Relaxation of photoexcited silver chloride

Relocalization of excess carriers from shallow levels to deep levels is observed in addition to carrier recombination during thermal relaxation of photoexcited silver chloride. Experimental dependences of the parameters of the photostimulated luminescence flash (released light sum and kinetic coefficient) on the relaxation time and temperature are explained within a three-level model including a recombination (luminescence) level, a deep level with energy ΔE ≈ 1.8 eV, and a shallow level with energy ΔE ≈ 0.03 eV with respect to the conduction-band bottom. It was shown that Ag⁺ ion adsorption caused a decrease in the relocalization activation energy from 0.17 to 0.03 eV, which is attributed to the surface nature of the centers responsible for the initial relaxation stage.     

半导体纳米颗粒载流子的超快弛豫过程

分析了纳米颗粒的能级结构,建立了载流子弛豫的简化模型,运用数值模拟方法讨论了激发密度、表面态密度及俘获态电子的弛豫率对弛豫过程的影响。讨论结果表明,激发密度的增大及表面态的减少都会导致表面态上电子的饱和,使导带上出现电子的积累,导带电子寿命增大;深俘获态电子的弛豫是影响材料响应速度的主要因素。最后应用此模型对近红外泵浦探测实验的结果进行分析,表明模型可望在实验结果分析上得到应用。     

Energy relaxation of photoexcited hot electrons at very low temperatures

The scattering of electrons with energy $\text{?<}\text{1}\text{2}\text{ms}{}^2$ by acoustical phonons at very low temperatures T?ms² is investigated.     

Simulation of ultrafast relaxation of photoexcited electrons via analytical distribution functions

We propose an analytic representation to study electron relaxation during an ultrafast process in a semiconductor quantum well. Gauss-type energy functions are used to simulate the peaks of nonthermal electrons, while the background electrons are described by a Boltzmann distribution function. The time variations of parameters describing the amplitudes and widths of Gauss-type functions, and the temperature of background electrons, are determined by solution of the Boltzmann equation with electron-electron and electron-phonon interactions.     

Effect of the diameter of the photoexcited region on the picosecond relaxation of bleaching in a thin layer of GaAs

It is found experimentally that the relaxation of bleaching in GaAs, which takes place when charge carriers are photogenerated by a high-power picosecond optical pulse, is slowed as the beam diameter F increases. Relaxation of the bleaching is caused by a decrease in the concentration of carriers due to recombination-induced superluminescence in GaAs. It is found that as the diameter F increases, the rate of superluminescence recombination slows, although the intensity of the superluminescent emission should increase. This apparent contradiction is explained with the help of theory. Fiz. Tekh. Poluprovodn. 32, 542–545 (May 1998)     

Photoelectric and luminescent properties of dysprosium-doped silver chloride

The influence of dysprosium doping on the photoelectric and luminescent properties of AgCl crystals is studied by methods of microwave photoconductivity and photoluminescence. Doping affects both the loss kinetics of photogenerated electrons and luminescence spectra and parameters of photostimulated burst of luminescence. It is shown that the charged [Dy_Ag^·· · V′_Ag]^· or neutral [Dy_Ag^·· · 2V′_Ag] ^x complexes are responsible for a new luminescence band peaked at 470 nm, which manifests itself at weight concentrations of the doping additive >10⁻⁶%. The long-wavelength shoulder at 570 nm in the photoluminescence spectra is attributed to intracenter transitions in the Dy³⁺ ions. The rate constant of the reaction of electron capture into the traps forming upon introduction of the dopant, k _t = (3–5) × 10⁻⁸ cm³ s⁻¹, is evaluated. It is assumed that the traps are Dy³⁺ dysprosium ions.     

The role of screening of the electron-phonon interaction in relaxation of photoexcited electron-hole plasma in semiconductors

The role of screening of the interaction of the electron-hole plasma with optical phonons is analytically evaluated by the example of gallium arsenide.     

Effect of zinc impurity on silicon solar-cell efficiency

Zinc is a major residue impurity in the preparation of solar-grade silicon material by the zinc vapor reduction of silicon tetrachloride. This paper projects that in order to get a 17-percent AM1 cell efficiency for the Block IV module of the Low-Cost Solar Array Project,¹the concentration of the zinc recombination centers in the base region of silicon solar cells must be less than 4 × 10¹¹Zn/cm³in the p-base n+/p/p+ cell and 7 × 10¹¹Zn/cm³in the n-Base p+/n/n+ cell for a base dopant impurity concentration of 5 × 10¹⁴atoms/cm³. If the base dopant impurity concentration is increased by a factor of 10 to 5 × 10¹⁵atoms/cm³, then the maximum allowable zinc concentration is increased by a factor of about two for a 17-percent AM1 efficiency. The thermal equilibrium electron and hole recombination and generation rates at the double-acceptor zinc centers are obtained from previous high-field measurements as well as new measurements at zero field described in this paper. These rates are used in the exact dc-circuit model to compute the projections.     

银粉的形状对低温固化导电银浆导电性能的影响

研究了银粉含量、形状、表面处理工艺对低温固化导电银浆导电性能的影响。结果显示,最理想的银粉质量含量在65%~70%之间。同时,鳞片状银粉和球形粉的混合体制成的浆料导电性能最佳。另外,最好的固化条件是150℃、2 h。     

Effect of deep impurity levels on Schottky barrier diode characteristics

In the presence of an arbitrary number of deep donor levels volt-ampere and volt-farad characteristics are obtained for the Schottky barrier diode which contains a thin dielectric layer between the metal and the semiconductor. The analysis of these characteristics shows that the deep levels can significantly influence both the capacitance and the rectifying properties of the Schottky diode; the thicker the dielectric layer, the greater the effect of the deep levels upon volt-ampere relationship and the lesser upon volt-farad one. One can determine the parameters of the deep levels from these relationships. The results of the calculation are in agreement with the data of the experiment performed.     

Effect of deep impurity on electric characteristics of epitaxial GaAs structures

The electric characteristics of the p ⁺-i-n ⁺ structures are analyzed for two types of GaAs epitaxial layers: the structures with an i layer based on undoped GaAs and an i layer based on GaAs:Cr. The forward currents of the first-type diodes are caused by recombination in the space-charge region. The reverse I–V characteristics at the voltages to 10–15 V are determined by the component of the generation current. At |U| > 20 V, the current growth is caused by the Poole-Frenkel effect, which is replaced by electron tunneling through the potential-barrier top with increasing the voltage as a result of the electron-phonon interaction. The forward branches of the I–V characteristics of the p ⁺-i-n ⁺ diodes with the i layer based on GaAs:Cr are explained by the unipolar injection in the semiconductor, which is replaced by the bipolar injection with increasing the voltage. The reverse I–V characteristics are linear in the range of 1–15 V; at |U| > 20 V, an increase in current is caused by the impact ionization.     

杂质吸收对1维光子晶体孪生缺陷模的影响

为了研究在1维光子晶体中掺杂具有吸收的零平均折射率材料而产生的孪生缺陷模特性,采用特征矩阵的方法进行了理论分析。结果表明,随着消光系数的变大,会使孪生缺陷模透射率先变大后变小,当其取某一特定值时,高低频缺陷模会出现最大值,但不能同时出现;具有吸收特性的介质在缺陷层中的位置不同,会改变孪生缺陷模透射率的响应曲线。这一结果对开发光子晶体新的应用有重要意义。     

Resistivity and hall-effect topography on photoexcited semi-insulating GaAs

A new non-destructive method is presented for obtaining true resistivity (ρ), mobility(μ), and electron concentration(n) topography on photoexcited, semi-insulating GaAs. The method is based on the use of two perpendicular light slits, which join four removable In contacts on the periphery of the wafer to form a classical Greek-cross configuration. By placing contacts all around the periphery the whole wafer can be mapped. We give results for 1.1 μm photoexcitation on a 3′ low-pressure, liquid-encapsulated Czochralski wafer and compare with EL2 results on the same wafer. A by-product of the analysis is the determination of electron lifetime. Finally, the possibility of nondestructive dark electrical topography is discussed.     

Effect of extended phosphorus diffusion gettering on chromium impurity in HEM multicrystalline silicon

We have investigated the extended phosphorus diffusion gettering (PDG) effect on chromium impurities (Cr) in p-type multicrystalline silicon (mc-Si) grown by Heat Exchanger Method (HEM). The study was made after phosphorous diffusion and according to different extended annealing temperatures. The secondary ion mass spectrometry (SIMS) analysis revealed a significant accumulation of ⁵²Cr in heavily phosphorus doped (HPD) region. Using quasi-steady state photoconductance (QSSPC) technique, the apparent lifetime dependent minority carrier density curves have been obtained. The results showed an increment of the bulk minority carrier lifetime for specific annealing temperatures. Appropriate calculations based on QSSPC results allowed us to determine the lifetime curves associated to gettered impurities. Their fitting by Shockley-Read-Hall (SRH) model reveal that the origin of the lifetime increment is the reduction of interstitial chromium (Cr_i) density in the bulk. Furthermore, the estimation of electron to hole capture cross-section ratio (k=σ_n/σ_p) through the modelling of apparent lifetime curves using Hornbeck–Haynes model, confirmed the effectiveness of Cr_i gettering and identified the nature of dominant recombination centres after gettering process.     

Effect of potential shape on the binding energy of the impurity states in nanotube

We analyze the effect of the additional repulsive core on the ground state energy of the off-axis neutral donor in GaAs/Ga_1-xAl_xAs cylindrical nanotube in the presence of the uniform magnetic field applied along the symmetry axis by using the recently developed fractal dimension method. Curves of the D⁰ ground state binding energies as a function of the donor distance from the axis and density states with randomly distributed donors show that the additional peaks in the curves of the density of impurity states appear due to the presence of the additional repulsive core in the middle's well. To take into account the mixing of the low lying subbands we express the wave function as a product of the combination of 1s and 2p_x,y wave functions with an unknown envelope function that depends only on electron-ion separation.     

Effect of tin impurity on the photoconductivity kinetics of thin amorphous layers of arsenic selenide

In thermally sputtered As₂Se₃ and As₂Se₃ + 0.1 at. % Sn films the tin impurity strongly influences the photoconductivity kinetics under stepped optical excitation. The tin quenches the “spike” on the section of increasing photocurrent, eliminates the dependence of the form of the decrease on the excitation intensity, and leads to a temperature-dependent delay in recombination onset. The effect of the impurity is attributed to an increase in trapping in deep localized states produced by the introduction of tin. Fiz. Tekh. Poluprovodn. 31, 836–840 (July 1997)     

Effect of the state of vacancy equilibrium on diffusion of chromium impurity in gallium arsenide

The results of studying the diffusion of Cr impurity in GaAs according to electrical measurements are reported. Dependences of the diffusion coefficient and limiting solubility of electrically active Cr atoms in GaAs on temperature (at fixed pressures of As vapors) and on the pressure of As vapors (at fixed temperatures) are determined. The dependence of the Cr diffusion coefficient in GaAs on the ratio between the volume of the sample under study to the volume of the cell in the case of pronounced deviation from the crystal’s stoichiometry towards Ga excess is established. The obtained experimental data are analyzed on the basis of concepts concerning the dissociative mechanism of migration of Cr atoms in the GaAs crystal lattice; according to this mechanism, the diffusion coefficient depends heavily on the concentration of Ga vacancies.     

Effect of randomness in the distribution of impurity ions on FET thresholds in integrated electronics

A model of the effect of random fluctuations in the number of impurity atoms in the depletion layer of a field-effect transistor (FET) is presented and analyzed. It is conducted that the range of space charge per unit area that must be anticipated on a chip containing N FET's each of area A is /spl Delta/S=q(2 ln N)/SUP 1/2/A/SUP -1/4/n~/SUP 1/2/. n~ is the doping level of the substrate.     

Streaming plasma instability of photoexcited electrons in semiconductors

It is shown that in semiconductors, in crossed steady electric and magnetic fields, at low lattice temperatures, the streaming plasma instability of photoelectrons is possible. The instability is studied in linear and nonlinear regimes. The electric field and electron mean velocity oscillations with frequency proportional to recombination rate are obtained.     

Transport of the photoexcited electron-hole plasma in InP

Transport properties of the photoexcited electron-hole plasma in n-type InP have been studied by the spatial-imaged, time-resolved Raman scattering technique with 30μm and 0.1μm spatial resolution for lateral and perpendicular transport, respectively, and on a picosecond time scale. The plasma density ranging from 1 × 10¹⁶ to 2 × 10¹⁷ cm⁻³ was deduced from fitting of the Raman spectra with the plasmon-LO phonon scattering theory which took into account the contributions from free holes. In contrast to the experimental results of Young and Wan who found that ordinary diffusion equation was sufficient to fit their transient plasma density-time profiles in semi-insulating InP, our experimental measurements have shown that perpendicular transport (i.e., expansion into the bulk crystal) of the plasma in n-type InP can be very well described by a modified diffusion equation including the effect of drifting away from the surface based on a hydrodynamic model. The transient plasma density-time profiles were studied at T = 300K and for an initial injected plasma density n 2 × 10¹⁷ cm⁻³. The plasma has been found to expand laterally at a velocity V 5 × 10⁴ cm/sec and perpendicularly into the crystal at a velocity Vp 1.5 × 10⁵ cm/sec.