Characterization of SnO2/Pb2CrO5 thin film/metal photovoltaic device

The photovoltaic behavior in a design of SnO₂/Pb₂CrO₅ thin film/metal (Au or Al) is described as functions of light intensity and wavelength for two different illumination directions. The Pb₂CrO₅ thin film in each device is formed over the SnO₂ coated glass substrate by an electron-beam evaporation technique. When illuminated from the metal side, the device with Au or Al shows the positive or the negative photovoltage, respectively. For the illumination from the SnO₂ side, the device with Au has the negative photovoltage at the short wavelength, and the positive one at the longer, while the device with Al has the negative photovoltage at both wavelength regions. These photovoltaic devices have two junctions at both sides of the Pb₂CrO₅ thin film. The band model of each device is also discussed.     

Time delays in lead-salt semiconductor diode lasers

Time delays of typically 15–17 have been measured directly for PbS_1–xSe_x, Pb_1–xSn_xSe and Pb_1–xSn_xTe diode lasers at injection levels just above threshold in each case. The corresponding minority carrier lifetimes, as determined using the one-carrier injection model, were typically 2–4.     

Design and Analysis of InGaN-GaN Modulation-Doped Field-Effect Transistors (MODFETs) for 90 GHz Operations

A Modulation-Doped Field-Effect Transistor (MODFET) structure having quantum wire channel realized in InGaN-GaN material system is presented. This paper presents design and analysis of a novel one-dimensional Modulation-Doped Field-Effect transistor (1D MODFET) in InGaN-GaN material system for microwave and millimeter wave applications. An analytical model predicting the transport characteristics of the proposed MODFET device is also presented. Analytical results of the current-voltage and transconductance characteristics are presented. The unity-current gain cutoff frequency (f _T) of the proposed device is computed as a function of the gate voltage V _G. The results are compared with two-dimensional GaN/AlGaN MODFET and HFET devices. The analytical model also predicts that 0.25 m channel length devices will extend the use of InGaN-GaN MODFETs to above 90GHz.     

Magnetism in hydrogenated YBa2Cu3O7 a comparison of μSR and NMR results

Hydrogenated YBa₂Cu₃O₇ with [H]/cell=2.0 was studied by X-ray diffraction, SR and¹H-NMR. For the first time, the hydride phase (16% larger c-axis) known from thin film experiments was seen in a bulk sample. A comparison of the SR and NMR results shows that the 15 mT site (2 MHz in SR) is the stable position for the proton and muon. The three other muon sites (4 MHz line and two exponentially decaying components) are metastable.     

GeO2-Core/SiO2-cladding optical fibers made by MCVD process for stimulated raman applications

GeO₂-core/SiO₂-cladding optical fibers (GESI fibers) and liquid core fibers with a cladding region of GeO₂ were designed and fabricated by the MCVD process. The attenuation level of the GESI fibers was about 0.5 dB/m in the near-infrared wavelength region at 2.35 m. GESI fibers showed a stimulated Raman scattering (SRS_ spectrum with six to seven Stokes shifts of 430 cm^–1. The spectrum of SRS expanded to 1.6 m when a Nd: YAG laser at a wavelength of 1.064 m was used.     

Integrated optical cross strip polarizer concept

Passing across an abrupt junction from a thick vertically bimodal waveguide to a thinner single mode segment, guided light can undergo complete destructive interference, provided that the geometry and the phases of the modes in the initial segment are properly adjusted. We propose to employ this effect to realize a simple polarizer configuration, using a strip that is etched from a planar waveguide. A beam of light is made to pass the strip perpendicularly. The light enters from the single mode waveguide outside the strip into the strip segment, which is configured to support two modes. At the end of the strip, apart from reflections, the amount of power that is guided in the following lower segment depends on the local phases of the two modes. These phases are different for TE and TM light, hence we may expect a polarization dependent power transfer, resulting in polarizer performance for a properly selected geometry. The paper describes in detail the modeling of the device in terms of rigorous mode expansion. Design guidelines and tolerance requirements for geometric and material parameters are discussed. For typical Si₃N₄/SiO₂ materials, our calculations predict a peak performance of 34 dB polarization discrimination and 0.3 dB insertion loss for a device with a total length of about 12 m that selects TE polarization at a wavelength of 1.3 m.     

A new doping superlattice photodetector

A new GaAs photodetector with high sensitivity in the whole 0.8–1.4m wavelength range has been fabricated from totally depleted GaAs doping superlattices grown by molecular beam epitaxy. Photoexcited electrons and holes are separated in real space by the space-charge field of the doping superlattice immediately after excitation, yielding a high quantum efficiency of this device. Because of the complete depletion, the doping superlattice behaves like a highly resistive material, which allows application of high electric field along the layers via selectiven ⁺ — andp ⁺ -electrodes. The sensitivity of this device at 1.3 m reaches more than 90% of the original band edge response at 0.85 m, and the external quantum efficiency amounts to 65% at 0.85 m. This excellent photoresponse at longer wavelengths arises from an extremely high electric field composed of the intrinsic space charge field and applied external field, and from the existence of pronounced tail states in the forbidden gap region of the superlattice.     

Letter: Trace Anomaly and Backreaction of the Dynamical Casimir Effect

The Casimir energy for massless scalar field which satisfies periodic boundary conditions in two-dimensional domain wall background is calculated by making use of general properties of renormalized stress-tensor. The line element of domain wall is time dependent, the trace anomaly which is the nonvanishing T for a conformally invariant field after renormalization, represent the back reaction of the dynamical Casimir effect.     

A mini transmissionγ-ray Compton polarimeter and measurements of the sign of magnetic moments of radioactive nuclei

A mini transmission-ray Compton polarimeter was developed for the measurement of the sign of magnetic moments of radioactive nuclei with low-temperature nuclear orientation. The signs of the magnetic moments of the following isotopes were determined:¹⁹³Os [=+0.7297(16) _N];^191m Ir [=+6.20(9) _N];¹⁹²Ir [=+1.924(10) _N];¹⁹⁴Ir [=+0.39(1) _N];^195m Pt [=–0.605(15) _N].Dedicated to Prof. Dr. P. Kienle on the occasion of his 60th birthday     

Moment evaluation for linear chain

A method has been derived to generate a structure of moments for frequency spectrum of a disordered crystal lattice with the use of digital computer. The moments are given by expressions containing mean values of powers of reciprocal masses of chain atoms or it is possible to directly carry out their evaluation. The derivation performed here for a linear chain is applicable even for more complex lattice types. Using the method described below, the structure of moments up to ₄₂ has been evaluated; numerically the moments up to ₅₀ have been evaluated. The values of ₂₂, ₂₄ and ₂₆ moments are given in appendix.     

Nanometer thin-film Ni-NiO-Ni diodes for 30 THz radiation

We report on the development of antenna-coupled thin-film nanometer Ni-NiO-Ni diodes which are used to detect 10.6 m CO₂-laser radiation. The Ni-NiO-Ni diodes have a minimum contact area of 0.056 m². This is smaller than those of any previously fabricated thin-film Metal-metalOxide-Metal (MOM) diodes. By measuring the second derivative of the dc current-voltage characteristics I(V), we demonstrate that the nonlinearity of the dc I(V) characteristics of our Ni-NiO-Ni diodes is larger than that of the dc I(V) characteristics of thin-film MOM diodes fabricated before by other authors. It is comparable to the nonlinearity of the dc I(V) characteristics of point-contact MOM diodes. Furthermore, we show that the polarisation-dependent infrared response of the Ni-NiO-Ni diodes is due to antenna coupling and that the polarisation-independent response is mainly of thermal origin. Consequently, the heating of the Ni-NiO-Ni diodes is due to the absorption of the incident CO₂-laser radiation in the SiO₂, and dissipation of the laser-induced ac antenna currents in the antenna.     

A stochastic model of deposition processes with nucleation

We study an interacting particle system on a one-dimensional infinite lattice and one-dimensional lattices with a periodic boundary. In this system, each site of the lattice may be either empty or occupied and initially all the lattice sites are empty. The evolution of the system is defined as follows: an empty site waits an exponential time with mean 1 and becomes occupied, and an occupied site becomes empty at a time which is distributed exponentially with mean _k, wherek is the number of occupied neighboring sites of this site in the current state of the system. We show that the mean number of the occupied sites of the lattice, considered as a function of time, may possess a convex part. A sufficient condition for this is that ₀ is large and _k,k1, are small. The studied system has been proposed recently as a mathematical model of certain deposition processes, in particular those which exhibit nucleation caused by lateral attractive interaction between the deposited molecules. Our research was motivated by the observation that the density of deposited molecules contains a convex part, over some time interval, if the attractive forces are strong, while this density is a concave function of time if these forces are weak or absent. Our result agrees with this observation.     

Photoconduction and polarization effects in a heat-treated Au/Pb2CrO5/SnO2 film device

2 CrO₅/SnO₂ sandwich-structured film device (1.39 μm thick) was measured at room temperature as a function of frequency in the range 5 Hz-5 kHz, both in the dark and under illumination with visible light of different intensities. The Pb₂CrO₅ film was prepared at a substrate temperature of 200 °C and annealed at a temperature of 460 °C, and has been characterized to be polycrystalline-rich in sizable micro-grains. The experimental frequency-dependence of the total ac-impedance was found to be adequately described over the entire frequency range used by a proposed equivalent RC-circuit model that took into consideration the contributions of the bulk, grain-boundaries, and electrode–Pb₂CrO₅ interface to the device’s ac behavior. Bulk conduction within crystalline grains due to the semiconductivity of Pb₂CrO₅ and space-charge effects in the highly resistive grain-boundary regions have been found to dominate the device’s ac-behavior at frequencies higher than 100 Hz and were strongly dependent on light intensity. The light-intensity behavior of the circuit-parameters associated with grain-boundary effects can be understood by the use of grain-boundary trapping models. The effect of interfacial space-charge polarization in the region near the electrode–Pb₂CrO₅ junction has been noted to be most significant at the low-frequency side and was not highly affected by illumination of the device. Received: 13 February 1997/Accepted: 30 July 1997     

Functional integration of microdevices by field assisted manipulation and trapping

A novel programmable force field method is presented which enables controlled electric field assisted transport and localization of microdevices at silicon chip substrates. Electrically addressable chips bearing n×n arrays of receptor electrode sites are developed and field directed assembly methods are optimized for on-chip transport, trapping and integration of sub-100 m discrete GaAs-based optoelectronic devices. Tweezer-less field assisted manipulation and trapping of discrete 50 m diameter 670 nm emitting GaAs-based light emitting diodes is achieved. Following assembly in this manner, the LED devices are permanently integrated by solder reflow bonding to the receptor sites enabling direct device electrical characterization and successful demonstration of light emission. PACS 81.16Dn; 81.05.Hd; 42.82.Fv; 42.82.Gw     

X-ray coherence and ultra small angle resolution at grazing incidence and exit angles

We measure the nonspecular x-ray scattering at grazing incidence and exit angles from a GaAs surface, modulated by an one-dimensional lateral grating of effectively variable periodicity 1 md60 m. Due to the projection onto the sample surface, the lateral coherence length is enlarged by a factor of more than 100. The line broadening of the diffraction maxima is used to deduce the number of periods that add up coherently for a given periodd and given angle of incidence. We demonstrate that the scattering geometry used allows for large coherently illuminated lengths on the sample and ultra small angle resolution of one- or two-dimensional objects. Thus structures of m size and larger will be accessible by coherent x-ray scattering.     

A planar electrooptic beam splitter/modulator with a pair of parallel electrodes

A new planar electrooptic beam splitter with a pair of parallel electrodes is proposed and its characteristics are demonstrated on LiNbO₃. At a voltage up to 80 V and a 9.5 m electrode separation, the two output beams can be scanned over a total angle of 3° in the guide plane. The structure can also be applied to amplitude modulation, requiring 15 V for complete on-off modulation. The device permits convenient fabrication and has a potential to operate at high speeds.     

Trilinear generally covariant equations

Field equations for n-frames h ^a that are possible in the theory of absolute parallelism are considered. It is shown that in three cases the equations can, after the substitution h ^a =H^pH ^a (H=det H ^a , p is an n-dependent constant), be written in a trilinear form that contains only the matrix H _a and its derivatives and not H ^a . It is shown that the equations are still regular for degenerate but finite matrices H _a if rank H _a 2.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 2, pp. 22–27, February, 1991.     

High efficiency cw far infrared lasers at 119 μm and 127 μm

The optically pumped FIR laser lines at 119 m from CH₃OH and at 127 m from¹³CD₃OH are known to be the most powerful in the far infrared spectral region. We report on efficiency measurements for our waveguide laser system. The effect of various parameters was investigated, resulting in the highest efficiency ever reported for the 119 m line. The Stark effect and others parameters of the 127 m were measured, and a new¹³CD₃OH laser line at 175 m discovered, with the same pump transition. These measurements are helpful for completing the assignment already proposed for the 127 m line.     

An acoustooptic method of measuring the noise equivalent power of optical heterodyne systems

The noise equivalent power of optical heterodyne detection at 10.6 m has been measured with a method based on Raman-Nath diffraction of a CO₂ laser beam. One of the frequency shifted first order diffracted beams is used as the signal radiation. The local oscillator radiation is obtained by splitting off a part of the laser beam incident upon the device used for the acoustooptic diffraction. The signal power can be varied over a large dynamic range by changing the acoustic input power. A study of the probable errors shows that the total error in the NEP measurement is less than 30%.     

Microwave–assisted synthesis of <Emphasis Type="Italic">submicrometer</Emphasis> GaO(OH) and Ga<Subscript>2</Subscript>O<Subscript>3</Subscript> rods

Submicrometer sized gallium oxide hydroxide (GaO(OH)) and gallium oxide (Ga₂O₃) rods have been successfully fabricated on a large scale by refluxing an aqueous solution of Ga(NO₃)₃ and NH₄OH in a simple domestic microwave oven (DMO). The structures, morphologies, compositions and physical properties of the as–synthesized and calcined products have been characterized by powder X-ray diffraction (XRD), transmission electron microscopy (TEM), selected area electron diffraction (SAED), selected area energy dispersive X-ray spectroscopy (SAEDS), thermo gravimetric analysis (TGA), differential scanning calorimetry (DSC), and energy dispersive X-ray (EDX) analysis. TEM images show that submicrometer sized as–synthesized Ga O(OH) rods have diameters of 0.3–0.5 m and lengths of 3.2–3.5 m. The calcined product consists of submicrometer rods with diameters of 0.4–0.5 m and lengths of 5–5.5 m. XRD, EDX and SAED analysis together indicate that the as–synthesized product has an orthorhombic gallium oxide hydroxide (GaO(OH)) crystal structure, and that the calcined product is rhombohedral Ga₂O₃. A possible mechanism for the formation of submicrometer sized GaO(OH) rods is discussed briefly.