Effects of the parasitics on the time response of RCE-PDs

Resonant cavity enhanced photodetectors (RCE-PDs) are promising candidates for applications in high-speed optical communications and interconnections. However, because parasitics effects of these high-speed photodetectors can significantly degrade the performance of the photodetector, then they must be carefully considered. Here, an accurate model for the time response of the RCE-PDs that includes the effects of their parasitics is presented. The effects of an inductor that may be added in series with the load resistor are also studied and it is shown that the external inductor can improve the performance of the photodetector because it compensates some of the degradations resulting from capacitive parasitics. The effects of the parasitics have been investigated for different dimensions of the photodetectors, different values of both the load resistance and the added inductor and also for different multiplication gains for the case of RCE-avalanche photodetectors.     

Frequency response of avalanche photodetectors with separateabsorption and multiplication layers

We present analytical expressions for the frequency response of avalanche photodetectors (APDs) with separate absorption and multiplication regions (SAM). The effect of the electric field profile in the multiplication layer on frequency response is considered for the first time. Previous theories have assumed that the multiplication layer is very thin and the peak electric field, which corresponds to the effective multiplication plane, is positioned away from the absorption layer. This is a poor assumption for many devices, and in particular for silicon hetero-interface photodetectors (SHIPs). We present a theoretical model in which the thickness of the multiplication layer is arbitrary and the peak electric field may be positioned arbitrarily in relation to the absorption layer. We also consider the effects of parasitics, transit-time, and avalanche buildup time. Both front and back illumination from either multiplication layer or absorption layer are considered. The calculated results are compared with experimental results for existing SHIP's and performance predictions are also made for optimized SHIP structures. SHIP APDs with gain-bandwidth product in excess of 500 GHz are possible     

Analysis, optimization, and SPICE modeling of resonant cavity enhanced p-i-n photodetector

We present a detailed analysis, optimization, and SPICE modeling of the resonant-cavity-enhanced p-i-n photodetector (RCE-p-i-n-PD). Time response, frequency response, and the quality factor of RCE-p-i-n-PD are calculated for different thicknesses of the active layer and for different areas of the photodetector. The standing-wave effect is examined for all these calculations. The effect of the parasitic inductor is studied, and then an optimization is applied to the photodetector to get the optimal value of thickness of the active layer and the series inductor values. Two cases are compared, one with an inductor (L) in series with the load resistor (R/sub L/), and another without this inductor. High performance is obtained in the first case with an inductor, and its optimal values are obtained. A SPICE model for this high-speed photodetector is also presented, and the transfer function of this model is compared for different parameters of the device. Finally, predictions from this SPICE model are compared with published experimental results.     

二维材料光电探测器及光场增强的研究进展

随着现有社会的不断发展,对光电探测器的需求不断提高,但现有传统材料探测器的发展已进入瓶颈期,亟需新材料的出现,使光电探测器得到进一步的发展.石墨烯等新型二维材料相比于传统材料,具有可做成原子级尺寸、能带可调、具有柔韧性等突出优点.可满足当今社会对光电探测器性能,尺寸等方面更高需求.因此二维材料光电探测器被广泛研究,取得...     

高速长波长谐振腔增强型光探测器的瞬态性能研究

基于谐振腔增强型(RCE)光探测器的实际设计和制作模型,提出了综合器件的隔离层及器件的串联电阻、结电容等参数的高速长波长RCE光探测器的瞬态响应特性的表达式,包括器件的冲击响应、阶跃响应和脉冲响应.从理论上详细地研究了高速长波长RCE光探测器的瞬态响应特性,最后给出了不同器件结构参数的计算结果.     

SAGCM-APD增益影响因子分析与优化

应用二维漂移扩散模型研究具有分立吸收层、渐变层、电荷层和倍增层结构(SAGCM)的InGaAsP-InP雪崩光电探测器(APD),仿真分析了不同电荷层、倍增层厚度和掺杂浓度对电场分布、电流响应及击穿电压的影响,特别是参数变量对增益计算模型的影响,载流子传输过程的时间依赖关系和倍增层中所处位置的影响,仿真结果表明:较高掺杂浓度和较薄电荷层结构可以改变器件内部的电场分布,进而提高增益值.当入射光波长为1.55μm,光功率为500 W/m2时,光电流响应量级在10-2A;阈值电压降低到10V以下,击穿电压为42.6V时,器件倍增增益值大于100.     

Calculating the photocurrent and transit-time-limited bandwidth ofa heterostructure p-i-n photo-detector

We have calculated the photocurrent and transit-time-limited bandwidth of a heterostructure p-i-n photodetector. The effective heights of potential barriers at the heterojunction interfaces in the valence band and conduction band have been calculated at different bias voltage and grading lengths for InP-In_0.53Ga_0.47As and Al_0.2Ga_0.8As-GaAs systems. The rates of thermionic emission from the trap can then be easily estimated for each type of material system at an applied bias and for a particular thickness of the grading layer. An expression for current through the photodetector in the presence of traps has been derived by solving rate equations for an arbitrary distribution of photogenerated carriers in the absorption region. Frequency-domain calculations are used to find the transit-time-limited 3-dB bandwidths of the photodetector. It has also been indicated how the results could be used to estimate the bandwidth of the photodetector without performing the exact calculations in the presence of interface trapping. The results from the present model show good agreement with experimental data already reported in the literature for conventional and resonant-cavity-enhanced p-i-n photodetectors     

A thin-film waveguide photodetector using hydrogenated amorphoussilicon

Metal-silicon-metal cladding layers on dielectric waveguides exhibit coupling and absorption characteristics that make them useful as photodetectors for integrated optical applications. Multilayer computer-modeling techniques were applied to waveguide photodetectors in order to investigate field and power distributions, as well as the attenuation and phase response in the guiding region. A waveguide photodetector based on amorphous silicon was fabricated and demonstrated     

Effects of collector epitaxial layer on the switching speed of high-performance bipolar transistors

The importance of the epitaxial layer in designing the scaled-down high-performance bipolar transistors is well accepted, but its effect on the performance of the conventional switching transistors for logic application is not quite observable, because it is usually overwhelmed by the large parasitics of these devices. For self-aligned transistors having very small parasitics, its effect becomes so significant that it is observable in the power-delay characteristics of the switching circuits. We built self-aligned transistors on epitaxial layers of different thicknesses. The measured switching speed of transistors with thicker epitaxial-collector layers is faster at lower currents due to the lower collector capacitance; but it is slower at higher currents due to the base stretching. The present experimental results provide direct confirmation of the design theory [1].     

Modeling circuit parasitics. 1

Circuit parasitics are components that don't show up in the schematic but do show up in the circuit's behavior. They are there because of Maxwell's equations. The author describes ways of estimating and predicting the values of such parasitics. The common sources of circuit parasitics considered can be classified by their contribution of resistive, inductive, or capacitive elements to the model. The author concentrates on resistive circuit parasitics and considers conductor resistance modeling and modeling resistance of dielectric and magnetic materials     

Electromagnetic modeling of quantum-well photodetectors containingdiffractive elements

An analytical approach for modeling optical fields in quantum-well infrared photodetectors was developed by using a rigorous solution of the corresponding electromagnetic problem. Its application includes structures having a large number of dielectric layers, which may contain gratings having arbitrary profiles and metal-strip arrays acting as electrodes. By representing the fields inside complex photodetector structures in terms of interconnected transmission-line units, this approach helps considerably to clarify the role of each constituent of the photodetector. Examples involving realistic situations reveal that the presence of metal electrodes may affect the photodetection operation in a large class of grating structures. In particular, we show that the sensitivity of specific photodetector configurations can be enhanced by choosing grating parameters that optimize the overall photodetecting performance     

Modeling of InGaAs MSM photodetector for circuit-level simulation

An accurate model for In_0.53Ga_0.47As metal-semiconductor-metal (MSM) photodetectors is presented for circuit-level simulation. Dark and dc current characteristics are investigated and modeled. To accurately simulate the large-signal response of MSM photodetectors, impulse response functions and convolution integrals are implemented into SPICE. The transit-time limitation is also incorporated into the small-signal analysis. Most circuit parameters preserve the physical meaning. S-parameter measurements are used to find the circuit parameters critical to transient and ac analyses. Results are compared with experimentally obtained data, and excellent agreement is obtained consistently on InGaAs photodetectors of different sizes     

PbS量子点同质P-N结光电探测器

PbS胶体量子点因其带隙可调、可溶液加工、吸收系数高等优异特性而广泛应用于光电探测器领域。然而基于光电二极管结构的PbS量子点光电探测器通常会使用不同的材料来制备N型层,从而增加了器件设计和工艺的复杂性,不利于这类光电探测器未来在面阵成像芯片中的应用。为简化制备工艺,提出了一种PbS量子点同质P-N结光电探测器,仅通过一种工艺过程实现了器件P型层和N型层的制备。经测试,探测器对不同入射光强度的探测表现出了良好的线性响应;在0.5 V反向偏压作用下,器件在700 nm处的响应度为0.11 A/W,比探测率为3.41×1011 Jones,展现出了其对弱光探测的优异能力。结果表明文中提出的PbS量子点同质PN结光电探测器有助于推动其在面阵成像领域中的发展。     

0.1～325GHz频段InP DHBT器件在片测试结构建模

给出了InP DHBT器件在片测试用到的开路和短路结构的等效电路模型.模型拓扑结构基于物理结构建立,并对其在亚毫米波段的高频寄生进行相对完整的考虑.模型的容性和阻性寄生采用解析提取技术,从开路结构低频测试数据中获取.模型的高频趋肤效应采用传统物理公式计算初值,并结合短路测试结构的低频解析提取结果对计算公式进行修正,使其适用于实际测试结构建模.模型拓扑结构和参数提取方法,采用0. 5μm InP DHBT工艺上设计所得开路、短路测试结构进行验证.模型仿真和测试所得S参数在0. 1～325 GHz频段内吻合地很好.     

基于顶栅调控界面的石墨烯高增益光电探测器

利用Silvaco TCAD软件对石墨烯作为新一代二维半导体材料具有的光学电学特性进行仿真建模,计算得到了不同掺杂类型石墨烯的转移特性曲线.进而对基于顶栅调控的石墨烯-硅光电导型光电探测器进行了建模与仿真,发现顶栅电压可以通过调控石墨烯载流子类型及浓度来改变石墨烯与硅异质结的内建电势,实现提高增益的目的.基于此制备了栅控石墨烯-硅光电探测器并测得与仿真结果一致的规律,实验中该器件在1 550 nm波段展现出良好的光电性能.研究结果对红外光电探测器的性能优化具有指导意义.     

Ⅱ类超晶格红外探测器多层膜背增透研究

Ⅱ类超晶格材料相对较小的吸收系数限制了超晶格焦平面探测器的探测性能,通过在焦平面背面镀制增透膜,可有效提升器件的量子效率。研究采用仿真计算,设计了GaSb基InAs/GaSb超晶格探测器的多层背增透膜结构,并在GaSb衬底和超晶格焦平面探测器上进行了制备,实验结果验证了该薄膜具有提升探测器响应性能的作用。     

Monolithic millimeter wave optical receivers

A single stage monolithic millimeter wave optical receiver circuit was designed and fabricated using a metal-semiconductor-metal (MSM) photodetector and a pSeudomorphic Modulation Doped Field Effect Transistors (SMODFET) on a GaAs substrate for possible applications in chip-to-chip and free space communications. The MSM photodetector and the SMODFET epitaxial material were grown by molecular beam epitaxy (MBE). Device isolation was achieved using an epitaxially grown buffer between the MSM detector layers and SMODFET. The photodetector was designed for maximum absorption at optical wavelength of 770 nm light and the SMODFET impedance matching network was optimized for 44 GHz. The monolithic millimeter wave optical receiver circuit achieved 3 dB gain over a photodetector at 39 GHz, which was the limit of the measurement system. TOUCHSTONE model of the circuit indicated 6.6 dB gain over the photodetector and 5.7 dB total gain including the insertion loss of the photodetector at 44 GHz     

Germanium photodetectors on Silicon-on-insulator grown with differential molecular beam epitaxy in silicon wells

In this paper we propose a method for growing fast Germanium pin photodetectors in pre-patterned areas on a Silicon-on-insulator substrate. The layers are deposited by means of molecular beam epitaxy and structured by chemical mechanical polishing. A comparison of the electrical and optical characteristics between a photodetector grown with the proposed method and a reference detector grown on a planar Silicon substrate is made indicating only minor differences.     

光探测器芯片小信号等效电路模型的建立

提出了一种光探测器芯片小信号等效电路模型及其建立方法.首先根据光探测器的物理结构确定其等效电路模型,模型考虑了影响光探测器高频性能的主要因素.然后精确测量了光探测器芯片的S参数,通过遗传算法对测量的S参数进行拟合,最终计算出模型的各个参量.在130MHz～20GHz范围内的实验结果表明,模型仿真结果与测量结果相吻合,证明了建模方法的可靠性.该模型有效地模拟了光探测器芯片的高频特性,利用该模型可以对光探测器及相应光电集成器件进行电路级仿真和优化.     

Frequency response and modeling of resonant-cavity separateabsorption, charge, and multiplication avalanche photodiodes

A theoretical model incorporating the mechanism of resonant absorption of the multiple reflected lightwaves is presented for the frequency response of resonant-cavity (RC) separate absorption, charge, and multiplication (SACM) avalanche photodiodes (APDs). The derived theoretical expressions are general and can be readily applied to many other RC and non-RC APDs. These analytical expressions also allow for fast computation of the frequency response and bandwidth characteristics. Combining this frequency response theory with expressions of multiplication gain and ionization coefficients, an efficient approach is proposed for modeling the general performance characteristics of RC APDs. The modeling approach is applied to an InGaAs-AlGaAs RC SACM APD. The computed results are demonstrated, and the results of -3 dB bandwidth are comparable to experimental work. The validity of the modeling parameters is also discussed. It is further found that the normalized frequency response is unaffected when the value of the absorption coefficient is changed, suggesting that the standing-wave effect within the RC structure may not influence the bandwidth characteristics