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.     

Discrete tunneling of holes in porous silicon

It is pointed out that in the partial oxidation of porous silicon (PS) formed on heavily doped crystals, the topology of the pores can result in the formation of an anisotropic material with strings of nanometersized silicon granules embedded in insulating silicon dioxide SiO₂. In this range of granule sizes the correlation effects in the tunneling of electrons (holes) are strong on account of their Coulomb interaction. This should be manifested as discrete electron and hole tunneling at temperatures comparable to room temperature. The room-temperature current-voltage characteristics of n ⁺-PSp ⁺-p ⁺ diode structures with a PS interlayer on p ⁺-Si, which exhibit current steps on the forward and reverse branches, are presented. The current steps are attributed to discrete hole tunneling along the silicon strings in SiO₂. Pis’ma Zh. éksp. Teor. Fiz. 67, No. 10, 794–797 (25 May 1998)     

Characteristics of the formation of radiation defects in silicon structures

The method of deep-level transient spectroscopy is used to investigate aspects of the formation of radiation defects in silicon p ⁺-n diffusion structures when bombarded by accelerated electrons. It is shown that for base thicknesses of the p ⁺-n structures in the range 0.2–0.6mm a substantial change in the concentration of the radiation defects formed in this way is observed, having a maximum at 0.25 mm. Below 0.2 mm and above 0.6 mm the concentration of radiation defects exhibits a weak dependence on base thickness. The observed effect is explained by variation of the relative concentrations of vacancies and interstitial silicon atoms in the base during formation of p ⁺-n pairs. Zh. Tekh. Fiz. 69, 121–123 (January 1999)     

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)     

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.     

Electron beam induced current investigation of planar photodiode structures on InSb crystals

Multielement planar photodiode structures produced on InSb crystals using Be⁺ ion implantation to form a p ⁺-n junction and anodic oxidation to protect the surface are studied in the Electron Beam Induced Current (EBIC) mode. It is found that the initial crystal doping level affects the EBIC distribution across the crystal surface outside the planar boundaries of the p ⁺-n junction. It is shown that the most perfect p ⁺-n junctions are formed on crystals with the highest resistivity when the lowest values of the implantation energy and dose are applied and pulse photon postimplantation annealing is used. The diffusion lengths in all the types of the structures in study are estimated. It is found that the level of anodic oxide charging by the electron beam depends on the electrolyte composition used in the anodic treatment.     

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.     

Positron annihilation from excited states of [X-e+] systems

The relative probabilities for the radiative de-excitation 2p₊ → ls₊ versus 2γ-annihilation for the hdot; ns²np⁶2p₊, ²P state of the [X^-e⁺] system with X = F, Cl, Br, and I are presented. It is shown that a positron captured into a 2p₊ orbital undergoes annihilation with electrons of the system instead of radiative transition to the ground state of the [X^-e⁺] system.     

幻数尺寸Li-n-1,Lin,Li+ n+1(n=20,40)团簇的几何结构、电子与光学性质的第一性原理研究

基于密度泛函理论,采用第一性原理分子动力学模拟退火方法,对Li^-_n-1,Li_n,Li⁺_n+1 (n=20,40)的最低能量结构进行了全局搜索. 发现锂团簇的生长模式是以单个或多个嵌套的正多面体为核心,其余原子以五角锥为基本单元围绕核心生长. 基于最低能量结构的第一性原理电子结构计算得到锂团簇的分子轨道能级分布与无结构凝胶模型给出的电子壳层完全一致. 在总电 关键词： 团簇 电子结构 极化率 光吸收     

Equivalent circuit of silicon diodes subjected to high-fluence electron irradiation

Silicon diodes with a p ⁺-n junction made in a 48-μm-thick phosphorus-doped silicon epilayer (resistivity ρ = 30 Ω cm) grown on antimony-doped Si(111) wafers (ρ = 0.01 Ω cm) are studied. The diodes are irradiated by high-energy (3.5 MeV) electrons with fluences from 5 × 10¹⁵ to 2 × 10¹⁶ cm⁻². It is shown that the conventional equivalent circuit of the diode that consists of a parallel RC network and a series-connected resistor inadequately describes the dependence of the dielectric loss tanδ on variable current frequency f in the range 1 × 10²–3 × 10⁷ Hz. Another equivalent circuit is suggested that includes not only the capacitance and resistance of the n-base (the latter increases because radiation-induced defects are compensated for by shallow donors) but also the f dependence of the capacitance of the space-charge region, which is due to retarded charge exchange between deep-level radiation-induced defects.     

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.     

Microwave photoconductivity relaxation time in a bifacial silicon solar cell base in the vicinity of a p-n junction

Microwave photoconductivity relaxation time depending on light intensity is studied in n ⁺-p-p ⁺ silicon solar cells. The results from experiments performed under conditions of open-circuit and short-circuit currents are in agreement with the simulated data. The relaxation times of microwave photoconductivity are found for a part of the base region adjacent to the n ⁺-p junction.     

Spin-dependent recombination in a silicon p-n junction

Like the spin-denendent photoconductivity in pure silicon, the current of a silicon n⁺-p junction is found to be affected by electron spin resonance. The experiment shows that the same centers are responsible for the recombination in the diode and in pure silicon, that only the recombination in the space-charge region of the junction is spin-dependent and that the effect in this region is very large. A tentative model for the electron-hole recombination in silicon is proposed.     

Powerful diode nanosecond current opening switch made of <Emphasis Type="Italic">p</Emphasis>-silicon (<Emphasis Type="Italic">p</Emphasis>-SOS)

The nanosecond semiconductor diode-based opening switch (SOS-diode) capable of switching currents with densities up to several tens of kiloamperes per cubic centimeter represents a p⁺p’Nn⁺ silicon structure fabricated by the deep simultaneous diffusion doping (to about 200 μm) of n-Si by Al and B from one side and P from the other. In the SOS mode, first a short pulse of forward current passes through the diode and then a fast-growing pulse of reverse voltage is applied. A resulting pulse of reverse current carries away injected holes and thereby forms a plasma front in the p’ layer, which moves toward the p’N junction. When the hole concentration in the flow exceeds the dopant concentration in the p’ layer, a space charge region arises in this layer, the resistivity of the diode increases sharply, and the current switches to a load connected parallel to the diode. Early results concerning an alternative configuration of the SOS diode are presented. Here, the diode was made by the rapid simultaneous diffusion of B and P from the opposite sides of a p-Si wafer to a depth of 60-80 μm. If a short pulse of forward current is passed through such a p⁺pn⁺ structure and a pulse of reverse voltage is then applied, a plasma front arising in the p⁺ region moves toward the p⁺p interface through the heavily doped (i.e., low-resistivity) p⁺ region. Having crossed this interface, the front passes into a low-doped region, where the hole concentration in the flow becomes much higher than the dopant concentration and a space charge region causing the current to pass to the load forms at once. It is shown experimentally that, all other things being the same, the time of current breaking in the p-SOS-diode is roughly twice as short as in the conventional n-SOS-diode, switched currents are considerably lower, and the fabrication technique of p-SOS-diodes is much simpler. Ways of optimizing the design of the semiconductor structure of the p-SOS-diode to further raise the speed are outlined.     

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     

The Numerical Simulation of the Nanosecond Switching of a <Emphasis Type="Italic">p</Emphasis>-SOS Diode

Abrupt high-density reverse current interruption has been numerically simulated for switching from forward to reverse bias in a silicon p⁺P₀n⁺ structure (p-SOS diode). It has been shown that the current interruption in this structure occurs as a result of the formation of two dynamic domains of a strong electric field in regions in which the free carrier concentration substantially exceeds the concentration of the doping impurity. The first domain is formed in the n⁺ region at the n⁺P⁰ junction, while the second domain is formed in the P⁰ region at the interface with the p⁺ layer. The second domain expands much faster, and this domain mainly determines the current interruption rate. Good agreement is achieved between the simulation results and the experimental data when the actual electric circuit determining the electron–hole plasma pumping in and out is accurately taken into account.     

Effect of structure doping profile on the current switching-off process in power semiconductor opening switches

Using a physicomathematical model, the process of current breaking in power semiconductor opening switches was investigated in p ⁺-p-n-n ⁺ structures with different doping profiles. The model takes account of the actual doping profile of a structure, diffusion and drift of current carriers in a strong electric field, recombination via deep impurities and Auger recombination, and impact ionization in a dense plasma. The calculation of the electrical circuit of an opening switch is based on solution of Kirchhoff’s equations. It has been shown that in the nanosecond regime of breaking superhigh current densities with densities of the interrupted currents from a few to tens of kA/cm², the dominant factor in the current breaking process is the width of the p-region in the initial doping profile of a structure. An increase in the p-region width from 100 to 200 μm makes the velocity of the excess plasma front propagating in the p-region in the reverse pumping stage higher by a factor of 5–7. Higher propagation velocity of the plasma front makes the current breaking process more intensive, which is manifested in the shorter current breaking time and higher overvoltage across the opening switch.     

Phase interactions in TiN<Subscript>x</Subscript>(TiB<Subscript>x</Subscript>)-<Emphasis Type="Italic">n</Emphasis>-Si-<Emphasis Type="Italic">n</Emphasis><Superscript>+</Superscript>-Si contacts and their thermal degradation due to rapid thermal annealing

The temperature stability of TiN_x(TiB_x)-n-Si-n ⁺-Si, Au-TiN_x(TiB_x)-n-Si-n ⁺-Si, and Au-Ti(Mo)-TiN_x(TiB_x)-n-Si-n ⁺-Si Schottky-barrier contacts subjected to rapid thermal annealing in hydrogen at temperatures T=400, 600, and 800°C is studied. It is shown that structural and morphological transformations and the related degradation of electrophysical characteristics in interstitial alloys (titanium nitrides and borides) start at 600°C. Reasons for the degradation of the barrier properties of titanium borides and nitrides are discussed.     

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.     

Potential of chemical rounding for the performance enhancement of pyramid textured p-type emitters and bifacial n-PERT Si cells

We have investigated the effects of chemical rounding (CR) on the surface passivation and/or antireflection performance of AlO_x- and AlO_x/SiN_x:H stack-passivated pyramid textured p⁺-emitters with two different boron doping concentrations, and on the performance of bifacial n-PERT Si solar cells with a front pyramid textured p⁺-emitter. From experimental results, we found that chemical rounding markedly enhances the passivation performance of AlO_x layers on pyramid textured p⁺-emitters, and the level of performance enhancement strongly depends on boron doping concentration. Meanwhile, chemical rounding increases solar-weighted reflectance (R_SW) from ∼2.5 to ∼3.7% for the AlO_x/SiN_x:H stack-passivated pyramid textured p⁺-emitters after 200-sec chemical rounding. Consequently, compared to non-rounded bifacial n-PERT Si cells, the short circuit current density Jsc of 200-sec-rounded bifacial n-PERT Si cells with ∼60 and ∼100 Ω/sq p⁺-emitters is reduced by 0.8 and 0.6 mA/cm², respectively under front p⁺-emitter side illumination. However, the loss in the short circuit current density Jsc is fully offset by the increased fill factor FF by 0.8 and 1.5% for the 200-sec-rounded cells with ∼60 and ∼100 Ω/sq p⁺-emitters, respectively. In particular, the cell efficiency of the 200-sec-rounded cells with a ∼100 Ω/sq p⁺-emitter is enhanced as a result, compared to that of the non-rounded cells. Based on our results, it could be expected that the cell efficiency of bifacial n-PERT Si cells would be improved without additional complicated and costly processes if chemical rounding and boron doping processes can be properly optimized.