Dark count in single-photon avalanche diodes:A novel statistical behavioral model

Dark count is one of the inherent noise types in single-photon diodes,which may restrict the performances of detectors based on these diodes.To formulate better designs for peripheral circuits of such diodes,an accurate statistical behavioral model of dark current must be established.Research has shown that there are four main mechanisms that contribute to the dark count in single-photon avalanche diodes.However,in the existing dark count models only three models have been considered,thus leading to inaccuracies in these models.To resolve these shortcomings,the dark current caused by carrier diffusion in the neutral region is deduced by multiplying the carrier detection probability with the carrier particle current at the boundary of the depletion layer.Thus,a comprehensive dark current model is constructed by adding the dark current caused by carrier diffusion to the dark current caused by the other three mechanisms.To the best of our knowledge,this is the first dark count simulation model into which incorporated simultaneously are the thermal generation,trap-assisted tunneling,band-to-band tunneling mechanisms,and carrier diffusion in neutral regions to evaluate dark count behavior.The comparison between the measured data and the simulation results from the models shows that the proposed model is more accurate than other existing models,and the maximum of accuracy increases up to 31.48%when excess bias voltage equals 3.5 V and temperature is 50℃.     

Pile-up correction in characterizing single-photon avalanche diodes of high dark count rate

Although as a single-photon detector, the single-photon avalanche diode (SPAD) may be applied to multi-photon conditions. At a minimum, SPADs with a high dark count rate (DCR) demand a higher value of photon number per pulse to improve the signal-to-noise ratio. In this case, and without correction, severe pile-up distortion may induce a system error in the measurement of photon detection efficiency (PDE) and timing jitter. In this paper, we study the pile-up distortion in SPAD characterization by numerical simulation and experimentation, and introduce a pile-up correction method for the precise characterization of PDE and timing jitter in immature SPADs with an unintentionally high DCR. The results of this study are useful in the development of future SPADs.     

Quick single-photon detector with many avalanche photo diodes working on the time division

Due to the limit of response speed of the present single-photon detector, the code rate is still too low to come into practical use for the present quantum key distribution (QKD) system.A new idea is put up to design a quick single-photon detector.This quick single-photon detector is composed of a multi-port optic-fiber splitter and many avalanche photo diodes (APDs).Au of the ports with APDs work on the time division and cooperate with a logic discriminating and deciding unit driven by the clock signal.The operation frequency lies on the number N of ports, and can reach N times of the conventional single-photon detector.The single-photon prompt detection can come true for high repetition-rate pulses.The applying of this detector will largely raise the code rate of the QKD, and boost the commercial use.     

Silicon diodes in avalanche pulse-sharpening applications

Silicon diodes operated in an avalanche breakdown mode can he used to reduce, or sharpen, the rise times of driving pulses. Proper operation of a diode in this manner requires the application of a driving pulse with sufficient time rate of change of voltage dV/dt. The rapidly changing reverse bias produces an electron-hole plasma of sufficient density that the electric field strength in the n region of a p⁺-n-n⁺ structure is significantly reduced and the plasma is essentially trapped. In effect, the plasma generation causes the device to transition from a high-impedance state to a low-impedance state in a short period of time, and thus acts as a fast closing switch. This paper provides an overview of this mode of operation. A simplified theory of operation is presented. A comparison is made among the results of numerical modeling, the theory of operation of the silicon avalanche shaper (SAS) diode, and the theory of operation of the trapped-plasma avalanche-triggered transit (TRAPATT) mode of operation of a diode. Based on the results of numerical modeling, conclusions are drawn on what factors most greatly affect the performance of avalanche shaper diodes, and one optimized design is provided     

Tunneling from dislocation cores in silicon Schottky diodes

Selfquenching of the photocapacitance and of the reverse photocurrent in Schottky diodes made on dislocatedn-type silicon was discovered. A phenomenological model explaining this, rather unexpected, phenomenon is proposed. The model requires an introduction of a new mechanism of diode conductance via dislocation lines. Crucial for this mechanism is the possibility of electron tunneling from dislocation to the conduction band.     

Enhanced solar-blind ultraviolet single-photon detection with a Geiger-mode silicon avalanche photodiode

Solar-blind ultraviolet detection is of great importance in astronomy and industrial and military applications.Here, we report enhanced solar-blind ultraviolet single-photon detection by a normal silicon avalanche photodiode(Si APD) single-photon detector with a specially designed photon-collecting device. By re-focusing the reflected photon from the Si chip surface on the detection area by the aluminum-coated hemisphere, the detection efficiency of the Si APD at 280 nm can be improved to 4.62%. This system has the potential for high-efficiency photon detection in the solar-blind ultraviolet regime with low noise.     

Spectral method for characterization of avalanche photodiode working as single-photon detector

In this Letter, a new method for avalanche photodiode characterization, based on the spectral analysis of the photocurrent produced during an avalanche, is proposed. The theory is developed, and an experimental characterization of an avalanche photodiode working in the Geiger mode with CW laser is performed.     

Indirect optical crosstalk reduction by highly-doped backside layer in single-photon avalanche diode arrays

A method of reducing indirect optical crosstalk in single-photon avalanche diode arrays is investigated by TCAD simulations. The reduction is accomplished by taking advantage of an enhanced optical absorption in a highly-doped Si layer on the backside of the wafer. A simulation environment was developed to give information about optical crosstalk by incorporating the experimental optical constants of the materials constituting the crosstalk-reduction layer. It is shown that the indirect optical crosstalk is greatly reduced by increasing the thickness and doping of the layer. A crosstalk reduction of 5 orders of magnitude is gained with addition of 1-μm-thick \(\hbox {PureB}/\upalpha \hbox {-Si}\) stack for the array processed on a p-type substrate, while the same reduction is achieved with a 1-μm-thick highly-doped Si layer (As, \(1.1\times 10^{20}\, \hbox {cm}^{-3}\)) for an array processed on an n-type substrate.     

工艺导致的机械应力对深亚微米CMOS器件的影响

随着CMOS器件的不断微缩,硅有源区面积的缩小,工艺导致的机械应力对器件的影响越来越显著,许多工艺步骤会造成有源区应力的累积.应力不仅导致器件性能对版图产生依赖性,而且带来各种可靠性问题,影响芯片的长期使用寿命.在很多情况下,应力相关的问题直接影响芯片制造的良率.在总结各种应力来源的基础上,回顾了到目前为止人们所观察或理解的应力对CMOS器件性能和可靠性的各种影响,提出了分析和解决工业生产中应力相关问题的基本思路. 关键词： 机械应力 CMOS     

Afterpulsing characteristics of InGaAs/InP single photon avalanche diodes

In Ga As/In P single photon avalanche diodes（SPADs） are more and more available in many research fields. They are affected by afterpulsing which leads to a poor single photon detection probability. We present an In Ga As/In P avalanche photodiode with an active quenching circuit on an application specific integrated circuit（ASIC）. It can quench the avalanche rapidly and then reduce the afterpulse rate. Also this quenching circuit can operate in both free-running and gated modes.Furthermore, a new technique is introduced to characterize the influence of the higher order of afterpulses, which uses a program running on a field programmable gate array（FPGA） integrated circuit.     

Mechanisms for the occurrence of stochasticity of oscillations in avalanche transit-time diodes

Radiophysics and Quantum Electronics -     

Temperature dependent characteristics of submicron GaAs avalanche photodiodes obtained by a nonlocal analysis

In this paper, using a nonlocal analysis we have extracted the temperature dependent ionization coefficients and threshold energies of submicron GaAs avalanche photodiodes (APDs) with multiplication region thicknesses as narrow as 49 nm, from electron and hole injection photo-multiplication processes. These extracted parameters have been used to predict the temperature dependence of APDs characteristics, such as mean gain, 3 dB-bandwidth, gain-bandwidth product, excess noise factor, performance factor, and breakdown field, over a temperature range of 20 K to 290 K. In the nonlocal analysis we have taken the effects of nonuniform electric filed within the multiplication region and its surrounding depletion regions, injected carrier’s initial ionization energy, carrier’s spatial ionization rate as well as the carrier’s dead space and its previous ionization history into account. We have shown that our predicted gain values are in excellent agreement with existing experimental data measured by others.     

Noise minimization via deep submicron system-on-chip integration in megapixel CMOS imaging sensors

Infrared sensor designers have long maximized S/N ratio by employing pixel-based amplification in conjunction with supplemental noise suppression. Instead, we suppress photodiode noise using novel SoC implementation with simple three transistor pixel; supporting SoC components include a feedback amplifier having elements distributed amongst the pixel and column buffer, a tapered reset clock waveform, and reset timing generator. The tapered reset method does not swell pixel area, compel processing of the correlated reset and signal values, or require additional memory. Integrated in a 2.1 M pixel imager developed for generating high definition television, random noise is ∼8e-at video rates to 225 MHz. Random noise of ∼30e-would otherwise he predicted for the 5 μm 5 μm pixels having 5.5 fF detector capacitance with negligible image lag. Minimum sensor S/N ratio is 52 dB with 1920 by 1080 progressive readout at 60 Hz, 72 Hz and 90 Hz. Fixed pattern noise is <2 DN via on-chip signal processing. The paper presented there appears in Infrared Photoelectronics, edited by Antoni Rogalski, Eustace L. Dereniak, Fiodor F. Sizov, Proc. SPIE Vol. 5957, 595701 (2005).     

Mapping of electrostatic potential in deep submicron CMOS devices by electron holography

Quantitative two-dimensional maps of electrostatic potential in device structures are obtained using off-axis electron holography with a spatial resolution of 6 nm and a sensitivity of 0.17 V. Estimates of junction depth and variation in electrostatic potential obtained by electron holography, process simulation, and secondary ion mass spectroscopy show close agreement. Measurement artifacts due to sample charging and surface "dead layers" do not need to be considered provided that proper care is taken with sample preparation. The results demonstrate that electron holography could become an effective method for quantitative 2D analysis of dopant diffusion in deep-submicron devices.     

Effect of STI-induced mechanical stress on leakage current in deep submicron CMOS devices

The shallow trench isolation (STI) induced mechanical stress significantly affects the CMOS device off-state leakage behaviour. In this paper, we designed two types of devices to investigate this effect, and all leakage components, including sub-threshold leakage ($I_{\rm sub})$, gate-induced-drain-leakage ($I_{\rm GIDL})$, gate edge-direct-tunnelling leakage ($I_{\rm EDT})$ and band-to-band-tunnelling leakage ($I_{\rm BTBT})$ were analysed. For NMOS, $I_{\rm sub}$ can be reduced due to the mechanical stress induced higher boron concentration in well region. However, the GIDL component increases simultaneously as a result of the high well concentration induced drain-to-well depletion layer narrowing as well as the shrinkage of the energy gap. For PMOS, the only mechanical stress effect on leakage current is the energy gap narrowing induced GIDL increase.     

Investigation of avalanche photocurrent at the edge of fundamental absorption band in Schottky diodes

The relative importance of the contribution of two mechanisms, that of the change in the collection of photocurrent carriers and that of the shift of the edge of fundamental absorption of light in strong electric fields in Schottky photodiodes, to the observed spectral dependence of the avalanche photocurrent is asessed.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 12, pp. 83–86, December, 1985.     

Nonlocal analysis to study of the impact ionization and avalanche characteristics of deep submicron Si devices

In this paper, we have presented electric field dependence of the electron and hole impact ionization coefficients and threshold energies in submicron Si diodes with intrinsic region thicknesses down to 31 nm. To do so, we have used a nonlocal analysis, in order to take the effects of arbitrary distribution of ionization events in both space and time domains and the effects of enhancement in the average speed of those carriers which ionize early in their trajectories as well as nonuniform electric fields in the multiplication region and its surrounding ambient, carrier’s dead space history and its spatial ionization rate, into consideration all in one comprehensive analytic model.