Radiation-induced conduction in quantum-confined p +-n silicon junctions

Electron-beam diagnostics are used to study the radiation-induced conduction of supershallow p ⁺-n silicon junctions obtained by nonequilibrium boron diffusion. Current-voltage (I–V) characteristics of radiation-induced conduction of a both forward-and reverse-biased p ⁺-n junction are demonstrated for the first time, which has been made possible by the presence of self-organized transverse quantum wells inside a supershallow p ⁺ diffusion profile. The variation of the dark-current I–V characteristics with electron irradiation dose shows that formation of self-organized longitudinal quantum wells inside supershallow p ⁺ diffusion profiles favors an increase of the breakdown voltage in p ⁺-n silicon junctions. Fiz. Tverd. Tela (St. Petersburg) 41, 1871–1874 (October 1999)     

Electrical characterization and modeling of Au/MEH-PPV/porous n+-GaAs/n+-GaAs heterojunction in direct and alternating current mode

Assembled heterojunction was fabricated by spin-coating poly[2-methoxy-5-(2′-ethyl-hexyloxy)-1,4-phenylene-vinylene)] (MEH-PPV) thin layers on straight and porous n⁺-GaAs substrates. The current–voltage and capacitance–voltage studies have shown an abrupt junction behavior with current conduction governed by SCLC and thermionic modes. Andersons' rules were used to determine depletion width and balance bands discontinuities for both heterojunctions. Capacitance and conductance vs. frequency techniques were used to evaluate the density of interface states. Density values obtained from both techniques were in a good agreement.     

Some properties of CdS/p-Ge heterojunctions grown by chemical transport

Some physical properties of CdS/p-Ge heterojunctions made by chemical vapour deposition of single crystal CdS epitaxial layers on (111)p-type nearly degenerate Ge substrates are reported. the equilibrium energy band diagram is discussed in the light of junction capacitance measurements as a function of frequency and of the reverse bias. The presence of interface states in the CdS band gap, with a density maximum at 1.1 eV below the equilibrium Fermi level has been shown. A model for the acceptor nature of the electronic states of misfit dislocations in CdS is suggested. The temperature dependence of theI-V characteristics has been measured in the temperature range 77–300 K. Models for the current flow in both direct and reverse bias conditions are discussed, taking into account the tunneling-recombination or generation-tunneling mechanisms throúgh interface states.     

The influence of tunneling effects on the efficiency of heterojunction solar cells

A theoretical model is developed which presents the transport properties through the space charge region of ap ⁺ n heterojunction solar cell, whereby not only recombination through interface states but also tunneling through potential barriers is taken into account. It is investigated whether tunneling can give rise to optimum heterojunction structures which have better efficiencies that without tunneling. It is found that only if the strongly doped semiconductor has an optimum bandgap and the weakly doped semiconductor a larger bandgap, tunneling can make the structure optimum. In all other cases of optimum structures, tunneling deteriorates the efficiency. Work supported by the Energy R. D. programmes of the Commission of European Communities and the Belgian Ministry of Science.     

Tunneling current-voltage characteristics of Ti-silicide/p− Si/p+ Si Schottky diodes

The tunneling current-voltage characteristics of Ti-silicide/p^– Si/p⁺ Si Schottky diodes are analyzed to study the Ti/Si interface properties. By using an MBE-grown 7 nm p^– Si spacer layer, well-defined tunneling structures are obtained. The sharply peaked density of states in a Ga-impurity band is used as a tunneling probe. A state density gap 100 meV around the Fermi energy is observed for a rapidly (20s) annealed (T=550°C) reacted sample. The gap is interpreted by a Ti-rich interfacial silicide film of about 1 nm.     

The characteristics of high current amorphous silicon diodes

Amorphous siliconp−n junctions with various doping profiles have been prepared by the glow discharge technique and the effect of the barrier profile on electrical properties investigated. Current densities of up to 40 A cm⁻² with rectification ratios of 10⁴–10⁵ were obtained withn ⁺−ν−p ⁺ structures. The diode quality factor has also been investigated, both in the dark and under illumination.     

High-voltage fast diode with “soft” recovery

High-voltage fast silicon p ⁺ Nn ⁺ diodes used in almost all modern electrical energy converters must have a low residual voltage in the conducting state, but can simultaneously be rapidly switched to the off state with low commutation losses without producing a surge overvoltage. Such a combination of parameters is usually ensured by producing the profile concentration distribution for recombination centers in the N base with a peak of the p ⁺ N junctions. Such a distribution is produced by irradiating the p ⁺ Nn ⁺ diode in vacuum by protons or α particles on the side of the p ⁺ N junctions. We report on the results of testing of diodes in which profile distribution for the centers is obtained using a simpler and more productive method by electron bombardment in a certain energy range in air. It is shown using the specially designed devices with a blocked voltage up to 5 kV that all dynamic characteristics of the diodes correspond to the world standard, and the residual voltage in the conducting state for the working current density is approximately 30% lower.     

Conductance spectroscopy of resistive switching Pt/Nb:STO single crystal Schottky junctions in air and vacuum

We investigated the admittance spectra of resistive switching Pt/Nb-doped SrTiO₃ single-crystal junctions at different resistance states in air and vacuum. The analyses showed that the carrier lifetime at the traps was largely varied depending on the resistance state, indicating the surface potential modification. The ambient dependence suggested that the charges at the trap states were affected by the oxygen adsorption/desorption at the surface. The conductance spectroscopy method clearly revealed the importance of the interface trap states in the resistive switching behavior.     

Photoluminescence as a tool for the study of the electronic surface properties of gallium arsenide

Electronic surface parameters of GaAs have been determined from a qualitative and quantitative analysis of the relative photoluminescence intensity at 300 K. Characteristics of etched (100) surfaces ofn- andp-type liquid phase epitaxial GaAs have been found to be governed by negative surface charges. A density of charged surface states of about 10¹² cm⁻² and a band bending of 0.59 eV have been found forn-type material with an electron concentration of 1.1×10¹⁷ cm⁻³. Forp-type samples with hole densities ranging from 6×10¹⁵ to 4.3×10¹⁸ cm⁻³ the estimated density of negatively charged surface states was below 2×10¹¹ cm⁻², and the band bending was not more than a few kT.     

Electron traps in CdS single crystals obtained by admittance spectroscopy on the hetero- and Schottky junctions

The electron trap parameters in semiconducting CdS single crystals were obtained by admittance spectroscopy on its hetero- and Schottky junctions, and the trap depths obtained were 0.065, 0.09, 0.15 0.20, and 0.40 eV. The capture cross-section of the shallowest trap on the Cd-face of the crystals was about 10⁻¹⁹ cm², one order smaller than that of the bulk crystal. The resolving power of the employed method was about 50 meV to distinguish the two traps with different depths. The results of the computer simulation of this method suggested that the trap can be determined when the trap density is at least one order lower than the donor density. The calculated density of the each trap was 1×10¹⁵ cm⁻³ for the shallowest trap and 2×10¹⁶ cm⁻³ for the remaining traps, respectively.     

Computer studies on the space charge dependence of avalanche zone width and conversion efficiency,of single driftp +nn+ andn +pp+ indium phosphide impatts

The effect of mobile space charge on avalanche zone width and conversion efficiency of single drift region (SDR) indium phosphide impatts at 12 and 60 GHz has been investigated. The results show thatp ⁺nn⁺ InP diodes have a narrower avalanche zone and a higher conversion efficiency compared ton ⁺pp⁺ diodes for both the frequencies at normal operating current densities. The expansion of avalanche zone and efficiency degradation at high current levels are more pronounced inp ⁺nn⁺ at 12 GHz and inn ⁺pp⁺ at 60 GHz.     

The effect of bound states in microwave waveguides on electromagnetic wave propagation

The transmission of a TE microwave field with a frequency ω through Λ, T, and X waveguide junctions filled with a ferromagnetic is considered. These junctions are known to have bound states with below-cutoff frequencies. A probing microwave radiation with a frequency Ω applied to the scattering region generates magnetic oscillations with frequencies ω+nΩ (where n=0, ±1, ±2, ...), which resonantly combine with the bound waveguide states. This effect provides for a new method of studying bound waveguide states and efficiently controlling the transmission of microwave radiation.     

Analysis of integrated thyristor switching-off by a reverse gate pulse current

To increase the maximum power current density of an integrated n⁺p'Nn'p⁺-type thyristor during switching-off by a current pulse in the control circuit, the injection of electrons from the n⁺ emitter should be interrupted before the recovery of the collector p'N junction. This has been done using a rapidly increasing reverse gate current pulse with an amplitude equal to the amplitude of the power switched-off current. After the interruption of the emitter injection, the remaining current through the device is the current of holes extracted from the collector region via the gate electrode. Like in insulated gate bipolar transistors (IGBTs), the physical mechanism that limits the maximum density of the switch-off current is the dynamic avalanche breakdown, which is initiated by the holes extracted through the space charge region of the collector p'N junctions.     

ac admittance of CdZnS/p-GaAs heterojunctions

Admittance measurements have been performed to reveal trap levels within the space charge region of CdZnS/p-GaAs heterojunctions prepared by chemical vapour deposition in the close-spaced geometry. The presence, between GaAs and the CdZnS layer, of a transition region containing a high concentration of acceptor-like traps is hypothesized. Taking into account electric field effects, a ionization energy greater than 0.28 eV is estimated for the trap state.     

Shell-model calculation of51V using pairing-plus-surface-tensor-interaction

Employing⁴⁸Ca as the core, the structure of⁵¹V is studied in the framework of a conventional shell-model. A pairing-plus-surface-tensor-interaction is used as the effective two-body interaction. Besides all configurations arising from 1f _7/2 and 2p _3/2 single-particle orbits, configurations of the form wheren ₁+n ₂=3 (the number of extracore protons) andn ₂ = 1, 2 are also considered. Low-lying energy levels are calculated and a satisfactory agreement with the experimental values is obtained. Our calculated density of states is higher than that reported previously. We also present theB(E2) values for transitions between low-lying levels and the spectroscopic factors for the⁵⁰Ti (³He, d)⁵¹V reaction. The dependence of the interaction parameters on the mass number of the core nucleus is also studied.     

Pulse characteristics of Hg0.8Cd0.2Te n +-p junctions

The pulse characteristics of Hg_0.8Cd_0.2Te n ⁺-p junctions are investigated. It is shown that the shape of the voltage pulse appearing in a junction on passage of a forward (reverse) current is determined by the recombination (generation) of nonequilibrium electrons in the hole region. An increase in the current pulse causes the appearance of an electric field, which draws electrons into the interior of the base region, and leads to variation of their lifetime because of the complex structure of the n ⁺-p junction. Zh. Tekh. Fiz. 67, 130–133 (July 1997     

Trap centers in Au-implanted MOS structures

Trap centers in the Si-SiO₂ interface region of MOS structures doped by ion implantation of gold have been investigated using constant capacitance deep level transient spectroscopy (CC-DLTS). Gold doses of 10¹²–3 × 10¹³ cm^–2 were implanted into the back surface of the wafers and were then redistributed during a diffusion anneal for 30 min at 1100° or 900° C. Three Au-related trap levels have been observed in the interface region, which were attributed to the Au-donor (E _v +0.35 eV), the Au-acceptor (E _v +0.53 eV), and the Au-Fe complex (E _v +0.45 eV). The trap concentration profiles show that the Si-SiO₂ interface affects the Au concentration in a depth range of 1 m from the interface and that gettering of Au occurs at the interface. The interface state density is independent of the Au concentration at the interface even for concentrations of 10¹⁵ cm^–3.     

Analysis of the R0A product in n+-p Hg1−xCdxTe photodiodes

The influence of different junction current components (diffusion current for radiative and Auger 7 recombination mechanisms, tunneling and depletion layer currents) on the R₀A product of n⁺-p -Hg_1−xCd_xTe photodiodes is considered. The considerations are carried out for the 77–300 K temperature region and 1–15 μm cutoff wavelength. Optimum doping concentrations in the p-type region of n⁺-p abrupt junctions are determined, taking into account the influence of the tunneling current and of a fixed surface charge density of the junction passivation layer. Results of calculations are compared with experimental data reported by many authors. An attempt is made to explain the discrepancy between theoretical calculations and experimental data.     

Space-Like Submanifolds with Constant Scalar Curvature

Let M ⁿ be a space-like submanifold in a de Sitter space M _p ^n+p (c) with constant scalar curvature. This Letter gives intrinsic conditions for M ⁿ to be totally umbilical.     

Hydration-induced conformational changes in protonated 2,4-pentanedione in the gas phase

Starting with H⁺[CH₃C(O)CH₂C(O)CH₃] (denoted H⁺PD), the protonated diketone-water clusters H⁺PD(H₂O) _n (n = 1–3) have been characterized by density functional theory calculations in combination with vibrational predissociation spectroscopy to explore the conformational changes of a protonated bifunctional ion solvated by water in the gas phase. Theoretical calculations for H⁺PD revealed that the ion contains an intramolecular hydrogen bond (IHB), with two oxygen atoms bridged by the extra proton in an O—H⁺ … O form. Attachment of one water molecule to it readily ruptures this IHB, replacing the H⁺ by the H₃O⁺ moiety. Further replacement of the IHB by two water molecules occurs at n = 2 and the ?C(O)CH₂C(O)- chain is fully opened (or unfolded) after transfer of the extra proton to the water trimer at n = 3. To verify the computational findings, infrared spectroscopic measurements were performed using a vibrational predissociation ion trap spectrometer to identify cluster isomers from the signatures of hydrogen bonded and non-hydrogen bonded OH stretching spectra of H⁺PD(H₂O)_2,3 produced in a corona discharge supersonic expansion. Besides open form isomers, evidence for the formation of water-bridged structures has been found for H⁺PD(H₂O)₃ at an estimated temperature of 200 K. A detailed illustration of the unfolding steps as well as the energy profiles for the evolution of a two-water bridge isomer from the protonated H⁺PD monomer are analysed pictorially (including both stable intermediates and transition states) in the present investigation.