Investigation of the thermal stability of picosecond gallium arsenide dynistor switches

The operation of GaAs n⁺-p-i-n ⁰-p ⁺ dynistor structures has been demonstrated experimentally under conditions of reversible avalanche breakdown at temperatures up to 200 °C with switching times remaining under 140 ps. A numerical simulation refined the influence of various parameters of the semiconductor on the temperature dependence of the switching characteristics. Pis’ma Zh. Tekh. Fiz. 24, 73–78 (August 12, 1998)     

Effect of electron irradiation attenuated by aluminum screens on the electrical parameters of p-n silicon structures

We have studied the influence of irradiation by 6-MeV electrons via flat aluminum screens with thicknesses d = 2−14 mm (mass thicknesses, 0.5–3.8 g/cm²) on the properties of p ⁺-n-n ⁺ silicon structures, including the nonequilibrium charge carrier lifetime (τ), reverse current (I _R), and forward current-voltage (I-U) characteristics. In the case of a screen with d = 14 mm (3.8 g/cm²), the irradiated structures exhibit significantly smaller changes in I _R values and I-U curves compared to those for d = 2–12 mm, whereas a decrease in τ (from 20 to 1.5 μs) is the same.     

Critical importance of the single-level approximation to account for the highly nonmonotonic dependences of carrier lifetimes on recombination impurity concentration

This paper is a continuation of an analysis regarding an increase in the lifetimes of nonequilibrium electrons π_n and holes πp by several orders of magnitude, observed with increasing concentration of recombination centers. It is shown that a substantial increase in πn and πp may also occur for three charge states of the recombination impurities N, and the curves πn=f(N) and π n=f(N) may each have two minima and maxima. Pis’ma Zh. Tekh. Fiz. 23, 39–45 (April 12, 1997)     

Determination of the uniformity of the carrier lifetime in a material from the profile of the amplitude spectrum of an ion detector

An analysis is made of charge transport in the neutral base of a p ⁺-n structure as a result of its diffusion to the boundary of the p-n junction under conditions where nonequilibrium carriers are generated by single α-particles. It is assumed that nonuniformity of the carrier lifetime (τ), described by a Gaussian distribution, exists over the area of the structure. The profile of the transported charge spectrum is calculated for these conditions and its correlation with the measure of nonuniformity τ is obtained. Since the tracks of the diffusing α-particles occupy an extremely small volume, recording them is equivalent to local probing of the material for τ. It is suggested that the calculated function should be used as a calibration function to determine the spread of τ values in materials. The method is tested on Si for a surface-barrier structure by recording 8.78 MeV π-particles. Pis’ma Zh. Tekh. Fiz. 24, 44–50 (March 12, 1998)     

Investigation of the process of voltage distribution over elements of a high-power semiconductor current interrupter

The process of voltage distribution over serially connected elements of a high-power semiconductor current interrupter in the stage of current breakage is studied within the framework of a previously developed physicomathematical model. It is established that a mechanism is operative that provides for the voltage drop leveling between unit structures of the p ⁺-p-n-n ⁺ type with various depths X _p of the p-n junctions. The mechanism is related to the fact that the formation of a strong field region on the stage of current breakage in the unit structures with larger X _p begins later, but the expansion of this region proceeds faster than the same processes in the units with smaller X _p .     

Subnanosecond avalanche switching in high-voltage silicon diodes with abrupt and graded p-n junctions

The phenomenon of delayed avalanche breakdown in high-voltage silicon diodes has been studied for the first time using an experimental setup with specially designed resistive coupler as a part of a high-quality matched measuring tract. Three types of diode structures with identical geometric parameters and close stationary breakdown voltages within 1.1–1.3 kV have been studied, including p ⁺-n-n ⁺ structures with abrupt p-n junctions and two different p ⁺-p-n-n ⁺ structures with graded p-n junctions. Upon switching of all structures, a voltage step with an amplitude above 1 kV and a rise time of ～100 ps at a breakdown voltage of about 2 kV is formed in the load. However, switching to a state with low (～150 V) residual voltage has been observed only in the structures with an abrupt p-n junction, while the voltage in structures with graded junctions only decreased to a level of ～1 kV, which is close to the stationary breakdown voltage.     

Direct bonding of silicon wafers with a diffusion layer

The possibility of solid-phase direct bonding of silicon wafers having p ⁺-or n ⁺-type diffusion layers with a high surface dopant concentration has been demonstrated for the first time. Pis’ma Zh. Tekh. Fiz. 24, 1–5 (March 26, 1998)     

Features of changes in electrical parameters of silicon p-n structures upon high-temperature electron irradiation

The effect of the temperature mode of 4-MeV electron irradiation on the change in the basic electrophysical characteristics of silicon diffused p ⁺-n-n ⁺ structures has been studied. It has been shown that the temperature of the crystal and integrated intensity during irradiation have a significant effect on the parameters of formation of radiation defects and the pattern of their distribution in different regions of silicon p ⁺-n-n ⁺ structures.     

Behavior of epitaxial GaAs layers as α particle detectors

The properties of epitaxial GaAs-based p ⁺-n structures used as light-ion (α particle) were studied. A comparison is made with the latest published data on the possibilities of present-day semi-insulating GaAs (SI-GaAs). It is noted that the content of impurities and structural defects forming deep levels in the band gap of the material is two orders of magnitude lower in epitaxial layers. The deep levels determine the conditions of transport of nonequilibrium carriers in the detector, allowing for trapping of the carriers, and they also determine the electric-field profile. The charge-carrier lifetime was found to be ≥ 200 ns. This is two orders of magnitude longer than the values for SI-GaAs, in complete agreement with the lower content of deep centers. It is shown how deep centers influence the field profile, forming a quite large region of low field values. Pis’ma Zh. Tekh. Fiz. 24, 8–15 (April 12, 1998)     

Photovoltaic X-ray detectors based on epitaxial GaAs structures

A new type of the photovoltaic X-ray detector based on epitaxial p ⁺-n-n′-n ⁺ GaAs structures is proposed, which provides for a high efficiency of charge carrier collection in a nonbiased operation regime at room temperature. The GaAs structures were grown by vapor phase epitaxy on heavily doped n ⁺-GaAs substrates. The X-ray sensitivity range covers the effective energies from 8 to 120 keV. The maximum output signal in the short-circuit regime is 30 μA min/(Gy cm²). The detector response to γ-radiation from a ¹³⁷Cs[660 keV] radioactive isotope was measured.     

Ion beam deposition of photoactive nanolayers for silicon solar cells

The ion beam deposition of photoactive silicon nanolayers through the bombardment of a single-crystal silicon target with an Ar⁺ ion beam has been analyzed using computer simulation. The model thus derived is consistent with experimental data on the growth of silicon nanolayers on 100-mm-diameter c-Si(p) substrates. The process conditions have been optimized experimentally: pressure, 10⁻⁴ Pa; substrate temperature, 550 ± 50°C; target-substrate distance, 240 ± 5 mm; target-beam angle, 45° ± 2°; accelerating voltage, 450–600 V. Under these conditions, the radial asymmetry of 300-nm-thick c-Si(n) layers is within 10 nm, which reduces the efficiency of c-Si(n ⁺)/c-Si(p)/c-Si(p ⁺) solar cells by no more than 0.3%.     

Nonequilibrium processes in Hg1−x CdxTe n +−p junctions in a magnetic field

The results of measurements of the relaxation and current-voltage characteristics of Hg_{1− x} Cd_xTen ⁺−p junctions in a magnetic field are presented. It is shown that the lifetime of the nonequilibrium electrons in the p-type region undergoes an increase in a magnetic field, which can be associated with the heterogeneous distribution of defects from the junction boundary. The current-voltage characteristics in a magnetic field exhibit suppression of the diffusion component of the current and an increase in the contribution of the generation-recombination channel, as well as the appearance of shunting channels, which are associated with the influence of the surface. Pis’ma Zh. Tekh. Fiz. 23, 88–94 (October 26, 1997)     

<Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">n</Emphasis> junctions in ZnO implanted with group V ions

n-Type ZnO〈Ga〉 films were implanted with 150-keV N⁺ (As⁺) ions to a dose of 7 × 10¹⁵ cm⁻² and then annealed in atomic oxygen at different temperatures. p-Type conductivity was obtained at annealing temperatures in the range 770–870 K. The parameters of the p-type layers were determined by photoluminescence spectroscopy, secondary ion mass spectrometry, and Hall effect measurements. According to the Hall data, the p-type layers had a resistivity of ∼30 Ω cm, carrier mobility of ∼2 cm²/(V s), and carrier concentration of ∼10¹⁸ cm⁻³. The electroluminescence spectra of the p-n junctions produced by ion implantation showed a band at 440 nm, due to recombination via donor-acceptor pairs.     

Point-Contact Spectroscopy in Mn-Doped MgB2 Single Crystals: Effects of Magnetic Impurities in a Two-Band Superconductor

We performed point-contact spectroscopy (PCS) measurements in Mg_1−x Mn _x B₂ single crystals, with x≤0.015 and bulk T _c down to 13.3 K. The gaps Δ _σ and Δ _π were obtained by fitting the conductance curves of the point contacts with the two-band Blonder–Tinkham–Klapwijk (BTK) model. Both Δ _σ and Δ _π decrease with the critical temperature of the junctions T _c ^A , but remain clearly distinct down to the lowest critical temperature (T _c ^A ≅9 K). Once analyzed within the Eliashberg theory, the gap trends as a function of T _c ^A can be explained by a doping-induced increase in the pair-breaking scattering within the σ band, with smaller contributions from the π-π or the σ-π channels.     

Test beam results of Current Injected Detectors (CID) irradiated up to 5×10 1 MeV neq/cm

Two full size strip detectors were investigated in this study: one with p⁺ strips (p⁺/n⁻/n⁺) and another with n⁺ strips (n⁺/p⁻/p⁺). Both detectors, are made of magnetic Czochralski silicon (MCz-Si) and irradiated to S-LHC fluencies, were tested with 225 GeV muon beam in the CERN H2 area. The Current Injected Detector (CID) sensors were operated in a cooling box capable of providing a −53 °C temperature. Results indicate a relative charge collection efficiency (CCE) at 5×10¹⁵ n_eq/cm² above 30% in irradiated p⁺/n⁻/n⁺ CID detector at 600 V bias voltage. The signal to noise ratio of this CID module was about eight and a forward current of 30 μA was needed for detector biasing. In standard reverse bias, the same detector could not provide a sufficiently large signal for particle tracking purposes. A p-type (n⁺/p⁻/p⁺) sensor was irradiated to a fluence of 2×10¹⁵ n_eq/cm² and measured under the same test beam conditions. According to the theory of CIDs developed by the CERN RD39 Collaboration, this detector module could be biased up to only 230 V due to the low irradiation fluence. The CCE at 230 V was 35% in CID operation and 20% when reverse biased.     

New p-ary sequence family with low correlation and large linear span

In this paper, for an odd prime p and positive integers n, m, and e such that n = me, a new family S{\mathcal{S}} of p-ary sequences of period p ⁿ − 1 with low correlation and large linear span is constructed. It is shown that S{\mathcal{S}} has maximum correlation 1+p^[(n+2e)/2]{1+p^{n+2e\over 2}}, family size p ⁿ , and maximal linear span [((m+3)n)/2]{{(m+3)n\over 2}}. When m is even, the proposed family S{\mathcal{S}} contains Tang, Udaya, and Fan’s construction as a subset. Furthermore, when n is even and e=1, S{e=1, \mathcal{S}} has the same correlation and family size, but larger linear span compared with the construction by Seo, Kim, No, and Shin.     

High Dynamic Range SQUID Readout for Frequency-Domain Multiplexers

A 16-SQUID array has been designed and fabricated, which shows 0.12 μΦ ₀ Hz^−1/2 flux noise at 4.2 K. The readout amplifier based on a cryogenic silicon-germanium bipolar transistor employs short-delay negative flux feedback and reaches 7 MHz bandwith for a 1 Φ _0p-p signal. The −1 dB compression is reached approximately at 4.2 Φ _0p-p amplitude when the signal frequency is 1 MHz. In the feedback mode the flux noise is anomalously increased to 0.35 μΦ ₀ Hz^−1/2.      

On the accuracy of quantitative measurements of the local surface potential

The region of the main potential drop in a sharp p ⁺−n ⁺ junction in GaAs has been studied using the conventional and gradient scanning Kelvin probe force microscopy (KPFM) techniques. It is shown that the gradient method offers advantages for quantitative measurements. An algorithm for the program implementing the gradient KPFM method on standard commercial atomic-force microscopes is proposed. It is established that the layer of adsorbed water contributes to the measured width of the main potential drop region.