Excess Noise Characteristics Research Articles

A comparative study of impact ionization and avalanche multiplication in InAs, HgCdTe, and InAlAs/InAsSb superlattice

We use an ensemble Monte Carlo transport approach to calculate and compare the impact ionization and avalanche photodiode excess noise characteristics in three materials—a band-engineered InAlAs/InAsSb type-II superlattice, bulk InAs, and HgCdTe—all with an identical bandgap of 370 meV at 250 K. The electronic band structures and energy–momentum conservation conditions are used to calculate the impact ionization rates, carrier histories, multiplication gains, and excess noise characteristics. The calculated impact ionization coefficients and excess noise factors indicate a single carrier species multiplication in all three materials under low applied electric fields. We find the ratio of impact ionization coefficients to be k=7×10−4 for InAs and 3×10−4 for HgCdTe under an applied field of 50 kV/cm, and the superlattice to be k<10−6 at fields up to 400 kV/cm. The bulk materials experience avalanche breakdown as the applied field increases, transitioning to Geiger mode behavior at gains above 103 for InAs and 104 for HgCdTe. However, this breakdown is absent from the superlattice at the highest fields considered in this study due to hole confinement, indicating superior performance compared to the bulk materials. Our results demonstrate the role of superlattice band engineering in designing quality avalanche photodiode materials.

Ionization coefficients and excess noise characteristics of AlInAsSb on an InP substrate

For short-wavelength infrared (SWIR) avalanche photodiodes, a separate absorption, charge, and multiplication design is widely used. AlInAsSb on an InP substrate is a potential multiplication layer with a lattice match to absorber candidates across the SWIR. Our new measurements demonstrate that AlInAsSb on InP is a promising multiplier candidate with a relatively low dark current density of 10−4 A/cm2 at a gain of 30; a high gain, measured up to 245 in this study; and a large differentiation of electron and hole ionization leading to a low excess noise, measured to be 2.5 at a gain of 30. These characteristics are all improvements over commercially available SWIR detectors incorporating InAlAs or InP as the multiplier. We measured and analyzed gain for multiple wavelengths to extract the ionization coefficients as a function of an electric field over the range 0.33–0.6 MV/cm.

Recombination processes in MBE grown Al0.85Ga0.15As0.56Sb0.44

Quaternary AlGaAsSb alloys have exhibited low excess noise characteristics as gain regions in avalanche photodiodes. In this work, optical spectroscopy techniques are used to demonstrate the recombination dynamics in molecular beam epitaxy grown Al0.85Ga0.15As0.56Sb0.44 with temperature variation. Photoluminescence (PL) measurements at 8–50 K show that the bandgap varies from 1.547 to 1.527 eV. The radiative recombination processes in the alloy were found to be dictated by the complexities of antimony (Sb) incorporation during the growth. Time-resolved PL (TRPL) measurements show a change in initial carrier lifetimes of ∼3.5 µs at 8 K to ∼1 µs at 30 K. The knowledge of carrier dynamics from optical characterization methods such as PL and TRPL can be employed to contribute to shorter feedback loops for improvement of alloy fabrication in addition to enhancing growth processes.

Low Excess Noise of Al0.85Ga0.15As0.56Sb0.44 Avalanche Photodiode From Pure Electron Injection

Avalanche photodiodes (APDs) are used in optical receivers of high-speed optical communication systems to improve signal-to-noise ratio over conventional photodiodes. Low excess noise characteristics are crucial for APDs to preserve the benefits associated with high internal gains. In this work, we presented room temperature data of avalanche gain and excess noise factors of Al <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.85</sub> Ga <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.15</sub> As <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.56</sub> Sb <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.44</sub> APDs using pure and mixed carrier injection profiles. Using pure electron injection, the best possible excess noise performance for a given avalanche width was measured with an excess noise factor <; 2 for gains up to 25. This is the lowest excess noise reported for this material system at high gain. Two other injection profiles with increased portion of injected holes worsened the excess noise performance, confirming the need to use pure electron injection for the best possible APD noise performance. The data reported in this article is available from the ORDA digital repository (https://doi.org/10.15131/shef.data.15082455).

High gain and low excess noise InGaAs/InP avalanche photodiode with lateral impact ionization.

In this paper, modeling for a lateral impact ionization InGaAs/InP avalanche photodiode (APD) has been performed based on a device simulator, i.e., Silvaco ATLAS. Compared with traditional APDs, the lateral impact ionized APD has much higher gains as well as lower excess noise. The internal gain for our newly proposed lateral APD is over 1000-near the breakthrough voltage. In addition, the excess noise characteristic of this device is also discussed with three-dimensional dead space multiplication theory, and the calculated effective $k$k value is obviously lower than traditional InGaAs/InP APDs. Because of the high gain and low excess noise characteristics, the proposed APD can be widely applied for optical detection with high sensitivity.

Optoelectronic properties of multiple quantum barriers nano-scale avalanche photo diodes

The important optoelectronic properties like spectral response, excess noise characteristics, time and frequency response of multiple quantum barrier (MQB) nano-scale avalanche photodiodes (APDs) based on Si~3C-SiC material system have been studied. A self-consistent simulation method based on quantum drift-diffusion model has been presented. Simulation results show that the Si~3C-SiC MQB nano-APDs are capable of detecting significantly longer wavelengths as compared to infrared flat Si APDs. The multiplication gain and excess noise factor (ENF) of the MQB APDs have been calculated by varying the number of quantum barriers (QBs). The numerically calculated ENF values of MQB APDs have been compared with the ENF of Si flat conventional APDs of similar dimensions and it is observed that the use of QBs leads to significant reduction in ENF of the APDs. Simulation results also show that MQB nano-APDs possess significantly faster time response and wider frequency response as compared to the Si counterparts.

High-Speed Avalanche Photodiodes With Wide Dynamic Range Performance

In this work, we demonstrate a novel top-illuminated avalanche photodiode (APD) with high-speed and wide dynamic range performance for coherent lidar applications, which needs simultaneous processing of weak light reflections from the object and a strong optical local-oscillator (LO) signal at the receiving end. By taking advantage of a partially depleted p-type In0.53Ga0.47As absorbing layer and a thin In0.52Al0.48As multiplication layer (88 nm), the demonstrated APDs exhibit a wide optical-to-electrical bandwidth (16 GHz) and high responsivity (2.5 A/W at 0.9 Vbr) near the saturation output current which is as high as >8 mA. Furthermore, the measured low excess noise (k = 0.14) characteristics of this device ensure its wide dynamic range performance. In addition, it should be noted that the measured nonlinear behaviors of these APDs are quite different from those of typical fast p-i-n photodiodes (PDs), which always show serious degradation in their O-E bandwidths at their saturation output. On the other hand, the measured bias dependent 3-dB O-E bandwidth of the demonstrated APDs can be pinned at 16 GHz without any degradation at around the saturation current output. Such distinct nonlinear APD behaviors can be attributed to the space-charge-screening effect induced gain reduction under high-power operation.

Multiple Quantum Barrier Nano-avalanche Photodiodes - Part I: Spectral Response

Background: The spectral response of Multiple Quantum Barrier (MQB) nano-scale avalanche photodiodes (APDs) based on Si~3C-SiC material system shows considerable responsivity of the device within a very wide wavelength range which includes some portion of Ultra- Violet (UV) spectrum (200- 90 nm), visible spectrum (390-770 nm), near-infrared (700-1400 nm), short-wavelength infrared (1400-3000 nm) and mid-infrared (3000-4000 nm) wavelengths. It has already been concluded from preceding studies that Si~3C-SiC MQB APDs shows better spectral response and excess noise characteristics as compared to equivalent conventional APDs based on Si. Moreover, the superiority of the illumination through p+-side (ITPS) structure has been observed among two probable optical illumination configurations such as illumination through n+- side (ITNS) and illumination through p+-side (ITPS) structures. Methods: In this paper, the time and frequency responses of Si~3C-SiC MQB APDs have been investigated. A very narrow rectangular pulse of pulse-width of 0.4 ps has been used as the input optical pulse having 850 nm wavelength incident on the p+-side of the MQB APD structures (i.e. ITPS is considered here) and corresponding current responses have been calculated by using a rigorous simulation method developed by the authors; finally the frequency responses of the devices are obtained via the Fourier transform of the corresponding pulse current responses in time domain. Results: The width of the current responses are limited to 4.7 and 3.1 ps in Si nano-APD and Si~3C-SiC MQB (consisting of five quantum barriers) nano-APD respectively for the input optical pulse of width 0.4 ps of 850 nm wavelength. On the other hand, the 3 dB upper cut-off frequencies of the above-mentioned diodes are obtained to be 68.63 and 82.64 GHz respectively. Conclusion: Simulation results show that MQB nano-APDs possess significantly faster time response and wider frequency response as compared to the flat Si nano-APDs under similar operating conditions.

Multiple Quantum Barrier Nano-avalanche Photodiodes - Part II: Excess Noise Characteristics

Background: Excess noise characteristics of Multiple Quantum Barrier (MQB) nanoscale avalanche photodiodes (APDs) based on Si~3C-SiC heterostructures have been studied in this part of the paper. The multiplication gain and Excess Noise Factor (ENF) of the MQB APDs have been calculated by varying the number of Quantum Barriers (QBs). Methods: The numerically calculated ENF values of MQB APDs have been compared with the ENF of Si flat conventional APDs of similar dimensions and it is observed that the use of QBs leads to significant reduction in ENF of the APDs under similar biasing and illumination conditions. Results: The enhanced ratio of hole to electron ionization rates in MQB structures as compared to the bulk Si APD structure has been found to be the primary cause of improvement in the noise performance of the MQB nano-APDs. Conclusion: Finally, the numerically calculated ENF of Si flat APD has been compared with the experimentally measured ENF of a commercially available Si APD and those are found to be in good agreement; this comparison validates the simulation methodology adopted by the authors in this paper.

Effects of carrier injection profile on low noise thin Al0.85Ga0.15As0.56Sb0.44 avalanche photodiodes.

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A High-Linearity Avalanche Photodiodes With a Dual-Carrier Injection Structure

This letter presents a novel avalanche photodiode (APD) featuring a unique absorber that provides high-linearity operation. Different from conventional APDs, this APD has an absorber at both sides of the avalanche layer. This configuration effectively suppresses hole accumulation and the space-charge effect in the absorber. The fabricated APD exhibits an improved 1-dB compression point corresponding to an input power of −6.3 dBm at a gain of 10. It was found that its excess-noise characteristics are comparable to those of conventional electron-injection type and InAlAs APDs even though the new APD operates according to a dual-carrier injection and multiplication principle.

Germanium/Silicon-Germanium Heterostructure Avalanche Photodiodes on Silicon

Near-infrared photodiodes (PDs) of Ge on Si have been widely studied in Si photonics for the optical communications (1.3–1.6 μm). Ge-based avalanche PDs (APDs) have been also studied for sensitive photodetections. There are mainly two different types of Ge APDs on Si. One utilizes Ge as the multiplication layer, i.e., Ge homojunction APDs [1], while the other one utilizes Si, i.e., Ge/Si heterojunction APDs [2]. Si is one of the best materials for the multiplication layer in terms of low excess noises, although relatively large applied voltage more than 20 V, corresponding to the electric field strength more than 300 kV/cm, is required to obtain the multiplication gain due to the small ionization coefficients. In order to realize low-noise and low-voltage Ge APDs, we have recently proposed a new structure utilizing Ge/graded-SiGe heterojunction multiplication layer [3]. As in Fig. 1(a), photo-generated holes are injected via the graded SiGe to the Ge multiplication layer. The band discontinuity at the graded-SiGe/Ge interface can enhance the impact ionization due to the sudden increase of kinetic energy across the interface. This is effective to realize low-noise and low-voltage Ge APDs [3]. In this work, such Ge/SiGe heterostructure APDs are fabricated, and the multiplication gain is measured. As a result, the growth temperature in ultrahigh-vacuum chemical vapor deposition (UHV-CVD) is found to be a key parameter to enhance the multiplication gain. UHV-CVD was used to grow Ge/graded-SiGe/Ge heterostructures for free-space APDs on Si. GeH4 and Si2H6 were used as the source gases. First, 350-nm-thick undoped Ge layer was directly grown on p+-Si using low/high-temperature two-step growth. The Ge buffer layer (~50 nm) was grown at 370°C, followed by the growth at an increased temperature. As an important parameter, we compared the growth temperature, 510°C and 580°C. Then, a 24-nm-thick SiGe layer with the graded Ge composition from 70% to 100% was grown at the same temperature of 510°C or 580°C. Finally, a 50-nm-thick Ge layer was grown, and P atoms were implanted to form the n-Ge optical absorption layer. The valence band discontinuity at the bottom Si0.3Ge0.7/Ge interface is as large as 0.1 eV, assisting holes to reach the threshold energy (~1.0 eV) required for the impact ionization. As a reference, a Ge homojunction APD without the SiGe layer was also fabricated. Figure 1(b) shows typical hole-initiated multiplication gain as a function of applied voltage. Photo-generated holes can be selectively injected from the top n-Ge absorption layer to the bottom SiGe/Ge multiplication layer, using the free-space illumination of 532 nm laser light whose penetration depth in Ge as large as 20 nm. The use of SiGe/Ge multiplication layer is found to increase the multiplication gain in comparison with the Ge homojunction APD, being effective for the low-voltage APD operation. Furthermore, the Ge/SiGe APDs formed at the lower growth temperature of 510°C showed larger multiplication gain than that for 580°C. This is ascribed to the formation of abrupt SiGe/Ge interface at the lower growth temperature, as confirmed by the x-ray diffraction measurements. Excess noise characteristics will be also presented. [1] L. Virot et al., Nature Commun. 5, 4957 (2014). [2] Y. Kang et al., Nature Photon. 3, 59 (2009). [3] Y. Miyasaka et al., Jpn. J. Appl. Phys. 55, 04EH10 (2016). Figure 1

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.

Effect of Wasted Space on Device Characteristics of Nitride-Based Avalanche Photodiodes

On the basis of our recently proposed theory [Jpn. J. Appl. Phys. 49 (2010) 114101], we report the effect of wasted space on the multiplication gain and excess noise characteristics of GaN-based avalanche photodiodes. By means of the Monte Carlo method, it is shown that with the adoption of the revised impact ionization coefficients, the multiplication gain exhibits an obvious discrepancy compared with conventional theory, and agrees well with that reported for InP. Moreover, the size-dependent impact ionization coefficients affect the noise properties under submicron scale, leading to a new feature different from InP and clarifying the reported experimental data.

Effect of Wasted Space on Device Characteristics of Nitride-Based Avalanche Photodiodes

On the basis of our recently proposed theory [Jpn. J. Appl. Phys. 49 (2010) 114101], we report the effect of wasted space on the multiplication gain and excess noise characteristics of GaN-based avalanche photodiodes. By means of the Monte Carlo method, it is shown that with the adoption of the revised impact ionization coefficients, the multiplication gain exhibits an obvious discrepancy compared with conventional theory, and agrees well with that reported for InP. Moreover, the size-dependent impact ionization coefficients affect the noise properties under submicron scale, leading to a new feature different from InP and clarifying the reported experimental data.

Avalanche Mechanism in p +-n −-n + and p +-n Mid-Wavelength Infrared Hg1−x Cd x Te Diodes on Si Substrates

Hg1−x Cd x Te mid-wavelength infrared (MWIR) p +-n −-n + and p +-n − avalanche photodiodes (APDs) with a cut-off of 4.9 μm at 80 K were fabricated on Si substrates. Diode characteristics, avalanche characteristics, and excess noise characteristics were measured on two devices. Temperature-dependent diode and avalanche characterization was performed. Maximum 3 × 106 Ω cm2 and 9 × 105 Ω cm2 zero-bias resistance times active area (R 0 A) products were measured for the p +-n −-n and p +-n devices at 77 K, respectively. Multiplication gains of 1250 and 410 were measured at −10 and −4 V for the p +-n −-n + and p +-n APDs at 77 K, respectively, in the front-illumination mode with the help of a laser with an incident wavelength of 632 nm. The gains reduce to 200 and 50 at 120 K, respectively. The excess noise factor in all APDs was measured to be in the range of 1 to 1.2.

Noise Attributes of LWIR HDVIP HgCdTe Detectors

Time series and Fourier-transform data on high-density vertically integrated photodiodes (HDVIP) at 0 and 50 mV reverse bias in the dark have been studied. The detectors have a cutoff wavelength λc (60 K) of 10.5 μm. Examination of the detector current time series and Fourier-transform curves of these devices reveals a variety of interesting characteristics: (i) time series displaying switching between four states characteristic of random telegraph signal (RTS) noise, the noise current power spectrum having Lorentzian or double Lorentzian type characteristics, (ii) time series data exhibiting wave-like characteristics with the noise current power spectrum being 1/f2-like at low frequencies, (iii) time series having a mean value independent of time with the noise current power spectrum being white, and (iv) time series nearly independent of time with the noise current power spectrum having 1/f characteristics. Although from a single array, the excess noise characteristics at low (mHz) frequencies were varied, most of the detectors measured fell into one of these four categories. The predominance of detectors examined had minimal excess low-frequency noise down to ~ 10 mHz. Detectors that displayed RTS noise in reverse bias were repeatable under subsequent measurement. However, when measured at zero bias, the same detectors exhibited no RTS noise, the noise current power spectrum being white in nature.

NOISE CHARACTERISTIC AND QUALITY INVESTIGATION OF ULTRAFAST AVALANCHE PHOTODIODES

A detailed study of photosensitivity and noise characteristics of ultrafast InGaAsP / InP avalanche photodiodes (APDs) with separate absorption, grading, charge and multiplication regions was carried out. Carrier multiplication and noise factors were evaluated. Noise origin in investigated APDs is 1/f, generation-recombination and shot noises. Different quality samples have been investigated and it is shown that noise characteristics well reflect APD quality problems. It is shown that low-frequency noise and excess shot noise characteristics are very sensitive to the APD quality problems and clear up physical processes in device structure. Noise characteristic analyses can be used for the APD quality problems revealing and optimal design development.

Low frequency noise in GaAs structures with embedded In(Ga)As quantum dots

Abstract Current–voltage and low frequency excess electrical noise characteristics of two different—Schottky diode and n-i-n diode—GaAs structures embedded with self-assembled In(Ga)As quantum dots are reported. We find the growth of quantum dots induces defects not only near the quantum dot but also extended to quite a distance toward the growth direction. In Schottky diode structure, comparing with the reference sample without the quantum dot layer, the current dependence of the low frequency noise spectral density indicated that the noise is from the generated interface states with the density increasing towards the band tail. Also the crystal quality of the Schottky diode including the quantum dot layer, deduced from the Hooge parameter, was slightly worse than that of the reference sample. For n-i-n diode structure, the current–voltage relation was linear, and a quadratic current dependence of the noise spectral density was observed. The Hooge parameter for the n-i-n structure was determined to be on the order of unity indicating the general degradation of the structure.

Avalanche Multiplication and Breakdown in 4H-SiC Diodes

The measured photomultiplication and excess noise characteristics of two 4H-SiC p-i-n diodes, with i-region widths of 0.105 μm and 0.285 μm, were modelled using a nonlocal multiplication model to determine the ionization threshold energies and the impact ionization coefficients of 4H-SiC. The modelled ionization coefficients accurately predicted the breakdown voltage of a 0.485 μm p-i-n structure. The breakdown voltage of 4H-SiC calculated using these parameters is approximately 7.2 and 4.6 times higher than that of similar Si and Al0.8Ga0.2As structures respectively. Dead space, the minimum distance required for carriers to equilibrate in the electric field, has to be taken into account to accurately predict the breakdown voltage in thin devices.