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Perovskite solar cells (PSCs) have emerged as one of the most promising candidates for photovoltaic applications. Low-cost, low-temperature solution processes including coating and printing techniques makes PSCs promising for the greatly potential commercialization due to the scalability and compatibility with large-scale, roll-to-roll manufacturing processes. In this review, we focus on the solution deposition of charge transport layers and perovskite absorption layer in both mesoporous and planar structural PSC devices. Furthermore, the most recent design strategies via solution deposition are presented as well, which have been explored to enlarge the active area, enhance the crystallization and passivate the defects, leading to the performance improvement of PSC devices.

Summary Tin-based perovskite solar cells (PSCs), with more consummate optical band gaps, lower exciton-binding energies, and higher charge-carrier mobility, have not attracted tremendous research efforts compared with the lead-based ones that have a record power conversion efficiency (PCE) of 24.2%. The major challenges for Sn-based research are significantly low open-circuit voltage, poor reproducibility, and environmental instability. It has been identified that the oxidation processes take place during the preparation of precursor solutions and fabrication of films, due to the low redox potential of the stannous absorption layer. Herein, we propose two strategies of crystal-resolving and recrystallization technology to reduce the oxidation process. As a result, PCEs of 8.9% (active area of 0.04 cm2) and 5.5% (active area = 1.01 cm2) are attained using the inverted p-i-n structure, which will lead to a revival of lead-free PSC research.

In this research, the use of indium gallium zinc oxide (IGZO) thin-film transistors (TFTs) with a porous oxide layer (POL) resulting from the mechanochemical treatment of spin-coated oxide films is suggested for the detection of visible light. Mechanochemical treatment is a new technique that uses cellophane tape to induce the selective formation of hydrophobic dots on the surface of the a-IGZO. These dots interfere with the deposition of the film during spin coating, resulting in pore formation. The IGZO TFT with a POL exhibits 341.32 A/W photoresponsivity, 1.10 × 106 photosensitivity, and 4.54 × 1010 Jones detectivity under 532 nm light illumination.

High-speed back-illuminated uni-traveling-carrier photodiodes at 1064nm were demonstrated grown on InP with 3dB bandwidth of 17.8 GHz at -5 V bias, using InGaAsP as absorption layer. PDs with 40um diameter deliver RF output power levels as high as 19.5 dBm at 13 GHz. This structure can achieve low dark current density of 10 nA per cm2 at -5V bias and quantum efficiency of 45.2% at 1064nm. An analytical model based on S-parameter fitting was built to extract parameter to access the bandwidth limiting factors.

A two-dimensional perovskite photonic crystal structure of Methylamine lead iodide (CH3NH3PbI3, MAPbI3) is rationally designed as the absorption layer for solar cells. The photonic crystal (PC) structure possesses the distinct “slow light” and band gap effect, leading to the increased absorption efficiency of the absorption layer, and thus the increased photoelectric conversion efficiency of the battery. Simulation results indicate that the best absorption efficiency can be achieved when the scattering element of indium arsenide (InAs) cylinder is arranged in the absorption layer in the form of tetragonal lattice with the height of 0.6 μm, the diameter of 0.24 μm, and the lattice constant of 0.4 μm. In the wide wavelength range of 400–1200 nm, the absorption efficiency can be reached up to 82.5%, which is 70.1% higher than that of the absorption layer without the photonic crystal structure. In addition, the absorption layer with photonic crystal structure has good adaptability to the incident light angle, presenting the stable absorption efficiency of 80% in the wide incident range of 0–80°. The results demonstrate that the absorption layer with photonic crystal structure can realize the wide spectrum, wide angle, and high absorption of incident light, resulting in the increased utilization efficiency of solar energy.

An effective stress absorption layer can reduce the reflection crack. It can help to extend the service life of road. In this research, an enhanced stress absorption layer of slow crack (ESALOSC) is proposed and compared with the ordinary SBS modified asphalt stress absorbing layer. The strain data of two stress absorption layers under different loads, speeds and temperatures are collected by embedding sensors in the road, and the dynamic response laws of the two stress absorption layers under different conditions are analyzed. The results show that the asphalt pavement is a viscoelastic body and the measured results are consistent with the theoretical solution of layered elasticity: both stress absorbing layers are subjected to pressure. According to the comparison between dynamic overload test and static overload test, the strain deviation between the two sections increases from 11.6% of static load to 25.2% of dynamic load (40 km/h). It indicates that the reinforced effect of geogrid is more obvious under dynamic load. By establishing the relationship between vehicle speed and dynamic response, a vehicle speed and dynamic response model for the ESALOSC is proposed. Based on the test data measured at four temperatures, a model of the temperature and dynamic response in the ESALOSC is proposed. The accuracy and effectiveness of the two models are verified by comparing with other experimental results. The ESALOSC is of great significance for improving the crack resistance of road. The research results provide technical support and theoretical model for the development of long-life pavement in China.

We have proposed a novel double-layer microwave absorber based on spinel ferrite Ni0.8Co0.2Fe2O4 nanofibers (NCFO NFs) and Ni-C hybrid NFs prepared via a facile electrospinning method combined with subsequent heat treatment. Electromagnetic and microwave absorption properties of the double-layer microwave absorbers, together with those of the single-layer ones, were systematically investigated in the frequency range of 2–18 GHz. The double-layer absorbers consisting of 50 wt% NCFO NFs/paraffin composite and 5 wt% Ni-C NFs/paraffin composite show superior microwave absorbing performance with stronger absorption and broader bandwidth as compared with the corresponding single-layer ones and many reported double-layer ones. As 1.5 mm thick NCFO NFs composite is used as the matching layer and 0.8 mm thick Ni-C NFs composite is employed as the absorption layer, the optimal reflection loss (RL) of the absorber reaches −84.9 dB at 17.0 GHz with an effective absorption bandwidth below −10 dB of 7.4 GHz ranging from 10.6 to 18 GHz. The enhancement of microwave absorption in the double-layer absorbers should be mainly ascribed to the improvement of impendence matching characteristics due to the efficient coupling and synergistic effect between two layers. These excellent properties demonstrate that our double-layer structures offer a new route to design microwave absorbers with lightweight and high absorption performance over a broad frequency range.

Extensive experimental characterization and TCAD simulation analysis have been used to study the dark current in Avalanche Photo-Diodes (APDs). The comparison between the temperature dependence of measurements and simulations points out that SRH generation/recombination is responsible for the observed dark current. After the extraction of the carrier lifetimes in the GaAs layers, they have been used to predict the APD collection efficiency of the photo-generated currents under realistic operation conditions and as a function of the photogeneration position inside the absorption layer.

This research builds upon the authors’ previous work that introduced and modeled a novel Gallium-Arsenide, Emitterless, Back-surface Alternating Contact (GaAs-EBAC) thin-film solar cell to achieve >30% power conversion efficiency. Key design parameters are optimized under an Air-Mass (AM) 1.5 spectrum to improve performance and approach the 33.5% theoretical efficiency limit. A second optimization is performed under an AM0 spectrum to examine the cell’s potential for space applications. This research demonstrates the feasibility and potential of a new thin-film solar cell design for terrestrial and space applications. Results suggest that the straight-forward design may be an inexpensive alternative to multi-junction solar cells.

A newly developed design of an absorber is described. In the new absorber, a horizontal annular perforated baffle with a directing conical bucket is situated on top of the upper layer of absorbent, which is covered by a layer of ceramic balls through a separating screen. Such a design assures a high degree of uniformity of the distribution of the input gas stream at the inlet to the absorption layer and produces an increase in the use efficiency of the absorption capacity of the adsorbent in vertical absorbers.

ABX3 crystalline perovskite material has many advantages: good photoelectric absorption property, high charge carrier mobility, good film formation, long charge carrier lifetime, and easy bandgap adjustment for absorption layer of perovskite solar cells. As a result, the power conversion efficiency (PCE) of the organic-inorganic halide perovskite solar cells (PSCs) has taken a tremendous step forward, from 3.9% in 2009 to a recently reported value over 25.5%. Thus, it shows great potential to compete with traditional silicon solar cells. However, PSCs preparing conditions are harsh and susceptible to environmental influences, thus leading to instability. Therefore, it is essential to prepare high-performance and stable PSCs in an air environment. This study aims to use the ion doping method to improve the performance and stability of PSCs and analyze the mechanism. This work focuses on enhancing PSCs efficiency and stability by performing FA+ and Cl– doping experiments on MAPbI3 films in air. The results show that a single Cl–-doping increases the carrier diffusion length, reducing the recombination of electrons and holes, and inducing the perovskite intermediate hydrate (CH3NH3)4PbI6·2H2O to form, promoting the crystallization of the thin film, and improving the device performance. On the other hand, a single FA+-doping will reduce the bandgap of perovskite and increase the short-circuit current density (JSC) of the device, and FA+ is susceptible to the influence of water vapor to induce a yellow δ-FAPbI3 perovskite film to form, which leads the device performance to degrade. However, the prepared co-doping Cl–, FA+ significantly improves overall PSCs device performance, yielding the highest PCE of 17.29%, and showing excellent stability by maintaining over 80% of the original PCE without any encapsulation after 1000-hour storage in ambient air.

Recently, two-dimensional materials are considered as potential materials for future electronic devices. Moreover, fabrication of two-dimensional heterojunction attract lots of attention. Here, we use a laser with metal-assisted oxidation method to construct WSe2/WO3 heterostructure. In the experiment, a plasma-assisted chemical vapor reduction (PACVR) process was applied to synthesis large area WSe2 layer. A layer of nickel metal was deposited as a first layer which will absorb the heat of laser and oxidize the top WSe2 layer, then a additional oxide layer was deposited between nickel layer and WSe2 layer to prevent the nickel metal layer from getting selenized when we used PACVR process to selenize the amorphous WO3 precursor. In the laser oxidation process, we choose 808 nm wavelength continuous wave laser as the laser source which will not absorb by WSe2 layer cause the laser energy is lower than bandgap of WSe2. Therefore, the nickel metal layer will absorb most of the laser energy then heat the top WSe2 layer under atmosphere. The top area of WSe2 heated by the metal layer will get oxidized into WO3 hence formed a heterojunction with the outer area which was not expose by laser. We also used photolithography to get different pattern of nickel layer which could control and limit the oxidized area by the metal layer but not by the laser exposure area. After the laser oxidation process, this WSe2/WO3 structure was further fabricated into photodetector showed its great possibility in future electronic applications.

The investigation of crystal growth is crucial for us to improve the film quality and photophysical properties of CH3NH3PbI3 (MAPbI3). In the two-step spin-coating process, the crystal structure could be modulated by controlling the growth conditions of PbI2 and CH3NH3I (MAI) layers. In this paper, the PbI2 layer was treated with annealing under different times. A liquid&ndash, liquid diffusion (LLD) mechanism is proposed to modify the deposition of MAI precursor solution and enhance the flatness of organic&ndash, inorganic hybrid perovskite film. Furthermore, the perovskite films are prepared using different concentrations of MAI. The evolution process of perovskite structure is observed by modulating the concentration of MAI. The spin-coating of moderate MAI tends to form high quality MAPbI3 films with enhanced absorption and carrier extraction capabilities. The high concentration of MAI would cause the perovskite phase transition, which provides a novel perspective to modulate the structure of organic&ndash, inorganic hybrid perovskite in the two-step spin-coating process, although it deteriorates the device performance.

In this work, the optical characteristics of electrodeposited Cu2O films was studied, and the depth of photogenerated carriers in Cu2O films was obtained. In order to improve the collection depth of the photogenerated carrier in ZnO/Cu2O solar cells, ZnO nanorod array were employed to construct composite-structure solar cells. The influence of the ZnO nanorod arrays on short-circuit current and open circuit voltage was systematically analyzed in the nanorod cells. For optimizing device performance, ordered ZnO nanorod arrays that incorporated design spacing that matched the carrier diffusion length of the absorption layer were used. Analyses of the photovoltaic properties revealed that ordered nanorod arrays with a proper spacing could improve carrier generation efficiency in high-efficient collection regions of the carriers. These observations indicate that nanorod spacing is an important variable in the construction of high-efficient nanorod-based solar cells.

The tremendous progress exhibited by Perovskite solar cells (PSCs) within the decade has made PSCs the fastest growing PV cell to date. The PSCs has exhibited increment in power conversion efficiency (PCE from 3.2% to 25.2% within a decade. In PSCs, usually MAPbX3 (X being Cl, Br and I) layer is used as an absorber layer. The incorporation of toxic Lead (Pb) is a matter of concern by some of the researchers. In order to deal with this Tin (Sn) is being used as an alternative of Pb. However, the performance of Sn based PSC still lags behind Pb based PSC. In this work, we demonstrate an efficient Sn based PSC with JSc of 32.6398 mA/cm2, Voc of 0.8946V, FF of 80% and PCE of 23.4%. The results exhibits the potential of Sn based PSCs which is not only efficient but also is environmental friendly. We study the impact of defect density and layer thickness of absorber layer over the performance of Sn based PSC. An analysis on the effect of doping in Electron Transport Layer (ETL) and Hole Transport Layer (HTL) over the performance of Sn based PSC is also conducted.

A comparative investigation in the cell performance of Copper Indium Gallium Selenide (CIGS) thin-film solar cell has been reported. The main objective behind our work is to present the effect of the doping concentration on each layer i.e. window layer (ZnO), buffer layer (CdS) and absorption layer (CIGS) in the CIGS solar cell to find out the optimum doping concentration using ADEPT 2.0, a 1D simulation software. The device parameters are optimized separately for each layer. Energy conversion efficiency is calculated from light J-V characteristics curve. A total-area efficiency of 19·75% for ZnO:Al/i-ZnO/CdS/CIGS based thin-film solar cells has been reported.

In concentrated solar power systems (CSP), solar receivers need to have high light absorption and high durability at elevated temperatures. In this study, we preset high absorption, high durability coatings for solar receivers in CSP plants. Black pigments and TiO2 porous structure were created to enhance optical properties, while the coating film was formed with 3 layers (base layer, absorption layer and top coating) to enhance durability. It is shown that this coating is stable at 850°C after 100 hours of aging, while keeping a solar-weighted absorptance value of 96-97%. This is higher absorptance and higher durability than conventional coatings used for CSP.

As solar light was mainly absorbed by absorb layer in thin film solar cells, the quality of absorb layer has a great effect on the performance of solar cells. Based on the diffusion drift model of carrier in copper indium gallium selenide (CIGS) solar cells, and then the key parameters are analyzed. Combining with the experimental results of others, this paper discusses the absorption layer’s thickness influence on the open circuit voltage, short circuit current, filling factor and conversion efficiency of the copper indium gallium selenium based solar cells. The results show that the absorption layer’s thickness always affects the performance parameters of the battery. Open circuit voltage increased with increasing thickness and reached saturation above 2μm. Short circuit current increased first and then decreased, then reaches its maximum value at about 2μm thickness. Conversion efficiency is similar to the short circuit current properties. While the fill factor decreased with the increase of thickness above 1^m. This can provide theoretical support for the design of better device structures.

Cu2ZnSnS4is considered as the ideal absorption layer material in next generation thin film solar cells due to the abundant component elements in the crust being nontoxic and environmentally friendly. This paper summerized the development situation of Cu2ZnSnS4thin film solar cells and the manufacturing technologies, as well as problems in the manufacturing process. The difficulties for the raw material’s preparation, the manufacturing process, and the manufacturing equipment were illustrated and discussed. At last, the development prospect of Cu2ZnSnS4thin film solar cells was commented.

Cu-deficient Cu[(In,Ga)(Zn,Sn)]Se2 (CIGZTSe) films with the expected composition of 60% Cu(In,Ga)Se2 (CIGSe) and 20% Cu2ZnSnSe4 (CZTSe) were prepared by paste printing of cermet nanopowder and selenization at 550–650°C for 1 h. The cermet powder contained metallic Cu, Zn, and Sn and ceramic In2Se3, and Ga2Se3 nanopowders. The CIGZTSe films were single phase and had dense and larger grain size of 1–3 μm. Composition analyses of this CIGZTSe films were executed to demonstrate the defect behavior and the variations of electrical properties with selenization temperature. Our solar cell device made with this film as absorption layer showed power conversion efficiency of 0.86%.

InGaAs/InP single-photon avalanche diodes (SPADs) are widely used in practical applications requiring near-infrared photon counting such as quantum key distribution (QKD). Photon detection efficiency and dark count rate are the intrinsic parameters of InGaAs/InP SPADs, due to the fact that their performances cannot be improved using different quenching electronics given the same operation conditions. After modeling these parameters and developing a simulation platform for InGaAs/InP SPADs, we investigate the semiconductor structure design and optimization. The parameters of photon detection efficiency and dark count rate highly depend on the variables of absorption layer thickness, multiplication layer thickness, excess bias voltage and temperature. By evaluating the decoy-state QKD performance, the variables for SPAD design and operation can be globally optimized. Such optimization from the perspective of specific applications can provide an effective approach to design high-performance InGaAs/InP SPADs., 6 pages, 7 figures. Accepted for publication in Applied Optics

Over the past few years, the power conversion efficiency of perovskite solar cells have shown a tremendous progress from 3.8% in 2009 to 23.3% in 2018. Perovskites have exhibited excellent advantages in photovoltaic devices and other promising optoelectronic devices owing to their exceptional material properties, including direct and tunable bandgaps, strong light absorption, high electron/hole mobilities, long charge carrier lifetimes and diffusion lengths. The outstanding performance of perovskite solar cells is closely related with the deposition techniques and material composition of perovskite films. The preparation process of perovskite film is crucial for obtaining high efficiency devices, and it usually requires to fabricate a high coverage, compact and uniform perovskite layer. At present, the preparation technology of perovskite absorption layer mainly includes one-step processing, two-step processing, dual-source thermal evaporation processing, vapor-assisted solution processing and some scalable processing methods, and there are many reports and summaries about this work. However, perovskites still have some shortcomings such as insufficient light absorption range, poor long-term stability, the lead toxicity, which need to be overcome to realize higher power conversion efficiency and further product application. Compositional control engineering of perovskite materials becomes one of the effective ways to solve the above problems, but the summary of the research in this area is still lacking. In this review, we summarize the recent progress on the perovskite materials with different component systems, including organic-inorganic lead halide perovskite, all-inorganic lead halide perovskite, low-lead perovskite and lead-free perovskite. We also discuss some representative material compositions and the research on their corresponding preparation methods, the optimization of device structure and the effects on the device performance. Moreover, we compare and summarize the advantages and disadvantages of perovskite materials with different component systems. The purpose is to provide ideas on how to improve the efficiency and stability of perovskite solar cells through compositional controlling, and finally realize commercial application.

This paper presents characteristics of surface acoustic wave (SAW) gas sensor for detecting volatile gases such as ethanol gas by measuring the phase shift of output signal. A delay-line with a center frequency of 400 MHz was fabricated on Y-Z substrates. Experimental results, which showed the phase change of the output signal under the absorption of volatile gas on sensor surface, were presented. The sensitivities of SAW delay lines coated with polyurethane films were greatly increased compared to those for uncoated devices. This SAW gas sensor system may be well suited for a high sensitivity electronic nose system.

This paper reports on the study of the black gold thin film as the absorption layer in the near infrared spectrum. The fabrication of the black gold thin film was achieved by a thermal evaporation technique in N2 atmosphere. Different evaporation conditions were attempted to optimize the absorbance of the black gold coating, especially the atmosphere pressure and the mass of evaporation source. The long-standing problem of black gold’s adhesion with the substrate was solved by fuming 502 superglues into the black gold layer, which had almost no impact on the absorbance performance. Layers produced at N2 atmosphere of 3×103 Pa show an absorbance exceeding0.9 inthe near infrared.

We have developed a new thin film pyroelectric IR sensor with micro cavity structure, which consists of infra-red absorption layer using carbon-modified resin membrane on the infra-red detecting azea. And we were able to find the best sensor design rule or thermal conductance: G for micro cavity size, and Pt electrode width and thickness. The developing sensor has realized a high-performance of sensing characteristic that responsivity: Rv, and detectivity: D* were 2400V/W, and 6.6×107cm√Hz/W at 20Hz, respectively.In the future, the developing sensor is expected the wide applications for high accurate human detection and non-contact temperature detection.

We present images in the 450 and 850 μm continuum of the edge-on galaxy NGC 891. These measurements, carried out with the recently commissioned Submillimeter Common-User Bolometer Array, provide the deepest images yet of a nearby galaxy in the submillimeter wave band. We detect dust emission from 2/3 of the optical disk and confirm the presence of dust chimneys escaping from the main absorption layer up to z-heights of nearly 2 kpc. A comparison between the submillimeter surface brightness along the major axis with that corresponding to the IRAS 60 and 100 μm filters implies that large amounts of cold dust (~15 K) are present in the disk (in fact, an order of magnitude more grain material than the warm dust detected by IRAS). These cold grains predominate at larger galactic radii.

The concept of co-catalytic layer structures for controlled laser-induced chemical vapor deposition of carbon nanotubes is established, in which a thin Ta support layer chemically aids the initial Fe catalyst reduction. This enables a significant reduction in laser power, preventing detrimental positive optical feedback and allowing improved growth control. Systematic study of experimental parameters combined with simple thermostatic modeling establishes general guidelines for the effective design of such catalyst/absorption layer combinations. Local growth of vertically aligned carbon nanotube forests directly on flexible polyimide substrates is demonstrated, opening up new routes for nanodevice design and fabrication.

Reducing the spatial aliasing error of the angular spectrum method by using an absorption layer is investigated in this paper. The acoustic equation including the absorption layer is presented and is transformed in the spatial frequency domain, where an implicit analytic solution is readily available. Its approximation, which is more suitable for numerical simulation, is derived and is numerically implemented. The comparisons between the present method and available methods demonstrate its validity and advantages.

Cataloged from PDF version of article. We report on the design, fabrication, and characterization of solar-blind Schottky photodiodes with low noise and high detectivity. The devices were fabricated on n-/n+ AlGaN/GaN heterostructures using a microwave compatible fabrication process. True solar-blind operation with a cutoff wavelength of similar to274 nm was achieved with Al(x)Ga(1-x)N (x=0.38) absorption layer. The solar-blind detectors exhibited

Improve the low-frequency acoustic performance of sound absorption coating of submarine is a hot issue. Based on the theory of sound wave normally impinging on the absorption layer of 2D,the 2D shaft mode of frustum-of-a-cone cavities is established by finite element COMSOL, which is test to analyze the absorption characteristics combined structural parameters. The calculation results indicate that under the condition of the same perforation rate ,the absorption performance of multi-layered material anechoic coating is better than that of single-layered material anechoic coating, especially to the performance of low-frequency; the absorption performance of frustum-of-a-cone cavities is better than that of cylindrical and ellipsoidal structures. With the perforation rate is increasing,the absorption performance of anechoic coating in low-frequency improve..Choosing the appropriate cavity structure is important. And the future acoustic optimization of the multi-layered frustum-of-a-cone cavities anechoic coating is guided by the study.

The rivers of Eastern Cuba are characterized by small size, different orography, and moistening. Theoretical aspects of the conditions of absorption formation, values of absorption and infi ltration up to the level of the ground water in the river basins of Eastern Cuba are analyzed with the use of the genetic runoff theory and the linear-correlation model. The dependence of the absorption layer from the geomorphological factor makes it possible to distinguish the layer of surface detention from the general absorption layer before the beginning of water formation (the formation of gravitational water) and during the runoff. The dependence of the infiltration layer from the absorption layer turns out to be rather reliable. However, there is some value on the axis of the infiltration layer which characterizes the presence of the hidden infiltration layer when there is no absorption. It is supposed that in this case the surface and underground catchments are distinguished and there is water exchange between separate subterranean flows.

An apparatus and method to attenuate vibration and acoustic noise are provided. One apparatus includes a first layer formed from a non-metal material having a predetermined level of resistance to deformation to define a frequency response based on a vibrating frequency. The non-metal material has a profile defined by at least one sinusoid. The apparatus also includes a second layer defining an absorption layer coupled to the first layer. The second layer adds a body of mass adjacent the first layer.

We present a novel GeSi electro-absorption (EA) modulator design on a silicon-on-insulator platform. The GeSi EA modulator is constructed based on the Franz-Keldysh (FK) effect. The light is evanescent-coupled into the GeSi absorption layer from the rib Si waveguide. A contnet of 1.19% Si in SiGe absorption layer is chosen for C (1528–1560 nm) band operation. Simulation shows a high (3 dB) bandwidth of ～ 64 GHz and extinction ratio of 8.8 dB. Especially the insertion loss is as low as 2.7 dB.

An InAlAs avalanche photodiode (APD) that has large bandwidth (>18.5 GHz) and high multiplied responsivity is demonstrated. The APD has a vertically illuminated structure with a thick absorption layer of 1 μm. The fabricated APD achieves the maximum 3 dB bandwidth of 23 GHz at the multiplied responsivity of 4.06 A/W and the 3 dB bandwidth of 18.5 GHz at high multiplied responsivity of 9.1 A/W. The multiplied responsivity-bandwidth product 18.5 × 9.1 = 168 A/W-GHz is the largest value ever reported for an APD for 25 Gbit/s operations.

The drift-diffusion theory is adopted to simulate the bandwidth and the saturation characteristics of InGaAs/InP uni-traveling-carrier (UTC) photodetector. According to the experiment results, we analyze the physical mechanisms in high speed and high power UTC photodetector. It is shown that introducing the cliff layer and the gradually doped absorption layer can enhance the saturation characteristic obviously. Electric field collapse in the absorption layer leads to the saturation, and RC constant is still a limitation factor for device with diameter larger than 20 μm. In this paper we point out the effective methods to improve device performance.