Dynamics of electron-hole plasma in semiconductor opening switches for ultradense currents

A physicomathematical model for calculating the dynamics of the electron-hole plasma in semiconductor opening switches for ultradense currents is developed. The model takes account of the real doping profile of a semiconductor p ⁺-p-n-n ⁺ structure and the following elementary processes in the electron-hole plasma: current-carrier diffusion and drift in high electric fields, recombination on deep impurities and Auger recombination, and collisional ionization in a dense plasma. The electrical pumping circuit of the opening switch is calculated by solving the Kirchhoff equations. The motion of the plasma in the semiconductor structure is analyzed on the basis of the model. It is shown that for ultrahigh pumping levels the interruption of the current in the opening switch occurs in the heavily doped regions of the p ⁺-p-n-n ⁺ structure and is due to saturation of the particle drift velocity in high electric fields. Zh. Tekh. Fiz. 67, 64–70 (October 1997)     

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.     

半导体断路开关电路-流体耦合数值模拟

为了研究掺杂结构为p+-p-n-n+的半导体断路开关的ns脉冲截断机理,根据流体力学方程和全电流方程推导出半导体断路开关内部载流子运动满足的电流-电压关系表达式,提出了一种外电路方程和载流子流体力学方程联立求解的1维耦合数值模型。采用该模型对半导体断路开关的ns脉冲截断过程进行了数值模拟,模拟结果表明:在截断过程中,n-n+结处的载流子数密度首先开始明显降低,并出现高电场,随后p+-p结处也出现类似现象,随着载流子的抽取,高电场区域向p-n结处快速移动,最终在p-n结处完成截断,而基区载流子数密度在截断前后无明显变化。     

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.     

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     

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.     

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.     

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.     

A new approach to determine accurately minority-carrier lifetime

Electron or proton irradiations introduce recombination centers, which tend to affect solar cell parameters by reducing the minority-carrier lifetime (MCLT). Because this MCLT plays a fundamental role in the performance degradation of solar cells, in this work we present a new approach that allows us to get accurate values of MCLT. The relationship between MCLT in p-region and n-region both before and after irradiation has been determined by the new method. The validity and accuracy of this approach are justified by the fact that the degradation parameters that fit the experimental data are the same for both short-circuit current and the open-circuit voltages. This method is applied to the p⁺/n-InGaP solar cell under 1 MeV electron irradiation.     

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.     

Charge transfer mechanism in high-purity silicon-basedn +-π-p + structures

Results of experimental investigations into current-voltage characteristics of n⁺-π-p⁺ structures based on high-purity silicon doped with boron are presented. It is shown that the I–V characteristic at high injection levels is described by Stafeev's theory, when the thickness d of the π-region is smaller than or close to three ambipolar diffusion lengths L_a. For a current density J above (3–50) A/cm² at varying temperatures, the I–V characteristic obeys a relation usually occurring in the case where charge-carrier recombination in the n⁺ and p⁺-regions dominates that found in the π-region. The effect of mutual electron-hole scattering on the behavior of the I–V characteristic is evident at J>630 A/cm³. For d/L_a=9, the I–V characteristic at high injection levels is treated by the theory of double carrier injection into a semiconductor with consideration for diffusion corrections. In the temperature range below 200–276 K, the I–V curve for all samples studied exhibits a linear dependence on J followed by a portion corresponding to a maximum occupancy of recombination levels by injected electrons. Here the Fe or Au donor levels presumably act as recombination levels. The electron and hole capture areas (cross sections) by recombination centers are roughly estimated. Siberian Physicotechnical Institute at Tomsk State University. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 7, pp. 35–45, July 2000.     

Surface effect on the reverse current of Al x Ga1−x Sbp−n structures

The effect of an invertedp-region along the free surface ofn-Al _x Ga_1−x Sb on the reverse current ofp−n structures from the given solid solution is analyzed. Expressions which describe “collection” of the inverted layer current on the cylindrical surface of ann-region are discussed. The contribution of the near-surface and bulk components to the reverse current ofp−n structures with a semi-infiniten-region is estimated. For structures with a two-layern-region of finite thickness we have calculated the dependence of the near-surface current on the voltage across thep−n structure, the thickness of then-region, and its composition and doping level. We have compared the calculated current-voltage characteristics with experiment using a Al_0.15Ga_0.85Sbp−n structure as an example. Tomsk State University, Tomsk. Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, Vol. 42, No. 1, pp. 34–40, January, 1999.     

Photoluminescence and EPR of porous silicon formed on <Emphasis Type="Italic">n</Emphasis><Superscript>+</Superscript> and <Emphasis Type="Italic">p</Emphasis><Superscript>+</Superscript> single crystals implanted with boron and phosphorus ions

The effect of combined doping by shallow donor and acceptor impurities on boosting the quantum yield of porous-silicon photoluminescence (PL) in the visible and near IR range was studied using phosphorus and boron ion implantation. Nonuniform doping of samples and subsequent oxidizing annealing were performed before and after porous silicon was formed on silicon single crystals strongly doped by arsenic or boron up to ≈10¹⁹ cm^?3. The concentration of known P_b centers of nonradiative recombination was controlled by electron paramagnetic resonance. It is shown that there is an optimal joined content of shallow donors and acceptors that provides a maximum PL intensity in the vicinity of the red part of the visible spectrum. According to estimates, the PL quantum yield in the transitional n ⁺⁺-p ⁺ or p ⁺⁺-n ⁺ layer of porous silicon increases by two orders of magnitude as compared to that in porous silicon formed on silicon not subjected to ion irradiation.     

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.     

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.     

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)     

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)     

n‐type silicon solar cells with surface‐passivated screen‐printed aluminium‐alloyed rear emitter

Aluminium‐doped p‐type (Al‐p⁺) silicon emitters fabricated by means of a simple screen‐printing process are effectively passivated by plasma‐enhanced chemical‐vapour deposited amorphous silicon (a‐Si). We measure an emitter saturation current density of only 246 fA/cm², which is the lowest value achieved so far for a simple screen‐printed Al‐p⁺ emitter on silicon. In order to demonstrate the applicability of this easy‐to‐fabricate p⁺ emitter to high‐efficiency silicon solar cells, we implement our passivated p⁺ emitter into an n⁺np⁺ solar cell structure. An independently confirmed conversion efficiency of 19.7% is achieved using n‐type phosphorus‐doped Czochralski‐grown silicon as bulk material, clearly demonstrating the high‐efficiency potential of the newly developed a‐Si passivated Al‐p⁺ emitter. (© 2008 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

The Influence of Collisions in the Space Charge Sheath on the Ion current Collected by a Langmuir Probe

The current/voltage characteristics of a cylindrical Langmuir probe have been studied in Ar⁺/electron afterglow plasmas in helium carrier gas under truly thermal conditions at 300 K using our flowing afterglow/Langmuir probe (FALP) apparatus. The orbital motion limited (oml) ion and electron current regions of the probe characteristics have been explored over a wide range of the reduced probe voltage (up to ～ 100) and over a wide range of electron (n_e) and ion (n₊) number densities (1.6 × 10⁷ to 1.5 × 10¹⁰ cm^?3) at a constant pressure of the He carrier gas of 1.2 Torr. The observed increase of the probe ion currents above those predicted by collisionless oml theory, resulting in an apparent increase of the measured ion number density above n_e in the plasma, is explained by the enhancement in the ion current collection efficiency due to collisions of ions with neutral gas atoms in the space charge sheath surrounding the probe. The continuous change in the exponent, χ, of the power-law dependence,i₊ ∞ V of the ion current, i₊, on the probe voltage, V_p from 0.5 at the highest n₊ (smallest sheath) towards 1.0 at the lowest n₊ (large sheath) indicates that the ion current collection from the plasma changes from the oml current regime at the high n₊ to the continuum regime at the low n₊ when the ions undergo multiple collisions with the helium atoms in the space charge sheath and thus “drift” towards the probe.     

Numerical modeling of an InAsSb/InAsSbP double heterojunction light emitting diode for mid-infrared (2–5 μm) applications

The numerical model of a Mid-infrared (MIR) P⁺–InAs_0.48Sb_0.22P_0.30/n⁰–InAs_0.89Sb_0.11/N⁻–InAs_0.48Sb_0.22P_0.30 double heterostructure light emitting diode (DH-LED) has been reported in this paper. The governing equation of the structure has been solved numerically under the condition of high injection using fourth order Runge-Kutta method employing the shooting algorithm. The numerical model takes into account all dominant radiative and non-radiative recombination processes, surface recombination velocity and self-absorption in the active layer of DH-LED. The DH-LED has been simulated for mid-infrared applications by considering modulation bandwidth and its dependence on active layer width, doping concentration, and injected carrier density. The effect of surface recombination velocity on the quantum efficiency, peak light intensity for different values of active layer width and doping concentration has been estimated numerically. The rise time of the structure has been evaluated by considering transient response for a step current of 50 mA. The output power of DH-LED has been computed as a function of bias current and compared/ contrasted with the reported analytical and experimental results.