Electrical properties of p +/n + In0.53Ga0.47As tunnel diodes grown by liquid phase epitaxy

p ⁺/n ⁺ In_0.53Ga_0.47As tunnel diodes were prepared by liquid phase epitaxy and their electrical properties were characterized. These devices exhibit large forward conductances (2.59×10^{3 –1} cm^–2), high peak current densities (793 A/cm²) and large peak to valley current ratios (16.2). These devices offer great promise as intercell ohmic contacts (IOCs) for InP-based, onolithic multijunction solar cells.     

Polycrystalline silicon S-diode fabricated using phosphorus thermal diffusion along grain boundaries

Electrical activity of grain boundaries (GB) in polycrystalline silicon films can stand duty as an additional factor of action on its properties. At present paper it has been studied polycrystalline silicon epitaxial films grown by CVD-method at low-resistivity n ⁺-type poly-Si substrates. A p ⁺-n junction of 0,5 m deep was formed by ion implantation of boron. The effect of thermal annealing (TA) on I-V characteristics of the p ⁺-n-n ⁺ structures was studied. It was founded that the region with negative resistivity is appeared in I-V characteristic after TA in vacuum at 800°C for 1 hour. Investigations by means of C-V and temperature characteristics of samples show that the S-image of the I-V characteristics is caused by phosphorus diffusion along GB that give rise to conduction of the charge carriers along GB. For the first time it was shown the opportunity of the creation of low-cost poly-Si S-diode by TA.     

Electrical properties of p +/n + InGaAsP tunnel diodes with a bandgap of 0.95 eV grown by liquid phase epitaxy

p ⁺/n ⁺ InGaAsP tunnel diodes with a bandgap of 0.95 eV were fabricated by liquid phase epitaxy and their electrical properties were characterized. Forward conductances of 500 ^–1 cm^–2, peak current densities of 28.5 A/cm² and peak to valley current ratios of 14.3 were obtained at room temperature. These devices were incorporated successfully as Intercell Ohmic Connections (IOCs) for an InP-based, two-terminal monolithic multijunction tandem solar cell.     

Evolution of the Electroluminescence Spectra and the Acoustic Emission of the Epitaxial Structures of GaAsP

The dependence of the spectral position of the electroluminescence bands of epitaxial light-emitting diode n ⁺–n–p structures (GaAs_0.15P_0.85) on the density of a direct heterojunction current at different successive instants of time — before an acoustic emission and after it — has been revealed. The shifts of the electroluminescence bands accompanied by acoustic emission can be divided into three types according to the density of the current: (1) short-term shifts due to relaxation of the defect structure of a sample — at relatively low currents, (2) the magnitude of the reverse shift being determined by the current density — at large currents, and (3) formation of an IR band (1.5–1.1 eV) with irreversible degradation changing in the red (1.75 eV) and green (2.19 eV) bands of the electroluminescence spectrum — at ultrahigh currents (100–200 A/cm²).     

Semiconducting structures and devices based on gallium arsenide with deep centers

We have examined the characteristics of nontraditional gallium arsenide -v-n type device structures, in which p-n junctions are formed by doping the semiconductor with deep centers. The properties of -v-n structures are established by processes of charge trapping at deep centers under the effect of an external bias or exposure to a wide spectral range of electromagnetic radiation. The nature of formation of S-type negative differential resistance for a reverse biased -v-n structure and the mechanism of high speed switching (with a switching time of (0.4–5)×10^–10 sec) were analyzed. The results of an investigation of the effects of optical radiation, x-rays, -radiation and high energy charged particles on the structures are discussed and the characteristics of new devices constructed using -v-n structures are presented. These devices include high speed avalanche S-diodes and triodes, wide spectral band photodiodes (=0.2–10 µm) and detectors for x-rays, -radiation, and relativistic electrons.V. D. Kuznetsov Siberian Physical-Technical Institute, State University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 9, pp. 33–44, September, 1992.     

γ-decay of the particle-hole states with the highest spins in208Pb

²⁰⁸Pb has been excited with inelastic heavy ion scattering of 350 MeV⁶⁴Ni and 420 MeV⁸²Se on a thick²⁰⁸Pb target. With - coincidence measurements 2 new decays of the 10⁺ isomer, namely a 34.5 keVE2-transition to 8 ₂ ⁺ and a 857.7 keVE3 transition to 7^– have been found and the wavefunctions of the participating levels deduced. An observed gamma cascade of 295.3, 348.0, 865.4 and 340.2 keV on top of the 10⁺ isomer is assigned to the particle-hole states with the highest spins 14^– 6744.1 keV13^– 6448.9 keV12⁺ 6100.9 keV11⁺ 5235.6 keV10⁺ 4895.4 keV.This work has been supported in part through the agreement on scientific cooperation between Poland and Germany.     

Characteristics of a photovoltaic X-ray detector based on a GaAs epitaxial structure

The characteristics of a photovoltaic X-ray detector based on the GaAs p ⁺-n-n′-n ⁺ epitaxial structure grown using gas-phase epitaxy are studied. Typical current-voltage and capacitance-voltage characteristics of the epitaxial structures are analyzed together with the built-in electric field profile in the n-GaAs depleted region. The efficiency of charge accumulation in the photovoltaic detector is measured for zero bias and for a bias voltage of 17 V. It is shown that the GaAs-based photovoltaic X-ray detector can operate with zero bias voltage at room temperature. The sensitivity of the detector is measured as a function of the effective energy of X-rays and the angle of incidence of X-ray photons.     

A Note on Universality of the Distribution of the Largest Eigenvalues in Certain Sample Covariance Matrices

Recently Johansson and Johnstone proved that the distribution of the (properly rescaled) largest principal component of the complex (real) Wishart matrix X*X(X ^t X) converges to the Tracy–Widom law as n,p (the dimensions of X) tend to in some ratio n/p>0. We extend these results in two directions. First of all, we prove that the joint distribution of the first, second, third, etc. eigenvalues of a Wishart matrix converges (after a proper rescaling) to the Tracy–Widom distribution. Second of all, we explain how the combinatorial machinery developed for Wigner random matrices in refs. 27, 38, and 39 allows to extend the results by Johansson and Johnstone to the case of X with non-Gaussian entries, provided n–p=O(p ^1/3). We also prove that _max(n ^1/2+p ^1/2)²+O(p ^1/2 log(p)) (a.e.) for general >0.     

Numerically stable solution of coupled channel equations: The local reflection matrix

The second order linear Schrödinger equation is transformed to a first order nonlinear differential equation for a quantityp=(iq ^–1 –)/(iq ^–1 +). In a coupled channel problem all quantities occurring in this equation includingq (the WKB wave number) are matrices andp may be calledlocal reflection matrix. This quantity is closely related to the logarithmic derivative of the Schrödinger function but has no singularities in the classically allowed region. In the asymptotic region where the potential is constant the local reflection matrix approaches the physical reflection matrix. In a pure reflection problem (with an infinite potential on one side) this is the fullS-matrix, in a transmission problem (with an activation barrier of finite height) unitarity of theS-matrix can be used to determine most quantities of physical interest fromp. While standard logarithmic derivative methods can become instable for transmission problems the solution with the local reflection matrix is completely stable both for reflection and transmission problem.     

Computer simulation of the small-signal admittance and negative resistance of double avalanche region IMPATT diodes

A generalized small-signal computer simulation of double avalanche region (DAR) n ⁺-p-v-n-p ⁺ Si and InP IMPATT diodes has been carried out for different frequencies and current densities taking both drift and diffusion of charge carriers into account. The simulation results show that both symmetrically and asymmetrically doped devices based on Si and InP exhibit discrete negative conductance frequency bands separated by positive conductance frequency bands. The magnitudes of both negative conductance and negative resistance of InP devices are larger than those of Si devices in case of symmetrical and asymmetrical diodes. Further, the negative resistance profiles in the depletion layer of these diodes exhibit a single peak in the middle of the drift layer in contrast to double peaks in double drift region diodes.     

CMOS 1/f noise: n-channel versus p-channel

This note reports on the noise of CMOS devices. It is shown experimentally that a weak boron threshold implant (10¹² cm^–3) can influence the 1/f noise levels. For wafers with threshold adjustment the p-channel noise decreases whilst the n-channel noise increases. The changes in the n/p noise ratio with/without threshold implantation are predicted using a simple model in conjunction with carrier profile simulations.     

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).     

A possible way to promote antihydrogen formation via metastable antiprotonic helium atoms

A new way to promote antihydrogen formation via the recently discovered long-lived metastable states of antiprotonic helium atoms is discussed. Recombination processes such ase ^– ¯pHe⁺⁺ +e ⁺ e ^– e ⁺ ¯p + He⁰ are possible in this respect.Dedicated to Prof. Dr. P. Kienle on the occasion of his 60th birthday     

Threshold Characteristics of Infrared Photodetectors Based on GeSi/Si Heterojunctions

The possibilities of using emission photodetectors based on the p ⁺–GeSi/p–Si heterojunctions in the spectral range 8–12 m are considered. The dependences of spectral detectivity and noise-equivalent temperature difference on the temperature and detector parameters are analyzed.     

Electrooptical Kerr constant and third-order susceptibility measurements in nematic liquid crystals and their mixtures

We report for the first time the determination of the real part of the third order nonlinear susceptibilities ⁽³⁾ (–, , 0, 0) in the isotropic phase of two nematic liquid crystalsp-(ethoxybenzylidine)-p-butylaniline (EBBA) andp-(methoxybenzylidene)-p-butylaniline (MBBA) from electrooptic Kerr effect experiments. The highest value of ⁽³⁾ observed near nematic-to-isotropic transition temperature, at 632.8 nm is found to be 1.067×10^–20 m²V^–2 for EBBA and 6.602×10^–20 m²V^–2 for MBBA.     

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.     

Degenerate four-wave-mixing spectroscopy in NaH

We performed DFWM spectroscopy on X ^–1+–A ¹⁺ transitions in NaH produced in an indirect photochemical reaction between Na(3p) and H₂ and detected v=1, 2 and 3 ground state vibrational levels of NaH molecules, whereas with resonance enhanced CARS, we observed v=0 levels only. This different sensitivity can be explained by considering the Franck-Condon-factors and the relevant damping coefficients for the corresponding transitions in the NaH molecule. Time resolved DFWM spectroscopy showed that NaH(v=1) molecules effectively live much longer than Na(3p) atoms which merely follow the laser excitation pulse.     

Instabilities of an electron cloud in a Penning trap

We have measured the storage instabilities of electrons in a Penning trap at low magnetic fields. These measurements are carried out as a function of the trapping voltage, for different magnetic fields. It is seen that these instabilities occur at the same positions when the trapping voltage is expressed as a percentage of the maximum voltage, given by the stability limit. The characteristic frequencies at which these instabilities occur, obey a relation that is given by n _zω _z + n ₊ω ₊ + n _-ω _- = 0, where ω _z, ω ₊ and ω _- are the axial, perturbed cyclotron and the magnetron frequencies of the trapped electrons respectively, and the n's are integers. The reason for these instabilities are attributed to higher order static perturbations in the trapping potential. Received 5 August 2002 / Received in final form 14 October 2002 Published online 17 December 2002 RID="a" ID="a"Present address: Dept. of Physics, Rampurhat College, Rampurhat, Birbhum, West Bengal, India. RID="b" ID="b"e-mail: werth@mail.uni-mainz.de     

Current transport in Pd2Si/n-Si(100) Schottky barrier diodes at low temperatures

The forward current-voltage (I–V) characteristics of Pd₂Si/n-Si(100) Schottky barrier diodes are shown to follow the Thermionic Emission-Diffusion (TED) mechanism in the temperature range of 52-295 K. The evaluation of the experimentalI–V data reveals a decrease of the zero-bias barrier height ( _b0) and an increase of the ideality factor () with decreasing temperature. Further, the changes in _b0 and become quite significant below 148 K. It is demonstrated that the findings cannot be explained on the basis of tunneling, generation-recombination and/or image force lowering. Also, the concepts of flat band barrier height and T ₀-effect fail to account for the temperature dependence of the barrier parameters. The 1n(I _s /T ²) vs 1/T plot exhibits nonlinearity below 185 K with the linear portion corresponding to an activat ion energy of 0.64 eV, a value smaller than the zero-bias barrier height energy (0.735 eV) of Pd₂Si/n-Si Schottky diodes. Similarly, the value of the effective Richardson constant A** turns out to be 1.17 × 10⁴ A m^–2 K^–2 against the theoretical value of 1.12 × 10⁶ A m^–2 K^–2. Finally, it is demonstrated that the observed trends result due to barrier height inhomogeneities prevailing at the interface which, in turn, cause extra current such that theI–V characteristics continue to remain consistent with the TED process even at low temperatures. The inhomogeneities are believed to have a Gaussian distribution with a mean barrier height of 0.80 V and a standard deviation of 0.05 V at zero-bias. Also, the effect of bias is shown to homogenize barrier heights at a slightly higher mean value.     

Hot carrier effects in double injection phenomena

Carrier heating is shown to be responsible for unusualI(V) characteristics observed in small-sizep ⁺ nn ⁺ silicon on sapphire (SOS) devices. The classical quadratic law of the semiconductor regime becomes linear for high fields. The influence of dimensions and doping is experimentally checked and a model, based on the regional approximation method, is proposed. The key role is assumed by the hot-carrier region, growing from the cathode, where the electron and hole mobilities are field dependent: µ~E^–. A full agreement with the experiment in SOS is found for=0.5. The operating of hot carrierp ⁺ nn ⁺ devices can be described concretely with usual formalism by using the concept of effective carrier mobilities, which depend on the applied voltage.