Palladium-iron: A giant-moment magnetic thermometer for the millikelvin temperature range

We have calibrated the temperature dependence of the susceptibility ofbar|Pb+2.2 at. ppm Fe and ofbar|Pd+11 at. ppm Fe with an NBS superconducting fixed point device and with a Pt NMR thermometer in the temperature range 4.5 mK to 208 mK. In this temperature range, the data follow a Curie law with deviations of less than 1%. Its properties seem to makebar|Pd–Fe the most attractive thermometric substance for the temperature range 0.3 mK to 500 mK. For example, ourbar|Pd–Fe thermometer has a time constant of 1 s at 10 mK and of 0.1 s atT>30 mK.Dedicated to K. Dransfeld on the occasion of his 60th birthday     

Monolithic integration technology between microlens arrays and infrared charge coupled devices

In this paper, we develop an integration technology between Si microlens and 256(H)×256(V) element PtSi Schottky-barrier infrared charge coupled device (IR-CCD) to improve the optical responsivity of CCD sensor. The refractive microlenses with the pixel size of approximately 28×28 μm² is directly fabricated on the backside of CCD substrate to focus the incident irradiation onto the active area. For the integration device the fill factor is improved by a factor of 2.1. As a result, the IR-CCD image sensors operating at 77 K indicate an approximate 0.06–0.4 increase in relative optical responsivity in the spectral range of from 1 to 5 μm. CCD imaging quality with microlens has been improved comparing to that without microlens to a great extent.     

Study of current drain during electrochemical etching of polycarbonate detectors

Polycarbonate (PC) detector is one of the common detectors for neutron and radon gas detection. Using this detector it is possible to measure the dose in mSv, by counting tracks/cm² on an etched surface. In this paper, a special procedure has been suggested to determine the dose based on current drain during the etching process. In these experiments the effects of voltage, frequency, effective etched area, PC detector's thickness, etched area (one side or two sides), etching solution temperature and dose absorbed by the PC foil have been studied.The results obtained show the current drain variation for a voltage of 200–1600 V, a frequency of 2–10 kHz, effective area with a diameter of 2–12 cm, PC thickness of 125–250–375– and a temperature of etching solution of 25–.Lexan PC foils were exposed to doses of of neutrons. The unexposed foils were considered as the background (BG) foils. Most of the experiments were performed at a voltage of 800 V, a frequency of 2 and 8 kHz, foil thickness of , diameter of effective etched area of foils of 2, 6 and 12 cm, temperatures of 25 and and the etching process from 0 up to overload stage. Overload stage occurs when the foil becomes so thin due to growth of the tracks that it leads to sparking between phase and null that makes a hole in the foil.Current drain curves versus the function of the etching time are absolutely different for various doses from zero (BG) to 10 rad (BG up to ). This is true especially for the time interval from 3 h of etching up to overload stage. In this way, it is possible to obtain a calibration of PC detector net current drain based on its absorbed dose.In this experiment, the number and diameter of tracks and their relation with drain current and PC foil residual thickness at overload stage have been studied.The same experiment has been performed for various concentrations of radon gas (Bq/m3) as well.     

Contactless RF methods for measuring electrophysical parameters of semiconductors

We review promising contactless radio frequency (RF) methods for performing localized diagnostics on semiconductors by using quasi-stationary devices. These are resonant systems operating in the frequency range from 100 kHz to 1 GHz that feature high spatial localization of the probe electromagnetic field in small geometrical volumes of the semiconducting samples. A properly chosen operating frequency provides both high spatial resolution and good conversion transconductance for the measured parameter, the detector signal for a wide range of materials with resistivities from 10^–3 to 10⁹ ·cm. We discuss the design of quasi-stationary devices for multiparameter, nondestructive, contactless monitoring of semiconducting ingots, wafers, and structures. We examine methods for measuring resistivity, mobility, and free charge-carrier lifetimes in semiconductors. We describe automated systems and instruments for nondestructive, contactless measurement of parameter distribution over the surface of semiconductor wafers and structures with a spatial resolution of 1 mm. We present the technical specifications of these instruments.V. D. Kuznetsov Siberian Physicotechnical Institute, Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 45–63, September, 1992.     

Kink instability of the semiconductor plasma in silicon parallelepipeds

Experimental results on the onset of the kink instability of the semiconductor plasma in silicon p⁺-p-n⁺ structures are analyzed. The structures were parallelepipeds. The experiments were carried out over the temperature range from 77 to 300 K. The shape of the current-voltage characteristics and that of the threshold curves of the test samples are discussed. The frequency and amplitude of the alternating current which arises as a result of the kink instability are described as a function of the electric field and the magnetic induction at levels substantially above the excitation threshold.V. D. Kuznetsov Siberian Physicotechnical Institute, Tomsk State University. Scientific-Research Institute of Semiconductor Devices. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 5, pp. 103–110, May, 1992.     

An electrical characterization of a hetero-junction nanowire (NW) PN diode (n-GaN NW/p-Si) formed by dielectrophoresis alignment

This is a report on the electrical characterization of gallium nitride (GaN) nanowire (NW) p–n junction diodes. These diodes were formed by assembling n-GaN NWs on p-Si (1 0 0) substrates using alternating current (AC) dielectrophoresis (DEP). The AC DEP was optimized with a bias voltage of 15 V_p−p at a frequency of 1 kHz. The hetero-junction single GaN nanowire p-n diode (n-GaN NW/p-Si) showed well-defined current rectifying behavior with a forward voltage drop of 1.2–2.0 V at a current density of 10–60 A/cm². The GaN nanowire p–n diodes had a high parasite resistance in the range of >470 kΩ. We observed that these high resistances were mostly the result of the metal contacts to the n-GaN NWs. We also found that these parasite resistances were reduced by the formation of an additional capping layer on the top of the n-GaN NW as well as high temperature annealing.     

Excess capacitance of ZnO-Au varactors

Doped ZnO single crystals were deposited with gold and indium in 1×10^–8 Torr vacuum. The lithium-doped ZnO single crystals and the gold interface revealed not only a Schottky diode but also varactor characteristics. TheI-V andC-V characteristics of ZnO:Li-Au devices were determined in the 0–140 mV and 0–1.5 V ranges.The frequency dependence of ZnO:Li-Au varactors was investigated in the 6–550 kHz range and the value of the most efficient varactor frequency was found to be 50 kHz for the lithium-doped samples prepared.To bring further insight into the matter the concept of excess capacitance was introduced and 1/C ²=f(–V) curves were rearranged between 0–150 mV where Schottky characteristics are non-linear. The excess capacitance values of lithium-doped varactors were determined at four different frequencies and ranged from 26 pF at 50 kHz to 70 pF at 6kHz.Finally, the bulk donor concentrations of the single crystals were calculated from the modifiedC-V curves to beN _D= 3×10²⁰ m^–3. On the other hand, the bulk donor concentration determined from the non-modifiedC-V curves wasN _D=1.02×10²² m^–3.     

Dielectric relaxation in Ih ice

Relaxation processes in Ih ice are studied in the temperature interval 77–27G°K and frequency band 5 Hz–500 kHz. A new maximum in thermally stimulated currents was found at 97°K, clarifying the nature of the relaxing defects. The parameters of the peaks of the thermally stimulated currents at 97, 127, 139, and 158°K are determined, and the concentrations of L defects and oriented H₂O dipoles are evaluated.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 10, pp. 72–76, October, 1986.     

Surface-field induced interband tunneling in InAs

Metal/insulator/semiconductor junctions are prepared on degeneratep-type InAs substrates with hole concentrations ranging from 2.3×10¹⁷ cm^–3 to 2.7×10¹⁸ cm^–3. The low work function of the top metal Yb, Al, or Au and charged interface states influence a two-dimensional (2D) electron inversion layer at the InAs surface. The insulator barrier that is formed by thermal oxidation is designed sufficiently thin, so that the bias voltage applied at the metal electrode mainly drops across the depletion layer separating the electron channel from the bulk. The current-voltage (I–V) characteristics exhibit strong negative differential conductance due to interband, tunneling from the 2D subband into the 3D valence band with peak-to-valley current ratios up to 3.1, 18, and 32 at 300 K, 77 K, and 4.2 K, respectively. In agreement with a theoretical model based on coherentelastic tunneling, the form of the I–V curves resembles those of double-barrier resonant tunnel devices rather than those of 3D Esaki diodes. The series resistance is obtained from the saturation of the differential conductance dI/dV at high forward bias and from the shift of structures in d² I/dV ² arising from phonon assisted tunneling.Dedicated to G. Lautz on the occasion of his 65th birthday     

Novel mid-IR laser based on hybrid AlGaAsSb/InAs/CdMgSe heterostructure

We report on the development of a novel design of a mid-IR laser combining III–V and II–VI compounds in a “hybrid” double heterostructure. It possesses large (1.5 eV) potential barriers both for injected electrons and holes, suppressing their leakage from the active region, and provides strong optical confinement. An AlGaAsSb/InAs/CdMgSe laser diode with a III–V/II–VI heterovalent interface at the 0.6 μm-InAs active region has been grown by molecular beam epitaxy on an InAs substrate. Despite a far from optimal defect density at the CdMgSe/InAs interface and high losses inherent for bulk active region of the laser, the structure demonstrates lasing at 2.8 μm (up to 100 K) in the pulsed regime with a threshold current density of 3–4 kA/cm². Type II InSb monolayer insertions into an InAs layer show bright photoluminescence at 3.8 μm (77 K), confirming the great potential of the InAs-based nanostructure active region for longer wavelength applications.     

Fluorescence and the state of U(VI) in very dilute solutions

Uranyl nitrate, uranyl carbonate, and alkali solutions of U(VI) have been examined at 77° K at 4.2×10^–7 to 8.4×10^–4 M. The state of U(VI) in these solutions is determined.We are indebted to Professor P. N. Palei for direction, to V. I. Lebedev for the flame-photometric determination of Na, and to A. Ya Volkova for recording the powder pattern.     

A Si nano–micro-wire array on a Si(111) substrate and field emission device applications

A large number of Si wires on Si(111) can be fabricated selectively by the vapor–liquid–solid growth method with a high aspect ratio greater than 100. The diameter of the wire can be controlled from less than a micron to a few hundred microns. We propose a novel smart field electron emission device using silicon nano-wires fabricated by this vapor–liquid–solid growth method, and demonstrate field electron emission with a quite low operation voltage from a gated silicon nano-wire. The threshold voltage is about 13 V, and the value is similar to those for gated carbon-nanotube field emitters. The emission current reaches 10 nA at 15 V gate voltage.     

Electrical characteristics of a metal–insulator–semiconductor memory structure containing Ge nanocrystals

A metal–insulator–semiconductor structure device with Ge nanocrystals in SiO₂ was synthesized and the electrical characteristics were investigated. Capacitance–voltage (C–V) curves show hysteresis and the measurements indicate that the device has charge storage effects and stores more holes than electrons. For decreasing measurement frequencies from 1 MHz to 500 Hz, both branches of the C–V hysteresis shift in the positive voltage direction. The slope of the left flank of the C–V hysteresis curve becomes stretched out with decreasing frequency. The slope of the right one appears frequency independent, while there is a small hump/step on the right flank of the C–V hysteresis curve for the lower frequency cases (500 Hz and 1 kHz). The role of Si/SiO₂ interface states is discussed.     

Studies of divacancy in Si using positron lifetime measurement

The charge state dependence of positron lifetime and trapping at divacancy (V₂) in Si doped with phosphorus or boron has been studied after 15 McV electron irradiation up to a fluence of 8.0×10¹⁷ e/cm². The positron trapping cross sections for V ₂ ^2– , V ₂ ^– and V ₂ ⁰ at 300 K were about 6×10^–14, 3×10^–14 and 0.1–3×10^–14 cm², respectively. For V ₂ ⁺ , however, no positron trapping was observed. The marked difference in the cross sections comes from Coulomb interaction between the positron and the charged divacancy. The trapping rates for V ₂ ⁰ and V ₂ ^2– have been found to increase with decreasing temperature in the temperature range of 10–300 K. These results are well interpreted by a two-stage trapping model having shallow levels with energy of 9 meV (V ₂ ⁰ ) and 21 meV (V ₂ ^2– ). The appearance of a shallow level for V ₂ ⁰ can not be explained by a conventional Rydberg state model. The lifetime (290–300 ps) in V ₂ ⁰ is nearly constant in the temperature range from 10 to 300 K, while that in V ₂ ^2– increases from 260 ps at 10 K to 320 ps at 300 K. The lifetime (260 ps) in V ₂ ^2– is shorter than that in V ₂ ⁰ at low temperature, which is due to the excess electron density in V ₂ ^2– . At high temperature, however, the longer lifetime of V ₂ ^2– than that of V ₂ ⁰ is attributed to lattice relaxation around V ₂ ^2– .     

Electrical properties of metal-vanadium-borate glass-gallium arsenide structures

The results of a study of the electrical properties of MIS structures based on n-type GaAs are presented. The static current-voltage characteristics and the dependences of the capacitance and active conductance on the voltage on the MIS structure in the frequency range of the test signal from 22 to 10⁵ Hz at room temperature and in the temperature range 295–367 K at a frequency of 10³ Hz are analyzed in detail. A method is proposed for determining the total density of surface states N_ts, which determine the position of the Fermi energy on the semiconductor surface for MIS structures with large N_ts.V. D. Kuznetsov Siberian Physicotechnical Institute at Tomsk State University. Translated from Izvestiya Vysshykh Uchebnykh Zavedenii, Fizika, No. 11, pp. 99–108, November, 1992.     

An IR-Radiometer with Internal Signal Modulation

An infrared (IR) radiometer electrical circuit on the basis of photoresistors and photodiodes made of silicon doped with zinc (Si) as well as the narrow bandgap semiconductor alloy Pb_0.78Sn_0.22Te is presented. In the circuit suggested a bridge with the photoreceiver connected to the radiometer input and immediately fed by signal generators functions as a radiation modulator. The threshold sensitivity turned out on a recorder is 2·10^–13 W·Hz^–1/2 (for the n⁺–n–n⁺ structures made of Si, =0.8–l.2m, T=300K); 1.4·10^–15W·Hz^–1/2 (for p⁺–n–n⁺ S-diodes on the basis of Si, =0.8–1.2m, T=300K) and 10^–12W·Hz^1/2 (for photodiodes on the basis of Pb_0.78Sn_0.22Te, =8–13m, T=77K).     

Coarse and Fine Control of the EPR Frequency of a Loop-Gap Resonator Using a Single-Turn Coil with a Varactor Diode Attached

Coarse control and fine control of the resonant frequency of a loop-gap resonator (LGR) operating at an electron paramagnetic resonance (EPR) frequency of ca. 650 MHz were achieved using a single-turn coil with a varactor diode attached (a frequency shift coil). When the distance between the LGR and the frequency shift coil was changed from 15 to 10 mm under the condition of constant voltage to the varactor diode (0 V), a shift of the resonant frequency of the LGR of ca. 20 MHz was observed (coarse frequency control). When the voltage applied to the varactor diode was changed from 0 to 15 V at the same distance between the LGR and the frequency shift coil (10 mm), a shift of the resonant frequency of the LGR of ca. 200 kHz was observed (fine frequency control). There were no significant changes in sensitivity of EPR measurements of a phantom (comprised of agar with a nitroxide radical and physiological saline solution) without and with the frequency shift coil. The EPR sensitivity did not change discernibly when the resonant frequency was shifted by the frequency shift coil. Furthermore, radio-frequency phase adjustment for homodyne detection could be performed by using the frequency shift coil without applying frequency modulation to the carrier wave.     

Structure formation and mechanisms of DC conduction in thermally evaporated nanocrystallite structure ZnIn2Se4 thin films

ZnIn₂Se₄ is of polycrystalline structure in as synthesized condition. It transforms to nanocrystallite structure of ZnIn₂Se₄ film upon thermal evaporation. Annealing temperatures influenced crystallite size, dislocation density and internal strain. The hot probe test showed that ZnIn₂Se₄ thin films are n-type semiconductor. The dark electrical resistivity versus reciprocal temperature for planar structure of Au/ZnIn₂Se₄/Au showed existence of two operating conduction mechanisms depending on temperature. At temperatures >365 K, intrinsic conduction operates with activation energy of 0.837 eV. At temperatures <365 K, extrinsic conduction takes place with activation energy of 0.18 eV. The operating conduction mechanism in extrinsic region is variable range hopping. The parameters such as density of states at Fermi level, hopping distance and average hopping energy have been determined and it was found that they depend on film thickness. The dark current–voltage characteristics of Au/n-ZnIn₂Se₄/p-Si/Al diode at different temperatures ranging from 293–353 K have been investigated. Results showed rectification behavior. At forward bias potential <0.2 V, thermionic emission of electrons from ZnIn₂Se₄ film over a potential barrier of 0.28 V takes place. At forward bias potential >0.2 V, single trap space charge limited current is operating. The trap concentration and trap energy level have been determined as 3.12×10¹⁹ cm⁻³ and 0.24 eV, respectively.     

Mid-infrared lasing from self-consistent quantum wells at a type II single broken-gap heterointerface

A new physical approach for the design of mid-IR lasers operating at 3–5 μm based on type II heterojunctions with effective electron–hole confinement owing to a large asymmetric band-offset at the interface (ΔE_C>0.6 eV and ΔE_V>0.35 eV) has been proposed. The creation of high barriers for carriers leads to their strong accumulation in the active region and increases the quantum emission efficiency of the spatially separated electrons and holes across the heteroboundary due to a tunnel-injection radiative recombination mechanism within the device. An extremely weak reduction of the electroluminescence (EL) intensity for the interface tunnelling-assisted emission band with increasing temperature from 77 to 300 K was observed. This coherent emission (λ=3.146 μm at 77 K) was totally polarised in the plane perpendicular to the p–n heterojunction plane, which means the laser emission was TM-polarised due to tunnelling-assisted light-hole–electron recombination across the interface.