Si Photodiode Research Articles

Silicon-based grid structure photodiode with selective UV enhancement

Aiming at boosting the low ultraviolet (UV) responsivity induced by the negative impact of the surface ‘dead layer’ in silicon-based conventional photodiode (CPD), Si photodiodes with five different structures, including both the novel grid structure photodiode (GSPD) and CPD, have been manufactured using thermal diffusion process and tested. The results show that the UV responsivity around 365 nm of GSPD could be as high as 6 times that of CPD, while the high visible (VIS) responsivity is sharply suppressed by the employment of grid shaped junction (GSJ) in the GSPD, which has realized the expectation of selective UV enhancement with prospect for application.

Investigation of charge collection in a silicon PIN photodiode

Ion Beam Induced Charge (IBIC) imaging with a 2MeV He+ microbeam has been used to investigate spectroscopic features and charge transport properties of a Hamamatsu S1223 silicon PIN photodiode. Pulse height spectra were collected with high lateral resolution at different reverse bias values between 0V and −100V. Pulse height maps and median energy maps were generated to observe the spatial variations of charge collection properties. Absolute charge collection efficiency was calculated along a line including the edge structure of the photodiode. Our results show that the charge collection is uniform within the sensitive area of the PIN diode but it is decreasing close to the edges. There are low energy satellite peaks and other structures in the spectra due to energy loss in the edge protecting surface coverages and incomplete charge collection in the near surface and undepleted regions. The investigated effects contribute to the further understanding of the operation of the Si photodiode and similar semiconductor device structures.

Radiation damage microstructures in silicon and application in position sensitive charged particle detection

Area selective irradiation using MeV ions having different ranges has been performed in a nuclear microprobe to produce radiation damage microstructures in silicon photodiodes. IBIC (Ion Beam Induced Charge) technique has been used for on line monitoring of radiation damage produced by different fluences of He, Li and O ions of MeV energies. Three-dimensional patterning of radiation damage structures may be used for different applications. By creating a region of constant damage gradient in Si photodiode, position sensitive radiation detection has been demonstrated.

Ge∕Si Photodiodes and Phototransistors with Embedded Arrays of Germanium Quantum Dots for Fiber-Optic Communication Lines

Photodetectors based on Ge/Si multilayer heterostructures with germanium quantum dots are fabricated for use in fiber-optic communication lines operating in the wavelength range 1.30–1.55 μm. These photodetectors can be embedded in an array of photonic circuit elements on a single silicon chip. The sheet density of germanium quantum dots falls in the range from 0.3 × 1012 to 1.0 × 1012 cm−2, and their lateral size is approximately equal to 10 nm. The heterostructures are grown by molecular-beam epitaxy. For a reverse bias of 1 V, the dark current density reaches 2 × 10−5 A/cm2. This value is the lowest in the data on dark current densities available in the literature for Ge/Si photodetectors at room temperature. The quantum efficiency of photodiodes and phototransistors subjected to illumination from the side of the plane of the p-n junctions is found to be 3% at a wavelength of 1.3 μm. It is demonstrated that the maximum quantum efficiency is achieved for edge-illuminated waveguide structures and can be as high as 21 and 16% at wavelengths of 1.3 and 1.5 μm, respectively.

Detector efficiency limits on quantum improvement

Although the National Institute of Standards and Technology has measured the intrinsic quantum efficiency of Si and InGaAs avalanche photo diode (APD) materials to be above 98% by building an efficient compound detector, commercially available devices have efficiencies ranging between 15 and 75%. This means bandwidth, dark current, cost, and other factors are more important than quantum efficiency for existing applications. For non-classical correlated photon applications, the system's correlated signal-to-noise ratio is proportional to (ηN)½ /(1 − η)½, rather than the classical signal-to-noise (ηN)½. Consequently, the detector design trade space must be re-evaluated. This paper systematically examines the generic detection process, lays out the considerations needed for designing detectors for non-classical applications, and identifies the ultimate physical limits on quantum efficiency.

Assessment of quality defects in macadamia kernels using NIR spectroscopy

Spectral data were collected of intact and ground kernels using 3 instruments (using Si-PbS, Si, and InGaAs detectors), operating over different areas of the spectrum (between 400 and 2500 nm) and employing transmittance, interactance, and reflectance sample presentation strategies. Kernels were assessed on the basis of oil and water content, and with respect to the defect categories of insect damage, rancidity, discoloration, mould growth, germination, and decomposition. Predictive model performance statistics for oil content models were acceptable on all instruments (R2 > 0.98; RMSECV < 2.5%, which is similar to reference analysis error), although that for the instrument employing reflectance optics was inferior to models developed for the instruments employing transmission optics. The spectral positions for calibration coefficients were consistent with absorbance due to the third overtones of CH2 stretching. Calibration models for moisture content in ground samples were acceptable on all instruments (R2 > 0.97; RMSECV < 0.2%), whereas calibration models for intact kernels were relatively poor. Calibration coefficients were more highly weighted around 1360, 740 and 840 nm, consistent with absorbance due to overtones of O-H stretching and combination. Intact kernels with brown centres or rancidity could be discriminated from each other and from sound kernels using principal component analysis. Part kernels affected by insect damage, discoloration, mould growth, germination, and decomposition could be discriminated from sound kernels. However, discrimination among these defect categories was not distinct and could not be validated on an independent set.It is concluded that there is good potential for a low cost Si photodiode array instrument to be employed to identify some quality defects of intact macadamia kernels and to quantify oil and moisture content of kernels in the process laboratory and for oil content in-line. Further work is required to examine the robustness of predictive models across different populations, including growing districts, cultivars and times of harvest.

Metastable phase formation in undercooled Fe–Co melts

Abstract Soft magnetic Fe–Co alloys display the primary fcc phase solidification for >18 at.% Co in conventional near-equilibrium solidification processes. Undercooled Fe–Co melt drops within the composition range of 70–50 at.% Fe have been investigated with the electromagnetic levitation technique. The solidification kinetics was measured in situ using a high-resolving Si photodiode. The melt drops were undercooled up to 263 K below the liquidus temperature and subsequently quenched onto a chill substrate in order to characterise the solidification sequence and the microstructure. The transition from stable fcc phase to primary metastable bcc phase has been observed after reaching a critical undercooling level which increases with rising Co content. The growth velocity drops obviously after transition to metastable bcc phase formation. Moreover, parabolic flight experiments were performed in order to study the phase selection under reduced gravity conditions. The investigation of the solidification events yielded a much smaller critical undercooling and an increased life time of the metastable bcc phase.

Soft x-ray emission from postpulse expanding laser-produced plasmas

A diagnostic spectrometer has been developed at the Naval Research Laboratory to measure the time resolved absolute intensity of radiation emitted from targets irradiated by the Nike laser. The spectrometer consists of a dispersive transmission grating of 2500 lines/mm or 5000 lines/mm and a detection system consisting of an absolutely calibrated Si photodiode array and a charge coupled device camera. In this article, this spectrometer was used to study the spatial distribution of soft x-ray radiation from low Z elements (primarily carbon) that lasted tens of nanoseconds after the main laser illumination was over. We recorded soft x-ray emission as a function of the target material and target orientation with respect to the incoming laser beam and the spectrometer line of sight. While a number of spectral features have been identified in the data, the instrument’s combined temporal and spatial resolution allowed observation of the plasma expansion from CH targets for up to ∼25 ns after the cessation of the main laser pulse. The inferred plasma expansion velocities are slightly higher than those previously reported.

Wavelength sensing by dual photodetectors

Abstract On the basis of the fact that the Si and InGaAs photodiodes have different spectral response curves, a new method for sensing the wavelength of laser beams is presented, and the common-mode rejection method to compensate the temperature sensitivity of the photodetectors is proposed. The advantage is that the measured results are independent of the incident direction of the light. It is shown that this method is simple and reliable. The spectral resolution could be less than ±5 nm in the wavelength region 500–1200 nm.

Integrated Hydrogenated Amorphous Si Photodiode Detector for Microfluidic Bioanalytical Devices

Hydrogenated amorphous silicon (a-Si:H) PIN photodiodes have been developed and characterized as fluorescence detectors for microfluidic analysis devices. A discrete a-Si:H photodiode is first fabricated on a glass substrate and used to detect fluorescent dye standards using conventional confocal microscopy. In this format, the limit of detection for fluorescein flowing in a 50-microm deep channel is 680 pM (S/N = 3). A hybrid integrated detection system consisting of a half-ball lens, a ZnS/YF3 multilayer optical interference filter with a pinhole, and an annular a-Si:H photodiode is also developed that allows the laser excitation to pass up through the central aperture in the detector. Using this integrated detection device, the limit of detection for fluorescein is 17 nM, and DNA fragment sizing and chiral analysis of glutamic acid are successfully performed. The a-Si:H detector exhibits high sensitivity at the emission wavelengths of commonly used fluorescent dyes and is readily microfabricated and integrated at low cost making it ideal for portable microfluidic bioanalyzers and emerging large scale integrated microfluidic technologies.

Diffusion length analysis and measurement in the base region of photodiodes

An experimental technique for determining the minority carrier diffusion length in the base region of SI photodiodes described. Optical arrangement has been suggested, in which the device was operated in the photoconductive mode and its photo-response in the wavelength region near the energy gap is measured. The ratio of incident light intensity to photocurrent is a linear function of reciprocal absorption coefficient the slope of which gives L n . In addition, a nonlinear least-squares analysis is also used to determine the diffusion length. Furthermore, it has been found that L n decreases as the absorbed dose of gamma rays increases.

Response of a silicon photodiode to pulsed radiation.

Both the integrated-charge and the peak-voltage responsivity of a 1-cm2 Si photodiode optimized for the extreme ultraviolet have been measured with 532-nm-wavelength pulsed radiation. The peak power of the optical pulse is varied from 35 mW to 24 kW with a pulse width of 8.25 ns. A decrease in responsivity is observed with increasing pulse energy, and a model is presented that accounts for the observed loss of responsivity. The integrated-charge responsivity decreases because the presence of photogenerated majority carriers increases the direct recombination rate. The peak-voltage responsivity is reduced because the electric susceptibility of the electrons and holes in the depletion region increases the capacitance of the device. The influence of an applied reverse bias on both responsivities is investigated. The integrated-charge responsivity is found to be identical, with a 1% uncertainty, to the cw responsivity of the device if the energy dependence is considered.

Quantum efficiency of silicon photodiodes in the near-infrared spectral range.

The quantum efficiency of silicon photodiodes and factors that might be responsible for the drop in quantum efficiency in the near-infrared spectral range were analyzed. It was shown that poor reflectivity from the rear surface of the die could account for a decrease in Si photodiode quantum efficiency in near-infrared spectral range by more than 20%. The photodiode quantum efficiency was modeled with an appropriate representation for the carrier-collection efficiency dependence on the die penetration depth. A corrected analytical expression for calculating the photodiode quantum efficiency is given. Some methods to improve the quantum efficiency of silicon photodiodes in near-infrared spectral range are discussed.

Development of neutron detector using the PIN photodiode with polyethylene (n,p) converter

A Si photodiode detector PIN-type 10/spl times/10 mm, with a slim film of a converter material capable of producing charged particles, was used as sensor of neutrons and it was projected to be used in an environment of a zero power reactor. Polyethylene n(CH/sub 2/), which produces recoil protons from the (n,p) interaction, was used to improve the detection efficiency. A mathematical model was applied to fit the experimental data and the optimal thickness of the converters was determined by the maximum point of the function. For an AmBe source, the optimum polyethylene layer thickness was of 0.105 cm (96.6 mg/spl middot/cm/sup -2/). The converter of polyethylene was capable to improve the detection efficiency to a factor of 16.4 compared to measurement without converter. The detector shows a good response (r=0.999372) to estimate the power variation during the operation of the zero power-type reactor (IPEN/MB-01).

Antireflection Layer Coating for the Red Light Detecting si Photodiode

The effect of antireflection layer on the reduction of optical loss has been investigated in Si photodiodes detecting red light with central wavelength of 670 nm. The theoretical analysis showed minimum reflection loss of 6% for the thickness of about in the -Si system with the single antireflection layer and no reflection loss for the XNthickness of / in the -Si system with double antireflection layer. In our experiments, Si photodiodes with the web-patterned -shallow diffusion region were fabricated by bipolar IC process technology and the devices were classified into three kinds according to the structure of /antireflection layer. The fabricated devices showed maximum spectral response in the optical spectrum of 650∼700 nm. The average photocurrents of the devices with the thickness of /X, and under the incident power, of -17 dBm were 3.2 uA, 3.5 uA and 3.1 uA, respectively.

Quantum efficiency of solar-blind semiconductor photodiodes in the far ultraviolet

A difficulty in diverse metrological applications is the measurement of relatively low intensity ultraviolet radiation signals in the presence of an intense visible radiation background. The development of a detector technology that combines the high efficiency and ease of use found in Si photodiodes with the solar-blind characteristics of many photoemissive devices would offer an ideal solution to this problem. Wide bandgap semiconductors (e.g. SiC, GaN and AlGaN) should combine sensitivity comparable to Si photodiodes with solar-blind response. We present ultraviolet quantum efficiency measurements of AlGaN Schottky and GaN p–i–n photodiodes demonstrating responsivity in the far ultraviolet to wavelengths as short as 116 nm (AlGaN Schottky devices) or 180 nm (GaN p–i–n devices) and several orders of magnitude reduction in efficiency for photon energies below the bandgap. The bandgap for GaN corresponds to 365 nm wavelength, and AlGaN devices exhibit cut-off wavelengths as short as 260 nm.

A bilateral comparison of spectral responsivity measurements in the spectral range 250 nm to 1800 nm between the NIST (USA) and the NRC (Canada)

This intercomparison of spectral responsivity between the National Institute of Standards and Technology (NIST) in the United States and the National Research Council (NRC) of Canada was carried out to test the level of agreement between the two laboratories for routine detector calibrations and also to support the uncertainties quoted by NIST and NRC in appendix C of the Mutual Recognition Arrangement (MRA) drawn up by the International Committee of Weights and Measures (CIPM). The comparison was carried out in two stages: 250 nm to 1100 nm using three silicon (Si) photodiodes, then 700 nm to 1800 nm using two germanium (Ge) and two indium gallium arsenide (InGaAs) detectors. This paper describes briefly the derivation of the spectral responsivity scales, measurement procedures and apparatus used for each laboratory. The results of the intercomparison are presented. In the spectral ranges from 250 nm to 1000 nm for silicon and 750 nm to 1700 nm for germanium and InGaAs, the agreement between the two laboratories is well within the combined uncertainties. In particular, in the 450 nm to 1000 nm spectral range, the agreement is better than ±0.2%. In the 900 nm to 1600 nm spectral range, the agreement is typically ±0.5%. Consequently, the results of this intercomparison are shown to support the uncertainties claimed by NIST and NRC in their routine calibrations, and in their appendix C entries of the MRA.

Evaluation of CsI(Tl)-PIN diode array tiling schemes

Methods of tiling scintillator-photodiode detector arrays were investigated. Si photodiodes coupled to CsI(Tl) scintillation crystals are being considered for high-resolution (/spl sim/1 mm) gamma-ray imaging. Large area (/spl sim/200 cm/sup 2/) detectors can be assembled by tiling together modular arrays. The goal of the tiling schemes was to maintain uniform pixel pitch and detector performance across the seam where the arrays join. The perimeter of the array has an insensitive area that can be an appreciable fraction of a pixel size when using 1 mm pixels. One tiling scheme used smaller pixels at the edge of the arrays to compensate for this insensitive area (partial PIN method). A second approach used a scintillator light-sharing technique to cover the insensitive area (segmented method). The partial pixel method resulted in worse energy resolution and sensitivity in the partial pixels compared to the full pixels (20% and 30% FWHM at 140 keV for edge and corner pixels, respectively, versus 12% in full pixels, with relative corner pixel sensitivity of /spl sim/50%), but successfully maintained spatial resolution and pixel pitch. The segmented crystal light-sharing method demonstrated 17%-20% FWHM energy resolution (at 140 keV) in the edge pixels, /spl sim/85% relative sensitivity, and provided good pixel identification (i.e., good spatial resolution). However, the segmented crystal method is considerably more complex to implement, compared with the partial pixel method.

Radiation damage induced in Si photodiodes by high-temperature neutron irradiation

Results are presented of a detailed study of the effects of high-temperature 4-MeV neutron irradiation on the performance degradation of Si pin photodiodes together with the radiation-induced defects, observed by deep level transient spectroscopy (DLTS). It was found that the dark current increases after irradiation, while the photocurrent decreases. After irradiation, two majority electron capture levels with (E c -0.22 eV) and (E c -0.40 eV) were induced in the n-Si substrate, while one minority hole capture level with (E v + 0.37 eV) was found. Additionally, the degradation of the device performance and the introduction rate of the lattice defects decreases with increasing irradiation temperature. For a 250 °C irradiation, the reduction of the reverse current is only 20% of the starting value. This result suggests that the creation and recovery of the radiation damage proceeds simultaneously at high temperatures.

Radiation damage of Si photodiodes by high-temperature irradiation

Results are presented of a detailed study of the effects of high-temperature 4-MeV neutron irradiation on the performance degradation of Si pin photodiodes. The macroscopic device performance is correlated with the radiation-induced defects observed by DLTS. It was found that the dark current increases after irradiation, while the photocurrent decreases. After irradiation, two majority electron capture levels (Ec 0.40 eV) were induced in the n-Si substrate. Additionally, degradation of device performance and the rate of introduction of lattice defects decrease with increasing irradiation temperature. For 250 °C irradiation, the reduction of the photocurrent is only 10% of the starting value. This result suggests that the creation and recovery of radiation damage proceed simultaneously at high temperatures.