Avalanche Multiplication Of Carriers Research Articles

A high-performance selenium nanoflake-based avalanche photodetector

Photodetectors are now indispensable in our daily lives, and there is a pressing need to explore new materials and mechanisms that can push the boundaries of device performance. Two-dimensional (2D) van der Waals (vdW) semiconductors have emerged recently as a promising material platform with exceptional optoelectronic properties, making them particularly suitable for high-performance photodetectors. However, photoinduced carrier generation in conventional 2D vdW photodetectors are usually limited, and new mechanisms need to be introduced to enhance device performance. Herein, we report a high-performance avalanche photodetector based on selenium (Se) nanoflakes. Our device achieves a high photoresponsivity (R) and specific detectivity (D*) of 361 A·W−1 and 2.4 × 1012 Jones, respectively. These figures of merit are two orders of magnitude higher than that in conventional Se photoconductive photodetectors. As a large bandgap vdW semiconductor, the Se channel allows the application of an extremely large bias voltage across it, and the resulting high electric field leads to the avalanche multiplication of carriers, which lays the groundwork for the improved device performance.

Ga2O3 Schottky Avalanche Solar‐Blind Photodiode with High Responsivity and Photo‐to‐Dark Current Ratio

AbstractSolar‐blind photodetectors have attracted extensive attention due to their advantages such as ultra‐low background noise and all‐weather. In this study, the planar Ti/Ga2O3/Au Schottky avalanche photodetector (APD) is fabricated based on β‐Ga2O3 epitaxial film on the sapphire substrate grown by metal–organic chemical vapor deposition. The Schottky APD exhibits a high responsivity of 9780.23 A W−1, an ultrahigh photo‐to‐dark current ratio of 1.88 × 107, an external quantum efficiency of 4.77 × 106%, a specific detectivity of 9.48 × 1014 Jones, with an ultrahigh gain of 1 × 106 under 254 nm light illumination at 60 V reverse bias, indicating high application potential for solar‐blind imaging. The superior photoresponse performances ascribe to the effective carrier avalanche multiplication, which contributes to the high photocurrent, and the high quality Schottky junction depletion, which leads to the low dark current.

Mott memristors based on field-induced carrier avalanche multiplication

We present a theory of Mott memristors whose working principle is the nonlinear carrier avalanche multiplication in Mott insulators subject to strong electric fields. The internal state of the memristor, which determines its resistance, is encoded in the density of doublon and hole excitations in the Mott insulator. In the current-voltage characteristic, insulating and conducting states are separated by a negative-differential-resistance region, leading to hysteretic behavior. Under oscillating voltage, the response of a voltage-controlled, nonpolar memristive system is obtained, with retarded current and pinched hysteresis loop. As a first step towards neuromorphic applications, we demonstrate self-sustained spiking oscillations in a circuit with a parallel capacitor. Being based on electronic excitations only, this memristor is up to several orders of magnitude faster than previous proposals relying on Joule heating or ionic drift.

High-performance germanium avalanche photodetector for 100 Gbit/s photonics receivers.

A high-bit rate and low-bias voltage waveguide-integrated vertical germanium avalanche photodetector is reported with doping optimization. This scheme alleviates the necessity of complex epitaxial single-crystal silicon layer and multiple ion implantation schemes. The optical absorption and carrier avalanche multiplication gain occur in the same germanium layer. The maximum gain is estimated to be 112.4 at an input power of -30.2dBm. With the input optical power of -16.1dBm, the gain-bandwidth product of nearly 141 GHz is obtained at 7.8 V bias. Meanwhile, a 4.6 dB sensitivity improvement for 60 Gbit/s signal reception is demonstrated with an avalanche gain of 5.1 at a soft-decision forward-error correction threshold (SD-FEC), i.e., bit-error-rate of 2×10-2. The absolute sensitivities of photonics receivers are -21, -18.6, -15.9, and -11.5dBm for 40, 60, 80, and 100 Gbit/s non-return-to-zero signals at the SD-FEC threshold. These demonstrated characteristics enable the reliable and robust on-chip photodetection for energy efficienct silicon photonic interconnects in the future.

Impact ionization in HgCdTe avalanche photodiode optimized to 8 µm cut–off wavelength at 230 K

If the impact ionization occurs in a region of high electrical field then it can result in avalanche multiplication of carriers. This process is used in avalanche photodiodes enabling individual photons to be detected when the incident flux of light is very low. HgCdTe is an almost ideal material for avalanche photodiodes, however to achieve the highest performance in near-room temperatures, a careful design of device structure is needed, to reach the highest performance in near-room temperatures. N+-ν-p-P+ photodiode meets the requirements of the separated absorption and multiplication regions. This paper describes the results of research aimed at investigation of the impact ionization mechanism in HgCdTe N+-ν-p-P+ photodiode optimized for 8 μm cut-off wavelength at 230 K. The results show that the parameters of the ν-region greatly influenced on the distribution of the electric field and the generation rate due to the impact ionization. In addition, ν-region has the effect on reduction of undesirable tunneling in the space charge region. For this purpose, it is necessary to keep the doping in this region as low as possible and to extend the energy gap in relation to the absorbing region.

Применение радиационно-термической обработки для подавления ч увствительности кремниевых микросхем к одиночным радиационным эффектам

The paper analyses the possibility to reduce the sensitivity of silicon integrated circuits (ICs) to single radiation effects by means of radiation-thermal treatment including irradiation in charged particle accelerators and subsequent low-temperature heat treatment. It is shown that reduction in sensitivity to single radiation effects is provided by formation of thermostable recombination centers in semiconductor IC structure in necessary concentrations. At the same time a decrease in primary photocurrent generated by heavy charged particles or high-energy protons, reduction in transfer coefficients of parasitic bipolar transistors forming thyristor structures, reduction in carrier avalanche multiplication coefficients at high electric field strengths can be provided. Radiationthermal treatment can be introduced in the manufacturing process of ICs of various classes at the end of the manufacturing cycle and does not require correction of the basic technology. A possible undesirable growth of inverse currents and preservation of values of other electrical parameters within acceptable values when using radiation-thermal treatment is provided by choosing optimal modes of irradiation and annealing which are established in the course of experimental tests. The calculated evaluation has shown that using radiation-thermal treatment in the technology of IC fabrication can provide a decrease in the effective collection length of non-equilibrium charge carriers generated under the influence of single radiation effects by at least 10 times which allows considering radiation-thermal treatment as an effective technological tool to suppress the sensitivity to single radiation effects.

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.

Plasmonic Transition Metal Carbide Electrodes for High-Performance InSe Photodetectors.

We demonstrate the application of MXenes, metallic 2D materials of transition-metal carbides, as excellent electrode materials for photonic devices. In this study, we have fabricated an InSe-based photodetector with a Ti2CTx electrode. The photodetector with few-layer, atomically thin, Ti2CTx (MXene) electrodes shows the avalanche carrier multiplication effect, which leads to high device performance. To improve the performance of the InSe/Ti2CTx avalanche photodetector, we can pattern Ti2CTx into nanoribbon arrays (a plasmonic grating structure), which enhances light absorption of the photodetector. The plasmonic InSe/Ti2CTx avalanche photodetector exhibits low dark current (3 nA), high responsivity (1 × 105 AW-1), and high detectivity (7.3 × 1012 Jones).

Operation of voltage termination structure in silicon n+-p-p+ detectors with Al2O3 field isolator grown by Atomic Layer Deposition method

This study focuses on evaluating the properties of voltage termination structure (VTS) with multiple guard rings in n+-p-p+ silicon detectors with Al2O3 field isolation films processed by Atomic Layer Deposition (ALD) method. The dependences of the ring potential over the guard rings with respect to bias voltage were studied experimentally and compared with the results of simulations using negative charge Qf in Al2O3 films as a parameter. The agreement of the experimental and calculated punch-through voltages switching the ring operation verified that the punch-through model built for the p+-n-n+ detectors passivated with positively charged SiO2 layers is also applicable for the n+-p-p+ detectors with Al2O3 field isolator with negative charge polarity. The results indicated an efficient potential distribution over the VTS rings. The amount of the oxide charge was shown to be an essential parameter for the detector performance. From the comparison of the experimental data and simulations for Si detector with the used design and processing technology, Qf of -(4–7)×1011 cm−2 was found to be the value explaining the properties of VTS in the detector under study. The simulations showed that Qf of -7×1011 cm−2 is an upper limit critical for the appearance of high electric field regions in the VTS. The increase in the silicon resistivity to 20 kωcm was found to be an efficient way to reduce the electric field below the value initiating the carrier avalanche multiplication.

Observation and discussion of avalanche electroluminescence in GaN p-n diodes offering a breakdown electric field of 3 MV cm−1

We report on the first observation of avalanche electroluminescence resulting from band-to-band recombination (BTBR) of electron hole pairs at the breakdown limit of Gallium Nitride p-n diodes grown homo-epitaxially on single crystalline GaN substrates. The diodes demonstrated a near ideal breakdown electric field of 3 MV cm−1 with electroluminescence (EL) demonstrating sharp peaks of emission energies near and at the band gap of GaN. The high critical electric field, near the material limit of GaN, was achieved by generating a smooth curved mesa edge with low plasma damage, using etch engineering without any use of field termination. The superior material quality was critical for such a near-ideal performance. An electric field of 3 MV cm−1 recorded at the breakdown resulted in impact ionization, confirmed by a positive temperature dependence of the breakdown voltage. The spectral data provided evidence of BTBR of electron hole pairs that were generated by avalanche carrier multiplication in the depletion region.

Study of the Lifetime of High-Power GaAs PCSSs Under Different Energy Storage Modes

This paper presents an experimental study on the lifetime of high-power gallium arsenide photoconductive semiconductor switches (PCSSs) under different energy storage modes. Under the capacitive energy storage mode, the lifetime of a PCSS was increased by a factor of 10 through a reduction in the capacitor size, which reduces the hold-time of the carrier avalanche multiplication. Under the transmission line energy storage mode, the lifetime of a PCSS was increased by more than twofold by reducing the bias electric field, which reduces the degree of the carrier avalanche multiplication. Additionally, the influence of various factors on device lifetime and the failure mechanisms are discussed. The experimental results and analysis indicate that electrode erosion and stress damage are the two leading factors that induce the failure of high-power PCSSs.

80 MeV Carbon Ion Irradiation Effects On Advanced 200 GHz Silicon-germanium Heterojunction Bipolar Transitors

The total dose effects of 80 MeV carbon ions and 60 Co gamma radiation in the dose range from 1 Mrad to 100 Mrad on advanced 200 GHz Silicon-Germanium heterojunction bipolar transistors (SiGe HBTs) are investigated. The stopping and range of ions in matter (SRIM) simulation study was conducted to understand the energy loss of 80 MeV carbon ions in SiGe HBT structure. Pre- and post-radiation DC figure of merits such as Gummel characteristics, excess base current, ideality factor, DC current gain, damage constant, neutral base recombination, avalanche multiplication of carriers and output characteristics were used to quantify the radiation tolerance of the devices. The excess base current, current gain and damage constant for 80 MeV carbon irradiated SiGe HBTs show more degradation when compared to 60 Co gamma irradiation. The ideality factor for 80 MeV carbon ions irradiated SiGe HBTs is also more when compared to 60 Co gamma irradiated SiGe HBTs. The SiGe HBTs shows minimal degradation in current gain at collector current levels (~ 1 mA) where the circuits are biased even after 100 Mrad of total dose. Therefore SiGe HBTs are became the reliable candidate for deep space exploration programs and high energy physics experiments (HEP) like large hadron colliders (LHCs). Copyright © 2015 VBRI press.

(Invited) Reliability of SiGe HBTs in Long-Term Operation

Introduction In the ongoing development towards RF circuits with still higher operation frequencies SiGe HBT technologies continuously have to prove their competitiveness against advanced Si CMOS and compound semiconductor millimeter-wave circuits. Yet, besides excellent RF performance at circuit operation frequencies – meanwhile even well beyond 100 GHz –customer focus is also put on operating constraints (“safe operating area”, SOA) and long-term reliability of the devices.If the HBT power load in a circuit stays within the SOA limits but collector voltage surpasses open-base breakdown voltage (BVCEO) or the emitter-base (EB) diode is reverse biased a gradual decrease of the HBT current gain (“beta ageing”) can usually be observed (Fig. 1a). This beta degradation is correlated to an increase of the base recombination current caused by recombination centers (“traps”) at dielectric interfaces. These again are being created by hot carrier injection (“HCI”).This interface trap generation and the gradual character of ageing are in contrast with device failure of III-V devices where defects are generated inside the semiconductor and failure shows more abrupt and end-of-life characteristics [1].Concerning HBT reliability the questions to address then are: What is the maximum HBT beta degradation tolerable for any specific circuit operation? Will it stay within this limit during the anticipated circuit life-time (up to 20 years for space applications)? Our intention therefore was to develop an ageing function which describes base current change or beta degradation, respectively, as function of electrical stressors, ambient temperature, and stress time. The experimental setups to evaluate ageing are forward and reverse bias stress conditions which we applied for up to 1000h and in a temperature range from -40°C up to 150°C. Operation Constraints The SOA to which device operation should be restricted can be derived from the common-base output characteristics which indicate device instabilities by current pinch-in or electro-thermal runaway. For low-voltages electro-migration will define maximum current densities. The latter can to be avoided be defining proper design guidelines for the metal line layout. Interface Defect Generation and Annihilation Even within SOA sufficiently high electrical fields in the collector-base (CB) space charge region will trigger avalanche carrier multiplication there and part of them will be accelerated towards EB and CB spacer oxides interfaces (HCI). Subsequently, interface traps will be created by de-passivation of Si dangling bonds. Trap density is expected to evolve as Nit ~ tα with α ≈ 0.25 [2] as long as the reaction is far from saturation (i.e. trap density becomes comparable to the total areal density of interface dangling bonds). Contrary, thermal activated hydrogen re-passivation of traps leads to beta recovery. Electrical Stress and Annealing Tests Currently, two types of electrical stress tests have been established as basis for SiGe HBT reliability evaluation:Forward “mixed-mode” (MM) stress with applied VCB,stress > BVCEO and forced emitter current density JE,stress up to a few times the value corresponding to peak-fT,“REV” stress with reverse biased BE junction. Additionally, to study defect annealing we applied a combination of high current and VCB,stress > BVCEO at ambient temperatures up to 150°C to achieve junction temperatures well above 200°C. Figure 1a shows as an example the impact of 100 h REV stress and subsequent anneal on a HBT with 250 GHz peak-fT from IHP’s 0.13 µm BiCMOS technology [3]. At VBE = 0.7 V over 90% beta reduction can be observed during reverse stress (2) but annealing with junction temperature reaching 300°C lead to almost complete beta recovery (3). Ageing Function The additional trap recombination saturation currents have been evaluated as function of the relevant stressors [4]IBEr,MM = f(VCB,stress, IE,stress, Tambient)·tα IBEr,REV = f(VEB,stress, Tambient)·tα and can be added to the according compact model base current. Figure 1b shows for example base current increase as function of VEB,stressafter 100h of REV stress. This ageing function can be used to predict HBT ageing and its impact on circuit performance during circuit life cycle.

ZnO-based ultraviolet avalanche photodetectors

By virtue of the carrier avalanche multiplication caused by an impact ionization process occurring in MgO insulation layer, zinc oxide (ZnO)-based ultraviolet (UV) avalanche photodetectors (APDs) have been fabricated from Au/MgO/ZnO/MgO/Au structures. The responsivity of APDs can reach 1.7 × 104 A W−1, and the avalanche gain of the photodetectors is about 294 at 73 V. Considering that no previous report on ZnO APDs can be found, the results reported in this paper may promise a route to high-performance ZnO UV photodetectors.

Ultraviolet emissions realized in ZnO via an avalanche multiplication process

Au/MgO/ZnO/MgO/Au structures have been designed and constructed in this study. Under a bias voltage, a carrier avalanche multiplication will occur via an impact ionization process in the MgO layer. The generated holes will be drifted into the ZnO layer, and recombine radiatively with the electrons in the ZnO layer. Thus obvious emissions at around 387 nm coming from the near-band-edge emission of ZnO will be observed. The reported results demonstrate the ultraviolet (UV) emission realized via a carrier multiplication process, and so may provide an alternative route to efficient UV emissions by bypassing the challenging p-type doping issue of ZnO.

Restriction on the gain in collected charge due to carrier avalanche multiplication in heavily irradiated Si strip detectors

Recent experiments on silicon detectors developed by the CERN-RD50 collaboration for very high luminosity colliders showed a significant enhancement of the collected charge Qc in Si detectors irradiated to the fluence of 1015–1016neq/cm2 if the devices were operated at high bias voltage. The enhancement arises from carrier avalanche multiplication in high electric field of the junction. However, calculated and experimental results indicated that a maximum Qc enhancement is much lower than the signal gain in avalanche photodiodes. The study of the collected charge in Si n-on-p strip detectors described here is focused on the restriction of the internal gain in irradiated Si strip detectors. It is demonstrated that (1) the gain in the collected charge due to avalanche multiplication is strongly restricted by the negative feedback arisen from a space charge limited current (SCLC negative feedback), which is an inherent property of heavily irradiated Si detectors with high concentration of radiation-induced defects; (2) the dependence of the gain on fluence is nonmonotonous due to competition between enhanced carrier trapping at high fluence and avalanche multiplication, which correlates with recent experimental results; (3) SCLC negative feedback makes the internal gain practically insensitive to the design of the detector region with high electric field. The results of this study show that the avalanche multiplication effect can be efficient in improving the radiation performance of Si detectors developed for the sLHC in a limited fluence range, which luckily covers the range expected in the upgraded LHC experiments.

MgZnO avalanche photodetectors realized in Schottky structures

AbstractMgZnO‐based ultraviolet avalanche photodetectors (APDs) have been fabricated from Au/MgO/Mg0.44Zn0.56O/MgO/Au Schottky structures. The carrier avalanche multiplication is realized via an impact ionization process occurring in the MgO layer under relatively large electric field. The APDs exhibit an avalanche gain of 587 at 31 V bias, and the response speed of the APDs is in the order of microseconds.magnified image(© 2013 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Operational voltage of silicon heavily irradiated strip detectors utilizing avalanche multiplication effect

Recent results on the collected charge Qc in heavily irradiated Si strip detectors developed by RD50 collaboration for the high luminosity operation of the LHC (sLHC) showed a significant Qc enhancement if the detectors were operated at a bias voltage beyond 1000 V. To explain these results, a physical model based on carrier avalanche multiplication in high electric fields near a n+-p junction was developed at the Ioffe Physical-Technical Institute. This study represents an extension of the model, whose goal is finding the detector bias voltage and the other operating conditions which lead to such charge enhancement. The electric field distribution and collected charge in heavily irradiated Si strip detectors are calculated at different conditions: bias voltage, temperature, radiation fluence and strip detector geometry. It is demonstrated that: a) the minimum operational voltage, which initiates the avalanche process, depends on the fluence (being 500 V and 1500 V for LHC and sLHC fluence range, respectively); b) in avalanche multiplication mode the electric field near the n+-strips is stabilized via potential redistribution inside the detector and formation of a pronounced DP electric field profile and is about 300 kV/cm; and c) the model predicts that the maximum collected charge in detectors irradiated to (2–5) × 1015 neqcm−2 is larger than in a non-irradiated detector that nicely agrees with the experimental data. Another factor, which gives an enhanced avalanche multiplication at lower bias voltage, is the electric field focusing near the strips which then also leads to an enhancement of Qc.

50 MeV Li3+ ion irradiation effects on advanced 200 GHz SiGe HBTs

The total dose effects of 50 MeV lithium (Li3+) ions on 200 GHz (8HP) silicon–germanium heterojunction bipolar transistors (SiGe HBTs) are studied in total doses ranging from 300 krad to 10 Mrad. The different electrical characteristics, such as the Gummel characteristics, dc current gain (h FE), neutral base recombination, avalanche multiplication of carriers (M−1) and output characteristics (I C–V CE), were studied before and after Li3+ ion irradiation. The results of 50 MeV Li3+ ion irradiation on SiGe HBTs are compared with 60Co gamma irradiation results in the same dose ranges.

Avalanche effect in Si heavily irradiated detectors: Physical model and perspectives for application

Abstract The model explaining an enhanced collected charge in detectors irradiated to 1015–1016 neq/cm2 is developed. This effect was first revealed in heavily irradiated n-on-p detectors operated at high bias voltage ranging from 900 to 1700 V. The model is based on the fundamental effect of carrier avalanche multiplication in the space charge region and in our case is extended with a consideration of p–n junctions with a high concentration of the deep levels. It is shown that the efficient trapping of free carriers from the bulk generation current to the deep levels of radiation induced defects leads to the stabilization of the irradiated detector operation in avalanche multiplication mode due to the reduction of the electric field at the junction. The charge collection efficiency and the detector reverse current dependences on the applied bias have been numerically simulated in this study and they well correlate to the recent experimental results of CERN RD50 collaboration. The developed model of enhanced collected charge predicts a controllable operation of heavily irradiated detectors that is promising for the detector application in the upcoming experiments in a high luminosity collider.