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.     

Nanoparticle-induced enhancement and suppression of photocurrent in a silicon photodiode

Nanoparticles are capable of both enhancing and suppressing the photocurrent in a silicon diode when deposited on the active face of the device. Photocurrent imaging of the individual nanoparticles and nanoparticle aggregates responsible for this effect reveals that Au nanospheres, nanoshells, and nanoshell dimers each exhibit unique wavelength-dependent suppression-enhancement characteristics. In contrast, silica nanospheres provide a sizable and relatively uniform photocurrent enhancement across the same spectral range (532-980 nm). Unusual light-harvesting behavior observed correlates with a highly complex energy flow (optical "vortexing") for the forward scattered light of plasmon resonant nanoparticles into the device.     

New model for the internal quantum efficiency of photodiodes based on photocurrent analysis

A new expression for the internal quantum efficiency of a photodiode is presented. It is obtained from the analysis of the photocurrent generated within the diode, considering the power and the cross-sectional diameter of the incident beam. The model explains variations of the internal quantum efficiency with irradiance that are not explained by other existing models, although this experimental fact was already known. The well-known phenomenon of supraresponsivity is also explained with this model. Finally, we show the dependence of the internal quantum efficiency on the variables involved in the model.     

Characterization of novel active area silicon avalanche photodiodes operating in the geiger mode

Abstract

We present a method for characterizing avalanche photodiode (APD) photon-counting detector efficiency as a function of active area. Various shallow-junction silicon APDs having a novel active area were manufactured and tested. We show that cylindrical and checkquerboard-shaped active areas have dark counts two orders of magnitude lower than standard circular devices with an equivalent active area. A parallel implementation of small active areas creates gettering sites for defects to migrate to, which is believed to create relatively defect-free active areas as the perimeter-to-area ratio is increased. However, a compromise between a large perimeter-to-area ratio and a structure useful for practical applications must be considered to optimize the detector.     

Single-photon counting for the 1300-1600-nm range by use of peltier-cooled and passively quenched InGaAs avalanche photodiodes

We evaluate the performance of various commercially available InGaAs/InP avalanche photodiodes for photon counting in the infrared at temperatures that can be reached by Peltier cooling. We find that dark count rates are high, and this can partially saturate devices before optimum performance is achieved. At low temperatures the dark count rate rises because of a strong contribution from correlated afterpulses. We discuss ways of suppressing these afterpulses for different photon-counting applications.     

The use of silicon photodiodes in a CsI(Tl) calorimeter

The properties of silicon photodiodes and low-noise preamplifiers have been studied. The selection of optimal operating parameters for the use of photodiodes in a CsI shower detector is discussed.     

Production and performance of the inFOCmicroS 20-40-keV graded multilayer mirror

The International Focusing Optics Collaboration for microCrab Sensitivity (InFOCmicroS) balloonborne hard x-ray telescope incorporates graded Pt/C multilayers replicated onto segmented Al foils to obtain the significant effective area at energies previously inaccessible to x-ray optics. Reflectivity measurements of individual foils demonstrate our capability to produce a mass quantity of multilayered foils with a rms roughness of 0.5 nm. The effective area of the completed mirror is 78 and 22 cm2 at 20 and 40 keV, respectively. The measured half-power diameter is 2.0 +/- 0.6 are min (90% confidence). The successful completion of this mirror demonstrates its applicability to future x-ray telescopes such as Constellation-X.     

Application of photoconductivity decay and photocurrent generation methods for determination of minority carrier lifetime in silicon

Minority carrier lifeline, τ, is one of the most important parameters which has a decisive effect on the performance of silicon devices based on excess carriers. The value of τ is greatly affected by the presence of impurities and defects in silicon and its value provides a fair indication of quality of the material. Photoconductivity decay (PCD) and photocurrent generation (PCG) methods are simple and low cost methods of measurement of minority carrier lifetime in silicon wafers. However, their application requires care. The PCD method can give quite misleading results in case of polycrystalline wafers if there exists potential barriers at the grain boundaries which may affect majority carrier mobility significantly. PCG needs creation of an inducedp ₊-p-n ₊ structure of substantially good quality that should not degrade with time. For PCG method the T measurement under vacuum conditions provides correct and consistent results.     

Annealing behavior of thin polycrystalline silicon films damaged by silicon ion implantation in the critical amorphization range

Thin polycrystalline silicon films were amorphized by silicon ion implantation at two different angles and subsequently annealed at 525°C. The structure of the as-deposited, as-implanted and annealed films was examined using Raman spectroscopy, transmission electron microscopy and the optical appearance method. Two distinct phases were found to coexist in the as-implanted films: one phase consists of a mosaic of crystallites surrounded by amorphous silicon and the other consists of only amorphous silicon. The mosaic phase was due to ion beam channeling through properly oriented polycrystalline grains. The implantation angle was found to determine whether the film recrystallizes upon annealing by a solid phase epitaxial mechanism using the surviving crystallites as seeds.     

Measurements of the mechanical Q of single-crystal silicon at low temperatures

Measurements of the mechanical quality factor Q in a single crystal of silicon vs. temperature have been made. A value of 2 × 10⁹ has been measured at T = 3.5K.Supported in part by the National Science Foundation.     

Giant enhancement of the carrier mobility in silicon nanowires with diamond coating

We show theoretically that the low-field carrier mobility in silicon nanowires can be greatly enhanced by embedding the nanowires within a hard material such as diamond. The electron mobility in the cylindrical silicon nanowires with 4-nm diameter, which are coated with diamond, is 2 orders of magnitude higher at 10 K and a factor of 2 higher at room temperature than the mobility in a free-standing silicon nanowire. The importance of this result for the downscaled architectures and possible silicon-carbon nanoelectronic devices is augmented by an extra benefit of diamond, a superior heat conductor, for thermal management.     

Photoresponse of a silicon multipixel photon counter in the vacuum ultraviolet range

Photoresponse of a silicon multipixel photon counter (MPPC) operating in the Geiger breakdown regime has been studied at wavelengths λ = 115, 121, 128, 160, and 175 nm. It is established that radiation intensity at these wavelengths can be measured by MPPC at room temperature in the photon-count mode with efficiency on a level of 2%.     

Measurements of superconducting Nb3Sn cavities in the GHz range

Superconducting Nb3Sn Cavities have potential advantages over rf cavities with Nb surfaces To test possible applications and to improve the understanding of Nb3Sn coatings on Nb, rf cavities have been measured between 1.5 and 8K and between 0.1 and 7GHz. The temperature dependence of the surface resistance R(T) indicates weak superconducting spots with transition temperaturesTmin{c}max{ast} < 1K andTmin{c}max{ast} simeq 2.5K. The normal conducting spotsTmin{c}max{ast} lsim 1K cause the large rf residual lossesR'_{res} propto f^{2}observed up to date. The spots withTmin_{c}max_{ast} simeq 2.5K cause temperature dependences ofR'(T)between 2 and 6K, where RBCS(Nb3Sn) is still negligible. In line withR_{res} propto f^{2}, the lowest rf lossesR_{res} < 2.10^{-9}Omegaand the highest field strengthB_{crit} = 83 m^{T}(wedgeE_{peak} = 29have been observed at the lowest frequency 0.1GHz measured. Surface resistance and penetration depth measurements have shown that grain boundaries or hydrogen clusters do not cause the weak spots observed withTmin{c}max{ast} < 2.5K. The origin and the chemistry of the weak spots withTmin{c}max{ast} lsim 1K, which cause the largeR_{res} propto f^{2}and the lowB_{crit} (T) simeq const, are still not clear. They seem related to the Nb3Sn surface. The weak spots withTmin{c}max{ast} simeq 2.5K consist most likely of Nb6Sn5, which in cooling below 950°C precipitates due to the excess Sn present in Nb3Sn coatings grown in Sn vapor.     

Absorption enhancement of near infrared in Te doped nanoporous silicon

In this paper, the optical properties of Te doped nanoporous silicon have been studied. The nanoporous silicon was fabricated by using alkaline etching and electrochemical anodization. The etched nanoporous silicon was injected with Te atoms by ion implantation. These nanostructures formed in electrochemical anodization directly affect the optical properties of nanoporous silicon such as reflectance, transmittance and absorptance. According to the optical measurement, the absorptance of the Te doped nanoporous silicon is over 80 % in the wavelength range from 250 to 1,100 nm. The absorptance of Te doped nanoporous silicon at wavelength longer than 1,100 nm is almost four times of that of untreated silicon, indicating that the ion implantation of Te element increases the NIR absorption of nanoporous silicon considerably.     

建筑材料放射性现场检测

本文对影响建材表面γ空气比释动能率测量的几个因素作了研究，提出 了一种建材放射性现场检测力法和剂量限制要求，并对实验和理论计算结果进行了讨论，二者之间有较好的一致性。