Response Of Avalanche Photodiodes Research Articles

Photo-Electric response of 4H-SiC APDs at High-Level incident flux

In many applications, the highest and lowest detectable flux are both important for single photon avalanche photodiodes (APDs). The photocurrent and single-photon-counting performance of 4H-SiC APDs are investigated under a wide-range incident flux. Experimental results show that the photocurrent is sub-linearly with the incident photon rate at high-level incident flux. In addition, the ratio of photon count rate to dark count rate is non-monotonic when the incident flux increases. The highest detectable flux of the 4H-SiC APD can be extended from 3 × 103 photons/s·μm2 to more than 4 × 104 photons/s·μm2 by reducing the threshold voltage and increasing the reverse voltage.

Effect of the Series Resistance on the Current Response of a HgCdTe Avalanche Photodiode Under High-intensity Nanosecond Irradiation

We investigate the nonlinear signal current response of a Hg0.72Cd0.28Te avalanche photodiode (APD) irradiated by high-intensity, finite-duration laser pulses. At high irradiation levels and/or high gains, carrier-induced perturbations in the junction electric field and avalanche gain strongly influence the temporal behavior of the APD current. The total series resistance will play a major role here, and four values of the series resistance were used for mapping out the APD response. When striving for maximum achievable bandwidth, the internal junction capacitance and the internal series resistance set the ultimate limits for an APD. A signal analysis of these high-intensity nonlinear gain effects should therefore begin with an intrinsic APD, and proceed with adding appropriate external series resistances. A simultaneous modeling of the entire external circuit is then required. To this end, we have combined full-band Monte Carlo (MC) transport simulation in the active multiplication zone with conventional circuit modeling outside. We demonstrate how overshoot/undershoot and rapid oscillations in the signal current evolve in time as a function of the chosen external series resistances at two different high-intensity irradiation levels. Oscillations are shown to persist slightly beyond the duration of the laser pulse when operating the diode within the junction transit time-limited regime. The periodicity of the oscillations is related to the junction transit time and remains only weakly dependent on irradiation levels and external resistance values until we enter the resistance–capacitance (RC)-limited case. Here, a change occurs where oscillations are smoothed out as external series resistances are increased further.

Drop-casting CsPbBr3 perovskite quantum dots as down-shifting layer enhancing the ultraviolet response of silicon avalanche photodiode

Since the absorption zone of ultraviolet (UV) photons with high energy is limited to a few tens of nm on the surface, the high defect density caused by the processes, such as ion implantation, leads to a weak response of the silicon avalanche photodiode (APD) in the ultraviolet band. In this work, the integration of the inorganic perovskite quantum dots (QDs) film by drop-casting as the down-shifting layer is reported for enhancing the UV response of Si APD. The light generated current increases 100% under the 365 nm light emitting diode. The response of the Si APD is improved in the entire ultraviolet band. In particular, the responsivity of APD is increased by 78% at 340 nm with an exceedingly EQE of 92%. In summary, the perovskite QDs film as a down-shifting layer provides an effective and low-cost method to improve the UV response of Si APD.

Study on non-linearity response of 4H-SiC APD

UV photon counting detection technology based on 4H-SiC Avalanche photodiodes (APDs) has been widely used in virus inactivation system, quantum communication and other UV detection fields. When the ultraviolet signal is enhanced, the detection accuracy will also decrease due to the nonlinear characteristics of the photoelectric response. Therefore, the physical mechanism and nonlinear error source of the photoelectric response of 4H-SiC APD were analysed, and a photoelectric response characteristic testing system was built. The theoretical and experimental results show that the photocurrent increases linearly when the incident photon number is high, and the multi-photon incident results in the nonlinear phenomenon of photon count. Reducing device bias and increasing threshold voltage can significantly improve the nonlinear phenomenon of photoelectric response, and the maximum linear operating range of the device can be extended from 10 7s -1 to more than 10 9s -1.

Simulation and Modeling Time Response of Double Carrier Avalanche Photodiodes

Avalanche photodiodes (APDs) is a particularly sensitive semiconductor device that employs the photoelectric effect to convert light into electricity. APDs can be used in some typical applications, i.e. imaging, optical fiber communications, range finding, laser scanners and laser microscopy. In APDs, avalanche multiplication occurred due to impact ionization when the devices operating at high electric fields. Unfortunately, avalanche multiplication decreases the time response of APDs. The time response of an APD can be characterized by its current response which is represented by the mean current as a function of time. This paper discusses a method to estimate the time response of double-carrier multiplication avalanche photodiodes (APDs). The model, called The Random Path Length (RPL), generates random path length for a carrier to impact ionize and takes account of dead space distance into the calculation. Dead space distance is the minimum distance to travel by a carrier to gain the adequate energy to start first ionization. The RPL is applied into an ideal structure which is assumed has a dimensionless multiplication length, w = 1.0, with electrons and holes moving in constant speeds, ve = vh = v, for various dead spaces distances, d*. In this research, a computer code is generated to compute the mean impulse response, i(t), and the standard deviation, s(t), of APDs all as a function of time.

Fabrication and Analysis of Thin Film CdTe/CdS-Based Avalanche Photodiodes

Thin film CdTe/CdS-based avalanche photodiodes (APDs) are fabricated and characterized successfully. A separated absorption and multiplication CdTe/CdS p-i-n-i-n APD is proposed, fabricated, and analyzed. Compared with the conventional p-i-n APD, the p-i-n-i-n structure reduces the probability of premature micro-plasma breakdown, raises the gain from 147 to 473 and reduces the work voltage from 29 V to 21 V. The responsivity of APDs can reach 60 AW $^{-1}$ and the avalanche gain of the photodiodes is about 473 at 22 V. Considering that no previous report on CdTe/CdS-based APDs can be found, the results reported in this letter may promise a route to high-performance CdTe/CdS thin film photodiodes.

The response characteristics of avalanche photodiodes to ultrashort pulsed laser

The physical model of avalanche photodiode (APD) response to ultrashort pulsed laser is established. Numerical simulation of APD response characteristics is focused and presented. The simulated results show that the response peak voltage degrades approximately linearly with the laser pulse duration narrowing when the peak power of laser pulse keeps unchanged. Meanwhile, when the energy of input pulse laser is at the same quantity, the response peak voltage keeps invariably in different pulse duration. Moreover, the pulse duration of response voltage is determined by the sensitivity of APD itself, and the input duration of ultrashort pulsed laser could not be recognized by the APD. Experiments are carried out and the experimental results are in good agreement with simulated data.

Comparison of waveguide avalanche photodiodes with InP and InAlAs multiplication layer for 25 Gb/s operation

2.5 and 10 Gb/s InP/InGaAs avalanche photodiodes (APDs) have been widely used in optical communication systems. However, the study on InP/InGaAs APDs above 10 Gb/s is insufficient. Recently, high-speed and high-sensitivity APDs for 100 Gb/s or even 400 Gb/s optical communication systems have drawn a lot of attention. On basis of the physical model for frequency response of APD including the dead space effect, a waveguide separate absorption, grading, charge, and multiplication (WG-SAGCM) InP/InGaAs APD has been designed for 25 Gb/s operation. Also, the frequency response of WG InAlAs/InGaAs APD was also simulated, which is perfectly in accordance with the experimental data. The comparison between InP/InGaAs APD and InAlAs/InGaAs APD with the same thickness of multiplication layer shows that the speeds of carriers in the nonionization layers are also important for the gain-bandwidth characteristics of SAGCM WG-APD. The higher drift velocity of carriers returned from multiplication layer and the lower drift velocity of carriers injected into multiplication layer result in a higher gain-bandwidth product and a higher dc gain. This work is helpful for the design of high-speed APDs.

Response of CMS avalanche photo-diodes to low energy neutrons

The response of the Avalanche Photo-diodes (APDs) installed in the CMS detector at the LHC to neutrons from 241AmBe and 252Cf sources is reported. Signals in size equivalent to those of up to 106 photo-electrons with the nominal APD gain are observed. Measurements with an APD with the protective epoxy coating removed and with the source placed behind the APD show that there is an important response due to recoil protons from neutron interactions with the hydrogen in the epoxy, in addition to signals from neutron interactions with the silicon of the diode. The effective gain of these signals is much smaller than the diode's nominal gain.

Temperature dependence of the thin dead layer avalanche photodiode for low energy electron measurements

We have investigated the temperature dependence of the Hamamatsu spl 6815 Avalanche Photodiode (APD) response, when used as an low energy electron detector, over the temperature range from - 9 to 30 ∘ C . In order to make precise measurements, relevant to the particles of interest, electrons were actually used to calibrate the APD response. The gain variation over the temperature was - 1.2 % / K at 10 ∘ C for a nominal bias voltage. Although a slight dead layer effect was found, the linearity of the response was excellent over all measured temperatures, and the variation of the energy resolution was acceptably small to maintain good performance. The temperature effects can be readily canceled out with an active bias voltage control based on the ambient temperature so long as the internal gain is maintained between 15 and 20.

Equivalent Circuit Modeling of Separate Absorption Grading Charge Multiplication Avalanche Photodiode

In this paper, a novel equivalent circuit model for the frequency performance of separate absorption grading charge multiplication (SAGCM) avalanche photodiode (APD) is developed. This model includes effects of carrier transit time, avalanche buildup time, and parasitic RC elements. Based on the equivalent circuit model, frequency and bandwidth characteristics of SAGCM APD can be simulated in advance to device fabrication, and the simulation results are in good agreement with experimental data. Conventional pin photodiodes can also be simulated as a special case when M=1. In addition, the frequency response of SAGCM APDs and pin photodiodes with different illumination directions are investigated.

Single-photon time response of reach-through APD

Time response of avalanche photodiode (APD) is very important in photon counting systems, and there are many models for circuit simulation. But these studies generally based on the carrier rate equations of steady-state condition, disagree with the single-photon-indicate condition. In this paper, a time response function based on an integration of APD’s sub-domain carriers for reach-through APD arising from a single photo-carrier is derived. The analytical results are shown to be in good accord with experimental results.

Current impulse response of thin InP p+–i–n+ diodes

The simulation of current impulse response using random response time model in avalanche photodiode (APD) is presented. A random response time model considers the randomness of times at which the primary and secondary carriers are generated in multiplication region. The dead-space effect is included in our model to demonstrate the impact on current impulse response of thin APDs. Current impulse response of homojunction InP p+–i–n+ diodes with the multiplication widths of 0.1 and 0.2μm are calculated. Our results show that dead-space gives a slower decay rate of current impulse response in thin APD, which may degrade the bit-error-rate of the optical communication systems.

A simplified approach to time-domain modeling of avalanche photodiodes

A simplified algorithm for calculating time response of avalanche photodiodes (APDs) is presented. The algorithm considers the time course of avalanche processes for the general case of position-dependent double-carrier multiplications including the dead space effect. The algorithm is based on a discrete time setting ideally suited for computer modeling and can be applied to any APD structure. It gives a fast and accurate estimation of the time and frequency response of APDs. As an example, the present method is applied to InP-InGaAs separate absorption, grading, charge, and multiplication (SAGCM) APDs. The variation of multiplication pain with bias voltage and 3-dB electrical bandwidth at different multiplication gain obtained using the new algorithm show good agreement with experimental results. The algorithm can be used to study temperature dependence of APD characteristics and can be easily extended to calculate the excess noise factor.

Responsivity of avalanche photodiodes in the presence of multiple reflections

It is shown theoretically, and verified experimentally, that a photodiode, illuminated by monochromatic light of varying wavelength, may show interference ripples in its responsivity, owing to multiple reflections between the diode front and back contact. The amplitude of the ripples is found to increase linearly with the avalanche multiplication factor.