1,929 research outputs found
Multi-Gain-Stage InGaAs Avalanche Photodiode with Enhanced Gain and Reduced Excess Noise
We report the design, fabrication, and test of an InGaAs avalanche photodiode (APD) for 950-1650 nm wavelength sensing applications. The APD is grown by molecular beam epitaxy on InP substrates from lattice-matched InGaAs and InAlAs alloys. Avalanche multiplication inside the APD occurs in a series of asymmetric gain stages whose layer ordering acts to enhance the rate of electron-initiated impact ionization and to suppress the rate of hole-initiated ionization when operated at low gain. The multiplication stages are cascaded in series, interposed with carrier relaxation layers in which the electric field is low, preventing avalanche feedback between stages. These measures result in much lower excess multiplication noise and stable linear-mode operation at much higher avalanche gain than is characteristic of APDs fabricated from the same semiconductor alloys in bulk. The noise suppression mechanism is analyzed by simulations of impact ionization spatial distribution and gain statistics, and measurements on APDs implementing the design are presented. The devices employing this design are demonstrated to operate at linear-mode gain in excess of 6000 without avalanche breakdown. Excess noise characterized by an effective impact ionization rate ratio below 0.04 were measured at gains over 1000
New Perspective on Passively Quenched Single Photon Avalanche Diodes: Effect of Feedback on Impact Ionization
Single-photon avalanche diodes (SPADs) are primary devices in photon counting systems used in quantum cryptography, time resolved spectroscopy and photon counting optical communication. SPADs convert each photo-generated electron hole pair to a measurable current via an avalanche of impact ionizations. In this paper, a stochastically self-regulating avalanche model for passively quenched SPADs is presented. The model predicts, in qualitative agreement with experiments, three important phenomena that traditional models are unable to predict. These are: (1) an oscillatory behavior of the persistent avalanche current; (2) an exponential (memoryless) decay of the probability density function of the stochastic quenching time of the persistent avalanche current; and (3) a fast collapse of the avalanche current, under strong feedback conditions, preventing the development of a persistent avalanche current. The model specifically captures the effect of the loadâs feedback on the stochastic avalanche multiplication, an effect believed to be key in breaking todayâs counting rate barrier in the 1.55âÎŒm detection window
Tunneling-assisted impact ionization fronts in semiconductors
We propose a novel type of ionization front in layered semiconductor
structures. The propagation is due to the interplay of band-to-band tunneling
and impact ionization. Our numerical simulations show that the front can be
triggered when an extremely sharp voltage ramp () is
applied in reverse direction to a Si structure that is connected in
series with an external load. The triggering occurs after a delay of 0.7 to 0.8
ns. The maximal electrical field at the front edge exceeds .
The front velocity is 40 times faster than the saturated drift velocity
. The front passes through the base with a thickness of
within approximately 30 ps, filling it with dense electron-hole plasma. This
passage is accompanied by a voltage drop from 8 kV to dozens of volts. In this
way a voltage pulse with a ramp up to can be applied to the
load. The possibility to form a kilovolt pulse with such a voltage rise rate
sets new frontiers in pulse power electronics.Comment: 12 pages, 6 figure
Large-Signal Simulation of 94 GHz Pulsed Silicon DDR IMPATTs Including the Temperature Transient Effect
In this paper large-signal modeling and simulation has been carried to study the frequency chirping due to temperature transients and the large-signal power and efficiency of pulsed silicon Double-Drift Region (DDR) Impact Avalanche Transit Time (IMPATT) device operating at 94 GHz. A large-signal simulation method based on non-sinusoidal voltage excitation incorporating the transient thermal effect has been developed by the authors. Results show that the device is capable of delivering a peak pulsed power output of 17.5 W with 12.8% efficiency when the voltage modulation is 60%. The maximum junction temperature rise is 350.2 K for a peak pulsed bias current of 6.79 A with 100 ns pulsewidth and 0.5 percent duty cycle; whereas the chirp bandwidth is 8.3 GHz
The merits and limitations of local impact ionization theory
Multiplication measurements on GaAs p+-i-n+s with i-region thicknesses, w, between 1 ÎŒm and 0.025 ÎŒm and Monte Carlo (MC) calculations of the avalanche process are used to investigate the applicability of the local ionization theory. The local expressions for multiplication are able to predict the measured values surprisingly well in p+-i-n+s with i-region thicknesses, w, as thin as 0.2 ÎŒm before the effect of dead-space, where carriers have insufficient energy to ionize, causes significant errors. Moreover, only a very simple correction to the local expressions is needed to predict the multiplication accurately where the field varies rapidly in abrupt one-sided p+-n junctions doped up to 1018 cm-3. However, MC modeling also shows that complex dead-space effects cause the local ionization coefficients to be increasingly unrepresentative of the position dependent values in the device as w is reduced below 1 ÎŒm. The success of the local model in predicting multiplication is therefore attributed to the dead-space information already being contained within the experimentally determined values of local coefficients. It is suggested that these should therefore be thought of as effective coefficients which, despite the presence of dead-space effects, can be still be used with the existing local theory for efficiently quantifying multiplication and breakdown voltages
Dynamic avalanche breakdown of a p-n junction: deterministic triggering of a plane streamer front
We discuss the dynamic impact ionization breakdown of high voltage p-n
junction which occurs when the electric field is increased above the threshold
of avalanche impact ionization on a time scale smaller than the inverse
thermogeneration rate. The avalanche-to-streamer transition characterized by
generation of dense electron-hole plasma capable to screen the applied external
electric field occurs in such regimes. We argue that the experimentally
observed deterministic triggering of the plane streamer front at the electric
field strength above the threshold of avalanche impact ionization but yet below
the threshold of band-to-band tunneling is generally caused by field-enhanced
ionization of deep-level centers. We suggest that the process-induced sulfur
centers and native defects such as EL2, HB2, HB5 centers initiate the front in
Si and GaAs structures, respectively. In deep-level free structures the plane
streamer front is triggered by Zener band-to-band tunneling.Comment: 4 pages, 2 figure
The impact of repetitive unclamped inductive switching on the electrical parameters of low-voltage trench power nMOSFETs
The impact of hot-carrier injection (HCI) due to repetitive unclamped inductive switching (UIS) on the electrical performance of low-voltage trench power n-type MOSFETs (nMOSFETs) is assessed. Trench power nMOSFETs with 20- and 30-V breakdown voltage ratings in TO-220 packages have been fabricated and subjected to over 100 million cycles of repetitive UIS with different avalanche currents IAV at a mounting base temperature TMB of 150°C. Impact ionization during avalanche conduction in the channel causes hot-hole injection into the gate dielectric, which results in a reduction of the threshold voltage VGSTX, as the number of avalanche cycles N increases. The experimental data reveal a power-law relationship between the change in the threshold voltage ÎVGSTX and N. The results show that the power-law prefactor is directly proportional to the avalanche current. After 100 million cycles, it was observed in the 20-V rated MOSFETs that the power-law prefactor increased by 30% when IAV was increased from 160 to 225 A, thereby approximating a linear relationship. A stable subthreshold slope with avalanche cycling indicates that interface trap generation may not be an active degradation mechanism. The impact of the cell pitch on avalanche ruggedness is also investigated by testing 2.5- and 4- m cell-pitch 30-V rated MOSFETs. Measurements showed that the power-law prefactor reduced by 40% when the cell pitch was reduced by 37.5%. The improved VGSTX stability with the smaller cell-pitch MOSFETs is attributed to a lower avalanche current per unit cell resulting in less hot-hole injection and, hence, smaller VGSTX shift. The 2.5-m cell-pitch MOSFETs also show 25% improved on -state resistance RDSON, better RDSON stability, and 20% less subthreshold slope compared with the 4-m cell-pitch MOSFETs, although with 100% higher initial IDSS and less IDSS stability with avalanche cycling. These results are important for manufacturers of automotive MOSFETs where multiple avalanche occurrences over the lifetime of the MOSFET are expected
Avalanche Photodiode Having Edge Breakdown Suppression
The present disclosure relates to an avalanche photodiode having edge breakdown suppression. The photodiode comprises a p contact and an n contact, as well as a plurality of device layers disposed between the p contact and the n contact. The device layers include, in order from the p contact to the n contact, a primary well, a decoupler layer, a multiplication layer, a charge sheet, an absorption layer, and a substrate. The layers are constructed so as to have particular volumes of charge which affects the order in which they deplete. With the preferred order of depletion, the multiplication layer will deplete before the decoupler layer and the decoupler layer will deplete before the charge sheet when a negative bias is applied to the avalanche photodiode. This results in a joint opening effect within the avalanche photodiode which effectively suppresses edge breakdown.Georgia Tech Research Corporatio
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