Low Excess Noise Factor Research Articles

Impact ionization coefficients and excess noise in Al0.55Ga0.45As0.56Sb0.44 lattice matched to InP

The avalanche multiplication and noise characteristics of Al0.55Ga0.45As0.56Sb0.44p–i–n and n–i–p structures grown lattice matched on InP have been investigated. From measurements undertaken using 530 nm illumination on several devices, the electron (α) and hole (β) impact ionization coefficients have been determined. While α only shows a relatively small increase compared to the higher Al composition alloys of AlxGa1−xAsSb, β is found to increase significantly. Although the β/α ratio is increased to ∼0.125–0.2, higher than the ∼0.003–0.02 seen in the higher-Al alloys, a relatively low excess noise factor of 2.2 was measured in the p-i-n with electron-initiated multiplication of 20. This noise performance is significantly lower than that predicted using a local-field model and comparable to some commercial silicon APDs. This avalanching material with a bandgap of ∼1.24 eV will have the advantages of a smaller band discontinuity with the absorber region and should also operate at a lower voltage.

New Crystal Photodiode Combination for Environmental Radiation Measurement

Here, a new design will be introduced to detect radiation in the environment with high efficiency. The designed structure consists of placing ZnS–Si APD and PIN photodiodes at the ends of conventional crystals such as NaI(Tl) and CsI(Tl). Since ZnS is transparent to photons with wavelengths between 340 and 10000 nm, photons coming from the crystals are absorbed directly in the depletion region and generate primary particles. With an increase in the number of generated primary particles, a stronger and cleaner signal is obtained. In the simulation work, the light generated by 30 keV–3 MeV gamma rays in the crystals was obtained using the Geant4 simulation code. The single-particle Monte Carlo technique was used to calculate the photodiode output signal for the crystal emission spectrum. The simulation results showed that the crystals and ZnS–Si photodiode structures formed a good combination. The high quantum efficiency and low excess noise factor make the ZnS–Si structure an excellent choice for scintillating light detection.

Non-Markovian Hole Excess Noise in Avalanche Amorphous Selenium Thin Films.

Enhancing the signal-to-noise ratio in avalanche photodiodes by utilizing impact ionization gain requires materials exhibiting low excess noise factors. Amorphous selenium (a-Se) as a wide bandgap at ∼2.1 eV, a solid-state avalanche layer, demonstrates single-carrier hole impact ionization gain and manifests ultralow thermal generation rates. A comprehensive study of the history dependent and non-Markovian nature of hot hole transport in a-Se was modeled using a Monte Carlo (MC) random walk of single hole free flights, interrupted by instantaneous phonon, disorder, hole-dipole, and impact-ionization scattering interactions. The hole excess noise factors were simulated for 0.1-15 μm a-Se thin-films as a function of mean avalanche gain. The hole excess noise factors in a-Se decreases with an increase in electric field, impact ionization gain, and device thickness. The history dependent nature of branching of holes is explained using a Gaussian avalanche threshold distance distribution and the dead space distance, which increases determinism in the stochastic impact ionization process. An ultralow non-Markovian excess noise factor of ∼1 was simulated for 100 nm a-Se thin films corresponding to avalanche gains of 1000. Future detector designs can utilize the nonlocal/non-Markovian nature of the hole avalanche in a-Se, to enable a true solid-state photomultiplier with noiseless gain.

Extremely low excess noise avalanche photodiode with GaAsSb absorption region and AlGaAsSb avalanche region

An extremely low noise Separate Absorption and Multiplication Avalanche Photodiode (SAM-APD), consisting of a GaAs0.52Sb0.48 absorption region and an Al0.85Ga0.15As0.56Sb0.44 avalanche region, is reported. The device incorporated an appropriate doping profile to suppress tunneling current from the absorption region, achieving a large avalanche gain, ∼130 at room temperature. It exhibits extremely low excess noise factors of 1.52 and 2.48 at the gain of 10 and 20, respectively. At the gain of 20, our measured excess noise factor of 2.48 is more than three times lower than that in the commercial InGaAs/InP SAM-APD. These results are corroborated by a Simple Monte Carlo simulation. Our results demonstrate the potential of low excess noise performance from GaAs0.52Sb0.48/Al0.85Ga0.15As0.56Sb0.44 avalanche photodiodes.

Area-dependent gain and noise characteristics of mid-wavelength infrared HgCdTe planar electron avalanche photodiodes

This paper mainly investigates the area-dependent gain and noise characteristics of mid-wavelength infrared (MWIR) Hg0.7Cd0.3Te planarelectron avalanche photodiodes (e-APDs) operated at 80 K. The 10-μm-radius diode exhibits low dark current in the magnitude of 10–13 A below −5.5 V, high gain up to 1270 at −10 V, and low excess noise factor between 1 and 1.2. The optimal performances are compromised by tunneling current, which should be further suppressed. Studies on variable-area diodes show that larger diodes have a reduced gain due to a smaller contribution from edge gain, as well as an increased 1/f noise and corner frequency due to higher defect density. From the gain and noise perspectives, HgCdTe e-APDs with smaller junction areas are more suitable for focal plane array (FPA) applications.

Simulation of Al0.85Ga0.15As0.56Sb0.44 avalanche photodiodes.

Al0.85Ga0.15As0.56Sb0.44 is a promising avalanche material for near infrared avalanche photodiodes (APDs) because they exhibit very low excess noise factors. However electric field dependence of ionization coefficients in this material have not been reported. We report a Simple Monte Carlo model for Al0.85Ga0.15As0.56Sb0.44, which was validated using reported experimental results of capacitance-voltage, avalanche multiplication and excess noise factors from five APDs. The model was used to produce effective ionization coefficients and threshold energies between 400-1200 kV.cm-1 at room temperature, which are suitable for use with less complex APD simulation models.

Temperature-Dependent Characteristics of HgCdTe Mid-Wave Infrared E-Avalanche Photodiode

This paper presents the characteristics of HgCdTe mid-wavelength infrared (MWIR) electron-initiated avalanche photodiodes (e-APDs) as a function of temperature under different biases. The devices show a low dark current density of the order of <inline-formula><tex-math notation="LaTeX">${10^{ - 7}} \text{A/cm}^2$</tex-math></inline-formula> at 80 K when the reverse bias voltage is below 4 V, with an exponential gain above 100 at &#x2212; 8 V. Low excess noise factor of around 1.2 is also demonstrated for the devices at 80 K. The dark current and gain characteristics at different temperatures are analyzed, along with the device simulation results. A varied-temperature impact ionization model for MWIR e-APD devices is adopted based on the experimental results. In addition, a significant increase of the dark current in the APD device is observed at high temperature under large reverse bias, which can be associated with the local electric field redistribution due to the accumulation of holes in the depletion region at high temperatures. The analysis presented in this work paves the way to achieve a high operating temperature (HOT) of the HgCdTe APD with further optimization.

Impact of Band Anticrossing on Band-to-Band Tunneling in Highly Mismatched Semiconductor Alloys

We theoretically analyze band-to-band tunneling (BTBT) in highly mismatched, narrow-gap dilute nitride and bismide alloys, and quantify the impact of the $\mathrm{N}$- or $\mathrm{Bi}$-induced perturbation of the band structure---due to band anticrossing (BAC) with localized impurity states---on the electric-field-dependent BTBT generation rate. For this class of semiconductors, the assumptions underpinning the widely employed Kane model of BTBT break down, due to strong band-edge nonparabolicity resulting from BAC interactions. Via numerical calculations based on the Wentzel-Kramers-Brillouin approximation we demonstrate that BAC leads, at fixed band gap, to reduced (increased) BTBT current at low (high) applied electric field compared to that in a conventional ${\mathrm{In}\mathrm{As}}_{1\ensuremath{-}x}{\mathrm{Sb}}_{x}$ alloy. Our analysis reveals that BTBT in ${\mathrm{In}\mathrm{N}}_{x}{\mathrm{As}}_{1\ensuremath{-}x}$ and ${\mathrm{In}\mathrm{As}}_{1\ensuremath{-}x}{\mathrm{Bi}}_{x}$ is governed by a field-dependent competition between the impact of $\mathrm{N}$ ($\mathrm{Bi}$) incorporation on (i) the dispersion of the evanescent Bloch band linking the valence and conduction band edges, which dominates at low field strengths, and (ii) the conduction- (valence-) band-edge density of states, which dominates at high field strengths. The implications of our results for applications in long-wavelength avalanche photodiodes (APDs) and tunneling field-effect transistors (TFETs) are discussed. For APDs, we describe that leakage currents in ideal dilute nitride and bismide devices are likely comparable to those in devices based on conventional III-V materials, but that the expected reduction of the hole impact ionization rate in ${\mathrm{In}\mathrm{As}}_{1\ensuremath{-}x}{\mathrm{Bi}}_{x}$ is promising from the perspective of obtaining low excess noise factor. For TFETs, we describe that $\mathrm{Bi}$ incorporation provides the potential to obtain both reduced subthreshold swing and increased on-state current, making ${\mathrm{In}\mathrm{As}}_{1\ensuremath{-}x}{\mathrm{Bi}}_{x}$ of interest for the development of low-power, high-speed devices.

Avalanche Multiplication Noise in GaN p–n Junctions Grown on Native GaN Substrates

GaN p–n junction diodes grown on native GaN substrates have been fabricated and characterized. The devices exhibit a positive temperature coefficient of breakdown obtained from variable temperature current–voltage measurements, confirming the impact ionization avalanche. The low‐frequency noise characteristics of these devices have been measured under forward and reverse bias conditions. The forward bias noise spectra are dominated by the 1/f noise, and the current spectral density is proportional to I1.6. Under reverse bias, the noise spectra show 1/f noise at reverse biases below the avalanche threshold. However, at reverse biases in the avalanche regime, the multiplication noise overwhelms the 1/f noise, resulting in a white noise spectrum. To further characterize the avalanche process, the excess noise factor, F, is obtained from the measured noise spectra of diodes biased in reverse avalanche. For the case of pure hole injection (achieved by incorporating a thin pseudomorphic In0.07Ga0.93N layer at the cathode of the device and illuminating with 390 nm UV light), a low excess noise factor is achieved. The impact ionization ratio α/β extracted from the multiplication noise ranges from 0.07 to 0.38 over the electric field ranging from 2.8 to 3.7 MV cm−1, consistent with the impact ionization coefficients reported previously using the photomultiplication method.

Evaluation of a HgCdTe e-APD based detector for 2 μm CO2 DIAL application.

Benefiting from close to ideal amplification properties (high gain, low dark current, and low excess noise factor), HgCdTe electron initiated avalanche photodiode (e-APD) technology exhibits state of the art sensitivity, thus being especially relevant for applications relying on low light level detection, such as LIDAR (Light Detection And Ranging). In addition, the tunable gap of the Hg1-xCdxTe alloy enables coverage of the short wavelength infrared (SWIR) and especially the 2μm spectral range. For these two reasons, a HgCdTe e-APD based detector is a promising candidate for future differential absorption LIDAR missions targeting greenhouse gas absorption bands in SWIR. In this study, we report on the design and evaluation of such a HgCdTe e-APD based detector. The first part focuses on detector architecture and performance. Key figures of merit are: 2.8μm cutoff wavelength, 200μm diameter almost circular sensitive area, 185K operating temperature (thermo-electric cooling), 22 APD gain (at 12V reverse bias), 360 kΩ transimpedance gain, and 60 fWHz-0.5 noise equivalent power (at 12V reverse bias). The second part presents an analysis of atmospheric LIDAR signals obtained by mounting the HgCdTe e-APD based detector on the 2μm differential absorption LIDAR developed at the Laboratoire de Météorologie Dynamique and dedicated to CO2 monitoring. Discussion emphasizes random and systematic errors in LIDAR measurements regarding breadboard detector characterization. In particular, we investigate the influence of parasitic tails in detector impulse response on short range DIAL measurements.

Reduction of dark current and gain increase in InAs avalanche photodiode with AlGaAs blocking layer

This article presents a new method to reduce the dark current and increase the avalanche gain in InAs avalanche photodiode (APD) by adding Al0.84Ga0.16As blocking layer. This photodiode has displayed a high avalanche gain around 400 in 8V bias voltage. Furthermore, a very low dark current and low excess noise factor between 0.1 and 1.9 in a temperature of 180K to 300K is observed. Finally, in comparison with other devices, a considerable increase of the gain along with decrease in dark current is observed.

Enhanced Carrier Multiplication in InAs Quantum Dots for Bulk Avalanche Photodetector Applications

Exploring the potentiality of enhancing the performance of avalanche photodiodes (APDs) using novel nanoscale structures is highly attractive for overcoming the bottleneck of avalanche probability. This work demonstrates, for the first time, multiplication enhancement of electron‐initiated photocurrent due to impact ionization in InAs quantum dots (QDs) within a GaAs APD structure. A five‐layer stacked 2.25 MLs InAs QD/50 nm GaAs spacer multiplication structure integrated into a separated absorption, charge, and multiplication GaAs homo APD results in up to six times higher multiplication factors in comparison to a reference device without QD over a temperature range of 77–300 K. In addition, extremely low excess noise factor in close proximity to that of silicon is also observed with an effective k eff factor below 0.1. This demonstration is of fundamental interest and relevant for future ultra efficient avalanche detector applications.

Low-Noise Speed-Optimized Large Area CMOS Avalanche Photodetector for Visible Light Communication

Mean-gain and excess-noise measurements are presented for a 350 × 350 μm2 P+/N-well/P-sub and a 270 × 270 μm2 N-well/P-sub avalanche photodetectors fabricated using 0.13-μm CMOS technology. The active area of the P+/N-well/P-sub device was divided into multiple subsections to decrease transit time and increase speed. For the P+/N-well structure, remarkably low excess-noise factors of 4.1 and 4 were measured at a mean gain of 16 corresponding to a k value of approximately 0.1, using a 542 (633) nm laser. For a variant N-well/P-sub structure, excess-noise factors of 6.5 and 6.2 were measured at a mean-gain of 16 corresponding to a k value of approximately 0.3. The proposed CMOS APDs with high gain, low noise, low avalanche breakdown voltage (below approximately 12 V) and low dark-currents (approximately nA) would be attractive for low-cost optical receivers in visible-light communication systems.

Multiplication gain and excess noise factor in thin SiC avalanche photodiodes

This work simulated the avalanche characteristics of 4H- and 6H-SiC avalanche photodiodes (APDs) at 0.1 µm, 0.2 µm and 0.3 µm avalanche widths. A Monte Carlo model with random ionization path length techniques is developed to simulate mean multiplication gain and excess noise factor in thin SiC APDs. Mean multiplication gain, breakdown voltage and excess noise factor are simulated based on the electric field dependent impact ionization coefficients with the inclusion of dead space effect. Our results show that hole-initiated impact ionization gives high multiplication gain with low excess noise factor in both devices. We observed that dead space effect is more pronounce in thin structure since it covers a significant portion of the avalanche region. In thick device structure, a high breakdown voltage is observed. A comparison between these two polytypes shows that 4H-SiC provides high multiplication gain with low excess noise factor than 6H-SiC.

OWC Using a Fully Integrated Optical Receiver With Large-Diameter APD

This letter presents a fully monolithically integrated receiver with a large-diameter avalanche photodiode (APD). Using a standard high-voltage 0.35-μm CMOS technology, the APD is implemented with separated absorption and multiplication regions optimizing the ionization ratio between holes and electrons. This optimized ionization ratio leads to a low excess noise factor of the APD, which considerably improves the receiver's sensitivity to -31.8 dBm at 1 Gbit/s (bit error rate <;10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> ). A 1-Gbit/s wireless optical communication link with a distance of 3.3 m is demonstrated. Due to the highly sensitive receiver, it is possible to omit any kind of input optics, resulting in a wide receiving angle of 68° for a bit error rate of <;10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">-9</sup> .

Performance evaluation of two SiPMs arrays coupled to pixelated scintillations for PET/MR applications.

The purpose of this study is to investigate the behavior of the new generation of SensL SiPM arrays, ArrayB and ArrayM, for PET/MR applications. The evaluation of the SiPMs performance underwent with pixelated GaGG and BGO scintillators with 2x2x5 mm3 pixel size and various coupling schemes for 511keV and 662keV energies. To acquire raw images, we used a symmetric resistive voltage division network and the 4x4 SiPMs anodes reduced to 2X and 2Y position signals. A FPGA Spartan 6 LX150T was used for triggering and digital processing of the pulses acquired using free running ADCs. The first step of our work was optimization of the bias voltage of the two SiPM arrays. The optimal bias voltage is a tradeoff between high photon detection efficiency and low excess noise factor. The SiPMs were coupled to homogeneous 16x16x10 mm3 CsITl scintillator and irradiated with 137Cs source. The energy resolution calculated in overvoltages between 26.5V and 30.5V for ArrayB and between 28.3V and 31.3V for ArrayM. The bias voltage with the best energy resolution was used for the evaluation of the SiPMs. The clear visualization of the GaGG and BGO crystal elements is expressed quantitatively by the mean peak-valley ratio of a horizontal profile in the raw images. The best optical coupling for the BGO was 2 mm thick glass. In the case of the GaGG 1 mm thick glass was adequate. The mean energy resolution of the GaGG scintillator is about two times better than the BGO for both type of SiPMs, after applying correction for their non-linear response. The low light output of the BGO scintillator in comparison with the GaGG as well as different emission spectra and the different PDE of the two types of SiPMs explain the differences in the behavior of the tested SiPMs arrays.

Low-Noise Avalanche Photodiode With Graded Junction in 0.15-&lt;inline-formula&gt; &lt;tex-math notation="TeX"&gt;$\mu{\rm m}$ &lt;/tex-math&gt;&lt;/inline-formula&gt; CMOS Technology

This letter presents the experimental characterization and noise modeling of a CMOS avalanche photodiode with pwell/n-iso active junction fabricated in a 0.15-μm standard CMOS process. The device exhibits a remarkably low excess noise factor F = 6 at a gain M = 50 in the blue spectral region, and F = 12 at M = 50 in the near-infrared. Gain and noise characteristics are accurately predicted using Hayat dead-space model applied to a linearly graded junction doping profile.

Temperature dependence of gain and excess noise in InAs electron avalanche photodiodes

Measurement and analysis of the temperature dependence of avalanche gain and excess noise in InAs electron avalanche photodiodes (eAPDs) at 77 to 250 K are reported. The avalanche gain, initiated by pure electron injection, was found to reduce with decreasing temperature. However no significant change in the excess noise was measured as the temperature was varied. For avalanche gain > 3, the InAs APDs with 3.5 µm i-region show consistently low excess noise factors between 1.45 and 1.6 at temperatures of 77 to 250 K, confirming that the eAPD characteristics are exhibited in the measured range of electric field. As the dark current drops much more rapidly than the avalanche gain and the excess noise remains very low, our results confirmed that improved signal to noise ratio can be obtained in InAs eAPDs by reducing the operating temperature. The lack of hole impact ionization, as confirmed by the very low excess noise and the exponentially rising avalanche gain, suggests that hole impact ionization enhancement due to band "resonance" does not occur in InAs APDs at the reported temperatures.

Low Noise Avalanche Photodiodes Incorporating a 40 nm AlAsSb Avalanche Region

A separate absorption and multiplication avalanche photodiode incorporating a 500 nm InGaAs absorption layer, InAlAs bandgap grading/field control layers, an AlAsSb field control layer and a 40 nm AlAsSb multiplication layer was grown and characterized. Responsivity of 436 mA/W was measured at the punch-through voltage. A deviation of Be doping concentration in our AlAsSb field control layer leads higher than intended electric fields in the InGaAs absorption layer and the InAlAs field control layer. Calculation of avalanche gain suggests that the gain in the InGaAs is low and therefore the gain and excess noise characteristics are dominated by impact ionization in the InAlAs field control layer and the AlAsSb multiplication layer. Despite this low excess noise factors corresponding to an effective electron to hole ionization coefficient ratio between 0.1 to 0.15, were measured. This is lower than that from an InAlAs pin diode with a 100 nm avalanche region.

HgCdTe Quantum Detection: from Long-Wave IR down to UV

A few years ago, visible detection was demonstrated using advanced substrate thinning processes on flip-chip hybridized HgCdTe focal-plane arrays, in both French and US laboratories. Constant quantum efficiency was demonstrated at LETI-Sofradir from the short-wave infrared (IR) (2.5 μm cut-off) down to the visible range in 2006, validating complete CdZnTe substrate removal. This paper presents and discusses HgCdTe photodiode spectral response characterization, focusing on the short-wavelength part of the spectrum. We confirm the extended sensitivity of middle- and long-wave diodes: constant quantum efficiency has been observed from 10 μm down to 230 nm in the ultraviolet (UV). Such a unique property may be useful for very large-bandwidth spectrometers requiring monolithic detectors. Avalanche gain of middle-wave avalanche photodiodes has also been investigated in both the visible and the UV range. We demonstrate here that the avalanche gain remains constant while keeping a very low excess noise factor. This result opens the way to low-flux applications in this wavelength range.