On the possibility of recording the radiation of the electromagnetic pulses generated by the electric discharges on board of a space vehicle by the ground-based radars

Necessary conditions are determined for recording the radiation of the electromagnetic pulses generated by the electric discharges on board of a space vehicle by the ground-based radars. The mean power-flow density of electric discharges at the Earth’s surface is obtained as a function of the discharge power and the altitude of the space vehicle trajectory. The minimum power-flow density of electric discharges at the Earth’s surface that can be recorded in the presence of the solar radiation is also found. The sensitivity of radar receivers that allows recording the radiation pulses generated by such electric discharges is estimated.     

Ultrahigh-speed photography of picosecond light pulses

A new technique for the display of picosecond light pulses is presented. Ultrashort (6 ps) green light pulses passing through a light-scattering medium are photographed from the side by a camera positioned behind a shutter of 10-ps framing time. The shutter is an ultrafast Kerr cell driven by infrared pulses 8 ps in duration. Color photographs show a bright spot on a dark background, revealing the unambiguous presence of well-isolated picosecond light pulses. The shape of the spot is the result of a convolution involving the three-dimensional shape of the green pulse and the time transmission function of the shutter, this function being dictated by the shape of the infrared pulse. The experiment indicates that a new technique for visualizing light pulses consists in simply observing their flight through a scattering medium from behind an ultrafast shutter having a framing time equal to the time resolution desired. The new technique has many advantages over the two-photon fluorescence display technique, such as higher sensitivity, wider spectral range, and easier interpretation. The ultrafast camera also can be used for the photographic measurement of ultrashort relaxation times in dielectrics and in fluorescent dyes.     

I/SUP 2/L timing circuit for the 1 ms-10 s range

An I/SUP 2/L timing circuit without external components is presented, which makes use of some specific I/SUP 2/L properties-operation at low power levels, light sensitivity, variable delay, and long maximum delay times. The circuit comprises 45 gates on a chip area of 0.3 mm/SUP 2/. It produces pulses from below 1 ms to more than 10 s which are inversely proportional to a single supply current. For this purpose, new methods for current splitting and amplification with I/SUP 2/L circuits are used. The temperature dependence of the output pulse width is better than 0.8 percent/K. If the circuit is irradiated by light, it produces pulses with a pulse width inversely proportional to the light intensity. For example, it can be used as an integrated exposure meter for all kinds of photographic applications.     

Longitudinally Excited CO<Subscript>2</Subscript> Laser with Short Laser Pulse like TEA CO<Subscript>2</Subscript> Laser

We have developed a longitudinally excited CO₂ laser with a short laser pulse similar to that of TEA and Q-switched CO₂ lasers. A capacitor transfer circuit with a low shunt resistance provided rapid discharge and a sharp spike pulse with a short pulse tail. Specifically, a circuit with a resistance of 10 M Ω provided a spike pulse width of 103.3 ns and a pulse tail length of 61.9 μs, whereas a circuit with a shunt resistance of 100 Ω provided a laser pulse with a spike pulse width of 96.3 ns and a pulse tail length of 17.2 μs. The laser pulses from this longitudinally excited CO₂ laser were used for processing a human tooth without carbonization and for glass marking without cracks.      

Compression of microwave pulses in a resonant system based on two waveguide T-joints

Research results for a resonant microwave compressor consisting of two waveguide T-joints are presented. When feeding the compressor with the help of a pulse magnetron with 2 MW power and 3.2 μs duration of microwave pulses the maximum power gain of 23 dB and the peak power of 400 MW is obtained in S-band for the 4 μs long pulses.     

The nature of electrical interaction of Schottky contacts

Electrical interaction between metal-semiconductor contacts combined in a diode matrix with a Schottky barrier manifests itself in an appreciable variation in their surface potentials and static current-volt-characteristics. The necessary condition for appearance of electrical interaction between such contacts consists in the presence of a peripheral electric field (a halo) around them; this field propagates to a fairly large distances (<30 μm). The sufficient condition is the presence of regions where the above halos overlap. It has been shown that variation in the surface potential and the current-voltage characteristics of contacts occurs under the effect of the intrinsic electric field of the contact’s periphery and also under the effect of an electric field at matrix periphery; the latter field is formed as a result of superposition of electric fields of halos which form its contacts. The degree of the corresponding effect is governed by the distance between contacts and by the total charge of the space charge regions for all contacts of the matrix: their number, sizes (diameter D _{i, j} ), concentration of doping impurities in the semiconductor N _D , and physical nature of a metal-semiconductor system with a Schottky barrier (with the barrier height φ _b ). It is established that bringing the contacts closer leads to a relative decrease in the threshold value of the “dead” zone in the forward current-voltage characteristics, an increase in the effective height of the barrier, and an insignificant increase in the nonideality factor. An increase in the total area of contacts (a total electric charge in the space charge region) in the matrix brings about an increase in the threshold value of the “dead” zone, a relative decrease in the effective barrier height, and an insignificant increase in the ideality factor.     

Investigation of the photovoltage in por-Si/p-Si structures by the pulsed-photovoltage method

Photovoltaic phenomena in the structures por-Si/p-Si were investigated by the pulsed photovoltage method in the time interval 100 ns-10 ms using irradiation with nanosecond laser pulses with photon energies 1.4, 2.0, 2.8, and 3.7 eV. The data obtained show that besides the barrier photovoltage, due to the separation of nonequilibrium charge carriers in the space-charge region of p-Si at the por-Si/p-Si interface, there also exists an efficient mechanism of photovoltage formation due to charging of the surface of the por-Si nanostructure. This mechanism is explained as “optical doping” of a semiconductor and develops in a manner peculiar to semiconductor nanostructures. Fiz. Tekh. Poluprovodn. 32, 613–619 (May 1998)     

Determination of the diffusion length of charge minority carriers using digital oscillography of surface photovoltage

A procedure for determining the diffusion length of charge minority carriers (CMCs), which uses digital oscillography to detect surface photovoltage (SPV), is considered. It is shown by experiments that the shape of pulses of SPV, excited by rectangular IR pulses, depends significantly on both their intensity and wavelength. It is shown that it is not valid to use a synchronous detector to measure the quasi-stationary SPV when determining the diffusion length of CMCs in semiconductors, because, in a number of cases, it results in an uncontrollable error that reaches 100% and more. A technique is developed for determining the diffusion length in silicon wafers and epitaxial structures with the specific resistance range 0.01–12 Ω cm, the diffusion length range 5–500 μm, and an error of not more than 8%.     

Photoelectrical memory in GaAs/AlGaAs multilayer quantum-well structures

An increase in the dark current (by 2–3 orders of magnitude) in GaAs/Al_xGa_1−x As multilayer quantum-well structures with x⋍0.4 is observed after illumination of the structures with optical light (λ<1.3 μm). This increase is sustained for an extended time (more than 10³ s) at low temperatures. It then decreases to its initial value upon heating of the sample. A model of the barrier with local sag of the conduction band facilitating tunneling is proposed. The conduction band sag and the magnitude of the current grow due to optical ionization of uncontrolled deep level clusters present in the barrier and decrease due to subsequent capture of electrons from the conduction band by the deep levels upon heating. Fiz. Tekh. Poluprovodn. 32, 209–214 (February 1998)     

Excilamps and their applications

The design and practical applications of excilamps having a dielectric barrier and capacitive structure and driven by nanosecond, high voltage pulses are described. A simple design lamp having forced cooling and an excitation generator was demonstrated to have a lifetime of more than one thousand hours. The results of an experimental study of capacitive and high voltage nanosecond discharge-driven excilamps are presented. The influence of the excitation regime and operating gas mixture pressure on the dielectric barrier discharge (DBD) driven excilamps' efficiency is discussed. The discharge formation and output radiation dynamics of DBD driven excilamps was experimentally studied for the first time.The practical applications of several lamps designed in the High Current Electronics Institute, Tomsk, Russia to photochemistry, photobiology and photomedicine are discussed.     

Optical spectra of microcrystals of the layered semiconductor PbI2 grown in glass matrices

The transmittance, luminescence, and Raman spectra in PbI₂ microcrystals of 2H polytype, grown in the voids of alkali-borosilicate glasses (void dimensions 4–30 nm), are investigated. Depending on the conditions of growth, the exciton states of the microcrystalline systems were found to shift toward higher energies by 35–60 meV relative to the free exciton energy in bulk single crystals as a result of the quantum-well effect. The resonant Raman spectra of PbI₂ microcrystals exhibit not only the conventional Raman component A _1g , but also components associated with the appearance of the E _u and A _2u optical phonons and the two-phonon processes. Fiz. Tekh. Poluprovodn. 32, 151–154 (February 1998)     

Characterization of Single Barrier Microrefrigerators at Cryogenic Temperatures

The experimental characterization of single barrier heterostructure thermionic cooling devices at cryogenic temperatures is reported. The device studied was a cylindrical InGaAs microrefrigerator, in which the active layer was a 1 μm thick In_0.527Al_0.218Ga_0.255As heterostructure barrier with n-type doping concentration of 6.68 × 10¹⁶ cm⁻³ and an In_0.53Ga_0.47As emitter/collector of 5 × 10¹⁸ cm⁻³ n-doping. A full field thermoreflectance imaging technique was used to measure the distribution of temperature change on the device’s top surface when different current excitation values were applied. By reversing the current direction, we studied the device’s behavior in both cooling and heating regimes. At an ambient temperature of 100 K, a maximum cooling of 0.6 K was measured. This value was approximately one-third of the measured maximum cooling value at room temperature (1.8 K). The paper describes the device’s structure and the first reported thermal imaging at cryogenic temperatures using the thermoreflectance technique.     

An investigation of microcrystalline films produced by a dc glow discharge in silane and hydrogen

Microcrystalline and amorphous Si:H films have been produced in a dc cathodic discharge in atmospheres containing silane diluted in hydrogen. The composition of the discharge atmosphere has a strong effect on the nucleation of microcrystalline Si:H films. Dopants such as boron enhance the formation of microcrystals while higher silanes such as disilane inhibit crystallization. The presence of other gases in the discharge atmosphere generally inhibits the formation of microcrystals. Research reported herein was supported by Solar Energy Research Institute, under Contract No. XG-0-9372-1, and by RCA Laboratories, Princeton, NJ, 08540, U.S.A.     

The sensitivity of Pt/InP Schottky barrier diode to H2 and O2

Gas sensitivity of Pt/InP Schottky barrier diode was characterized byI–V, C–V and complex impedance under different gas phase composition. The results show that the barrier height decreased when the device was exposed to a hydrogen-containing atmosphere, and the barrier height increased in an oxygen-containing atmosphere. The sensing mechanism was analyzed.     

Influence of the X-valley on the tunneling and lifetime of electrons in GaAs/AlAs heterostructures

The effective-mass approximation is used to calculate the probability for tunneling of an electron through a triangular barrier and its lifetime in the triangular quantum well formed by a GaAs/AlAs heterojunction and a strong electric field. It is shown that for such structures the tunneling probability into the X-valley can exceed the probability for tunneling into the Γ-valley by several orders of magnitude. The lifetime of an electron in the quasistationary state formed by the triangular heterobarrier is also essentially determined by tunneling to the X-valley and comes to ∼10⁻¹³–10⁻¹¹ s in fields E∼10⁵–10⁶ eV/cm. Fiz. Tekh. Poluprovodn. 31, 355–357 (March 1997)     

I-V characteristics of high-voltage 4H-SiC diodes with a 1.1-eV Schottky barrier

The I-V characteristics of high-voltage 4H-SiC diodes with a Schottky barrier ∼1.1 eV in height are measured and analyzed. The forward I-V characteristics proved to be close to “ideal” in the temperature range of 295–470 K. The reverse I-V characteristics are adequately described by the model of thermionic emission at the voltages to 2 kV in the temperature range of 361–470 K if, additionally, a barrier lowering with an increase in the band bending in the semiconductor is taken into account.     

High sensitivity,ultra-wide band divide-by-two circuit with frequency self-adaptive techniques

A high sensitivity, ultra wide-band toggle flip–flip divide-by-two circuit is presented in this study. Frequency self-adaptive load technique is proposed to increase the divider’s operating frequency range and sensitivity. Furthermore, the circuits operation principle and theory are analysized in detail. Measurement results exhibits that the proposed divider’s input sensitivity is enhanced, the operating frequency ranges from 150-MHz to 16.734-GHz, and the power consumption is 15 mW when input frequency is 16.734-GHz. The chip is implemented on a standard 0.13 μm CMOS process with 1.2 V supply voltage.     

Characteristics of PECVD grown tungsten nitride films as diffusion barrier layers for ULSI DRAM applications

We have developed tungsten nitride (W-Nitride) films grown by plasma enhanced chemical vapor deposition (PECVD) for barrier material applications in ultra large scale integration DRAM devices. As-deposited W-Nitride films show an amorphous structure, which transforms into crystalline, β-W₂N and α-W phases upon annealing at 800°C. The resistivity of the as-deposited films grown at the NH₃/WF₆ gas flow ratio of 1 is about 160 μω-cm, which decreases to 50 μω-cm after an rapid thermal annealing treatment at 800°C. In the contact holes with the size of 0.35 μm and aspect ratio of 3.5, the bottom step coverage of the tungsten nitride films is about 60%, which is about three times higher than that of collimated-TiN films. We obtained contact resistance and leakage current with the tungsten nitride barrier layer comparable to those with conventional collimated TiN films. The contact resistance and leakage current are stable upon thermal stressing at 450°C up to 48 h.     

Pulse Height Spectral Analysis of an Ozonizer Discharge and the Associated Joshi Effect†

Measurements by a single channel pulse height analyser of the amplitudes of the discharge pulses in H₂, He, Cl₂ and I₂ vapour excited by a. c. potentials in ozonizers of the Siemens type show a continuous pulse amplitude spectrum from above the noise level (～0·3 v) to a maximum amplitude whose value depends on the excitation potential. At a given value of the latter, the number of pulses diminishes rapidly with increasing amplitude both in the low (l-25 v) and high (55-99 v) amplitude regions, with a plateau of low slope in between. A side by side measurement of the Joshi effect (i.e. change ± Δi in the discharge current due to external light) revealed a definite dependence of the sign and magnitude of the Ai on the pulse amplitude in all the systems studied. Thus, on irradiation of the discharge by light from a 100 w lamp, the shorter ( <25 v) amplitude pulses showed a 100% increase in number while those of larger amplitudes diminished by 40 to 70 % and pulses of amplitudes above 30 v were completely suppressed.     

A Fully Differential Digital CMOS UWB Pulse Generator

A new fully digital CMOS pulse generator for impulse radio ultra-wideband (UWB) systems is presented. First, the shape of the pulse which best fits the FCC regulation in the 3.1–5 GHz sub-band of the entire 3.1–10.6 GHz UWB bandwidth is derived and approximated using rectangular digital pulses. In particular, the number and the width of pulses that approximate an ideal template are found through an ad hoc optimization methodology. Then a fully differential digital CMOS circuit that synthesizes the pulse sequence is conceived and its functionality demonstrated through post-layout simulations. The results show a very good agreement with the FCC requirements and a low power consumption.