InGaAs Photodetectors Research Articles

A thin-film laser, polymer waveguide, and thin-film photodetector cointegrated onto a silicon substrate

Planar lightwave circuits, which include optical passive and active components, can be integrated with electronics to form planar lightwave integrated (PLICs). Integration of PLICs onto standard electronic substrates (FR-4, Si) is an important step toward optical signal processing and signal distribution at the backplane, board, and chip level for sensing, interconnection, and other systems that utilize both optics and electronics. Further, if the topography of the entire planar optical system can mimic that of interconnection and integrated circuits, then the optics can be confined to the substrate plane, and the optical circuits begin to mimic electrical in format. Additionally, beam turning out of the plane of the system is no longer mandatory. In this letter, the first demonstration of a planar lightwave interconnection consisting of a thin-film InP-based laser, waveguide, and thin-film InGaAs photodetector (PD) heterogeneously integrated onto a SiO/sub 2/-Si substrate is reported. PD currents were measured as a function of laser bias current, and the laser to waveguide coupling efficiency was estimated at 22.6%.

Tensile strained Ge p-i-n photodetectors on Si platform for C and L band telecommunications

We demonstrate a 0.25% tensile strained Ge p-i-n photodetector on Si platform that effectively covers both C and L bands in telecommunications. The direct band edge of the Ge film has been pushed from 1550 to 1623 nm with 0.25% tensile strain, enabling effective photon detection in the whole L band. The responsivities of the device at 1310, 1550, and 1620 nm are 600, 520, and 100mA∕W under 0 V bias, which can be further improved to 980, 810, and 150mA∕W with antireflection coating based on calculations. Therefore, the device covers the whole wavelength range used in telecommunications. The responsivities at 1310 and 1550 nm are comparable to InGaAs photodetectors currently used in telecommunications. In the spectrum range of 1300–1650 nm, maximum responsivity was already achieved at 0 V bias because carrier transit time is much shorter than carrier recombination life time, leading to ∼100% collection efficiency even at 0 V bias. This is a desirable feature for low voltage operation. The absorption coefficients of 0.25% tensile strained Ge in the L band have been derived to be nearly an order of magnitude higher than bulk Ge. The presented device is compatible with conventional Si processing, which enables monolithic integration with Si circuitry.

Study of the excess noise associated with demodulation of ultra-short infrared pulses

The demodulation of ultra-short light pulses with photodetectors is accompanied by excess phase noise at the pulse repetition rate and harmonics in the spectrum of the photocurrent. The major contribution to this noise is power fluctuations of the detected pulse train that, if not compensated for, can seriously limit the stability of frequency transfer from optical to microwave domain. By making use of an infrared femtosecond laser, we measured the spectral density of the excess phase noise, as well as power-to-phase conversion for different types of InGaAs photodetectors. Noise measurements were performed with a novel type of dual-channel readout system using a fiber coupled beam splitter. Strong suppression of the excess phase noise was observed in both channels of the measurement system when the average power of the femtosecond pulse train was stabilized. The results of this study are important for the development of low-noise microwave sources derived from optical "clocks" and optical frequency synthesis.

Polarization-dependent responsivity: a study of germanium and indium gallium arsenide photodetectors

It is well known that the response of semiconductor photodetectors depends on the state of polarization of the incident light. The magnitude of this effect is quantified as the logarithm of the ratio of the maximum and minimum values of the responsivity when the detector is illuminated with completely polarized radiation of different polarization states. It will be referred to as polarization-dependent responsivity (PDR) (defined in analogy to polarization-dependent loss).A first set-up was developed to measure the average PDR of several germanium (Ge) and indium gallium arsenide (InGaAs) photodetectors between 1510 nm and 1610 nm, using a polarization scrambler. It has been observed that Ge and InGaAs photodetectors are sensitive to polarization, and that the magnitude depends on wavelength. It is shown that the PDR increases dramatically at wavelengths beyond the responsivity peak: this effect is especially strong for Ge, which has its peak near 1550 nm at room temperature, whose PDR is ⩽ 0.005 dB at 1550 nm and 23 °C, while it increases to 0.05 dB at the same wavelength when the detector is cooled to −10 °C.A second set-up was developed to measure the response of photodetectors to four main states of polarization at a grid of points on the active area with a small collimated beam, which is moved over the detector's surface using a motorized translation stage. With the power measured at each polarization state, we propose an adaptation of the Mueller matrix that allows us to obtain the first row of this matrix, so as to calculate the polarization axis vector for each point measured on the photodetector. Results lead us to suspect the existence of a polarization axis in photodetectors.

A Comparison of Lattice-Matched GaInNAs and Metamorphic InGaAs Photodetector Devices

AbstractThe dilute-nitride GaInNAs shows great promise in becoming the next choice for 1 eV photodetector and multi-junction photovoltaic applications due to the ability for it to be grown lattice-matched on GaAs substrates. This paper will present results from high-power photodetector devices fabricated from high-quality thick GaInNAs and metamorphic InGaAs materials grown by MBE. The internal quantum efficiency of rear-illuminated PIN photodiodes with thick GaInNAs films as the intrinsic region (roughly 62% at 1064 nm) is somewhat lower than comparable metamorphic InGaAs devices (roughly 75% at 1064 nm). However, the dark current density of the GaInNAs devices is also somewhat lower (roughly 3 μA/cm2 at 2×104 V/cm bias) than the InGaAs devices (roughly 20 μA/cm2 at 2×104 V/cm bias), while the breakdown voltages (beyond -20 V) are comparable. Materials characterization of each structure, including x-ray diffraction and room-temperature as well as temperature-dependent photoluminescence studies will be presented in order to explain the characteristics observed in the devices composed of the two different material systems.

InGaAs Photodetectors Cut-off at 1.9 μm Grown by Gas-SourceMolecular Beam Epitaxy

Using a linear graded InxGa1−xAs as the buffer layer,positive-intrinsic-negative wavelength-extendedIn0.6Ga0.4 As photodetectors with 50% cut-off wavelengthof 1.9 μm at room temperature were grown by using gas-source molecularbeam epitaxy, and their performance over a wide temperature range hasbeen extensively investigated. The detectors show typical dark currentat bias voltage 50 mV and the resistance–area product R0A of7 nA/765 Ωcm2 and 31 pA/404 kΩcm2at 290 K and 210 K, respectively. The thermal activation energy of thedark current in the temperature range 250–350 K is 0.488 eV.

Fabrication of 1.55-<tex>$mu$</tex>m Si-Based Resonant Cavity Enhanced Photodetectors Using Sol-Gel Bonding

In this work, a novel bonding method using silicate gel as the bonding medium was developed to fabricate an InGaAs narrow-band response resonant cavity enhanced photodetector on a silicon substrate. The bonding was performed at a low temperature of 350/spl deg/C without any special treatment on bonding surfaces and a Si-based narrow-band response InGaAs photodetector was successfully fabricated, with a quantum efficiency of 34.4% at the resonance wavelength of 1.54 /spl mu/m, and a full-width at half-maximum of about 27 nm. The photodetector has a linear photoresponse up to 4-mW optical power under 1.5 V or higher reverse bias. The low temperature wafer bonding process demonstrates a great potential in device fabrication.

Recent advances in InGaAs detector technology

Recent progress in the design and technology of InGaAs photodetectors operating in the 1.55-3.6 μm spectral range is presented. The performance of uncooled and Peltier-cooled InGaAs detectors is studied both theoretically and experimentally. Conventional and resonant cavity-enhanced devices are considered. In calculations band-to-band Auger processes as the dominant mechanisms of generation and recombination are taken into account. The optimized heterostructures are grown using molecular beam epitaxy on GaAs and InP substrates. Improvement of the performance of conventional photodiodes is achieved by the use of monolithic optical immersion. Further improvement of speed of operation can be reached for resonant cavity-enhanced photodiodes. This allows for a significant reduction of the transit time of photogenerated carriers, which is the main limitation to the speed of response of small-area optically immersed devices. They can be used for the detection of short-wavelength infrared radiation in the gigahertz range.

Application of laser ignition to hydrogen–air mixtures at high pressures

To optimise combustion in a wide field of applications, lasers represent attractive future alternative ignition sources, especially for internal combustion engines. Experiments were carried out in a high pressure, constant volume chamber (up to 25 MPa peak pressure and initial temperature of 473 K ). Laser induced ignition of different hydrogen–air mixtures (air/fuel equivalence ratio λ=1.8–8) was investigated, using different filling pressures ( p=0.5– 4.2 MPa ), different ignition energies (pulse energy PE=1– 50 mJ ), different chamber temperatures ( T=393– 473 K ) and different focal length lenses ( f=60, 120 mm ). A Q-switched Nd:YAG laser at 1064 nm with a pulse duration of about 5 ns was used for ignition. An InGaAs photodetector (800– 1800 nm ) and a piezoelectric pressure transducer were used to characterise the combustion. Gas mixtures between λ=2.5 and 3.6 showed knocking combustions. With increasing initial pressures the minimum pulse energy was decreasing.

1.5 μm to 0.87 μm optical upconversion using wafer fusion technology

Wafer fusion is an important processing tool for heterogenous integration of different materials regardless of their lattice constants. It removes the limitation of conventional epitaxial growth techniques and introduces a design parameter for achieving high performance semiconductor devices. In this article, we propose and demonstrate a 1.5 μm to 0.87 μm optical upconversion device based on wafer fusion technology. The device consists of an In0.53Ga0.47As (InGaAs) p-i-n photodetector and an AlGaAs/GaAs light-emitting diode (LED) integrated with wafer fusion. Incoming 1.5 μm light is absorbed by the InGaAs photodetector and generates a photocurrent. The resultant photocurrent drives the GaAs LED, which emits radiation at 0.87 μm. An internal quantum efficiency of 20% and an external quantum efficiency of 0.27% was obtained at room temperature. The results show the potential of the upconversion device in near-infrared imaging applications.

Thermally Induced Nonlinearities in High-Speed p-i-n Photodetectors

Nonlinearities in the responsivity of high-speed p-i-n photodetectors at high photocurrents can limit the useful dynamic range in photonic systems. This letter describes a nonlinearity in the quantum efficiency in InGaAs photodetectors designed for applications at 1.5 /spl mu/m is due to significant ohmic heating of the intrinsic region. Measured changes in responsivity of about 10% at photocurrents of 12 mA are attributed to a thermal bandgap shift, based on comparisons with temperature dependent measurements and a model of ohmic heating.

High Speed Ge Photodetectors on Si Platform for GHz Optical Communications in C+L Bands

ABSTRACTWe present a high speed, high responsivity, tensile strained Ge p-i-n photodetector selectively grown on Si platform that covers the whole C band and a large part of the L band for high capacity optical communications. The device shows a 3dB bandwidth of 2.5GHz and its responsivities at 1310nm and 1550nm are comparable to commercial InGaAs photodetectors currently used in telecommunications. The device has promising applications in Si microphotonics such as the fiber-to-the-home technology.

Physical modeling of a novel barrier‐enhanced quantum‐well photodetector device for optical receivers

AbstractA novel barrier‐enhanced InGaAs/InAlAs quantum‐well MSM photodetector with recessed electrodes is shown to be a promising high‐sensitivity, high‐speed device for optical receivers. Carrier transport simulations indicate very low, dark current at 10−6 A/m and electrical 3‐dB bandwidth at 50 GHz for a 1‐μm finger‐gap device. © 2004 Wiley Periodicals, Inc. Microwave Opt Technol Lett 40: 224–227, 2004; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.11336

A comparison of heavy ion and picosecond laser microbeams for investigating single event transients in InGaAs on InP photodetectors

The MeV ion and laser microbeams are the two most commonly used tools for examining the spatial and temporal dependence of charge collection processes that lead to single event phenomena in semiconductor devices. In this paper, we perform a detailed comparison of the fundamental differences that exist between the two methods for examining single event transients in InGaAs photodetectors. In particular, we compare results collected by transient laser and ion beam induced current for several ion species.

Calibration of an InGaAs photodiode at 1300 nm with a cryogenic radiometer and a diode laser

A single-element, windowless InGaAs photodetector has been calibrated against a cryogenic radiometer using a diode-laser source of wavelength 1296.9 nm (standard uncertainty u = 0.4 nm). This source differs from the gas lasers usually used with cryogenic radiometers in that the beam has an elliptical profile, is invisible to the naked eye, is not polarized, and is less spatially coherent. We describe the simple adaptations we have made to use this source with the cryogenic radiometer. In particular, we use a fibre-optic delivery system to prepare the beam, and an anti-reflection-coated window to admit the radiation. The relative uncertainty in this method of calibration is estimated to be 0.08% (1σ). The measured response (0.9752 A/W) differs from that obtained from the existing laboratory scale by 0.08%.

Noncontact nanosecond-time-resolution temperature measurement in excimer laser heating of Ni–P disk substrates

The thermal emission from a Ni–P disk substrate heated by a pulsed excimer laser is measured with nanosecond time resolution. A fast InGaAs photodetector is employed to capture the thermal emission signal. The spectral surface reflectivity is simultaneously measured in situ. The transient surface temperature is derived from the spectral thermal emission signal on the basis of Planck’s blackbody radiation intensity distribution. The experimental results and analytical solutions are compared and an important parameter involving the thermal diffusivity and conductivity in the transient temperature response of the material is evaluated.

Influence of buffer layer and processing on the dark current of 2.5 µm-wavelength 2%-mismatched InGaAs photodetectors

An extensive study is presented in which different buffer layers for the growth of 2.5 /spl mu/m wavelength mismatched InGaAs photodetectors are compared. The dark current of the photodetectors is measured to judge the quality of the buffer layers. These differ in material composition (InGaAs or InAsP), grading mechanism (linear or stepwise), total buffer-layer thickness and number of steps. It is shown that the detectors with a thick InAsP buffer, grown on a 2/spl deg/-off-oriented substrate, lead to the lowest dark currents. Different processing schemes are compared and it is shown experimentally that the dark current of a mesa-type detector consists of a part proportional to the circumference and one proportional to the detector area. The latter part is shown to be equal to the dark current of a planar Zn-diffused detector with the same dimensions.

Microwatt-power InGaAs photogenerator for lightwave networks

A 3×3 array of series-connected InGaAs photodetectors was used as a photogenerator to optically power a remotely-located microwatt-power optical shutter intended for use in a lightwave network. The conversion efficiency of the photogenerator was 7×10/sup -3/ A/W when the device was illuminated at 1550 nm from the output of a single-mode fiber; the open-circuit voltage was 2 V with 300 μW of incident power.

Waveguide-integrated InP-InGaAs-InAlGaAs MSM photodetector with very-high vertical-coupling efficiency

We report on a novel implementation of long-wavelength vertically-coupled waveguide-integrated metal-semiconductor-metal (MSM) InGaAs photodetectors which results in a significantly improved guide-to-absorber coupling efficiency. By employing an In/sub 0.53/Al/sub 0.31/Ga/sub 0.16/As buried strip waveguide embedded in InP, a coupling length of only 20 /spl mu/m is sufficient to obtain an internal quantum efficiency greater than 95%. Moreover, the photoresponse is found to be virtually independent of the polarization state of light coupled into the input waveguide. The device parameters agree with the results of eigenmode calculations.

An integrated, crystalline organic waveguide-coupled InGaAs photodetector

We describe a novel, integrated organic-inorganic waveguide/photodetector with an internal quantum efficiency of (53/spl plusmn/15%). Low-loss (2.7/spl plusmn/0.3 dB/cm at /spl lambda/=1.064 μm for 10-μm wide waveguides) crystalline organic waveguides are grown directly onto the pre-processed InGaAs photodetector by organic molecular beam deposition (OMBD) without affecting either the dark current or capacitance of the photodiode. The polarization-preserving nature of the waveguides suggests that a patterned substrate significantly influences the organic molecular orientation during vacuum deposition.