Multiplication Avalanche Photodiodes Research Articles

Ge-on-Si Avalanche Photodiodes With Photon-Trapping Nanostructures for Sensing and Optical Quantum Applications

High-sensitivity Ge/Si avalanche photodiodes (APDs) have recently gained attention for their application in sensing and optical communication due to their low cost and CMOS compatible process. However, compared to commercial III–V compound APDs, Ge/Si APDs usually suffer from the issue of relatively low primary responsivity. In this paper, we report Ge-on-Si separate absorption, charge, and multiplication avalanche photodiodes (SACM-APDs) with photon-trapping nanostructures to enhance light absorption. Besides, by optimizing the depth of the holes, the photon trapping structure could reduce the dark current without compromising the avalanche effect as confirmed by both simulations and experimental results. As a result, the responsivity of the photon trapping APDs increases by 20-50 % from that of control APDs at the 1,550 nm wavelength band. Furthermore, a quantum efficiency higher than 80% could be achieved at 1550 nm when the photon trapping Ge-on-Si APD is on Si-on-insulator (SOI) platforms as predicted by simulations. Our results demonstrate that the photon trapping Ge/Si APDs exhibit superior dark current, light absorption and gain than those of the control devices, which have the potential applications in sensing and optical quantum communications.

Separate absorption, charge, and multiplication staircase avalanche photodiodes

The wavelength 1550 nm is widely used in fiber-optic communications and imaging systems. Avalanche photodiodes (APDs) offer high sensitivity for detecting this wavelength. However, the noise caused by the stochastic nature of the impact ionization gain mechanism can temper the benefit of amplifying the signal. Here, we report a separate absorption, charge, and multiplication APD that uses a two-step staircase multiplication region exhibiting a near-unity excess noise factor. At a gain of four, the excess noise factor is approximately three times lower than conventionally used InGaAs/InP separate absorption, charge, and multiplication APDs. This improved excess noise coupled with 1550-nm operation offers the potential for enhanced performance in several key application areas.

High-speed InAlAs digital alloy avalanche photodiode

Digital alloy (DA) InAlAs on the InP substrate exhibits a lower excess noise compared to a traditional In0.52Al0.48As random alloy as the multiplication layer in avalanche photodiodes (APDs). This work implements DA InAlAs as the multiplication layer in a 1550 nm separate absorption, grading, charge, and multiplication APD and characterizes the performances through various analyses. The device reaches a maximum gain of 221 before avalanche breakdown, with a maximum gain-bandwidth product of more than 140 GHz. At 90% breakdown voltage, the dark current density is 4.1 mA/cm2, and the responsivity is 0.48 A/W at unit gain. Excess noise factors were identified, yielding an effective k value of around 0.15, which is lower than that of random alloy In0.52Al0.48As APDs (k ∼0.2). These findings show that DA InAlAs has the potential to be a promising material for high-performance APDs.

Waveguide-Integrated Ge/Si Avalanche Photodiode with Vertical Multiplication Region for 1310 nm Detection

Ge/Si separate absorption, charge, and multiplication avalanche photodiodes (SACM APDs) coupled with waveguides have shown significant potential as high-sensitivity, low-noise, and high-speed photodetectors for optical communications. In this study, we present a waveguide-integrated Ge/Si SACM APD fabricated on an eight-inch silicon photonics platform. The device exhibits a primary responsivity of 0.68 A/W at the unit gain voltage of 6 V for the O-band (1310 nm) wavelength, with a 10 μm-long and 1 μm-wide Ge layer. Additionally, the device demonstrates a 3 dB bandwidth of 25.7 GHz, with an input optical power of −16.8 dBm. The largest gain bandwidth product (GBP) is 247 GHz at a gain of 9.64 and a bias voltage of 15.7 V. The eye diagram is open at the bias voltage of 16 V, with a capacity to receive 28 Gbps of data. This APD shows potential for application in high-speed data transmission systems.

Investigation of Ga2O3/diamond heterostructure solar-blind avalanche photodiode via TCAD simulation

A Ga2O3/diamond separate absorption and multiplication avalanche photodiode (SAM-APD) with mesa structure has been proposed and simulated. The simulation is based on an optimized Ga2O3/diamond heterostructure TCAD physical model, which is revised by repeated comparison with the experimental data from the literature. Since both Ga2O3 and diamond are ultra-wide bandgap semiconductor materials, the Ga2O3/diamond SAM-APD shows good solar-blind detection ability, and the corresponding cutoff wavelength is about 263 nm. The doping distribution and the electric field distribution of the SAM-APD are discussed, and the simulation results show that the gain of the designed device can reach 5 × 104 and the peak responsivity can reach a value as high as 78 A/W.

High-gain low-excess-noise MWIR detection with a 3.5-µm cutoff AlInAsSb-based separate absorption, charge, and multiplication avalanche photodiode

Mid-wavelength infrared (MWIR) detection is useful in a variety of scientific and military applications. Avalanche photodiodes can provide an advantage for detection as their internal gain mechanism can increase the system signal-to-noise ratio of a receiver. We demonstrate a separate absorption, charge, and multiplication avalanche photodiode using a digitally grown narrow-bandgap Al0.05InAsSb absorber for MWIR detection and a wide bandgap Al0.7InAsSb multiplier for low-excess-noise amplification. Under 2-µm illumination at 100 K, the device can reach gains over 850. The excess noise factor of the device scales with a low k-factor of ∼0.04. The unity-gain external quantum efficiency of the device attains a peak of 54% (1.02 A/W) at 2.35 µm and maintains an efficiency of 24% (0.58 A/W) at 3 µm before cutting off at ∼3.5 µm. At a gain of 850, the device has a gain-normalized dark current density of 0.05 mA/cm2. This device achieves gains more than double that of the state-of-the-art InAs detectors and achieves gain-normalized dark current densities over two orders of magnitude lower than that of a previously reported MWIR Al0.15InAsSb-based detector.

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.

Narrow bandgap Al0.15In0.85As0.77Sb0.23 for mid-infrared photodetectors.

Mid-IR is a useful wavelength range for both science and military applications due to its low atmospheric attenuation and ability to be used for passive detection. However, many solutions for detecting light in this spectral region need to be operated at cryogenic temperatures as their required narrow bandgaps suffer from carrier recombination and band-to-band tunneling at room temperature leading to high dark currents. These problems can be alleviated by using a separate absorption, charge, and multiplication avalanche photodiode. We have recently demonstrated such a device with a 3-µm cutoff using Al0.15In0.85As0.77Sb0.23, as the absorber, grown on GaSb. Here we investigate Al0.15In0.85As0.77Sb0.23 as a simple PIN homojunction and provide metrics to aid in future designs using this material. PL spectrum measurements indicate a bandgap of 2.94 µm at 300 K. External quantum efficiencies of 39% and 33% are achieved at 1.55 µm and 2 µm respectively. Between 180 K and 280 K the activation energy is ∼0.22 eV, roughly half the bandgap of Al0.15In0.85As0.77Sb0.23, indicating thermal generation is dominant.

Experimental Demonstration of the Impact of the Parameters of Floating Guard Ring on Planar InP/InGaAs-Based Avalanche Photodiodes’ Performance and Its Optimization

Suppression pre-breakdown in planar separated absorption, grading, charge and multiplication (SAGCM) avalanche photodiodes (APDs) with the help of Floating Guard Ring (FGR) is still a research hotspot. In this paper, a lattice-matched InP&#x002F;InGaAs-based SAGCM structure is grown by Metal-Organic Chemical Vapor Deposition and thus the planar 50 &#x03BC;m photosensitive area APDs with different FGR structures are fabricated using zinc diffusion process. The effects of the different lengths of FGR (4 &#x03BC;m, 8 &#x03BC;m, 12 &#x03BC;m, 16 &#x03BC;m), and the different distances between FGR and the Zn diffused p&#x002B; region (4 &#x03BC;m, 6 &#x03BC;m, 8 &#x03BC;m, 10 &#x03BC;m) on the optoelectrical characteristics are deeply studied. The results from optical microscope, scanning electron microscope and current-voltage curves reveal that there is an optimal length and distance for the punch-through and breakdown voltage. Furthermore, the nA-level dark current, gain (<i>M</i>) of up to 10 at breakdown voltage, responsibility as high as 9.01 A&#x002F;W at <i>M</i> &#x003D; 10 and quantum efficiency equaling to 72&#x0025; are also tested and calculated, proving the good performance of our devices. The optimized FGR parameters and related structure are expected to be helpful for obtaining high-performance, small-size InP&#x002F;InGaAs-based APDs.

Temperature Dependence of the Impact Ionization Coefficients in AlAsSb Lattice Matched to InP

The temperature dependence of the ionization coefficients of AlAsSb has been determined from 210 K to 335 K by measuring the avalanche multiplication in a series of three <i>p^&#x002B;-i-n^&#x002B;</i> and two <i>n^&#x002B;-i-p^&#x002B;</i> diodes. Both electron and hole ionization coefficients reduce at approximately the same rate as the temperature increases but much less so than in InAlAs or InP. This results in a significantly smaller breakdown voltage variation with temperature of 13 mV&#x002F;K in a 1.55 &#x03BC;m thick <i>p^&#x002B;-i-n^&#x002B;</i> structure and a calculated 15.58 mV&#x002F;K for a 10 Gb&#x002F;s InGaAs&#x002F;AlAsSb separate absorption and multiplication avalanche photodiode (SAM-APD). Monte-Carlo modelling suggests that the primary reason for this reduced temperature dependence is the increased alloy scattering in the Sb containing alloy, reducing the impact of variation in phonon scattering rate with temperature.

Germanium-on-silicon avalanche photodiode for 1550 nm weak light signal detection at room temperature

To optimize the dark current characteristic and detection efficiency of the 1550 nm weak light signal at room temperature, this work proposes a Ge-on-Si avalanche photodiode (APD) in Geiger mode, which could operate at 300 K. This lateral separate absorption charge multiplication APD shows a low breakdown voltage (Vbr) in Geiger mode of -7.42 V and low dark current of 0.096 nA at unity gain voltage (VGain=1 = -7.03 V). Combined with an RF amplifier module and counter, the detection system demonstrates a low dark count rate (DCR) of 1.1×106 counts per second and high detection efficiency η of 7.8% for 1550 nm weak coherent pulse detection at 300 K. The APD reported in this work weakens the dependence of the weak optical signal recognition on the low environment temperature and makes single-chip integration of the single-photon level detection system possible.

InGaAs/InP SAGCM avalanche photodiode with a heterojunction multiplication layer

In this paper, the InGaAs/InP separate absorption, grading, charge, and multiplication avalanche photodiode (SAGCM-APD) with a heterojunction multiplication layer and a hybrid absorption layer has been simulated. Due to the effect of the heterojunction multiplication layer on avalanche photodiode collision ionization, compared with the traditional structure, the break-down voltage and the punch-through voltage of the structure with a heterojunction multiplication layer was reduced by 2 V. By optimizing the thickness of the heterojunction multiplication layer, the electrical performance of the device has been enhanced. The avalanche gain was 193.37, which is much higher than the conventional structure (51.65). Besides, the thickness of InP in the heterojunction multiplication layer affects the capacitance characteristics of the device.

Impact of Circular Layout on Characteristics in LSAMBM APD Based on SOI Film

Lateral separate absorption multi-buffer multiplication avalanche photodiode (LSAMBM APD) with rectangular layout based on SOI film had been investigated as a promising candidate in the high-speed weak-light detection application. In this article, the layout-dependent characteristics of LSAMBM APD were investigated furthermore. Comparing to rectangular layout, the circular layout could shorten the length and improve electric field intensity of absorption region under the same sensitive area. In this way, carriers’ drift velocity could be accelerated, and the photon-generated carriers would be more effectively separated to achieve high responsivity and fast frequency response in LSAMBM APD with circular layout. When the illumination wavelength was 400 nm and input optical power was 0.001 W/cm2, the circular layout could enhance LSAMBM APD to achieve high responsivity and fast frequency response under the reverse bias voltage of 8.11 V and 9.2 V, and reach to 1236.9A/W and 3.2GHz, respectively. All results revealed that the LSAMBM APD with circular layout was more appropriate to high-speed single photon detection systems.

Mid-wavelength infrared avalanche photodetector with AlAsSb/GaSb superlattice

In this work, a mid-wavelength infrared separate absorption and multiplication avalanche photodiode (SAM-APD) with 100% cut-off wavelength of ~ 5.0 µm at 200 K grown by molecular beam epitaxy was demonstrated. The InAsSb-based SAM-APD device was designed to have electron dominated avalanche mechanism via the band structure engineered multi-quantum well structure based on AlAsSb/GaSb H-structure superlattice and InAsSb material in the multiplication region. The device exhibits a maximum multiplication gain of 29 at 200 K under -14.7 bias voltage. The maximum multiplication gain value for the MWIR SAM-APD increases from 29 at 200 K to 121 at 150 K. The electron and hole impact ionization coefficients were derived and the large difference between their value was observed. The carrier ionization ratio for the MWIR SAM-APD device was calculated to be ~ 0.097 at 200 K.

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.

Separate absorption and multiplication solar-blind photodiodes based on p-NiO/MgO/n-ZnO heterostructure

High-performance solar-blind separate absorption and multiplication avalanche photodiodes (SAM-APDs) were fabricated based on a p-NiO/MgO/n-ZnO dual heterojunction structure. The prepared SAM-APDs exhibited a separated absorption and multiplication structure that used NiO and ZnO as absorption layers, and ultrawide-bandgap MgO as a multiplication layer. When the reverse-bias voltage exceeded 6 V, carrier avalanche multiplication occurred, and the avalanche gain reached a high value of 2.7 × 103, corresponding to a 1120% quantum efficiency, at a reverse-bias voltage of 10 V. These solar-blind SAM-APDs had an ultraviolet (UV) (310 nm)/visible (500 nm) rejection ratio as high as 563.6 at a 2 V reverse-bias voltage. These features render the SAM-APDs highly suitable for practical applications as UV solar-blind photodetectors.

A model for the jitter of avalanche photodiodes with separate absorption and multiplication regions

An improved version of the Random Path Length algorithm is used to simulate the time response of Separate Absorption and Multiplication Avalanche PhotoDiodes (SAM-APDs) in the linear regime. The model takes into account both the diffusion and the drift of carriers in the absorption region as well as impact ionization scattering events in the multiplication region. An extended formulation of Ramo’s theorem is used to determine the current waveforms. The new algorithm has been used to extract the jitter of the time response of avalanche photodiodes to photons, which is a relevant figure of merit for time of flight applications of SAM-APDs. It is found that an electric field in the absorption region small enough to avoid unwanted carrier multiplication or band-to-band tunneling, is beneficial to reduce the jitter. Furthermore, we have found that, in APDs working in the linear regime, the stochastic duration of the current pulse makes difficult the use of circuit techniques, such as crossover timing, with constant delay lines aimed at detecting the individual pulses. The problem is partly mitigated when SAM-APDs are used for the detection of high energy photons, such as X-rays.

Theoretical analysis for AlGaN avalanche photodiodes with mesa and field plate structure**Project supported by the Natural Science Research Project of Anhui University, China (Grant No. KJ2019A0644), the National Natural Science Foundation of China (Grant Nos. 61634002 and 61804089), the Natural Science Alliance Foundation, China (Grant No. U1830109), the Natural Science Foundation of Anhui Province, China (Grant No. 1708085MF149), the Chuzhou

To suppress the electric field crowding at sidewall and improve the detection sensitivity of the AlGaN separate absorption and multiplication (SAM) avalanche photodiodes (APDs), we propose the new AlGaN APDs structure combining a large-area mesa with a field plate (FP). The simulated results show that the proposed AlGaN APDs exhibit a significant increase in avalanche gain, about two orders of magnitude, compared to their counterparts without FP structure, which is attributed to the suppression of electric field crowding at sidewall of multiplication layer and the reduction of the maximum electric field at the p-type GaN sidewall in p–n depletion region. Meanwhile, the APDs can produce an obviously enhanced photocurrent due to the increase in cross sectional area of multiplication region.

Charge layer optimized 4H-SiC SACM avalanche photodiode with low breakdown voltage and high gain

An n-type charge layer was introduced into the 4H-SiC separated absorption and multiplication avalanche photodiode. The effect of the charge layer on the optoelectronic characteristics of the photodiode was modeled and studied to optimize the performance of the photodiode. According to the modeling results, 4H-SiC photodiodes were fabricated. A low breakdown voltage of 77.6 V and a significant gain of more than 105 were obtained. The peak responsivity for 270 nm illumination of the photodiode biased at −40 V was 83 mA W−1, corresponding to an external quantum efficiency over 38.2%. Both the simulated and experimental spectral responses are almost identical.

The Fabrication and Characterization of InAlAs/InGaAs APDs Based on a Mesa-Structure with Polyimide Passivation.

This paper presents a novel front-illuminated InAlAs/InGaAs separate absorption, grading, field-control and multiplication (SAGFM) avalanche photodiodes (APDs) with a mesa-structure for high speed response. The electric fields in the InAlAs-multiplication layer and InGaAs-absorption layer enable high multiplication gain and high-speed response thanks to the thickness and concentration of the field-control and multiplication layers. A mesa active region of 45 micrometers was defined using a bromine-based isotropic wet etching solution. The side walls of the mesa were subjected to sulfur treatment before being coated with a thick polyimide layer to reduce current leakage, while lowering capacitance and increasing response speeds. The breakdown voltage (VBR) of the proposed SAGFM APDs was approximately 32 V. Under reverse bias of 0.9 VBR at room temperature, the proposed device achieved dark current of 31.4 nA, capacitance of 0.19 pF and multiplication gain of 9.8. The 3-dB frequency response was 8.97 GHz and the gain-bandwidth product was 88 GHz. A rise time of 42.0 ps was derived from eye-diagrams at 0.9 VBR. There was notable absence of intersymbol-interference and the signals remained error-free at data-rates of up to 12.5 Gbps.