a grating, which sweeps the beam in space.

Time-multiplexed, optically-addressed, gigabit optical crossbar switch

A planar frequency tripler comprised of two semiconductor diode structures connected back-to-back by an n.sup.+ doped layer (N.sup.+) of semiconductor material utilizes an n doped semiconductor material for a drift region (N) over the back contact layer in order to overcome a space charge limitation in the drift region. A barrier layer (B) is grown over the drift region, after a sheet of n-type doping (N.sub.sheet) which forms a positive charge over the drift region, N, to internally bias the diode structure. Two metal contacts are deposited over the barrier layer, B, with a gap between them. To increase the power output of the diodes of a given size, stacked diodes may be provided by alternating barrier layers and drift region layers, starting with a barrier layer and providing a positive charge sheet at the interface of a barrier on both sides of each drift region layer with n-type .delta. doping. The stacked diodes may be isolated by etching or ion implantation to the back contact layer N.sup.+ and a separate metal contact deposited on each stacked diode.

Planar varactor frequency multiplier devices with blocking barrier

A new approach to long-wave-infrared (LWIR) technology is based on molecular beam epitaxy (MBE) growth of holeimmobilized doping superlattices (12) in narrow band gap III-V semiconductors, specifically, InAs and InSb. Such superlattices are incorporated into detector structures (10, 10', 10') suitable for focal plane arrays. The objective of this approach is an LWIR detector possessing the advantages of high detectivity performance, to wavelengths of at least about 16 .mu.m, at operating temperatures of 65K, where long-duration space refrigeration is plausible.

InAs hole-immobilized doping superlattice long-wave-infrared detector

A semiconductor diode structure useful for harmonic generation of millimeter or submillimeter wave radiation from a fundamental input wave is fabricated on a GaAs substrate. A heavily doped layer of n.sup.++ GaAs is produced on the substrate and then a layer of intrinsic GaAs on said heavily doped layer on top of which a sheet of heavy doping (++) is produced. A thin layer of intrinsic GaAs grown over the sheet is capped with two metal contacts separated by a gap to produce two diodes connected back to back through the n.sup.++ layer for multiplication of frequency by an odd multiple. If only one metal contact caps the thin llayer of intrinsic GaAs, the second diode contact is produced off the diode structure and connected to the n.sup.++ layer for multiplication of frequency by an odd multiple. If only one metal contact caps the thin layer of intrinsic GaAs, the second diode contact is produced to connect to the n.sup.++ layer for multiplication of frequency by an even number. The odd or even frequency multiple is selected by a filter. A phased array of diodes in a grid will increase the power of the higher frequency generated.

Millimeter-wave monolithic diode-grid frequency multiplier

Multiple quantum well (MQW) structures (12) are utilized to provide real-time, reliable, high-performance, optically-addressed spatial-light modulators (SLM) (10). The optically-addressed SLM comprises a vertical stack of quantum well layers (12a) within the penetration depth of an optical write signal 18, a plurality of space charge barriers (12b) having predetermined tunneling times by control of doping and thickness. The material comprising the quantum well layers has a lower bandgap than that of the space charge barrier layers. The write signal modulates a read signal (20). The modulation sensitivity of the device is high and no external voltage source is required. In a preferred embodiment, the SLM having interleaved doped semiconductor layers for driving the MQW photovoltaically is characterized by the use of a shift analogous to the Moss-Burnstein shift caused by the filling of two-dimensional states in the multiple quantum wells, thus allowing high modulation sensitivity in very narrow wells. Arrays (30) may be formed with a plurality of the modulators.

Photovoltaic driven multiple quantum well optical modulator

The use of stacked Schottky barriers (16) with epitaxially grown thin silicides (10) combined with selective doping (22) of the barriers provides high quantum efficiency infrared detectors (30) at longer wavelengths that is compatible with existing silicon VLSI technology.

Stacked silicide/silicon mid- to long-wavelength infrared detector

A novel infrared detector (20, 20', 20'), is provided, which is characterized by photon-assisted resonant tunneling between adjacent quantum wells (22a, 22b) separated by barrier layers (28) in an intrinsic semiconductor layer (24) formed on an n.sup.+ substrate (26), wherein the resonance is electrically tunable over a wide band of wavelengths in the near to long infrared region. An n.sup.+ contacting layer (34) is formed over the intrinsic layer and the substrate is n.sup.+ doped to provide contact to the quantum wells. The detector permits fabrication of arrays (30) (one-dimensional and two-dimensional) for use in imaging and spectroscopy applications.

Tunable quantum well infrared detector

A far infrared (FIR) range responsive photodetector. There is a substrate (28) of degenerate germanium. A a plurality of alternating impurity-band (32) and high resistivity (30) layers of germanium are disposed on the substrate (28). The impurity-band layers (32) have a doping concentration therein sufficiently high to include donor bands which can release electrons upon impingement by FIR photons of energy hv greater than an energy gap .epsilon.. The high resistivity layers (30) have a doping concentration therein sufficiently low as to not include conducting donor bands and are depleted of electrons. Metal contacts (36, 38) are provided for applying an electrical field across the substrate (28) and the plurality of layers (30, 32). In the preferred embodiment as shown, the substrate (28) is degenerate n-type (n.sup.++) germanium; the impurity-band layers (32) are n.sup.+ layers of germanium doped to approximately the low 10.sup.16 cm.sup.-3 range; and, the high resistivity layers (30) are n.sup.- layers of germanium doped to a maximum of approximately 10.sup.15 cm.sup.-3. Additionally, the impurity-band layers (32) have a thickness less than a conduction-electron diffusion length in germanium and likely to bein the range of 0.1-1.0 micron, the plurality of impurity-bands (33) is of a number such that the flux of FIR photons (20) passing therethrough will be substantially totally absorbed therein, the thickness of the high resistivity layers (30) is such compared to the voltage applied that the voltage drop in each the high resistivity layers (30) controls the occurance of impact ionization in the impurity-band layers (32) to a desired level.

Alternating gradient photodetector

Semiconductor devices, such as silicon-base MOS devices (10) and solar cells (50), degrade as a result of a variety of reasons, such as hot carriers, photons, and ionizing radiations. Degradation in such devices is cured by the presence of atomic hydrogen. Presently, such devices are exposed to atomic hydrogen during processing. However, a source of atomic hydrogen is not available to heal damage over the lifetime of the device. In accordance with the invention, a source (34, 60) of atomic hydrogen is provided in cooperative relationship with the devices. In a preferred embodiment, the source comprises a layer of palladium, disposed at an appropriate location. The palladium is charged with atomic hydrogen during packaging or encapsulating by exposure to a hydrogen-containing species. The palladium cracks the species to generate atomic hydrogen, which it stores and provides to the device on a real-time basis.

Hydrogen-stabilized semiconductor devices

Multiple quantum well (MQW) structures (24) are utilized to provide real-time, reliable, high-performance, optically-addressed spatial-light modulators (SLM) (10, 10'). Several embodiments are provided, including combination of MQW structures with PIN photodiodes of GaAs (12) or Si (12') to form two-dimensional arrays of pixel elements (92) on a single chip (90). In another embodiment, the optically-addressed SLM (50) comprises a vertical stack of MQW layers (52) within the penetration depth of an optical write signal (36), a plurality of space charge barriers (52b) having predetermined tunneling times by control of doping and thickness, whereby modulation sensitivity is high and no external voltage source is required. In yet another embodiment, the optically-addressed SLM (70) comprises a multiplicity of quarter-wave layers (72, 74) whose index of refraction is changed by changes in in the fields at the boundaries (80) responsive to the photocurrent generated by the incident write signal. The changes are read by use of a read signal (38) of a wavelength that is resonantly reflected (78) from the quarter-wave layers.

Multiple quantum well optical modulator

A metal thin oxide silicon (MTOS) optically-activated semiconductor device having respective thin, optically absorptive aluminum layers deposited over a thin oxide layer formed on a silicon substrate over a lightly doped, implant diffused region.

Laser activated MTOS microwave device

An induced junction solar cell is fabricated on a p-type silicon substrate by first diffusing a grid of criss-crossed current collecting n.sup.+ stripes and thermally growing a thin SiO.sub.2 film, and then, using silicon-rich chemical vapor deposition (CVD), producing a layer of SiO.sub.2 having inherent defects, such as silicon interstices, which function as deep traps for spontaneous positive charges. Ion implantation increases the stable positive charge distribution for a greater inversion layer in the p-type silicon near the surface. After etching through the oxide, to parallel collecting stripes, a pattern of metal is produced consisting of a set of contact stripes over the exposed collecting stripes and a diamond shaped pattern which functions as a current collection bus. Then the reverse side is metallized.

Induced junction solar cell and method of fabrication

An improved chemical vapor deposition reactor is characterized by a vapor deposition chamber configured to substantially eliminate non-uniformities in films deposited on substrates by control of gas flow and removing gas phase reaction materials from the chamber. Uniformity in the thickness of films is produced by having reactive gases injected through multiple jets which are placed at uniformally distributed locations. Gas phase reaction materials are removed through an exhaust chimney which is positioned above the centrally located, heated pad or platform on which substrates are placed. A baffle is situated above the heated platform below the mouth of the chimney to prevent downdraft dispersion and scattering of gas phase reactant materials.

Chemical vapor deposition reactor

Trap densities in dielectric films can be determined by tunnel injection measurements when the film is incorporated in an insulated-gate field-effect transistor (IGFET). Under applied bias to the transistor gate, carriers (electrons or holes) tunnel into traps in the dielectric film. The resulting space charge tends to change channel conductance. By feeding back a signal from the source contact to the gate electrode, channel conductance is held constant, and by recording the gate voltage as a function of time, trap density can be determined as a function of distance from the dielectric-semiconductor interface. The process is repeated with the gate bias voltage at different levels in order to determine the energy distribution of traps as a function of distance from the interface.

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Valencia, CA, United States of America

Joseph Maserjian