Types Of Photodiodes Research Articles

Design of an improved neutron dose equivalent dosimeter

This paper describes the design and development of a new active area neutron dosimeter. The design incorporates a traditional central detector with a moderator/filter arrangement and a number of outer PIN type photodiodes sensitised to thermal neutrons by the application of a lithium fluoride converter. The outer thermal detectors allow the determination of the neutron radiation field characteristics. The experimental programme has demonstrated that such an arrangement is capable of discriminating between various neutron fields and the usefulness of MCNP4b as a design tool.

Characterization of crosstalk between CMOS photodiodes

The crosstalk in CMOS photodiodes has been measured, at two wavelengths of 543 and 633 nm, by an experimental structure containing several types of photodiodes with varying dimensions. The role of the design of the junction in reducing crosstalk is studied. The measurements indicate that to reduce crosstalk it is essential to optically shield the gap between junctions and to reverse bias the adjacent junctions. Crosstalk is significantly reduced in double-junction photodiodes, but at the cost of lower quantum efficiency. The results indicate that with properly designed layout, the crosstalk may be small. However, there is a tradeoff between small crosstalk, reduced fill factor and quantum efficiency.

Dimensional effects in CMOS photodiodes

CMOS photodiodes with various structures and dimensions were measured and analyzed. The photodiode types under study include structures implemented by: n + (source implantation)/P-substrate, N-well/P-substrate, and p + (source implantation)/N-well/P-substrate. Long photodiodes with a narrow width varying between 2–50 μm were studied, in order to consider dimensional effects. For the design under study, a 2-D model is adequate while the overall photodiode size provides sufficient signal for measurement accuracy. The quantum efficiency, dark current and spectral noise behavior were measured and compared with simulations. The good fit between measurements and simulations indicates that the physical mechanisms and the technology parameters, which determine the performance of the CMOS photodiodes, are understood.

Spectral responsivity uncertainty of silicon photodiodes dueto calibration spectral bandwidth

A systematic study on the uncertainty in spectral responsivity ofsilicon photodiodes due to the calibration spectral bandwidth is presented.Two of the most common types of silicon photodiodes in the field of opticalpower measurements have been used in this work: one with thickness of about100 nm of SiO2 and the other with thickness about 27 nm of SiO2. It isshown that the spectral responsivity error will be negligible(⩽5×10-4) using a spectral bandwidth up to 20 nm in thecalibration if the effective wavelength of the spectral transfer function,including the distribution of the radiation source, is calculated and themeasured responsivity is assigned to that effective wavelength. In othercases, the error depends not only on the extent of the interval isolated bythe spectral analysis system but also on the shape of the spectral isolationfunction.

The impact of a large bandgap drift region in long-wavelength metamorphic photodiodes

A comparative study of two types of metamorphic double heterojunction long-wavelength photodiodes on GaAs substrates is performed in terms of their bandwidths and responsivities. A p-i-i-n heterostructure with a large bandgap drift layer (I-InAlAs) at the cathode end of the photoabsorption region (i-InGaAs) is compared experimentally and theoretically to a p-i-n structure without a drift layer. Both types of photodiodes were fabricated using an InGaAs-InGaAlAs-InAlAs double heterostructure design to simultaneously achieve high bandwidths and high responsivities. The inclusion of an I-InAlAs drift region resulted in p-i-i-n photodiodes with larger bandwidths than p-i-n photodiodes with the same areas, or conversely a p-i-i-n photodiode can be made larger than a comparable p-i-n photodiode, but achieve the same bandwidth. Therefore, p-i-i-n photodiodes provide larger optical fiber alignment tolerances and better coupling efficiency than p-i-n photodiodes with the same bandwidths, p-i-i-n photodiodes with 10-/spl mu/m-diameter optical windows typically exhibited low dark currents of 500 pA at 5-V bias, responsivities of 0.6 A/W, and a -3-dB bandwidth of 38 GHz for 1.55-/spl mu/m operation.

Metamorphic heterojunction bipolar transistors and P–I–N photodiodes on GaAs substrates prepared by molecular beam epitaxy

Metamorphic heterojunction bipolar transistor (M-HBT) structures and metamorphic P–I–N (M-PIN) photodiode structures were grown on GaAs substrates. A compositionally graded AlGaInAs buffer layer was used to expand the lattice constant to that of InP. Cross-sectional transmission electron micrographs of the M-HBT structure showed that the dislocations from compositional grading were predominantly localized in the buffer layer and that the device layers possessed planar interfaces. Secondary ion mass spectroscopy depth profiles of the 4×1019 cm−3 beryllium-doped In0.53Ga0.47As base layer exhibited sharp doping interfaces, indicating that metamorphic growth was not causing enhanced beryllium diffusion. The current gain of large emitter M-HBT devices approached the current gain for the same device structure grown on an InP substrate. A P–I–N photodiode structure was also grown metamorphically on a GaAs substrate and lattice matched on an InP substrate. Both types of photodiodes showed almost identical responsivities and bandwidths. A responsivity to 1.55 μm radiation of 0.55 A/W, which corresponds to an external quantum efficiency of 44%, was obtained with M-PIN photodiodes. The 3 dB bandwidths exceeded 20 GHz for M-PIN photodiodes with diameters of 25 μm or smaller. These results are very encouraging for the application of metamorphic technology to nonmajority carrier devices.

A low-power low-noise ultrawide-dynamic-range CMOS imager with pixel-parallel A/D conversion

A CMOS image sensor with pixel-parallel analog-to-digital (A/D) conversion fabricated with different array sizes and photodiode types in a three-metal 0.5-/spl mu/m process is presented. Nominal power dissipation is 40 nW per pixel at V/sub DD/=3.3 V. A/D conversion results from sampling a free-running photocurrent-controlled oscillator to give a first-order /spl Sigma/-/spl Delta/ sequence. The sensor displays dynamic range capability of greater than 150000:1 and exhibits fixed pattern noise correctable to within 0.1% of signal.

Electro-epitaxial lateral overgrowth of silicon from liquid-metal solutions

Monocrystalline silicon films are formed on patterned, metal-masked silicon substrates by a liquid-phase electro-epitaxial lateral overgrowth process. More specifically, silicon films are grown from liquid–metal solutions (molten bismuth saturated with silicon) by current-induced crystallization on stripe-patterned, tungsten-masked (111) silicon substrates. Growth temperatures range from 800°C to 1150°C, and a current density of 2–20A/cm2 is imposed across the silicon/melt interface to effect growth. Continuous (over 1cm2 areas) epitaxial layers of silicon are achieved on tungsten-masked substrates patterned with 10-μm wide stripe openings spaced 100μm apart. New types of solar cells and photodiodes, wherein the metal mask functions as a reflective “buried mirror” layer to increase optical coupling and internal quantum efficiency, are realized with this silicon liquid-phase electro-epitaxy process.

Spectral responsivity of various types of silicon photodiode at oblique incidence: comparison of measured and calculated values

The spectral responsivity of several types of silicon photodiode at oblique incidence (approximately 45 degrees) is investigated. Both windowless diodes and diodes that incorporate quartz windows are considered. The spectral responsivities are measured directly for both parallel and perpendicular polarized radiation. For comparison, the responsivity at oblique incidence is also calculated from the normal-incidence measured responsivity in conjunction with the reflectance values at normal and oblique incidence calculated from thin-film theory by use of the measured oxide thicknesses of the diodes and published data on the refractive indices of silicon and fused silica. A technique, believed to be novel, is described for accurately measuring the oxide thicknesses of the diodes. A comparison of calculated and measured responsivity values shows that, when imperfect polarizers are used, it may be more accurate over a certain spectral range to calculate the responsivities at oblique incidence rather than to measure them directly. The additional uncertainty associated with the calculated responsivity values at oblique incidence, with respect to the original source data for normal incidence, is +/-1% over a wide spectral range.

Pn photodiodes for pulsed laser rangefinding applications realized in standard CMOS/BiCMOS processes

This paper describes simulation of the operation of integrated high-speed pn photodiodes and verification of the results by means of measurements performed with two types of photodiode, one implemented in a standard 0.8 μm CMOS process and the other in a standard 1.2 μm BiCMOS process. The measured rise times and responsivities of the photodiodes were <5 ns and 0.28 A/W in the CMOS process and 30 ns and 0.31 A/W in the BiCMOS process. Furthermore, the suitability of the photodiode for 3D vision was investigated by designing an array of photodetectors and measuring the isolation between the detector blocks. The results confirm that the photodetectors and receiver for a pulsed laser rangefinder can be implemented on the same chip in a standard process without any process modifications.

Ultimate parameters of Hg 1–xCd xTe and InAs 1–xSb x n +–p photodiodes

Ultimate parameters of HgCdTe and InAsSb n +–p photodiodes for the 5-μm spectral region operating at a temperature of 220 K have been determined. Parameters of these devices are limited by noise coming from statistical processes of thermal generation and recombination of carriers. In the case of HgCdTe photodiodes, only two processes are important, Auger 1 and Auger 7, whereas in InAsSb photodiodes the Auger S process is dominant. It is proved that Hg 1– x Cd x Te and InAs 1– x Sb x photodiodes constructed optimally have similar detection parameters. In both types of photodiodes, broadening of the energy band gap in the n + region leads to a similar, almost twofold increase in the normalized detectivity.

Spectral and intensity dependence of spatially resolved two-photon conductivity defects on a GaAsP photodiode

Femtosecond laser excitation through a near-field scanning optical microscope is used to study spatially resolved defects in the two-photon conductivity of a GaAs0.6P0.4 diffusion type photodiode. Two types of defects are observed when the photodiode is excited with femtosecond pulses below the bulk band gap energy. Photocurrent enhancement defects show a higher photocurrent than the surrounding areas and are driven by both one-and two-photon processes. These defects are often correlated with pits in the photodiode surface. Photocurrent depression defects have the normal two-photon power dependence and are not associated with surface pits. Based on the low measured coverage of both defect sites, the performance of GaAsP in auto- and cross correlators will be unaffected in most situations. A deviation in alloy stoichiometry, in which localized areas are rich in arsenic while poor in phosphorus, provides the best explanation for the origin of the enhancement defects.

Optical tunnel-trap detector for radiometric measurements

We have designed and evaluated an optical trap detector that is simple to fabricate and convenient to use. The trap geometry is a triangular tube similar to a kaleidoscope, with two photodiodes in place of a mirror on each side. One version incorporates six 10 mm × 10 mm silicon photodiodes in a detector having a 7 mm diameter aperture. Spectral responsivity measurement results indicate that the quantum efficiency, evaluated at 10 nm increments from 450 nm to 950 nm, is greater than 99 %. Another version incorporates six 18 mm × 18 mm silicon photodiodes in a detector having a 12 mm diameter aperture. Spectral responsivity measurement results from this instrument are similar to those from the other one, but the quantum efficiency is lower. Spatial uniformity measurement results for the larger detector indicate that, over the 12 mm diameter area, response variations are less than 0.05 %. We have evaluated several fields-of-view and confirmed that, in a special case, the detector geometry will accommodate an input beam having a divergence as large as 14°. Design considerations are briefly described and may be used to create similar, scaled versions with other photodiode types and sizes.

Unified analytical expressions for transimpedance and equivalent input noise current of optical receivers

Unified analytical expressions are derived for calculating the equivalent input noise current and transimpedance of optical receiver front ends with arbitrary input matching network topologies. To be independent of any transistor or amplifier type, noise parameters are used to describe the noise behavior of the active device. A new characteristic frequency-dependent value, called photodiode intrinsic conductance, is introduced. This figure-of-merit allows one to compare the achievable equivalent input noise current and transimpedance of different types of photodiodes independently of amplifier type and geometry.

Charge transport mechanisms in HgMnTe photodiodes with ion etched p–n junctions

Infrared detectors with p–n junctions formed by ion etching of p-Hg 1− x Mn x Te ( x≈0.1) single crystals are reported. The diode structures exhibit appropriate rectifying properties and a typical photodiode behavior. The contribution of diffusion, generation–recombination, tunneling and avalanche processes to charge carrier transport in the photodiodes is investigated.

Determination of the electron–hole pair creation energy for semiconductors from the spectral responsivity of photodiodes

Ionizing radiation can be detected by the measurement of the charge carriers produced in a detector. The improved semiconductor technology now allows detectors operating near the physical limits of the detector materials to be designed. The mean energy required for producing an electron–hole pair, W, is a material property of the semiconductor. Here, the determination of W from the spectral responsivity of photodiodes is demonstrated. Using spectrally dispersed synchrotron radiation, different types of semiconductor photodiodes have been examined in the UV-, VUV-, and soft X-ray spectral range. Their spectral responsivity was determined with relative uncertainties between 0.4% and 1% using a cryogenic electrical-substitution radiometer as primary detector standard. Results are presented for silicon n-on-p junction photodiodes and for GaAsP/Au Schottky diodes at room temperature. The investigations for silicon covered the complete spectral range from 3 to 1500 eV, yielding a constant value W=(3.66±0.03) eV for photon energies above 50 eV, a maximum value of W=4.4 eV at photon energies around 6 eV, and a linear relation W= hν (one electron per photon) for photon energies below 4 eV. For GaAsP, we obtained a constant value of W=4.58 eV in the photon energy range from 150 to 1500 eV, with a relative uncertainty of 1–3%, depending on the photon energy.

Transmission-type position sensor for the straightness measurement of a large structure

A new position sensor has been fabricated which is suitable for detecting the accurate straightness reference of a laser beam. This is achieved by fabricating a four-cell type photodiode inside a Si micro-mesh structure. This sensor does not disturb the direction or the wave front of the reference laser beam as it absorbs only some of the incident photons and transmits the rest down stream. The straightness of ~1 m structures can be measured with ~1 µm accuracy at many points by placing the sensors in series.

Quantum efficiency of cesium iodide photocathodes in the 120–220 nm spectral range traceable to a primary detector standard

Differently prepared CsI samples have been investigated in the 120–220 nm spectral range for their quantum efficiency, spatial uniformity and the effect of radiation aging. The experiments were performed at the PTB radiometry laboratory at the Berlin synchrotron radiation facility BESSY. A calibrated GaAsP Schottky photodiode was used as transfer detector standard to establish traceability to the primary detector standard, because this type of photodiode – unlike silicon p-on-n photodiodes – proved to be of sufficiently stable response when exposed to vacuum ultraviolet radiation. The paper reviews the experimental procedures that were employed to characterize and calibrate the GaAsP photodiode and reports the results that were obtained on the investigated CsI photocathodes.

Spatially resolved femtosecond time correlation measurements on a GaAsP photodiode

Femtosecond photoconductive near-field microscopy on a GaAsP diffusion type photodiode is used to investigate the response of the pure semiconductor material and impurity defect sites. At an excitation energy of 780 nm, below the bulk band gap, impurity sites ≈1 μm in diameter are observed. These sites exhibit a linear dependence of photoconductivity on light intensity instead of the usual two-photon dependence. The linear response on the defect sites gives rise to a first-order interferometric autocorrelation, while the typical GaAsP semiconductor material in other regions yields a second-order interferometric autocorrelation, which can be used for determinations of temporal shape, phase, and linear chirp of pulses. The results indicate that high concentrations of impurity sites can limit the application of a GaAsP photodiode as a femtosecond auto- or cross-correlator.

Test results on hybrid photodiodes

We have made various measurements on four different types of Hybrid PhotoDiodes (HPDs) with and without magnetic fields. We confirmed that all the four HPDs were operational with a magnetic field with a strength of at least 1.5 T if the device axis was adjusted approximately parallel to the magnetic field direction. Origins of the gain variation in magnetic fields were also investigated.