Showing papers on "Responsivity published in 2006"

Plasma wave detection of terahertz radiation by silicon field effects transistors: Responsivity and noise equivalent power

Abstract: Si metal oxide semiconductor field effect transistors (MOSFETs) with the gate lengths of 120–300nm have been studied as room temperature plasma wave detectors of 0.7THz electromagnetic radiation. In agreement with the plasma wave detection theory, the response was found to depend on the gate length and the gate bias. The obtained values of responsivity (⩽200V∕W) and noise equivalent power (⩾10−10W∕Hz0.5) demonstrate the potential of Si MOSFETs as sensitive detectors of terahertz radiation.

Laser emission and photodetection in an InP/InGaAsP layer integrated on and coupled to a Silicon-on-Insulator waveguide circuit.

Abstract: Laser emission from an InP/InGaAsP thin film epitaxial layer bonded to a Silicon-on-Insulator waveguide circuit was observed. Adhesive bonding using divinyl-tetramethyldisiloxane-benzocyclobutene (DVS-BCB) was used to integrate the InP/InGaAsP epitaxial layers onto the waveguide circuit. Light is coupled from the laser diode into an underlying waveguide using an adiabatic inverted taper approach. 0.9mW optical power was coupled into the SOI waveguide using a 500mum long laser. Besides for use as a laser diode, the same type of devices can be used as a photodetector. 50mum long devices obtained a responsivity of 0.23A/W.

Facility for spectral irradiance and radiance responsivity calibrations using uniform sources

Abstract: Detectors have historically been calibrated for spectral power responsivity at the National Institute of Standards and Technology by using a lamp-monochromator system to tune the wavelength of the excitation source. Silicon detectors can be calibrated in the visible spectral region with combined standard uncertainties at the 0.1% level. However, uncertainties increase dramatically when measuring an instrument's spectral irradiance or radiance responsivity. We describe what we believe to be a new laser-based facility for spectral irradiance and radiance responsivity calibrations using uniform sources (SIRCUS) that was developed to calibrate instruments directly in irradiance or radiance mode with uncertainties approaching or exceeding those available for spectral power responsivity calibrations. In SIRCUS, the emission from high-power, tunable lasers is introduced into an integrating sphere using optical fibers, producing uniform, quasi-Lambertian, high-radiant-flux sources. Reference standard irradiance detectors, calibrated directly against national primary standards for spectral power responsivity and aperture area measurement, are used to determine the irradiance at a reference plane. Knowing the measurement geometry, the source radiance can be readily determined as well. The radiometric properties of the SIRCUS source coupled with state-of-the-art transfer standard radiometers whose responses are directly traceable to primary national radiometric scales result in typical combined standard uncertainties in irradiance and radiance responsivity calibrations of less than 0.1%. The details of the facility and its effect on primary national radiometric scales are discussed.

200 nm deep ultraviolet photodetectors based on AlN

Abstract: High quality AlN epilayers were grown on sapphire substrates by metal organic vapor deposition and exploited as active deep ultraviolet (DUV) optoelectronic materials through the demonstration of AlN metal-semiconductor-metal (MSM) photodetectors. DUV photodetectors with peak responsivity at 200nm with a very sharp cutoff wavelength at 207nm have been attained. The AlN MSM photodetectors are shown to possess outstanding features that are direct attributes of the fundamental properties of AlN, including extremely low dark current, high breakdown voltage, and high DUV to visible rejection ratio and high responsivity. The results demonstrate the high promise of AlN as an active material for DUV device applications.

Germanium-on-SOI Infrared Detectors for Integrated Photonic Applications

Abstract: An overview of recent results on high-speed germanium-on-silicon-on-insulator (Ge-on-SOI) photodetectors and their prospects for integrated optical interconnect applications are presented. The optical properties of Ge and SiGe alloys are described and a review of previous research on SOI and SiGe detectors is provided as a motivation for the Ge-on-SOI detector approach. The photodetector design is described, which consists of lateral alternating p- and n-type surface contacts on an epitaxial Ge absorbing layer grown on an ultrathin-SOI substrate. When operated at a bias voltage of -0.5 V, 10mumtimes10 mum devices have dark current Idark, of only ~10 nA, a value that is nearly independent of finger spacing S, between S=0.3mum and 1.3mum. Detectors with S=1.3mum have external quantum efficiencies eta, of 52% (38%) at lambda=895 nm (850 nm) with corresponding responsivities of 0.38 A/W (0.26 A/W). The wavelength-dependence of eta agrees fairly well with expectations, except at longer wavelengths, where Si up-diffusion into the Ge absorbing layer reduces the efficiency. Detectors with 10 mumtimes10 mum area and S=0.6mum have -3-dB bandwidths as high as 29 GHz, and can simultaneously achieve a bandwidth of 27 GHz with Idark=24 nA, at a bias of only -1 V, while maintaining high efficiency of eta=46%(33%), at lambda=895 nm (850 nm). Analysis of the finger spacing and area-dependence of the device speed indicates that the performance at large finger spacing is transit-time-limited, while at small finger spacing, RC delays limit the bandwidth. Methods to improve the device performance are presented, and it is shown that significant improvement in the speed and efficiency both at lambda=850 and 1300 nm can be expected by optimizing the layer structure design

Optic sensors of high refractive-index responsivity and low thermal cross sensitivity that use fiber Bragg gratings of >80° tilted structures

Abstract: For the first time to the authors' knowledge, fiber Bragg gratings (FBGs) with >80° tilted structures nave been fabricated and characterized. Their performance in sensing temperature, strain, and the surrounding medium's refractive index was investigated. In comparison with normal FBGs and long-period gratings (LPGs), >80° tilted FBGs exhibit significantly higher refractive-index responsivity and lower thermal cross sensitivity. When the grating sensor was used to detect changes in refractive index, a responsivity as high as 340 nm/refractive-index unit near an index of 1.33 was demonstrated, which is three times higher than that of conventional LPGs. © 2006 Optical Society of America.

Performance of Ge-on-Si p-i-n Photodetectors for Standard Receiver Modules

Abstract: Ge on Si p-i-n photodetectors with areas which are compatible with commercially available receivers have been fabricated and tested. A dark current density of 6 mA/cm2 at -1-V bias has been measured at room temperature; when heated to 85 degC, the measured dark current increases by a factor of nine. A responsivity of 0.59 A/W at 850 nm has been measured from these Ge detectors, which matches or exceeds commercially available GaAs devices. We have measured bandwidths approaching 9 GHz at -2-V bias from 50-mum diameter Ge detectors, and have observed eye diagrams comparable to those obtained from GaAs-based receivers at 4.25 Gb/s

Room temperature demonstration of GaN /AlN quantum dot intraband infrared photodetector at fiber-optics communication wavelength

Abstract: We fabricated a communication wavelength photodetector based on intraband transition in GaN∕AlN self-assembled quantum dot heterostructures. The quantum dot photodetector is based on in-plane transport and has a room temperature spectral peak responsivity of 8mA∕W at wavelength of 1.41μm. We use multipass waveguide geometry to show that the polarization sensitive optical absorption spectrum of the heterostructure is nearly the same as its photocurrent spectral response. This establishes that the detector’s response is due to the presence of quantum dots in its active layer. We use photoluminescence, transmission, and intraband photocurrent spectroscopy to consistently describe the alignment between the energy levels of the quantum dots and that of the wetting layer.

High responsivity 4H-SiC Schottky UV photodiodes based on the pinch-off surface effect

Abstract: In this letter, high responsivity 4H-SiC vertical Schottky UV photodiodes based on the pinch-off surface effect, obtained by means of self-aligned Ni2Si interdigit contacts, are demonstrated. The diode area was 1mm2, with a 37% directly exposed to the radiation. The dark current was about 200pA at −50V. Under a 256nm UV illumination, a current increase of more than two orders of magnitude is observed, resulting in a 78% internal quantum efficiency. The vertical photodiodes showed an ultraviolet-visible rejection ratio >7×103 and a responsivity a factor of about 1.8 higher than a conventional planar metal-semiconductor-metal structure.

Electrical properties of Ohmic contacts to ZnSe nanowires and their application to nanowire-based photodetection

Abstract: Multilayer Ti∕Au contacts were fabricated on individual, unintentionally doped zinc selenide nanowires with 80nm nominal diameter. Four-terminal contact structures were used to independently measure current-voltage characteristics of contacts and nanowires. Specific contact resistivity of Ti∕Au contacts is 0.024Ωcm2 and intrinsic resistivity of the nanowires is approximately 1Ωcm. The authors have also measured the spectral photocurrent responsivity of a ZnSe nanowire with 2.0V bias across Ti∕Au electrodes, which exhibits a turnon for wavelengths shorter than 470nm and reaches 22A∕W for optical excitation at 400nm.

Terahertz detection with tunneling quantum dot intersublevel photodetector

Abstract: The characteristics of a tunnel quantum dot intersublevel photodetector, designed for the absorption of terahertz radiation, are described. The absorption region consists of self-organized In0.6Al0.4As∕GaAs quantum dots with tailored electronic properties. Devices exhibit spectral response from 20to75μm (∼4THz) with peak at ∼50μm. The peak responsivity and specific detectivity of the device are 0.45A∕W and 108cmHz1∕2∕W, respectively, at 4.6K for an applied bias of 1V. Response to terahertz radiation is observed up to 150K.

Silicon-on-insulator waveguide photodetector with self-ion-implantation-engineered-enhanced infrared response

Abstract: We describe the fabrication and characterization of silicon-on-insulator, p+-i-n+ waveguide photodetectors with enhanced sensitivity to wavelengths around 1550nm. Increased sensitivity to sub-band-gap light results from the deliberate introduction of mid-band-gap defects via 1.5MeV silicon-ion implantation to a dose of 1×1012cm−2. For a waveguide of length of 6mm, an on-chip signal of 3.5dBm generates a photocurrent of 5μA while the defect-induced excess optical absorption is 8dB. Postimplantation annealing at a temperature of 300°C for 10min increases the photocurrent to 19μA, corresponding to a responsivity of 9mA∕W, while reducing the excess loss to 2dB. The devices described here are completely compatible with standard silicon processing and can be integrated easily with other photonic and electronic functionalities on the same silicon substrate.

A high responsivity, broadband waveguide uni-travelling carrier photodiode

Abstract: A 02 A/W responsivity waveguide-uni-travelling carrier photodiode with a -3 dB electrical frequency response > 108 GHz is demonstrated Up to -5 dBm electrical power at 110 GHz, and 28 mA photocurrent (DC excitation) were detected The photodiode was also integrated with an antenna to permit a record breaking emission of up to 148 μW at 457 GHz and 25 μW at 914 GHz

InAs/GaSb superlattice focal plane arrays for high-resolution thermal imaging

Abstract: The first fully operational mid-IR (3–5 μm) 256×256 IR-FPA camera system based on a type-II InAs/GaSb short-period superlattice showing an excellent noise equivalent temperature difference below 10 mK and a very uniform performance has been realized. We report on the development and fabrication of the detecor chip, i.e., epitaxy, processing technology and electro-optical characterization of fully integrated InAs/GaSb superlattice focal plane arrays. While the superlattice design employed for the first demonstrator camera yielded a quantum efficiency around 30%, a superlattice structure grown with a thicker active layer and an optimized V/III BEP ratio during growth of the InAs layers exhibits a significant increase in quantum efficiency. Quantitative responsivity measurements reveal a quantum efficiency of about 60% for InAs/GaSb superlattice focal plane arrays after implementing this design improvement.

A high-speed 850-nm optical receiver front-end in 0.18-/spl mu/m CMOS

Abstract: A high-speed optical interface circuit for 850-nm optical communication is presented. Photodetector, transimpedance amplifier (TIA), and post-amplifier are integrated in a standard 0.18-mum 1.8-V CMOS technology. To eliminate the slow substrate carriers, a differential n-well diode topology is used. Device simulations clarify the speed advantage of the proposed diode topology compared to other topologies, but also demonstrate the speed-responsivity tradeoff. Due to the lower responsivity, a very sensitive transimpedance amplifier is needed. At 500 Mb/s, an input power of -8 dBm is sufficient to have a bit error rate of 3middot10-10. Next, the design of a broadband post-amplifier is discussed. The small-signal frequency dependent gain of the traditional and modified Cherry-Hooper stage is analyzed. To achieve broadband operation in the output buffer, so-called "fT doublers" are used. For a differential 10 mVpp 231-1 pseudo random bit sequence, a bit error rate of 5middot10-12 at 3.5 Gb/s has been measured. At lower bit-rates, the bit error rate is even lower: a 1-Gb/s 10-mVpp input signal results in a bit error rate of 7middot10-14. The TIA consumes 17mW, while the post-amplifier circuit consumes 34 mW

Modeling of the temperature-dependent spectral response of In 1–χ Ga χ Sb infrared photodetectors

Abstract: A model of the spectral responsivity of In(1-x) Ga(x) Sb p-n junction infrared photodetectors has been developed. This model is based on calculations of the photogenerated and diffusion currents in the device. Expressions for the carrier mobilities, absorption coefficient and normal-incidence reflectivity as a function of temperature were derived from extensions made to Adachi and Caughey-Thomas models. Contributions from the Auger recombination mechanism, which increase with a rise in temperature, have also been considered. The responsivity was evaluated for different doping levels, diffusion depths, operating temperatures, and photon energies. Parameters calculated from the model were compared with available experimental data, and good agreement was obtained. These theoretical calculations help to better understand the electro-optical behavior of In(1-x) Ga(x) Sb photodetectors, and can be utilized for performance enhancement through optimization of the device structure.

Evaluation of a pyroelectric detector with a carbon multiwalled nanotube black coating in the infrared

Abstract: The performance of a pyroelectric detector with a carbon multiwalled nanotube coating was evaluated in the 0.9-14 µm wavelength range. The relative spectral responsivity of this detector was shown to be flat over most of the wavelength range examined, and the spectral flatness was shown to be comparable to the best infrared black coatings currently available. This finding is promising because black coatings with spectrally flat absorbance profiles are usually associated with the highest absorbance values. The performance of the detector (in terms of noise equivalent power and specific detectivity) was limited by the very thick (250 µm thick) LiNbO3 pyroelectric crystal onto which the coating was deposited. The responsivity of this detector was shown to be linear in the 0.06-2.8 mW radiant power range, and its spatial uniformity was comparable to that of other pyroelectric detectors that use different types of black coating. The carbon nanotube coatings were reported to be much more durable than other infrared black coatings, such as metal blacks, that are commonly used to coat thermal detectors in the infrared. This, in combination with their excellent spectral flatness, suggests that carbon nanotube coatings appear extremely promising for thermal detection applications in the infrared.

Partial-electroded ZnO pyroelectric sensors for responsivity improvement

Abstract: The design, MEMS fabrication and characterization of the ZnO pyroelectric sensor for improvement of responsivity are presented. Three groups of the sensor with various layer thickness, effective area, partially and fully covered electrode (FCE) were fabricated and investigated. The partially covered electrode (PCE) covers 50–65% area of the exposed surface for incident energy absorption. The un-covered ZnO will directly receive the incident laser energy and improve the absorption efficiency of the sensor. The measured data show that the partial-electroded sensors exhibits at least 4 times higher responsivity in the frequency range of 10–1000 Hz than the full-electroded sensors. The effects of other design parameters such as thickness of ZnO, SiO 2 and Si 3 N 4 on the responsivity are also discussed.

21-GHz-Bandwidth Germanium-on-Silicon Photodiode Using Thin SiGe Buffer Layers

Abstract: Backside-illuminated germanium photodiodes fabricated on silicon substrate with two Si xGe1-x buffer layers are reported. At 1.3 mum, the responsivity was 0.62 A/W for reverse bias greater than 0.1 V. The 3-dB bandwidth was 21.5 GHz at 10-V reverse bias, achieving a bandwidth-efficiency product of 12.6 GHz

Effects of rapid thermal annealing on device characteristics of InGaAs∕GaAs quantum dot infrared photodetectors

Abstract: In this work, rapid thermal annealing was performed on InGaAs∕GaAs quantum dot infrared photodetectors (QDIPs) at different temperatures. The photoluminescence showed a blueshifted spectrum in comparison with the as-grown sample when the annealing temperature was higher than 700°C, as a result of thermal interdiffusion of the quantum dots (QDs). Correspondingly, the spectral response from the annealed QDIP exhibited a redshift. At the higher annealing temperature of 800°C, in addition to the largely redshifted photoresponse peak of 7.4μm (compared with the 6.1μm of the as-grown QDIP), a high energy peak at 5.6μm (220meV) was also observed, leading to a broad spectrum linewidth of 40%. This is due to the large interdiffusion effect which could greatly vary the composition of the QDs and thus increase the relative optical absorption intensity at higher energy. The other important detector characteristics such as dark current, peak responsivity, and detectivity were also measured. It was found that the overa...

Evaluation of a pyroelectric detector with a carbon multiwalled nanotube black coating in the infrared

Abstract: The performance of a pyroelectric detector with a carbon multiwalled nanotube coating was evaluated in the 0.9-14 µm wavelength range. The relative spectral responsivity of this detector was shown to be flat over most of the wavelength range examined, and the spectral flatness was shown to be comparable to the best infrared black coatings currently available. This finding is promising because black coatings with spectrally flat absorbance profiles are usually associated with the highest absorbance values. The performance of the detector (in terms of noise equivalent power and specific detectivity) was limited by the very thick (250 µm thick) LiNbO3 pyroelectric crystal onto which the coating was deposited. The responsivity of this detector was shown to be linear in the 0.06-2.8 mW radiant power range, and its spatial uniformity was comparable to that of other pyroelectric detectors that use different types of black coating. The carbon nanotube coatings were reported to be much more durable than other infrared black coatings, such as metal blacks, that are commonly used to coat thermal detectors in the infrared. This, in combination with their excellent spectral flatness, suggests that carbon nanotube coatings appear extremely promising for thermal detection applications in the infrared.

Performance of Low-Dark-Current 4H-SiC Avalanche Photodiodes With Thin Multiplication Layer

Abstract: The authors report on the fabrication and performance of low-dark-current 4H-SiC avalanche photodiodes with a thin 180-nm-thick p - multiplication layer. At a photocurrent gain M of 1000, the dark current of a 100-mum-diameter device was 35 pA (0.44 muA/cm2). The peak unity-gain responsivity was 100 mA/W (external quantum efficiency=46%) at lambda=268 nm, and at high gain, a responsivity greater than 107 A/W was achieved. The excess noise factor corresponds to k=0.12. Time-domain pulse measurements indicate an RC-limited unity-gain bandwidth of 300 MHz

High-detectivity quantum-dot infrared photodetectors grown by metalorganic chemical-vapor deposition

Abstract: A mid-wavelength infrared photodetector based on InGaAs quantum dots buried in an InGaP matrix and deposited on a GaAs substrate was demonstrated. Its photoresponse at T=77K was measured to be around 4.7μm with a cutoff at 5.5μm. Due to the high peak responsivity of 1.2A∕W and low dark-current noise of the device, a specific peak detectivity of 1.1×1012cmHz1∕2W−1 was achieved at −0.9V bias.

Photovoltaic Schottky ultraviolet detectors fabricated on boron-doped homoepitaxial diamond layer

Abstract: A photovoltaic diode using tungsten carbide (WC) Schottky contact for deep ultraviolet (DUV) light detection is developed using a lightly boron-doped homoepitaxial diamond layer. The photodiode shows a quick dc response time lower than an instrumental time constant of 0.3 s. The responsivity varies linearly with the DUV light intensity. A discrimination ratio of 105 between 210 nm and visible light is achieved at zero bias. The short-circuit photocurrent at 220 nm decreases with increasing the temperature from 300 to 373 K, whereas the Schottky barrier height under illumination remains unchanged. Numerical and experimental analyses reveal that the interface states between diamond and WC play a major role in reducing the zero-bias responsivity at elevated temperatures.

Micromachined integrated pressure–thermal sensors on flexible substrates

Abstract: This paper presents the design, modeling and simulation of micromachined, integrated pressure–thermal sensors on flexible polyimide substrates. Finite element simulations were performed with polycrystalline silicon as the piezoresistor material on a suspended Si3N4 layer. These piezoresistors are connected to each other in a half-bridge Wheatstone configuration using flexible aluminum interconnects. Several different designs of integrated thermal–pressure sensors as well as pressure-only sensors were simulated to compute the sensor figures of merit such as the percentage change in piezoresistance in response to normal pressure, piezoresistor Wheatstone-bridge output voltage for varying skin curvature, bolometric response to broadband infrared radiation, thermal time constant and thermal conductance of the micromachined structures hosting the sensors to the substrate. For a perpendicular uniform pressure application of 50 kPa, a maximum Wheatstone-bridge output of 7.59 mV was computed for 1 V bias, corresponding to a piezoresistance change of 1.52%. When the skin is bent to a curvature of 2.2 mm, a maximum Wheatstone-bridge output voltage of 70 mV was calculated for the case when the sensors are aligned along the axis of bending. Thermal and optical calculations performed on the integrated thermal–pressure sensors showed a thermal time constant as low as 12.8 µs for a 1.9 µm thick silicon nitride membrane layer, with a responsivity of 270 V W−1 to a broad-band infrared radiation. This would be appropriate for applications requiring fast response but not high sensitivity. Integrated sensors on a thinner silicon nitride membrane layer of 0.5 µm, on the other hand, exhibited responsivity as high as 2000 V W−1, with a response time of 626 µs.

Room-temperature InAsSb photovoltaic detectors for mid-infrared applications

Abstract: Novel noncryogenic InAsSb photovoltaic detectors grown by molecular beam epitaxy are proposed and demonstrated. The quaternary alloy In0.88Al0.12As0.80Sb0.20 is introduced as a wide bandgap barrier layer lattice matched to the GaSb substrate. The valence band edge of In0.88Al0.12As0.80Sb0.20 nearly matches with InAs0.91Sb0.09, leading to more efficient transport of photogenerated holes. The resulting mid-infrared photovoltaic detector exhibits a 50% cutoff wavelength of 4.31 mum and a peak responsivity of 0.84 A/W at room temperature. High Johnson-noise-limited detectivity (D*) of 2.6times109 cmmiddotHz1/2/W at 4.0 mum, and 4.2times1010 cmmiddotHz1/2/W at 3.7 mum are achieved at 300 K and 230 K, respectively

A high-speed 850-nm optical receiver front-end in 0.18-μm CMOS

Abstract: A high-speed optical interface circuit for 850-nm optical communication is presented. Photodetector, transimpedance amplifier (TIA), and post-amplifier are integrated in a standard 0.18-μm 1.8-V CMOS technology. To eliminate the slow substrate carriers, a differential n-well diode topology is used. Device simulations clarify the speed advantage of the proposed diode topology compared to other topologies, but also demonstrate the speed-responsivity tradeoff. Due to the lower responsivity, a very sensitive transimpedance amplifier is needed. At 500 Mb/s, an input power of -8 dBm is sufficient to have a bit error rate of 3 ·10 -10 . Next, the design of a broadband post-amplifier is discussed. The small-signal frequency dependent gain of the traditional and modified Cherry-Hooper stage is analyzed. To achieve broadband operation in the output buffer, so-called "f T doublers" are used. For a differential 10 mV pp 2 31 - 1 pseudo random bit sequence, a bit error rate of 5 · 10 -12 at 3.5 Gb/s has been measured. At lower bit-rates, the bit error rate is even lower: a 1-Gb/s 10-mV pp input signal results in a bit error rate of 7 · 10 -14 . The TIA consumes 17 mW, while the post-amplifier circuit consumes 34 mW.

Radiometric characteristics of new diamond PIN photodiodes

Abstract: New PIN photodiode devices based on CVD diamond have been produced showing high responsivity in a narrow bandpass around 200 nm. A set of measurement campaigns was carried out to obtain their XUV-to-VIS characterization (responsivity, stability, linearity, homogeneity). The responsivity has been measured from the XUV to the NIR, in the wavelength range of 1 nm to 1127 nm (i.e. 1240 to 1.1 eV). The diamond detectors exhibit a high responsivity of 10 to 30 mA W−1 around 200 nm and demonstrate a visible rejection ratio (200 nm versus 500 nm) of six orders of magnitude. We show that these PIN diamond photodiodes are sensitive sensors in the 200 to 220 nm range, stable under brief irradiation with a good linearity and homogeneity. They will be used for the first time in a solar physics space instrument LYRA, the Large Yield RAdiometer.

A method for designing electromagnetic resonance enhanced silicon-on-insulator metal?semiconductor?metal photodetectors

Abstract: Methods of using a combination of electromagnetic resonance modes including surface plasmons and Fabry–Perot cavity resonances and other optical modes including Wood–Rayleigh anomalies and diffraction to enhance the performance of metal–semiconductor–metal photodetectors (MSM-PDs) fabricated on silicon-on-insulator (SOI) substrates are described. The characteristics of these optical modes are briefly described and their proper use in SOI MSM-PDs is described in detail. Three algorithms that model the electromagnetic field produced by the incident beam, the quasi-static electric field produced by the applied bias, and the charge carrier motion, recombination and induced photocurrent are integrated together in a time-dependent way to accurately calculate the bandwidth and responsivity for a series of optical pulses. By using a combination of optical modes, a structure with theoretical values of 50 GHz bandwidth and 0.17 A W−1 responsivity is designed. Other structures using different combinations of optical modes are described.