Gordon Wood Anderson

Advanced channelization for RF, microwave, and millimeterwave applications

An overview of the channelization function, the parallel signal processing techniques used in channelizers, the signal processing functions, and the critical channelizer parameters is given. Signal processing capabilities that use analog techniques suitable for channelized receivers are compared with those capabilities that can be obtained by using current or foreseen digital techniques. The receiver signal-processing needs are outlined, and the limitations of digital signal processing in terms of the overall receiver signal processing needs are discussed. Options and tradeoffs at the receiver and channelizer technology levels are discussed. Promising channelizer technologies, including components, that have been or potentially may be implemented with small volumes and moderate dynamic range are described. Parallel signal-processing methods, architectural techniques, and hardware for channelized receiver technologies that can be implemented in a small volume (tens of channels per in/sup 3/) with a moderately high dynamic range (>50 dB) are discussed. These include the surface-acoustic-wave (SAW), bulk-acoustic-wave (BAW), magnetostatic-wave (MSW), and acoustooptical (AO) channelizer technologies. The critical signal preprocessing functions required in channelized receivers before the needed information is passed on to the host computer, so that the host computer can be operated at a possible computation rate, are discussed, and the first successful monolithic integrated circuit preprocessor component for channelizers, is presented. >

Composition, Chemical Bonding, and Contamination of Low Temperature SiO x N y Insulating Films

The stoichiometry and contamination of low temperature layers grown by the pyrolytic decomposition of silane in an ammonia‐ and oxygen‐rich atmosphere on and Si substrates are reported. The chemical composition and chemical bonding properties of the films have been analyzed by Auger, nuclear reaction analysis, optical, Rutherford backscattering, and SIMS techniques. Capacitors were fabricated on Si and substrates, and the electrical characteristics were measured. The layers exhibited physical characteristics similar to those of thermally grown layers. Analysis of the films indicated a uniform distribution of Si and O throughout the films. The N concentration measured in the films ranged from 1 to 3% of the O concentration, depending on the growth parameters. The optical results indicated some evidence of small amounts of Si‒N and N‒H bonding. All films grown on Si substrates in the presence of or on substrates had In and Sb contamination throughout, with the In and Sb content increasing from the film/substrate interface to the surface.

Photodetector arrays and architectures for acousto-optical signal processing

A review of photodetector arrays and architectures is presented for acousto-optical (AO) signal processing applications, for which the demands on photodetector arrays are substantially greater than for image sensing applications. The primary design considerations for obtaining photodetector arrays with high dynamic range, high sensitivity, high speed, and low crosstalk are discussed. The current status and future needs for detector arrays for AO signal processing are presented. Several novel detector structures and concepts that have potential for future AO optical signal processing use are described.

Role of photodetectors in optical signal processing

Optical signal processing applications place demands on photodetector arrays beyond those encountered in image sensing applications. We review the basic requirements and show that increased dynamic range and nonlinear decision operations that lead to reduced output data rates are the key improvements needed for both 1-and 2-D arrays. Arrays of high-speed photodetector elements with integrated postdetection circuitry are also needed. Although we suggest some possible methods for achieving these goals, our main objective is to stimulate the photodetector community to design and fabricate more useful devices.

Optical and electrical properties of boron‐implanted amorphous germanium thin films

Amorphous germanium films were implanted to high boron levels, ∼1021/cm3 peak concentrations. Before and after implantation the conductivity measurements fit the relation logσ∼T−1/4 and no evidence of intravalence absorption was observed indicating that the Fermi level was near the center of the band gap. Thermoelectric power measurements indicated that the samples were weakly n type before implantation and p type after implantation. The position of the fundamental absorption edge shifted to lower energy upon implantation and to higher energies upon subsequent anneals. Implanted recrystallized films were strongly p type, exhibited intravalence absorption, and had very low dc activation energies.

Absorption tail and fundamental absorption edge in vanadium phosphate glasses

Optical measurements of the fundamental absorption edge and broad absorption tail of 50 mole% V2O5 vanadium phosphate glass films were made in the range 3850–30 000 cm−1 (2.6–0.33 μ) before and after reducing and oxidizing anneals. The absorption in the tail region of the fundamental absorption increased during reducing anneals and decreased during oxidizing anneals. A band at 19400 cm−1 (2.41 eV) was introduced by the reducing anneals. The band gap Eg was determined to be 2.71, 2.92, and 2.82 eV after successive anneals in oxygen, hydrogen, and oxygen, respectively. Evidence for direct forbidden transitions was observed from fundamental absorption edge measurements similar to that for crystalline V2O5. The concentration of reduced V4+ ions is concluded to be largely responsible for the variation of Eg and of the absorption tail.

Compressing photodetectors for long optical pulses using a lateral blooming drain structure

A compressing photodetector structure suitable for detecting continuous wave and long pulsewidth optical signals for applications such as acoustooptical signal processing and machine vision is described. Subthreshold injection of carriers over a photodetector blooming gate is used to generate a compressing transfer characteristic. The photodetector transfer characteristic is integrating at low light levels and logarithmically compressing at higher light levels. The output voltage at which logarithmic compression becomes dominant may be adjusted in a range extending below 5-nW incident optical power by varying the bias voltage difference between the photodetector blooming and imaging gates. The predictions of simulation models that were developed correlate well with the experimental measurements. >

Gallium arsenide metal-semiconductor-metal photodiodes as optoelectronic mixers for microwave single-sideband modulation.

Gallium arsenide (GaAs) metal-semiconductor-metal (MSM) photodetectors have unique properties including high-bandwidth, linearity, and biphase response that make them suitable as mixers and programmable weights for microwave and communications applications. An optical technique for microwave single-sideband modulation that uses GaAs MSM photodiodes as mixers is reported. It uses MSM Schottky photodiodes formed in a GaAs/Al(0.3)Ga(0.7)As materials system to detect microwave in-phase and quadrature signals on optical carriers. Modulation of the photodetector bias voltages results in a single-sideband modulation of the microwave signal. Radio frequency and undesired-sideband suppression of 36 and 27 dB, respectively, were achieved. The optical wavelength was 850 nm, and the bandwidth of the photodetectors was > or = 29 GHz.

Programmable frequency excision and adaptive filtering with a GaAs/AlGaAs/GaAs heterojunction photoconductor array

The first demonstration of acousto-optical excision using a GaAs photodetector array is reported. A maximum isolation of 40 dB was obtamed using a six element GaAs interdigitated finger double heterojunction photoconductor array. The center frequency was 45 MHz, and the swept bandwidth was 6 MHz. The response of discrete GaAs heterojunction photoconductors was linear with bias voltage, potentially making them useful for performing multiplication functions in optical analog filters. New concepts of using these photoconductors for optical adaptive filters are presented.

Planar, linear GaAs detector-amplifier array with an insulating AlGaAs spacing layer between the detector and transistor layers

Monolithic, high-speed planar, linear, parallel channel, ten-element GaAs detector-amplifier arrays with a 70- mu m detector center-to-center spacing have been fabricated using a GaAs-AlGaAs-GaAs epitaxial structure grown on semi-insulating GaAs. The AlGaAs layer provided excellent electrical isolation between the transistor and n-type photoconductor epitaxial layers. Rise and fall times of integrated detector-amplifier array channels of 650 ps and 1.1 ns, respectively, were measured at 0.84- mu m wavelength. The sensitivity of single, discrete, detector-amplifier channels was better than -34 dBm.<<ETX>>