Theoretical analysis of the influences of barrier-enhancementlayers on transient responses of MSM photodetectors

Transient responses of In_0.53Ga_0.47As MSM PDs with abrupt and graded barrier-enhancement layers are simulated by using an ensemble Monte Carlo technique. The effect of the graded layer on transient responses and an appropriate graded-layer thickness for achieving fast responses are discussed. Also, a relevant device scaling law is proposed for In_0.53Ga_0.,₄₇As MSM PDs with graded barrier-enhancement layers     

Design and Fabrication of Monolithic Distributed Traveling-Wave Photodetectors Integrated With Polymer Optical Waveguides

We have designed and fabricated monolithic distributed balanced traveling-wave metal-semiconductor-metal photodetectors (MSM PDs) distributed along single-mode polymer optical waveguides. We demonstrate that monolithically integrated polymer optical waveguides on a semiconductor can provide efficient optical interconnects in an optoelectronic circuit. A responsivity of 0.44 A/W and a 3-dB bandwidth of 10 GHz were obtained in a PD array with five MSM PDs. A high photocurrent of 7.3 mA was measured in an array having eight MSM PDs. Impulse response measurements were performed and the results were compared with frequency domain results.     

AlGaN Photodetectors Prepared on Si Substrates

AlGaN ultraviolet (UV) metal-semiconductor-metal (MSM) photodetectors (PDs) grown on silicon substrates were fabricated and characterized. With 5-V applied bias, it was found that dark current density of Al_0.2Ga_0.7N PDs on silicon substrate was only 7.5times10^-9 A/cm². With an applied bias of 7 V, it was found that peak responsivities were 0.09 and 0.11 A/W while UV/visible rejection ratios (i.e., peak wavelength: 420 nm) were 324 and 278 for Al_0.2Ga_0.8N and Al_0.3 Ga_0.7N MSM PDs, respectively. Moreover, the noise equivalent power of Al_0.2Ga_0.8N MSM PDs was estimated to be 3.5times10^-12 W     

A device model for metal-semiconductor-metal photodetectors and itsapplications to optoelectronic integrated circuit simulation

Poisson's equation, current-continuity equations, and a rate equation for charged traps are numerically solved in two dimensions, to explain the behavior of photogenerated carriers and electric fields in GaAs metal-semiconductor-metal photoconductors (MSM PDs). An analytical model is proposed on the basis of these solutions and implemented in a SPICE-like circuit simulator. Simulated transient responses for an MSM PD and a monolithic optoelectronic receiver, consisting of an MSM PD and a MESFET transimpedance amplifier, are in good agreement with measured results     

Effects of annealing treatment on the high temperature performance of 4H-SiC metal-semiconductor-metal ultraviolet photodiodes

The high temperature performance plays a crucial role in the high-temperature harsh environment detection. In this paper, the electrical and optical characteristics of 4H-SiC metal-semiconductor-metal (MSM) ultraviolet photodiodes (PDs) were investigated at high temperatures. The C-V measurement indicates that the 4H-SiC Schottky barrier diode is partially depleted at 40 V bias. Analysis of I-V data based on the thermionic emission theory demonstrates that the annealing treatment at 400 °C can effectively improve the homogeneity of Ni/4H-SiC Schottky barrier height. Experimental results confirm that the annealing treatment is beneficial not only to reduce the dark current and improve the photoresponse, but also to enhance the sensitivity for 4H-SiC MSM PDs. The sensitivity of 400 °C annealed MSM PDs (6.2 × 10³) is five times larger than that of as-deposited MSM PDs (1.3 × 10³) at 200 °C.     

Ga0.47In0.53As metal-semiconductor-metalphotodiodes using a lattice mismatchedAl0.4Ga0.6As Schottky assist layer

Metal-semiconductor-metal photodiodes (MSM PDs) with Ga_0.47 In_0.53As active layers were fabricated. The low Schottky barrier height of GaInAs was overcome by the insertion of a lattice mismatched AlGaAs intermediary layer between metal and GaInAs active layer. Fabricated MSM PDs utilising interdigitated metal electrodes formed by a self-alignment technique showed a fast rise and fall time of 650 ps, which was limited by the capacitance of the device. The gain of the device was less than 1     

Performance dependence of InGaAs MSM photodetectors on barrier-enhancement layer structures

The advantage of the graded superlattice layer over the abrupt junction is demonstrated for the continuous wave (CW) and pulse responses of InGaAs metal-semiconductor-metal photodetectors (MSM PDs). The measured pulsewidth of 44 ps for the 0.75 mu m MSM PD with the graded superlattice layer when corrected for the measurement system bandwidth implies an impulse response of 22 ps.<>     

Effects of finger dimension on low-frequency noise and optoelectronic properties of Ge metal-semiconductor-metal photodetectors with interdigitated Pt finger electrodes

We investigated the effect of interdigitated Pt finger electrode dimension on the low-frequency noise and optoelectrical properties of Ge metal-semiconductor-metal (MSM) infrared photodetectors (PDs). This dark current reduction led to an increase in the normalized photo current to dark current ratio (NPDR). The decrease in finger width/spacing facilitated the occurrence of the electric field crowding near contact electrode. This resulted in the image-force Schottky barrier lowering, which could be responsible for the increase in dark current. From the low frequency noise measurements performed at the frequencies in the range of 10 Hz–1 kHz, the Ge MSM PDs had 1/f^γ frequency dependence with γ ranging from 1.07 to 1.20, regardless of finger dimension. The current crowding, in particular at the vicinity of the finger electrodes, was more pronounced in the Ge MSM PDs having smaller finger width/spacing, which could be a main cause of the increase in the low frequency noise.     

GaN metal-semiconductor-metal photodetectors with low-temperature-GaN cap layers and ITO metal contacts

Nitride-based metal-semiconductor-metal (MSM) photodetectors (PDs) with low-temperature (LT) gallium nitride (GaN) cap layers and indium-tin-oxide (ITO) metal contacts were successfully fabricated. It was found that we could achieve three orders of magnitude smaller dark current by the introduction of the LT-GaN layer. For the PDs with LT-GaN cap layers, the maximum responsivity at 350 nm was found to be 0.1 and 0.9 A/W when the device was biased at 1 and 5 V, respectively. Operation speed of PDs with LT-GaN cap layers was also found to be faster than that of conventional PDs without LT-GaN cap layers.     

Effects of annealing on the performance of 4H-SiC metal–semiconductor–metal ultraviolet photodetectors

4H-SiC-based metal–semiconductor–metal (MSM) photodetectors (PDs) have been designed, fabricated, and characterized, in which nickel Schottky contacts were needed. Current–voltage and spectral responsivity measurements were carried out at room temperature to character the effect of annealing on the performance of the MSM devices. It was found to improve both Schottky barrier height and ideality factors after annealing at appropriate temperature. The chemical component depth profiles of XPS measurement showed nickel silicides were produced at the interface, leading to improvement of the Ni/4H-SiC contacts and the performance of the PDs. The MSM PDs with RTA had a lower dark current (0.45 pA at 5 V bias voltage), a typical responsivity of 0.094 A/W at 20 V and displayed peak response wavelength at 290 nm.     

High-Detectivity Nitride-Based MSM Photodetectors on InGaN–GaN Multiquantum Well With the Unactivated Mg-Doped GaN Layer

InGaN-GaN multiquantum-well (MQW) metal-semiconductor-metal (MSM) photodetectors (PDs) with the unactivated Mg-doped GaN cap layer were successfully fabricated. It was found that we could achieve a dark current by as much as six orders of magnitude smaller by inserting the unactivated Mg-doped GaN cap layer. For MSM photodetectors with the unactivated Mg-doped GaN cap layer, the responsivity at 380 nm was found to be 0.372 A/W when the device was biased at 5 V. The UV-to-visible rejection ratio was also estimated to be around 1.96 times 10³ for the photodetectors with the unactivated Mg-doped GaN cap layer. With a 5-V applied bias, we found that minimum noise equivalent power and normalized detectivity of our PDs were 4.09 times 10^-14 W and 1.18 times 10¹³ cmmiddotHz^0.5W^-1, respectively. Briefly, incorporating the unactivated Mg-doped GaN layer into the PDs beneficially brings about the suppression of dark current and a corresponding improvement in the device characteristics.     

Design and analysis of resonant cavity enhanced-waveguide photodetectors for microwave photonics applications

New structures for high quantum efficiency, high speed, and wavelength-selective photodetectors (PDs) are proposed. Regarding the main advantages of both resonant-cavity-enhanced (RCE) PDs and waveguide PDs (WGPDs) and the use of resonant behavior of microring waveguides, we present RCE-WGPD. The fundamental equation for quantum efficiency of microring PDs is derived and the important features of the device such as improvement of efficiency and wavelength selectivity are discussed.     

无催化剂气相沉积法直接制备用于紫外光检测的氧化锌纳米线网

对于环境检测和高速光通信而言,高性能紫外光电探测器是关键。利用气相沉积法在无催化剂条件下制备氧化锌纳米线网,在纳米线网上直接制备光电器件的性能得到了提高。结果显示,纳米线网光电探测器的光电流为60 A,大约是单根纳米线光电器件光电流的15倍。详细讨论纳米线网光电探测器的响应机制发现,在纳米线网内,纳米线与纳米线之间的结势垒高度决定了纳米线内部载流子的传输。当紫外光照射纳米线网光电探测器时,纳米线与纳米线之间结势磊高度的快速变低,从而提高光电器件的性能。     

Recent Progress of Heterojunction Ultraviolet Photodetectors: Materials,Integrations, and Applications

Ultraviolet photodetectors (UV PDs) with “5S” (high sensitivity, high signal‐to‐noise ratio, excellent spectrum selectivity, fast speed, and great stability) have been proposed as promising optoelectronics in recent years. To realize high‐performance UV PDs, heterojunctions are created to form a built‐in electrical field for suppressing recombination of photogenerated carriers and promoting collection efficiency. In this progress report, the fundamental components of heterojunctions including UV response semiconductors and other materials functionalized with unique effects are discussed. Then, strategies of building PDs with lattice‐matched heterojunctions, van der Waals heterostructures, and other heterojunctions are summarized. Finally, several applications based on heterojunction/heterostructure UV PDs are discussed, compromising flexible photodetectors, logic gates, and image sensors. This work draws an outline of diverse materials as well as basic assembly methods applied in heterojunction/heterostructure UV PDs, which will help to bring about new possibilities and call for more efforts to unleash the potential of heterojunctions.     

Design and analysis for a high-accuracy CCD

In order to improve the test accuracy of CCD,a new type of CCD device is proposed.Several columns(rows) of photoelectric diodes(PDs) are combined together,and staggered with the distance of H1=H/N,where H is the space between two adjacent PDs,and N is the number of columns(rows).The photoelectric signals are collected simultaneously by multi-channel A/D,and the accurate measurement result is obtained through appropriate signal processing.Without changing the size or space of PDs,more photographic pixels are arranged in the given direction within a finite length.Diameters of three standard poles are measured by a single CCD and two staggered CCDs,respectively with length of 30 mm and diameters of 5 mm,8 mm and 12 mm,respectively.The results show that the accuracy of double staggered CCDs is two times of that of single CCD.The new type of CCDs can avoid the impact of PD space theoretically and higher measurement accuracy can be obtained.     

金属?无机半导体?金属光电探测器的研究进展

金属?半导体?金属光电探测器(MSM-PDs)本身固有的高速、高响应率、易集成等特性使其在光纤通信、传感、制导等多个领域受到广泛关注。文中围绕金属?无机半导体?金属光电探测器展开综述。首先介绍了MSM-PDs的基本结构，包含共面和垂直两种类型。紧接着，介绍了MSM-PDs具体的工作原理，除了常见的光电导型及肖特基型工作原理，还介绍了以金属作为吸光层的热载流子光电探测器的工作原理。随后，详细介绍了以GaAs、InGaAs、Si/Ge等无机材料作为半导体层的MSM-PDs在过去所取得的研究进展。此外，还介绍了利用金属微纳结构拓展较宽带隙半导体材料MSM-PDs在红外波段响应特性的研究进展。最后，总结全文并对MSM-PDs未来的发展做出了展望。     

Simulation of the effects of defects in low temperature Ge buffer layer on dark current of Si-based Ge photodiodes

The influence of defects in low temperature Ge layer on electrical characteristics of p-Ge/i-Ge/n-Si and n-Ge/i-Ge/p-Ge photodiodes (PDs) was studied. Due to a two-step growth method, there are high defect densities in low-temperature buffer Ge layer. It is shown that the defects in low-temperature Ge layer change the band diagrams and the distribution of electric field, leading to the increase of the total dark current for p-Ge/i-Ge/n-Si PDs, whereas these defects have no influence on the dark current for n-Ge/i-Ge/p-Ge PDs. As a complement, a three-dimensional simulation of the total current under illumination was also performed.     

Enhancing the Photoelectric Performance of Photodetectors Based on Metal Oxide Semiconductors by Charge‐Carrier Engineering

Semiconductor‐based photodetectors (PDs) convert light signals into electrical signals via the photoelectric effect, which involves the generation, separation, and transportation of the photoinduced charge carriers, as well as the extraction of these charge carriers to external circuits. Because of their specific electronic and optoelectronic properties, metal oxide semiconductors are widely used building blocks in photoelectric devices. However, the compromise between enhancing the photoresponse and reducing the rise/decay times limits the practical applications of PDs based on metal oxide semiconductors. As the behaviors of the charge carriers play important roles in the photoelectric conversion process of these PDs, researchers have proposed several strategies, including modification of light absorption, design of novel PD heterostructures, construction of specific geometries, and adoption of specific electrode configurations to modulate the charge‐carrier behaviors and improve the photoelectric performance of related PDs. This review aims to introduce and summarize the latest researches on enhancing the photoelectric performance of PDs based on metal oxide semiconductors via charge‐carrier engineering, and proposes possible opportunities and directions for the future developments of these PDs in the last section.     

Room‐Temperature‐Operated Ultrasensitive Broadband Photodetectors by Perovskite Incorporated with Conjugated Polymer and Single‐Wall Carbon Nanotubes

In this work, room‐temperature‐operated ultrasensitive solution‐processed perovskite photodetectors (PDs) with near infrared (NIR) photoresponse are reported. In order to enable perovskite PDs possessing extended NIR photoresponse, novel n‐type low bandgap conjugated polymer, poly[(N,N′‐bis(2‐octyldodecyl)‐1,4,5,8‐naphthalene diimide‐2,6‐diyl) (2,5‐dioctyl‐3,6‐di(thiophen‐2‐yl)pyrrolo[3,4‐c]pyrrole‐1,4‐dione‐5,5′‐diyl)] (NDI‐DPP), which has strong absorption in the NIR region, is developed and then employed in perovskite PDs. By the formation of type II band alignment between NDI‐DPP with single‐wall carbon nanotubes (SWCNTs), the NIR absorption of NDI‐DPP is exploited, which contributes to the NIR photoresponse for the perovskite PDs, where perovskite is incorporated with NDI‐DPP and SWCNTs as well. In addition, SWCNTs incorporated with perovskite active layer can offer the percolation pathways for high charge‐carrier mobility, which tremendously boosts the charge transfer in the photoactive layer, and consequently improves the photocurrent in the visible region. As a result, the perovskite PDs exhibit the responsivities of ≈400 and ≈150 mA W^?1 and the detectivities of over 6 × 10¹² Jones (1 Jones = 1 cm Hz^1/2 W^?1) and over 2 × 10¹² Jones in the visible and NIR regions, respectively. This work reports the development of perovskite PDs with NIR photoresponse, which is terrifically beneficial for the practical applications of perovskite PDs.     

Free-Space Optical MIMO Transmission With$Q$-ary PPM

The use of multiple laser transmitters combined with multiple photodetectors (PDs) is studied for terrestrial, line-of-sight optical communication. The resulting multiple-input/multiple-output channel has the potential for combatting fading effects on turbulent optical channels. In this paper, the modulation format is repetition$Q$-ary PPM across lasers, with intensity modulation. Ideal PDs are assumed, with and without background radiation. Both Rayleigh and log-normal fading models are treated. The focus is upon both symbol-/bit-error probability for uncoded transmission, and on constrained channel capacity.