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1.
Impact ionization in thick multiplication regions is adequately described by models in which the ionization coefficients are functions only of the local electric field. In devices with thin multiplication lengths, nonlocal effects become significant, necessitating new models that account for the path that a carrier travels before gaining sufficient energy to impact ionize. This paper presents a new theory that incorporates history-dependent ionization coefficients, and it is shown that this model can be utilized to calculate the low-frequency properties of avalanche photodiodes (APD's) (gain, noise, and breakdown probability in the Geiger mode) and the frequency response. A conclusion of this work is that an ionization coefficient is not a fundamental material characteristic at a specific electric field and that any experimental determination of ionization coefficients is valid only for the particular structure on which the measurement was performed  相似文献   

2.
The system idea?solution of a complete problem in its full environment by systematic assembly and matching of parts to solve the whole problem in the context of the lifetime use of the system, considering all aspects?is one of the most important ideas of modern times. It has made possible the solution of complicated problems that previously could not be touched. However, there exists a rising tide of problems and general disgruntlement (expressed by many people) that indicates trouble. Therefore, the author speaks as an ``engineering critic' (intended in the sense of a music critic: ``Are we turning in a good performance?') and, contrary to the many who are taking the positive side of systems engineering, offers the negative side of the controversy.  相似文献   

3.
4.
Using a multi-feedback network representation, multiplication noise in two-stage and three-stage heterostructure avalanche photodiodes has been calculated for different degrees of carrier feedback over heterobarriers. Results show appreciable dependence of noise on carrier feedback in III–V compound APD's, the effect being less with larger number of stages.  相似文献   

5.
This is a review paper. It is written for engineers, in particular practicing control engineers, who are familiar with transfer functions but not with state-variable techniques. The objective of this paper is threefold. First, it is intended to supplement a recent invited paper. (See A. E. Bryson, Jr., and D. G. Luenberger in Proc. IEEE, vol. 58, Nov. 1970, pp. 1803-1811.) The results introduced there by use of state-variable concepts are redeveloped in the frequency domain. Second, it demonstrates to engineers that, for the class of single-input multiple-output systems and multiple-input single-output systems, some of the results developed in state-variable equations can be obtained directly in transfer functions, even with less computation. Finally, the advantage and the limitation of the transfer function approach are discussed.  相似文献   

6.
A new look at the antenna effect   总被引:1,自引:0,他引:1  
It is a widely held belief that plasma process-induced damage (PID) is caused, among other things, by plasma nonuniformities. These nonuniformities are caused by either nonoptimum reactor design and operation or nonflat wafer topography, the latter giving rise to electron shading that selectively inhibits one charge specie over another causing local surface charging. This charging builds over many cycles. While these phenomena are of serious concern, it is the object of this work to point out that there is an additional way to conceptualize the mechanism for PID in ac glow discharges. In this model, it is proposed that the net charge flux in each power supply half cycle is enough to induce a surface potential of sufficient magnitude to damage thin dielectrics. Semiquantitative arguments are made that outline how this mechanism is capable, in principle, of explaining a wide range of published empirical data. Notable among these predictions is that plasma PID can depend upon the size and shape of the antenna, behaves as though the stress were from a current source, and is only proportional to antenna ratio (AR) under special circumstances  相似文献   

7.
The effects of impact ionization in the InGaAs absorption layer on the multiplication, excess noise and breakdown voltage are modeled for avalanche photodiodes (APDs), both with InP and with InAlAs multiplication regions. The calculations allow for dead space effects and for the low field electron ionization observed in InGaAs. The results confirm that impact ionization in the InGaAs absorption layer increases the excess noise in InP APDs and that the effect imposes tight constraints on the doping of the charge control layer if avalanche noise is to be minimized. However, the excess noise of InAlAs APDs is predicted to be reduced by impact ionization in the InGaAs layer. Furthermore the breakdown voltage of InAlAs APDs is less sensitive to ionization in the InGaAs layer and these results increase tolerance to doping variations in the field control layer.  相似文献   

8.
9.
This paper is primarily tutorial in nature and presents an alternative derivation of the Barankin estimator. The approach presented here places clearly in evidence the significance of the choice of parameter points that one must make in obtaining a Barankin lower bound. Specifically, for any finite set of parameter points, the corresponding Barankin bound is the variance of the locally best estimator that is constrained to be unbiased at the chosen parameter points. In addition, the derivation of the Barankin theory presented here provides a new interpretation of the Cramér-Rao and Bhattacharyya bounds.  相似文献   

10.
In this paper, we develop a measure-theoretic version of the junction tree algorithm to compute desired marginals of a product function. We reformulate the problem in a measure-theoretic framework, where the desired marginals are viewed as corresponding conditional expectations of a product of random variables. We generalize the notions of independence and junction trees to collections of /spl sigma/-fields on a space with a signed measure. We provide an algorithm to find such a junction tree when one exists. We also give a general procedure to augment the /spl sigma/-fields to create independencies, which we call "lifting." This procedure is the counterpart of the moralization and triangulation procedure in the conventional generalized distributive law (GDL) framework, in order to guarantee the existence of a junction tree. Our procedure includes the conventional GDL procedure as a special case. However, it can take advantage of structures at the atomic level of the sample space to produce junction tree-based algorithms for computing the desired marginals that are less complex than those GDL can discover, as we argue through examples. Our formalism gives a new way by which one can hope to find low-complexity algorithms for marginalization problems.  相似文献   

11.
A new approach to the study of distributed RC notch filters is presented. The method is intended to impart a clearer understanding into the mechanism which causes the null to appear. It also leads to the introduction of different forms of notch filters than those previously considered.  相似文献   

12.
Expressions are derived for integrated-circuit yield as a function of active circuit area, using as a model random distributions of indistinguishable spot defects. Previous attempts to calculate integrated-circuit yield have used a nonrandom distribution of distinguishable spot defects as their model.  相似文献   

13.
1/f noise in HgCdTe photodiodes has been attributed to a variety of sources, most of which are associated with some form of excess current. At DRS, we have measured the 1/f noise in vertically integrated (VIP) and high-density vertically integrated photodiodes (HDVIP), over a wide range of compositions and temperature, for strictly well-behaved diffusion current limited operation. It is found that (1) the 1/f noise current is directly dependent on dark current density; (2) material composition and temperature are irrelevant, except in as much as they determine the magnitude of the current density; (3) in high-quality diodes, the 1/f noise is independent of background flux; and (4) surface passivation is relevant. These observations have been compared to the 1/f noise theory of Schiebel, which uses McWhorter’s fluctuation of the surface charge tunneling model to modulate diode diffusion current. Agreement is obtained with Schiebel’s theory for realistic surface trap densities in the 1012/cm2 range, which will obviously be characteristic of the passivation used. The relevance of this work relative to high operating temperature phtodiodes is discussed.  相似文献   

14.
Coding for avalanche photodiode (APD)-based direct-detection optical channels is investigated using a simple channel model that clearly points out the difference between the signal-dependent optical noise channel model and additive white Gaussian noise channel model. Coding and modulation are viewed as a single entity and the coding/modulation gain (CMG) is used to analyze and construct good codes for APD-based optical receivers. It is shown that the structure of block codes, when used in conjunction with on-off keying signaling, renders these codes fairly inefficient with respect to obtaining reasonable CMG on the optical channel. In contrast, codes (or modulations) that use fewer channel ones (pulses) than information ones per block can offer substantial CMG on the optical channel. For bandwidth-constrained applications, the authors propose using pulse-position modulation with more than one pulse per word to obtain reasonable CMG while consuming small amounts of bandwidth  相似文献   

15.
Experimental results obtained from supercritical c.w. GaAs transferred-electron reflection amplifiers at about 34 GHz are reported. Gains in excess of 20 dB have been observed with typical (gain)?×bandwidth products of 1.0?1.5GHz. The best noise figure is 18 dB, and this parameter is shown to be sensitive to the doping profile. The output power for 1 dB gain compression is typically 2.5?3.0 mW.  相似文献   

16.
We have investigated the properties of excess low frequency noise in illuminated mid wavelength infrared and long wavelength infrared HgCdTe photodiodes at zero bias. The current power spectrum (Si) dependence is usually close to inverse frequency (f), but substantial variations have been observed. The magnitude of l/f spectra is voltage independent for small bias voltages, but is proportional to the square of the photocurrent (I). Consequently, the l/f knee increases, with photocurrent. Variable area device studies indicate that the noise sources are more closely associated with the device area (Aj) than perimeter, indicating bulk limitations. The power spectrum can be represented by an empirical relationship of the form SiphI 2/fAj. This defines a figure of merit, αph which takes into the account the relationship between current dependence and device geometry. αph is device dependent, suggesting that randomly distributed defects play a role in the difference. This is also supported by noting that devices fabricated in material grown on lattice matched substrates have lower αph (10−16 cm2) than those fabricated in material grown on nonlattice matched substrates (10−14 cm2), which usually have two orders of magnitude larger dislocation density. We conclude that photo-induced l/f noise can be reduced via defect reduction and is not fundamental. Data on our best devices indicates that αph is somewhat lower for smaller band gap material. The temperature dependence of photo-induced excess low frequency noise is much weaker than that of bias induced excess low frequency noise, indicating unrelated generation mechanisms. In addition, photo-induced l/f adds in quadrature with bias induced l/f noise and is not well correlated in magnitude with either bias induced l/f noise or detector dark currents.  相似文献   

17.
The authors propose a new noise figure for avalanche photodiodes (APDs). This new noise figure overcomes the difficulty of estimating the internal multiplication and quantum efficiency in complex APD structures, such as III-V SAM APDs. Measurements of the new noise figure are presented for two commercial SAM APDs and the authors show theoretically that it represents a more complete figure of merit for comparing the performance of one APD with another, and with the ideal  相似文献   

18.
The fiber gain and noise figure in erbium (Er)-ytterbium (Yb) codoped fiber amplifiers are experimentally studied and theoretically modeled. The different fiber parameters for the model are found in separate characterization measurements. The comparison between the measured and calculated data show excellent agreement. In addition, we demonstrate the design process for a specific cladding-pumped fiber to find the optimum fiber length  相似文献   

19.
20.
It is well known that the gain-bandwidth product of an avalanche photodiode can be increased by utilizing a thin multiplication region. Previously, measurements of the excess noise factor of InP-InGaAsP-InGaAs avalanche photodiodes with separate absorption and multiplication regions indicated that this approach could also be employed to reduce the multiplication noise. This paper presents a systematic study of the noise characteristics of GaAs homojunction avalanche photodiodes with different multiplication layer thicknesses. It is demonstrated that there is a definite “size effect” for multiplication regions less than approximately 0.5 μm. A good fit to the experimental data has been achieved using a discrete, nonlocalized model for the impact ionization process  相似文献   

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