Schottky-barrier capacitance measurements for deep level impurity determination

The time dependence of a Schottky-barrier capacitance due to thermal excitation of trapping centres has been studied. An expression for the junction capacitance is derived which is not restricted to any special range of reverse bias nor to a special relation between shallow and deep impurity concentration. The concentration ratio of shallow to deep centres is calculated from the values of the capacitance at zero and infinite time. From a capacitance vs. time plot the trap emission rate for electrons e_n is obtained. Their energetic level within the forbidden band-gap is determined from the temperature dependence of e_n as well as from the capacitance-time variation. Experimental studies which do confirm the calculations were carried out on gold contacts on oxygen-doped n-type GaAs. Representative results of the investigated samples were: shallow donor density 3 × 10¹⁵ cm^?3, trap density 9·8 × 10¹⁵ cm^?3, electron emission rate 6 × 10^?2 sec^?1, energetic level 0·68 eV and capture cross section 7 × 10^?16 cm².     

Titanium in silicon as a deep level impurity

Titanium inserted in silicon by diffusion or during Czochralski ingot growth is electrically active to a concentration level of about 4 × 10¹⁴ cm^?3. Hall measurements after diffusion show conversion of lightly doped p type Si to n type due to a Ti donor level at E_C - 0.22 eV. In DLTS measurements of n⁺p structures this level shows as an electron (minority carrier) trap at E_C - 0.26 eV with an electron capture cross section of about 3 × 10^?15 cm² at 300°K. The DLTS curves also reveal a hole trap in the p type material. The e_p (300/T)² activation plot gives the level as E_V + 0.29 eV. The hole capture cross section is about 1.7 × 10^?17 cm² at 300°K and decreases with decreasing temperature and the corrected trap level becomes E_V = 0.26 eV. Ti in lightly doped (360 ohm-cm) n type material does not result in conversion to p type so this level is inferred also to be a donor.A Ti electrically active concentration of about 1.35 × 10¹³ cm^?3 in p type (N_A = 3.35 × 10¹⁵cm^?3) Si results in a minority carrier (electron) lifetime of 50 nsec at 300°K.     

Photovoltaic effect in the impurity absorption region of Si-structures with blocked impurity conductivity

A study is made of the field dependence of the photoconductivity in two-layer Si:Sb-and Si:Bstructures with blocked impurity-band conductivity and different thicknesses of the undoped (blocking) layer. The impurity concentration in the doped (active) layer was ≈10¹⁸ cm⁻³. Measurements were made at temperatures T=4–15 K for high (Φ∼10¹⁶ photons/cm² · s) and low (Φ<10¹⁴ photons/cm² · s) incident photon fluxes. A photovoltaic effect is observed in the Si:B structures with a thin (3 μm) blocking layer. It is found that a photovoltage develops for photons with energies exceeding the ionization energy of boron and its magnitude is independent of the photoexcitation intensity (for Φ>10¹³ photons/cm² · s) and, in the limit of low temperatures, it is close to the activation energy ɛ ₃ for jump conductivity in the active layer. The photovoltaic effect is explained by ballistic transit of the blocking layer by holes emitted from the contact which are then cooled in the active layer, as well as by the presence of a potential barrier ≈ɛ ₃ between the active and blocking layers. These factors are taken into account in a model for describing the major features of the dependence of the photovoltage on temperature and on the photon intensity and energy. Fiz. Tekh. Poluprovodn. 33, 456–463 (April 1999)     

Characterization of multiple deep level systems in semiconductor junctions by admittance measurements

The small signal admittance, Y, of a junction device, in the presence of deep lying majority carrier traps, is obtained as a solution to a simple differential equation (dC/dχ) = (C²/ε)?(ρ_ac/ψ_ac), where CY/jω is the complex capacitance, x is the distance within the depletion region from the neutral bulk semiconductor, ρ_ac is the a.c. incremental change in charge density at χ when the bias is incremented by ψ_ac. This equation can be numerically integrated with one boundary condition, the flat band capacitance of the bulk semiconductor. An analytic solution to the above differential equation is possible over a wide frequency range without the use of a truncated space charge approximation. The admittance of one half of a junction device can then be modelled by a 3p + 1 lumped element equivalent circuit involving 3p + 2 device parameters, where p is the number of species of deep lying majority carrier traps that are virtually unionized in the bulk. These circuit elements bear simple direct relationships to the deep level parameters. Impedance vs frequency measurements at a single bias and temperature yield only 2p + 1 equations and are not sufficient to define the elements uniquely. One therefore needs p + 1 additional equations for a unique synthesis. We also show how additional equations can be obtained from impedance vs voltage or temperature measurements.     

Electrical characterization of deep level systems in semiconductor junctions by admittance measurements

Deep level impurities in a semiconductor junction can be characterized by the frequency, temperature and bias dependence of the junction admittance. It will be shown briefly, that the build-up of the junction admittance from the bulk semiconductor to the junction interface can be given in terms of a first order differential equation. For a general case, the admittance of a junction device can then be obtained via a numerical integration of the differential equation. However, under certain simplifying assumptions one can obtain a simple analytic solution which can be modeled by an equivalent circuit consisting of lumped constant elements. The experimentally determined admittance of a Hf-In doped p-type Si as a function of temperature, frequency and bias, is correlated to the admittance determined from a numerical integration of the differential equation wherein four temperature independent parameters, via. the concentration, the ground state energy level and it’s associated degeneracy of the In in Si and the Schottky barrier height of Hf on p-type Si, determined by independent measurements, are used, and one temperature invariant parameter, the shallow level impurity concentration, N_s, and a temperature dependent parameter, the hole capture cross-section of In in Si, σ_p, are adjusted for the best fit. The value of N_s is found to agree within 19% of the volume average determined from Hall measurement and the magnitude and temperature dependence of σ_p is found to agree well with several previously reported values.     

Electromigration in width transition copper interconnect

Electromigration (EM) experiments are conducted for submicron dual damascene copper interconnects with width transition. The direction of electron flow (from narrow-to-wide segment and wide-to-narrow segment) and the ratio of lengths (e.g. ratio of narrow-to-wide segment lengths) are found to be significant factors in determining the life-time of such interconnects. About 69% shorter EM life-time is obtained for the case of electron flow from narrow-to-wide segment, and thus to avoid over estimation of EM life-time of such interconnect system, the direction of the electron flow should be chosen appropriately in the reliability assessment. On the other hand, it is found that the width transition location is not the failure site, and finite element model is presented to explain the experimental findings.     

Semiconductor steady state defect effective Fermi level and deep level transient spectroscopy depth profiling

The widely used deep level transient spectroscopy (DLTS) theory and data analysis usually assume that the defect level distribution is uniform through the depth of the depletion region of the n-p junction. In this work we introduce the concept of effective Fermi level of the steady state of semiconductor, by using which deep level transient spectroscopy depth profiling (DLTSDP) is proposed. Based on the relationship of its transition free energy level (TFEL) and the effective Fermi level, the rules of detectivity of the defect levels are listed. Computer simulation of DLTSDP is presented and compared with experimental data. The experimental DLTS data are compared with what the DLTSDP selection rules predicted. The agreement is satisfactory.     

Spin-peierls transition in the random impurity sublattice of a semiconductor

A study of electron spin resonance in uncompensated Ge:As semiconductor samples in the vicinity of the insulator-metal second-order phase transiti on reveals that the interaction of spins localized at As atoms brings about a distortion of the crystal lattice and enhances the localization. This effect occurs in the range of electron concentrations n = 3 × 10¹⁷—3.7 × 10¹⁷ cm^-3, just below the critical point of the phase transition. The effect is explained in the context of a model considering the spin-Peierls transition in the random impurity sublattice of the semiconductor, and its features, as compared to other known materials where the spin-Peierls transition is observed, are understood.     

Photoionization of deep impurity centers in quantum well structures

The absorption of light by photoionization of deep impurity centers in quantum well heterostructures is studied theoretically using a model with a maximally localized potential. Analytic expressions are found for the photoionization cross sections for light polarized perpendicular and parallel to the axis of the structure, disregarding the effect of the impurity potential on the continuum electronic states. The dependence of the frequency variation of the cross section on the charge state of the impurity after photoionization, as well as on the position of the impurity in the structure and the doping profile, is studied qualitatively near the absorption threshold. Fiz. Tekh. Poluprovodn. 33, 451–455 (April 1999)     

语音通信中的深度防御战略

语音服务、系统与数据IP网络的集成显然已经赢得了企业的关注和信赖,并促使他们作出了投资。但是在将语音技术引入IP环境时,很多IT、电话和业务管理人员都担心是否足够安全。语音通信需要与其它高水平安全数据应用同样严格的安全标准。语音呼叫中的信息,如战略性信息、个人信息或者财务信息一旦被拦截,都可能会像数据通信被窃听一样造成破坏性的影响。而且,如     

Charge-transfer theory in polycrystalline semiconductors with deep impurity centers

This paper discusses the static and dynamic properties of charge transfer through electrically active grain boundaries in polycrystalline semiconductors with deep impurity centers in the bulk of the grains. The admittance of the grain boundary is computed as a function of frequency and applied dc bias U _b. When U _b≠0, the admittance is mainly controlled by charge-exchange processes of the intergrain boundary states and to an insignificant extent by the charge exchange of deep traps in the bulk of the semiconductor. The application of this theory to the spectroscopy of intergrain boundary states is considered. Fiz. Tekh. Poluprovodn. 32, 690–696 (June 1998)     

Identification of a transition matrix of a Markov chain from noisy measurements of state

We consider the problem of recursively estimating the transition matrix of a regular Markov chain with a finite number of states using only noisy measurements of the state. The measurement noise sequence is assumed to be independent with known mean and unknown variance. We also discuss the convergence rates and computational aspects of the algorithms and the methods of accelerating them.     

量子棒中杂质极化子的内部激发态

通过坐标变换把量子棒的哈密顿量由椭球边界变为球形边界.采用线性组合算符和么正变换方法研究了量子棒中弱耦合杂质极化子的第一内部激发态能量、激发能量和从第一内部激发态到基态跃迁频率随量子棒的横向和纵向有效受限长度、库仑束缚势、椭球的纵横比的变化关系.结果表明:它们随库仑束缚势的增加而增大,随纵横比和有效受限长度的增加而减少.表现出量子棒珍奇的量子尺寸限制效应.     

Echo width of foam supports used in scattering measurements

Theoretically and experimentally determined echo widths of dielectric cylinders having circular, triangular, and quadratic cross sections have been compared. The cylinders were made of foam material having a relative dielectric constant of about 1.035. The purpose of the investigation was to find a cross section with a small echo width. The result can be used in selecting a proper support for test objects in backscattering measurement studies.     

Autosolitons in bistable system of silicon with deep impurity levels

Autosolitons in the bistable system of silicon associated with the thermal and electric-field ionization of In deep acceptor levels at a temperature of 77 K are experimentally found and investigated. It is shown that the positive feedback on the activator is related in the considered model of autosolitons to an increasing dependence of the lattice temperature on growth in the hole concentration, while the damping role of the inhibitor is associated with a decrease in the charge-carrier temperature during phonon-induced scattering. This leads to power-loss reduction and lattice-temperature restriction in the vicinity of autosolitons.     

GaInNAs薄膜中深能级弛豫过程的皮秒泵浦-探测研究

应用泵浦-探测方法研究了GaInNAs载流子动力学.差分透射强度随时间变化曲线表明,深能级中被俘获电子在光学瞬态吸收中起重要作用.为了模拟GaInNAs中光生载流子动力学过程和拟合泵浦-探测实验结果,采用了一个简化的微分方程模型,该模型能够解释被深能级俘获电子的弛豫过程,并可获得驰豫过程的时间常数.     

Resistivity and deep impurity levels in silicon at 300 K

Families of curves of the resistivity at 300 K for n- and p-type silicon doped with deep activation energy impurities are presented as a function of impurity concentration. These curves are based on analyses of Irvin's curves, applicable to the shallow activation energy impurities, and on the properties of the deeper activation energy impurities. These curves apply to impurities with activation energies that are independent of concentration. Since Irvin's p-type curve appears to be heavily influenced by Si:Ga data in the 10¹⁶-10¹⁸-cm^-3range, a boron curve is calculated for this range. This curve may be considered a correction to Irvin's p-curve in this impurity range.     

Study of platinum impurity atom state in vitreous arsenic selenide

Platinum atoms in the structure of As₂Se₃ glass are stabilized in the form of Pt²⁺ and Pt⁴⁺ ions and correspond to ionized states of the amphoteric two-electron center with negative correlation energy (Pt²⁺ is an ionized acceptor, and Pt⁴⁺ is an ionized donor), whereas the neutral state of the Pt³⁺ center appears to be unstable.     

Avalanche region width in various structures of IMPATT diodes

The avalanche region of one-sided and two-sided abrupt junctions has been studied. These are the structures most commonly utilized for IMPATT diodes. Numerical results are presented which show that n⁺-p Si diodes have much narrower avalanche regions, due to the unequal ionization rates in Si, than the complementary p⁺-n type. The implications of these results with respect to IMPATT diode design are discussed.