Avalanche Multiplication Factor Research Articles

Bidirectional multimode-fiber communication links using dual-purpose vertical-cavity devices

This paper describes the development of novel multimode-fiber (MMF) communication links that achieve half-duplex bidirectional transmission over a single fiber through the use of 850-nm dual-purpose GaAs vertical-cavity optoelectronic devices. The dual-purpose devices are fabricated by focused-ion-beam micromachining (FIBM) of standard vertical-cavity surface-emitting lasers (VCSELs) and are able to be switched between operation as either efficient laser sources or as resonant-cavity-enhanced avalanche photodetectors. An avalanche multiplication factor of 10 is achieved at a reverse-bias voltage of 12.3 V. A 1.25-Gb/s half-duplex bidirectional data communication link is demonstrated and shown to allow error-free transmission of binary data over 500 m of standard 50-mum-core-diameter MMF. Receiver sensitivities for transceivers based upon these devices are predicted for the first time to be comparable with conventional data communication transceivers. Furthermore, a half-duplex analog bidirectional system is constructed, which permits the transmission of advanced RF modulation formats over MMF. Link characterization by error-vector magnitude (EVM) is described. The dual-purpose vertical-cavity devices are employed for bidirectional transmission of 32-symbol quadrature-amplitude-modulated (32-QAM) signals on a carrier frequency of 2 GHz, relevant to many current wireless local-area network and cellular standards. EVM as low as 1.3% rms is observed for a 600-m link of 62.5-mum-core-diameter MMF

Theoretical investigation of quantum-dot avalanche photodiodes for mid-infrared applications

A novel midinfrared sensor, called the quantum-dot avalanche photodiode (QDAP), is proposed which is expected to have improved signal-to-noise ratio (SNR) in the presence of Johnson noise over its quantum-dot (QD) counterpart. In the QDAP, an intersubband QD detector is coupled with a thin, low-noise GaAs avalanche layer through a tunnel barrier. The avalanche layer provides the necessary photocurrent gain required to overcome Johnson noise and nearly achieve the dark-current-limited SNR of the QD detector. In the proposed three-terminal device, the applied biases of the QD-detector and the avalanche-photodiode sections of the QDAP are controlled separately. This feature permits the control of the QDs responsivity and dark current independently of the operating avalanche gain, thereby allowing the optimization of the avalanche multiplication factor to maximize the photocurrent's SNR. Notably, a heterojunction potential-barrier layer can also be utilized to further improve the SNR. For example, when the standard deviation of the Johnson noise is four times greater than the dark current, calculations show that the SNR enhancement offered by an avalanche multiplication factor of 5 results in relaxing the cooling requirement from 20 to 80 K.

Analytical on-state current model of polycrystalline silicon thin-film transistors including the kink effect

A simple analytical expression for the on-state current of polycrystalline silicon thin-film transistors is presented, valid in both linear and saturation regimes including the impact ionization effect. The maximum channel electric field and the avalanche multiplication factor are described in terms of an average trapped charge density at the grain boundary, varying with gate voltage due to the continuous energy distribution of the grain boundary trap states. Based on the parameters of the charge inversion voltage, effective carrier mobility and grain boundary barrier height which are extracted from the transfer characteristic at low drain voltage, the model reproduces the experimental output characteristics in devices with different gate lengths using few fitting parameters.

Impact Ionization in Thin Silicon Diodes

We study the breakdown behavior of thin, abrupt silicon pin-diodes, using a low-power optical technique which can directly measure the avalanche multiplication factors even in the presence of large tunneling currents. Our measurements agree with a simple model for nonlocal avalanche generation, and we use this model to extend the breakdown predictions to a broad class of doped diodes similar to those found in the base-collector region of bipolar devices. Based on this analysis, we make quantitative estimates for the BV/sub CEO/ breakdown of modern Si and SiGe high-speed bipolar transistors.

Substrate current based avalanche multiplication measurement in 120 GHz SiGe HBTs

A new substrate current-based technique for measuring the avalanche multiplication factor (M - 1) in high-speed SiGe heterojunction bipolar transistors (HBTs) is proposed. The technique enables M - 1 measurement at high operating current densities required for high-speed operation, where conventional techniques fail because of self-heating. Using the proposed technique, M - 1 was measured up to 10 mA/μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> on SiGe HBTs featuring 120 GHz peak f <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">T</sub> which occurs at J/sub C/ about 7 mA/μm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> . Implications for circuit applications are also discussed.

Theory of avalanche multiplication and excess noise in quantum-well infrared photodetectors

A theoretical treatment of the noise current of quantum-well infrared photodetectors in the presence of avalanche multiplication is presented. Avalanche multiplication results in a characteristic excess noise which is expressed as a function of the avalanche multiplication factor and the capture probability. The multiplication factor can thus be determined from the photoconductive gain and the noise gain.

Avalanche multiplication due to impact ionization in quantum-well infrared photodetectors: A quantitative approach

We investigate the influence of avalanche multiplication by impact ionization on the photoconductive gain and the noise gain in quantum-well infrared photodetectors (QWIPs). A quantitative method is presented allowing the avalanche multiplication factor M and its field dependence to be determined from the measured photoconductive gain and noise gain. The approach is demonstrated using an In0.30Ga0.70As/GaAs QWIP.

STUDY OF Al0.065Ga0.935Sb AVALANCHE PHOTODETECTORS FOR 1.55 μm OF WAVELENGTH BY LIQUID PHASE EPITAXY AT LOW TEMPERATURE

We report the results of a study of Al 0.065 Ga 0.935 Sb avalanche photodetectors grown on n-GaSb substrates. The devices have been fabricated from layers with the structure p-Al 0.13 Ga 0.87 Sb/n-Al 0.065 Ga 0.935 Sb:Te/n-GaSb (substrate) grown by liquid phase epitaxy (LPE) with a composition matched to detect light of 1.55 μm. The heterostructures were grown from Ga-rich solutions at 400°C. Just after their growth, the structures were subjected to baking processes inside the growth chamber. The baking time was varied and its influence on the breakdown voltages of the junctions was observed. Breakdown voltages up to 12 V, very low net donor concentration in the active layer (1E15 cm -3), and avalanche multiplication factors of around 50 have been obtained. The carrier concentration was determined by the C–V method. Photoluminescence and X-ray diffraction measurements were carried out to investigate the properties of the LPE-grown ternary layers, to determine the band gap and to estimate the quality of epitaxial layers. The photoresponses of the detectors are also presented.

Monte Carlo calculation of electron drift characteristics and avalanche noise in bulk InAs

Field dependent drift velocity results are presented for electron transport in bulk indium arsenide (InAs) material based on a Monte Carlo model, which includes an analytical treatment of band-to-band impact ionization. Avalanche multiplication and related excess noise factor (F) are computed as a function of device length and applied voltage. A decrease in F with increases in device length is obtained. The results suggest an inherent utility for InAs-based single-photon avalanche detectors, particularly around the 2 μm region of interest for atmospheric remote sensing applications.

Dead space effect in space-charge region of collector of AlGaAs/InGaAs p-n-p heterojunction bipolar transistors

Hole-initiated avalanche multiplication is investigated using an AlGaAs/InGaAs p-n-p heterojunction bipolar transistor (HBT). Both experimental measurements and theoretical calculation are used to determine the avalanche multiplication factor. A large departure is observed at low electric field when comparison is made between the measured data and theoretical results obtained from the standard ionization model. The comparison shows that the conventional impact ionization model, based on local electric field, substantially overestimates the hole avalanche multiplication factor Mp−1 in the AlGaAs/InGaAs p-n-p HBT, where a significant dead space effect occurs in the collector space-charge region. A simple correction model for the dead space is proposed, that allows the multiplication to be accurately predicted, even in a heavily doped structure. Based on this model, multiplication characteristics for different threshold energy of the hole are calculated. A threshold energy of 2.5 eV was determined to be suitable for describing the hole-initiated impact ionization process.

A comparative study of microstrip plate geometries as UV photosensors with reflective photocathodes: simulation

A numerical simulation of eight microstrip plate geometries operated in 760 torr of xenon was performed. The cathode widths and anode-to-cathode gaps were varied while the anode widths were held constant at 10 /spl mu/m. Avalanche multiplication factors as a function of position and total gains for all geometries were determined. Since optical positive feedback is a limiting factor in considering microstrip plates as vacuum ultraviolet (VUV) photosensors, the optical positive feedback of a CsI-coated microstrip plate used as a VUV photosensor for a gas proportional scintillator counter was estimated for all geometries. The geometry with the least optical positive feedback in this application was determined to have 160-/spl mu/m cathodes and cathode-to-anode gaps of 55 /spl mu/m.

Temperature stabilization of avalanche photodetectors in recirculation-type information systems

The influence of the temperature on the signal‐to‐noise ratio ξ in the optoelectronic recirculation circuit of an informationξmeasuring system with an avalanche photodetector has been analyzed. It has been established that the temperature dependence of the pulse power of an injection laser has an influence on the width and position of the maximum in the temperature dependence of ξ at the output of the photodetector in a recirculation‐type system. The methods of maintenance of the avalanche multiplication factor of a photodetector at a given level have been proposed and their efficiency has been estimated.

Is there avalanche multiplication in amorphous semiconductors?

A model of the avalanche carrier multiplication in amorphous materials is suggested. The model is based on the concept of sub-gap impact ionization controlled by thermally assisted dissociation of generated geminate pairs of carriers. The obtained results explain an experimentally observed positive temperature dependence of the avalanche multiplication factor in amorphous selenium.

Nonuniform doping of the collector in avalanche transistors to improve the performance of Marx bank circuits

It is shown that the avalanche multiplication factor of transistors, which plays a key role in the functioning of the Marx bank circuit, can be considerably enhanced when the collector has a Gaussian doping profile, compared to uniform doping. The limiting of the maximum field in the collector, and the base push out are the events involved in the occurrence of the current mode second breakdown of avalanche transitors in the Marx circuit. Calculations show that the limiting of the maximum field, followed by the base push out, is the sequence conducive to the enhancement of the avalanche gain. Preliminary experimental assessment of the doping profiles of the same model of transistors from two different manufacturers supports the proposed idea.

Modular approach of a high current MOS compact model for circuit-level ESD simulation including transient gate-coupling behaviour

A novel modular strategy for highly flexible modeling of ESD-capable MOS compact models is introduced. This high current MOS model comprises the important gate-coupling effect and an approximated formulation for the avalanche multiplication factor. This enormously enhances the computation stability and performance of the model. An easy but accurate parameter extraction procedure based upon the model equations is described. Measurement and simulation of an application example employing the new ESD-model within a CMOS output driver exhibit the relevance of dynamic gate-coupling for the ESD-reliability of the circuit.

Measurement of collector-base junction avalanche multiplication effects in advanced UHV/CVD SiGe HBT's

This paper presents measurements of the avalanche multiplication factor (M-1) in SiGe HBTs using a new technique capable of separating the avalanche multiplication and Early effect contributions to the increase of collector current with collector-base bias, as well as allowing safe measurements at practical current densities. The impact of collector doping, current density, Ge profile, and operation temperature are reported for the first time using measured and simulated results from a production quality UHV/CVD SiGe HBT technology. Limitations of the technique in the presence of significant self-heating are discussed. By turning on the secondary hole impact ionization, we revealed the difference in impact ionization between strained SiGe and Si in the presence of the dead space effect. Despite its smaller bandgap, the compressively strained SiGe layer shows an apparent decrease in the secondary hole impact ionization rate compared to Si.

Collector-base junction avalanche multiplication effects in advanced UHV/CVD SiGe HBTs

The collector-base junction avalanche multiplication factor (M-1) in SiGe HBTs is investigated using a new technique better tolerant to self-heating and collector-base leakage. The new technique provides higher accuracy at low current densities and enables M-1 to be measured at high current densities typically used in circuits. Comparisons with identically processed silicon control devices show that M-1 is not inadvertently increased by the incorporation of SiGe, despite its smaller bandgap. With cooling, M-1 first increases, and then saturates when T<117 K. A 2.3 V critical reverse CB voltage at which base current reversal occurs is observed down to 83 K, which is sufficiently high for today's bipolar and BiCMOS logic applications.

Temperature dependence of snap-back breakdown up to 300°C analyzed using circuit level model and simulation

The MOS snap-back breakdown and its temperature dependence were investigated up to 300°C using silicided LDD-NMOS transistors. The snap-back sustaining voltage increases from 8.25V at room temperature to 8.9V at 300°C (for L eff=0.56μm). By using extracted parameters for a simple lumped element model we explain this behaviour originating from an increasing avalanche breakdown voltage and slope of avalanche multiplication factor compensating the increase in bipolar gain with temperature.

A strained InAIAs/InGaAs superlattice avalanche photodiode with a waveguide structure for low bias-voltage operation

An InAIAs/InGaAs superlattice (SL) multiplication layer operating at an IC-power supply voltage was realized by introducing strain into the SL. Using this SL as an absorption and multiplication layer, edge-coupled InAIAs/InGaAs SL avalanche photodiodes with waveguide structures were demonstrated. An avalanche multiplication factor larger than 10 was achieved at a bias voltage of less than 7V. A wide 3 dB bandwidth of 8 GHz was obtained at a multiplication factor of 3 and a wavelength of 1.3 μm.

Single photo-electron and photon detection in a mercury resonance ionization photon detector (RID)

Avalanche detection of a laser enhanced ionization (LEI) signal has been studied in a resonance ionization detector (RID) cell containing mercury vapor at room temperature. An avalanche multiplication factor of more than 8000 was achieved. The limit of detection of Hg resonance radiation ( λ = 253.7 nm) was at the level of 0.5 quantum during the lifetime of the excited 6 3P 1 0 state. Detection of radiation from a conventional CW Hg discharge lamp source with a signal to noise ratio of more than 10 4 has been achieved.