BV/sub CEO/--BV/sub CBO/ separation and sharpness of breakdown in high-speed bipolar transistors

The effect of secondary impact ionization by the noninitiating carrier on the near avalanche behavior of high-speed n-p-n bipolar transistors is studied. We show that secondary collector ionization by generated holes traveling back toward the base layer significantly reduces BV/sub CBO/ if the hole ionization coefficient is higher than that of electrons [/spl beta//sub p/(E)>/spl alpha//sub n/(E)]: positive feedback associated with a strong secondary ionization sharpens the breakdown characteristic by speeding up carrier multiplication and decreases separation between the open-base collector-emitter (BV/sub CEO/) and the open-emitter base-collector (BV/sub CBO/) breakdown voltages. The effect of secondary ionization on the BV/sub CEO/-BV/sub CBO/ separation has not previously been described. Multiplication coefficient comparisons for representative InP, GaAs, and Si collectors indicate all structures can sustain low-current above BV/sub CEO/ operation from a transport (nonthermal) point of view, although the different degrees of secondary ionization in various semiconductors lead to fundamental differences when InP is compared to GaAs and Si since for the latter materials /spl beta//sub p/(E)相似文献   

在电子束控制放电KrF*激光器中发生电离不稳定性的判据与讨论

本文用相平面方法导出了电子束控制放电KrF激光器中稳态放电的判据,并讨论了E/P、F_2浓度以及外电离源强度对放电中发生电离不稳定性的效应.     

Determination of germanium ionization coefficients from small-signal IMPATT diode characteristics

Small-signal measurements of germanium IMPATT diode admittance in the frequency range from 2 to 8 GHz were taken for various current densities. These measurements were compared with the small-signal admittances calculated using the model developed by Gummel, Scharfetter, and Blue [1], [2]. Values for the ionization coefficients and saturated velocities for electrons and holes used for the calculations have been chosen to secure reasonable agreement between theory and experiment for the diode avalanche voltage, the frequencies at which the small-signal susceptance and conductance cross zero, and the slope and general shape of the admittance versus frequency curves. The calculated small-signal admittance characteristics of the n⁺-p-p⁺mesa diode investigated are quite sensitive to the saturated hole velocity and the field dependence of the ionization rates. For the operating junction temperature, the velocity which gives the best fit is resolvable to about 5 percent. The best fit velocity is in agreement with published values. However, the ionization coefficients determined give a substantially smaller dependence of ionization rate on electric field than was obtained by Miller [3]. The coefficients obtained can be fitted by Baraff's theoretical model [4] using a low value for r, the normalized ionization cross section, in order to obtain the small dependence on field. The values of the ionization rates determined here,alpha_{p}=2.15 times 10_{5} exp(-7.10 times 10_{5}V.cm^-1/E) cm^-1alpha_{n}=4.90 times 10_{5} exp(-7.90 times 10_{5}V.cm^-1/E) cm^-1are believed to be generally applicable to impact ionization effects in germanium semiconductor devices.     

Avalanche ionization rates measured in silicon and germanium at low electric fields

Ionization rates in semiconductors can be measured at low values of electric field using a new method involving a field-effect transistor (FET) structure which offers greater sensitivity than reverse biased p-n junction diode methods. Carriers of only one polarity cause ionization in the FET and no correction is required for ionization caused by carriers of the opposite polarity. Since secondary carriers resulting from ionization are attracted to a different terminal (gate or substrate) than that used to collect the primary carriers (drain), very small ionization currents can be detected. Values of electron ionization rate αnand hole ionization rate αpas low as 10^-3cm^-1have been obtained for silicon. The approximate relationshipalpha = alpha_{infin}e^{-b/E}is observed and the values of α at high fields correspond to those obtained conventionally. Values of αpfrom 0.04^-1to 0.4 cm^-1have been obtained for germanium. Analytical determination of electric field was provided by a solution of Poisson's equation for the field-effect structure. Difficulty in accurately determining the FET channel doping introduces a ± 30 percent uncertainty in electric field values. The method is applicable to any semiconductor material where junction, MOS, or Schottky barrier techniques can be used to construct field-effect transistors.     

The distribution of gains in uniformly multiplying avalanche photodiodes: Theory

Expressions are derived for the probabilityP_{n,m}that a pulse initiated bynelectrons (or holes) in a uniformly multiplying semiconductor diode will result in a total number of electrons (or holes)m, to give a gainm/n, and for the probabilityQ_{n,m}that the gain will bem/nor greater. It is shown that the distributions are far from Gaussian. The gain distributionP_{1,m}for a single photoelectron, for example, is shown to have a maximum value form = 1for any value of the average gainM=m/n. The derivations are valid for any electric field distribution and assume only that the hole ionization coefficientbeta(E) can be approximated by the relationbeta(E) =kalpha(E), wherealpha(E)is the electron ionization coefficient andkis a constant. A method of determining an effective value ofk, for cases wherebeta=kalphais not a good approximation, is presented. The results can be used to calculate the average gain and the mean square deviation from the average, giving results in agreement with previously published relations [1], [2]. The implications of this theory on the use of avalanche diodes for low-level photodetection are discussed. It is shown that in the near infrared, cooled avalanche photodiodes can compare favorably with the best available photomultiplier when used either in a photon-counting mode, or for the reliable detection of low-level laser pulses.     

Empirical modeling of LF gate noise in GaAs DCFET in impactionization regime

The evolution of the 1/f gate noise in GaAs DCFET has been analyzed in the impact ionization regime. As the drain bias Vd is raised, a steep increase of the 1/f gate current noise is observed in correlation with the triggering of the impact ionization mechanism. A novel and empirical model of the 1/f low frequency gate current noise S _ig measured in the impact ionization regime is proposed. The following relation fits it with an exponential law: S_ig=E exp (-F/Vd) (1/f), which is similar to the well-known dependence of the impact ionization rate α on the drain bias     

Implementation of nonlocal model for impact-ionization current inbipolar circuit simulation and application to SiGe HBT designoptimization

A nonlocal characterization of impact-ionization current is implemented in a compact but physical bipolar transistor model for predictive circuit simulation. The charge-based model, which is applicable to SiGe-base HBT's as well as Si BJT's, provides at each bias point, including ones in quasisaturation, the electric field distribution E(x) in the epi-collector, and a simplified form of the energy-balance equation enables characterization of carrier temperature T_e(x) from E(x). Numerical spatial integration of the T_e -dependent ionization rate yields the impact-ionization current as post-processing in the model routine. The nonlocal model is verified by applications to two advanced bipolar (HBT and BJT) technologies in which the device breakdown voltages, which are underestimated by the local-field model, are predicted. The utility of the nonlocal model in assessing design tradeoffs involving impact ionization (i.e., device breakdown versus circuit performance) is demonstrated by simulations based on the two mentioned technologies     

Monte Carlo calculation of the ionization and attachment coefficients in SF6in E × B fields

The ionization and attachment coefficients in SF6in E × B fields are calculated using the Monte Carlo simulation technique. Application of a magnetic field results in a change in the electron energy distribution, reduces the Townsend's first ionization coefficient, and increases the attachment coefficient at a constant value of the ratio of electric field to gas pressure.     

Drift velocity and ionization coefficient for holes in single-valley semiconductors

An analytical theory has been developed for drift velocity (V_d) and ionization coefficient (_h) of holes in silicon. Based on Boltzmann transport equation, expressions for drift velocity (V_d) and ionization coefficient (_h) are derived. The theoretical approach is based on calculation of the collision operator for ionization probability, approximated by a delta function. It is observed that the values of drift velocity (V_d) and ionization coefficient (_h) are in good agreement with experimental results for ionization length (l_io = 70 Å) and ionization energy (ε_i = 2.5 eV). This confirms the validity of the developed theoretical model for drift velocity and ionization coefficient of holes.     

Modeling of substrate current in p-MOSFET's

It is shown that the substrate current characterization method and modeling approach used for n-MOSFET's is also applicable to p-MOSFET's. The impact ionization rate extracted for holes is found to be 8 × 10⁶exp (-3.7 × 10⁶/E), where E is the electric field. Based on our measurement and modeling result, roughly twice the channel electric field is required for p-MOSFET's to generate the same amount of substrate current as n-MOSFET's. The hot-carrier-induced breakdown voltage is therefore also about two times larger.     

The Growth of Pre-breakdown Current in Helium†

The growth of pre-breakdown current across a uniform electric field discharge gap of finite dimensions has been calculated for helium. The current has been assumed to be amplified by electron ionization and by the production of secondary electrons at the cathode by positive ions, metastables and non-resonance radiation, with allowance made for the loss of secondary currant out of the discharge gap.

It has been shown that experimental measurements of the pre-breakdown current obtained for the range 3 ?1 torr^?1 cannot be analysed to give the electron ionization coefficient (α) without the help of subsidiary experiments to measure the relative abundance and secondary coefficients for the processes producing the secondary electrons. The analysis of these currents by the currents by the Townsend equations (1915) has been shown to give incorrect values of α, especially at the low E/p values where αT may be several times larger than α.     

The Growth of Pre-breakdown Currents in a Uniform Electric Field Gap†

The pre-breakdown current across a uniform electric field gap has been calculated in the presence of ionization by electron impact and secondary electron processes. The solution improves upon the Townsend equation (1915) by allowing for the loss of secondary electron current out of the discharge gap. By using the published results of other workers, it has been shown that pre-breakdown currents, measured in the presence of losses, have fitted both the proposed solution and the Townsend equation but for different values of the electron ionization coefficient and the secondary electron coefficient (denoted by α and γ, and α _T and γ _T respectively). For all gases α_T ≥ α and γ _T ≤ γ and the inequality existed for all E/p values when photon secondary processes were active. The largest disagreement (α _T / α = 1 → 1 and γ / _T = 20 → 1) was calculated for argon for E/ < v cm^?1 torr^?1.     

Comments, with reply, on `Impact ionization in GaAs MESFETs' by K.Hui, et al

In the above-named work (see ibid., vol.11, p.113-15, March 1990), Hui et al. proposed a method to measure impact ionization current in GaAs MESFETs and evaluated the impact ionization coefficient α_n in GaAs. For electric fields greater than approximately 1.5×10⁵ V-cm^-1, α_n can be fitted to the equation α_n=4.0×10 ⁶×exp (-2.3×10⁶/E). In the present work, the commenters performed careful measurements of gate current I_g in GaAs MESFET devices similar to those used by Hui et al., and they show that the ionization coefficient still fits the above equation down to α_n=10^-4 cm^-1 . These results extend the previous data by three orders of magnitude. In a reply, the original authors affirm that the commenters have significantly improved the accuracy of the data previously presented     

Temperature dependence of carrier ionization rates and saturated velocities in silicon

The temperature dependencies of the carrier ionization rates and saturated drift velocities in silicon have been extracted from microwave admittance and breakdown voltage data of avalanche diodes. The avalanche voltage and broadband (2–8 GHz) microwave small-signal admittance were measured for junction temperatures in the range 280 to 590 K. An accurate model of the diode was used to calculate the admittance characteristic and voltage for each junction temperature. Subsequently, the values of ionization coefficients and saturated velocities were determined at each temperature by a numerical minimization routine to obtain the best fit between the calculated values and measured data. The resulting ionization rates are well fitted by the temperature dependent model developed by Crowell and Sze from the Baraff ionization-rate theory. The carrier scattering mean free path lengths, average energy loss per collision, and relative ionization cross section are obtained from the best fit agreement between the scattering model and experimental data. The parameter values determined here relevent for use with the above theory are the following:Parameter Holes Electrons ε_r(eV) 0.063 0.063 ε_i(eV) 1.6 1.6 λ_oo(Å) 81.2 77.4 σ 0.391 0.593 The values and temperature dependence of the saturated carrier velocities determined are in good agreement with other published results. At 300 K the low field (E?10⁴ V/cm) saturated velocity for electrons and holes is 10.4 and 7.4×10₆ cm/sec, respectively. The results obtained in this study are of general use for the modeling of effects related to avalanche breakdown and high-field carrier transport in silicon.     

Ionization coefficients and breakdown voltages of cycloparaffin vapours

Townsend primary ionization coefficients have been measured and breakdown voltages deduced for cyeclopentane and eyclohexane vapours up to their respective saturation vapour pressure. corresponding to 46  E/p₀  20OO V cm^-1 torr^-1 at 0^°C and voltages up to 400KV. The Townsend relation α/p_o = A exp (—Bp0/E) is found to be obeyed over α/po range of 300 to 1 and the constants A and B are deduced. This allows the paraffin gases and vapours to be correctly categorized. Large electron avalanches exceeding exp (αd) = 10⁸ have once more been observed.     

碘乙烷分子共振增强多光子电离飞行时间的质谱研究

在４７３～４８３ｎｍ波长范围内对碘乙烷分子共振增强多光子电离（ＲＥＭＰＩ）飞行时间（ＴＯＦ）质谱（ＭＳ）作了研究。分析结果表明在该波段碘乙烷（Ｃ２Ｈ５Ｉ）分子吸收双光子激光能量跃迁激发至Ａ带的３Ｅ,２Ａ１及１Ａ２态,激发态分子碎裂成中性碎片,中性碎片再吸收光子电离,产生了Ｃ２Ｈ＋５和Ｉ＋离子。Ｃ２Ｈ＋５离子进一步吸收光子并碎裂形成了碘乙烷分子ＲＥＭＰＩ－ＭＳ中其他的碎片离子。     

Analytical threshold voltage model for ultrathin SOI MOSFETsincluding short-channel and floating-body effects

Short-channel effects (SCE) in ultrathin silicon-on-insulator (SOI) fully depleted (FD) MOSFETs are analyzed and an analytical model for threshold voltage, including the kink effect, is presented. The proposed model accounts for (1) a general nonuniform channel doping profile, (2) the drain-induced V_th- lowering enhancement resulting from the interaction of (a) impact ionization, (b) floating-body, and (c) parasitic-bipolar effects. Good agreement between the proposed model and experimental data is demonstrated. Impact ionization and floating-body effects dominate V_th lowering for drain voltages larger than V_dk≃B_i.λ_i/3, where B_i is the impact ionization coefficient, and λ_i is the impact ionization length, a structural parameter which, for a single-drain SOI MOSFET, coincides with the SCE characteristic length λ     

Avalanche multiplication factors in Ge and Si abrupt junctions

Analytical approximations for the multiplication factors Mnand Mpin Ge and Si one-sided abrupt junctions are given. The resulting expressions account for different α and β ionization rates and are quite accurate. With further approximations on the ionization integrals, very simple expressions of 1 -- 1/M both for electron and holes in the range of very low multiplication are obtained, depending from a single ionization rate.     

Field dependence of impact ionization coefficients in In/sub 0.53/Ga/sub 0.47/As

Electron and hole ionization coefficients in In/sub 0.53/Ga/sub 0.47/As are deduced from mixed carrier avalanche photomultiplication measurements on a series of p-i-n diode layers, eliminating other effects that can lead to an increase in photocurrent with reverse bias. Low field ionization is observed for electrons but not for holes, resulting in a larger ratio of ionization coefficients, even at moderately high electric fields than previously reported. The measured ionization coefficients are marginally lower than those of GaAs for fields above 250 kVcm/sup -1/, supporting reports of slightly higher avalanche breakdown voltages in In/sub 0.53/Ga/sub 0.47/As than in GaAs p-i-n diodes.     

Monte Carlo simulation of impact ionization rates in InAlAs-InGaAssquare and graded barrier superlattice

The Monte Carlo method is used to analyze impact ionization rates for electrons and holes in a 〈100〉 crystal direction In_0.52Al_0.48As-In_0.53Ga_0.47 As square and graded barrier superlattice. The calculated impact ionization rate ratio α/β is enhanced to more than 10 in a wide barrier and narrow-well square barrier superlattice. This is because the hole ionization rate β is greatly reduced in the narrower well superlattice, while the electron ionization rate α is less sensitive to well and barrier layer thickness. These results are explained by a combination of the ionization dead space effect for the barrier layer and the electron ionization rate enhancement in the well layer due to large conduction band edge discontinuity. Furthermore, it is found that in a graded barrier superlattice, the impact ionization rate ratio α/β is smaller than that for a square barrier superlattice having the same barrier and well thickness. This is due to the occurrence of hole ionization in the narrow bandgap region in graded barriers. The band structure effects on hot carrier energy distribution, as well as impact ionization, are also discussed