Improved Near-Infrared Spectral Responsivity Scale

A cryogenic radiometer-based system was constructed at the National Institute of Standards and Technology for absolute radiometric measurements to improve detector spectral power responsivity scales in the wavelength range from 900 nm to 1800 nm. In addition to the liquid-helium-cooled cryogenic radiometer, the system consists of a 100 W quartz-tungsten-halogen lamp light source and a 1 m single-grating monochromator for wavelength selection. The system was characterized and the uncertainty in spectral power responsivity measurements evaluated. A variety of photodetectors, including indium gallium arsenide photodiodes (InGaAs), germanium (Ge) photodiodes, and pyroelectric detectors, were subsequently calibrated. Over most of the spectral range, the spectral power responsivity of the photodetectors can be measured with a combined relative standard uncertainty of 0.4 % or less. This is more than a factor of two smaller than our previous capabilities, and represents a significant improvement in the near infrared (NIR) spectral power responsivity scale maintained at NIST. We discuss the characterization of the monochromator-based system and present results of photodetector spectral power responsivity calibrations.     

基于黑硅微结构的全硅PIN光电探测器

本文报道了一种基于黑硅微结构的全硅PIN光电探测器。该器件结合了黑硅结构宽光谱高吸收的特性,以及PIN光电探测器高量子效率高响应速度的特点,通过在传统硅PIN光电探测器结构的基础上增加黑硅微结构层,在不影响响应速度的条件下,提高了探测器在近红外波段响应特性。并且针对纵向结构垂直入射PIN光电探测器时量子效率与响应速度相矛盾的问题,提出了解决方案。测试结果表明,该器件的量子效率可达80%,峰值波长为940 nm,光响应度达到0.55 A/W,暗电流降至700 pA,响应时间为200 ns。     

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.     

A High-Performance Solution-Processed Organic Photodetector for Near-Infrared Sensing

Sensitive detection of near-infrared (NIR) light enables many important applications in both research and industry. Current organic photodetectors suffer from low NIR sensitivity typically due to early absorption cutoff, low responsivity, and/or large dark/noise current under bias. Herein, organic photodetectors based on a novel ultranarrow-bandgap nonfullerene acceptor, CO1-4Cl, are presented, showcasing a remarkable responsivity over 0.5 A W⁻¹ in the NIR spectral region (920–960 nm), which is the highest among organic photodiodes. By effectively delaying the onset of the space charge limited current and suppressing the shunt leakage current, the optimized devices show a large specific detectivity around 10¹² Jones for NIR spectral region up to 1010 nm, close to that of a commercial Si photodiode. The presented photodetectors can also be integrated in photoplethysmography for real-time heart-rate monitoring, suggesting its potential for practical applications.     

Development and Characterization of Sol-gel Derived Al Doped ZnO/p-Si Photodiode

The effect of Al doping on the J-V characteristics sol-gel derived of ZnO/p-Si photodiodes was investigated.The resistivity of Si was 0.1Ω·cm.ZnO films annealed at 500℃ were of the best quality.To investigate the spectral response of the photodiodes,the J-V characteristics were measured under different monochromatic lights at wavelength 420,530,570 and 630 nm.The diodes exhibit strong responsivity in the blue region at 420 nm.The responsivity is 0.22 A/W for Al doped (0.8 wt pct) photodiode,whereas for the undoped photodiode,it was much lower.An estimate of the responsivity as a function of wavelength has been made in terms of the width of depletion region of photodiodes.     

Numerical Modeling of Silicon Photodiodes for High-Accuracy Applications Part II. Interpreting Oxide-Bias Experiments

The semiconductor device modeling program PC-1D and the programs that support its use in high-accuracy modeling of photodiodes, all of which were described in Part I of this series of papers, are used to simulate oxide-bias self-calibration experiments on three different types of silicon photodiodes. It is shown that these simulations can be used to determine photodiode characteristics, including the internal quantum efficiency for the different types of photodiodes. In the latter case, the simulations provide more accurate values than can be determined by using the conventional data reduction procedure, and an uncertainty estimate can be derived. Finally, it is shown that 0.9997 ± 0.0003 is a nominal value for the internal quantum efficiency of one type of photodiode over the 440 to 460 nm spectral region.     

Stability under vacuum of silicon trap detectors and their use as transfer instruments in cryogenic radiometry

The stability of the responsivity of trap detectors under vacuum has been studied by means of a special chamber designed for the test of photodetectors at low pressure. The first experiments at a wavelength of 647 nm show that the responsivity variations are smaller than the uncertainties of the measurements, approximately 3 parts in 10(5), when the detector operates successively in air, under vacuum, and then again in air. Calculations based on experiments with single windowless photodiodes indicate that the change in trap responsivity that is due to vacuum effects should be smaller than 1 part in 10(5), at least in the visible part of the wavelength range. This stability makes trap detectors suitable for cryogenic radiometry when one uses transfer detectors under vacuum.     

Calibration of an extreme-ultraviolet transmission grating spectrometer with synchrotron radiation

The responsivity of an extreme-ultraviolet transmission grating spectrometer with silicon photodiode detectors was measured with synchrotron radiation. The spectrometer was designed to record the absolute radiation flux in a wavelength bandpass centered at 30 nm. The transmission grating had a period of 200 nm and relatively high efficiencies in the +1 and the -1 diffraction orders that were dispersed on either side of the zero-order beam. Three photodiodes were positioned to measure the signals in the zero order and in the +1 and -1 orders. The photodiodes had aluminum overcoatings that passed the desired wavelength bandpass centered at 30 nm and attenuated higher-order radiation and wavelengths longer than approximately 80 nm. The spectrometer's responsivity, the ratio of the photodiode current to the incident radiation power, was determined as a function of the incident wavelength and the angle of the spectrometer with respect to the incident radiation beam. The spectrometer's responsivity was consistent with the product of the photodiode responsivity and the grating efficiency, both of which were separately measured while removed from the spectrometer.     

Spectral reflectance and responsivity of Ge- and InGaAs-photodiodes in the near-infrared: measurement and model

The spectral reflectance and responsivity of Ge- and InGaAs-photodiodes at (nearly) normal and oblique incidence (45 degrees) were investigated. The derived data allow a calculation of the photodiodes responsivities for any incident angle. The measurements were carried out with s- and p-polarized radiation in the wavelength range from 1260 to 1640 nm. The spectral reflectance of the photodiodes was modeled by using the matrix approach developed for thin-film optical assemblies. The comparison between the calculated and measured reflectance shows a difference of less than 2% for the Ge-photodiode. For the InGaAs-photodiode, the differences between measured and calculated reflectance are larger, i.e., up to 6% for wavelengths between 1380 and 1580 nm. Despite the larger differences between calculated and measured spectral reflectances for the InGaAs-photodiode, the difference between calculated and measured spectral responsivity is even smaller for the InGaAs-photodiode than for the Ge-photodiode, i.e., < or =1.2% for the InGaAs-photodiode compared to < or =2.2% for the Ge-photodiode. This is because the difference in responsivity is strongly correlated to the absolute spectral reflectance level, which is much lower for the InGaAs-photodiode. This observation also shows the importance of having small reflectances, i.e., appropriate antireflection coatings for the photodiodes. The relative standard uncertainty associated with the modeled spectral responsivity is about 2.2% for the Ge-photodiode and about 1.2% for the InGaAs-photodiode for any incident angle over the whole spectral range measured. The data obtained for the photodiodes allow the calculation of the spectral responsivity of Ge- and InGaAs-trap detectors and the comparison with experimental results.     

Characteristics of III-nitride photodiodes with self-assembled quantum dots

In this work, it has been demonstrated that metal–semiconductor–metal (MSM) photodiodes (PDs) with InGaN self-assembled quantum dots (QDs) were fabricated and compared with conventional InGaN MSM photodiodes. The scanning near-field optical microscope (SNOM) results revealed that such InGaN nanostructures could have better absorption for the near-field light with the wavelength of 457–514 nm. It was found that the InGaN QD photodiode with lower dark current can operate in the normal incidence mode; we could achieve a much larger photocurrent to dark current contrast ratio from MSM photodiodes with nanoscale InGaN quantum dots. It was also found that the measured responsivity of MSM photodiodes with QDs and without QDs approximated to the same in the range of 390–460 nm. Furthermore, the photodiodes with QDs showed higher spectral response than that of the photodiodes without QDs at wavelengths < 350 nm and > 480 nm.     

Temperature Dependent Characteristics of Nonreach-Through 4H-SiC Separate Absorption and Multiplication APDs for UV Detection

Silicon carbide (SiC) separate absorption multiplication region avalanche photodiodes (SAM-APDs) for UV detection in harsh environment applications were designed and fabricated. The devices were intentionally designed to operate under nonreach-through conditions in order to eliminate field-induced leakage current. The gain of 2500 and quantum efficiency of ~45% at room temperature were achieved at the wavelength of 290-300 nm for a packaged device with an active area of 1 x 1 mm². The temperature dependency of the current-voltage characteristics and responsivity was examined in the temperature range from room temperature to 230degC.     

Effect of high-energy electron-beam irradiation on the optical properties of ion-beam-sputtered silicon oxynitride thin films

Silicon oxynitride thin films are prepared by ion-beam sputtering, and the optical properties and surface chemical composition are studied by spectrophotometric and x-ray photoelectron spectroscopy, respectively. It is seen that the films sputtered by use of nitrogen alone as the sputtering species from a silicon nitride target are completely transparent (k < 0.005) and have a refractive-index dispersion from 1.85 to 1.71 over the visible and near-infrared spectral regions, and the films show distinct spectral lines that are due to silicon, Si(2s), nitrogen, N(1s), and oxygen, O(1s). Sputter deposition of argon and of argon and nitrogen produces silicon-rich silicon oxynitride films that are absorbent and have high refractive indices. These films have a direct electronic transition, with a threshold energy of 1.75 eV. Electron irradiation transforms optically transparent silicon oxynitride films into silicon-rich silicon oxynitride films that have higher refractive indices and are optically absorbing owing to the presence of nonsaturated silicon in the irradiated films. The degradation in current responsivity of silicon photodetectors, under electron irradiation, is within 3% over the wavelength region from 450 to 750 nm, which is entirely due to the degradation of optical properties of silicon oxynitride antireflection coatings.     

Perovskite–Erbium Silicate Nanosheet Hybrid Waveguide Photodetectors at the Near‐Infrared Telecommunication Band

Methylammonium lead halide perovskites have attracted enormous attentions due to their superior optical and electronic properties. However, the photodetection at near‐infrared telecommunication wavelengths is hardly achievable because of their wide bandgaps. Here, this study demonstrates, for the first time, novel perovskite–erbium silicate nanosheet hybrid photodetectors with remarkable spectral response at ≈1.54 µm. Under the near‐infrared light illumination, the erbium silicate nanosheets can give strong upconversion luminescence, which will be well confined in their cavities and then be efficiently coupled into and simultaneously excite the adjacent perovskite to realize photodetection. These devices own prominent responsivity and external quantum efficiency as high as previously reported microscale silicon‐based subbandgap photodetectors. More importantly, the photoresponse speed (≈900 µs) is faster by five orders than the ever reported hot electron silicon‐based photodetectors at telecommunication wavelengths. The realization of perovskite‐based telecommunication band photodetectors will open new chances for applications in advanced integrated photonics devices and systems.     

Surface plasmon-enhanced nanopillar photodetectors

We demonstrate nanopillar-(NP) based plasmon-enhanced photodetectors (NP-PEPDs) operating in the near-infrared spectral regime. A novel fabrication technique produces subwavelength elongated nanoholes in a metal surface self-aligned to patterned NP arrays that acts as a 2D plasmonic crystal. Surface plasmon Polariton Bloch waves (SPP-BWs) are excited by the metal nanohole array resulting in electric field intensity "hot spots" in the NP. The NP periodicity determines the peak responsivity wavelength while the nanohole asymmetry produces polarization-dependent coupling of the SPP-BW modes. Resulting photodetectors have 0.28 A/W responsivity peaked at 1100 nm at a reverse bias of -5 V. Designs for further increasing the optical coupling efficiency into the nanopillar are explored. This technology has potential applications for plasmonically enhanced focal plane arrays and plasmonic photovoltaics.     

Piezo‐Phototronic Effect on Selective Electron or Hole Transport through Depletion Region of Vis–NIR Broadband Photodiode

Silicon underpins nearly all microelectronics today and will continue to do so for some decades to come. However, for silicon photonics, the indirect band gap of silicon and lack of adjustability severely limit its use in applications such as broadband photodiodes. Here, a high‐performance p‐Si/n‐ZnO broadband photodiode working in a wide wavelength range from visible to near‐infrared light with high sensitivity, fast response, and good stability is reported. The absorption of near‐infrared wavelength light is significantly enhanced due to the nanostructured/textured top surface. The general performance of the broadband photodiodes can be further improved by the piezo‐phototronic effect. The enhancement of responsivity can reach a maximum of 78% to 442 nm illumination, the linearity and saturation limit to 1060 nm light are also significantly increased by applying external strains. The photodiode is illuminated with different wavelength lights to selectively choose the photogenerated charge carriers (either electrons or holes) passing through the depletion region, to investigate the piezo‐phototronic effect on electron or hole transport separately for the first time. This is essential for studying the basic principles in order to develop a full understanding about piezotronics and it also enables the development of the better performance of optoelectronics.     

High‐Performance,Room Temperature,Ultra‐Broadband Photodetectors Based on Air‐Stable PdSe2

Photodetection over a broad spectral range is crucial for optoelectronic applications such as sensing, imaging, and communication. Herein, a high‐performance ultra‐broadband photodetector based on PdSe₂ with unique pentagonal atomic structure is reported. The photodetector responds from visible to mid‐infrared range (up to ≈4.05 µm), and operates stably in ambient and at room temperature. It promises improved applications compared to conventional mid‐infrared photodetectors. The highest responsivity and external quantum efficiency achieved are 708 A W^?1 and 82 700%, respectively, at the wavelength of 1064 nm. Efficient optical absorption beyond 8 µm is observed, indicating that the photodetection range can extend to longer than 4.05 µm. Owing to the low crystalline symmetry of layered PdSe₂, anisotropic properties of the photodetectors are observed. This emerging material shows potential for future infrared optoelectronics and novel devices in which anisotropic properties are desirable.     

International comparison of the spectral responsivities of silicon photodetectors

The results are considered of a comparison of the national scales of spectral responsivity of 18 national metrological laboratories including the All-Union Scientific-Research Institute of Optophysical Measurements (VNIIOFI) between themselves and with the scale of the International Bureau of Weights and Measures (BIPM) in the spectral wavelength range 250–1000 nm using two different types of silicon photodetector. The comparisons indicated satisfactory agreement between the results of measurements of spectral responsivity by the participating laboratories. The difference between the spectral responsivity scale of VNIIOFI and that of the BIPM did not exceed ±0.5% for the visible wavelength range and the near infrared. The maximum difference of the scales in the near ultraviolet wavelength range was 3.7%. Translated from Izmeritel'naya Tekhnika, No. 1, pp. 59–63, January, 1999.     

Ultra‐Broadband Flexible Photodetector Based on Topological Crystalline Insulator SnTe with High Responsivity

Topological crystalline insulators (TCIs) are predicted to be a promising candidate material for ultra‐broadband photodetectors ranging from ultraviolet (UV) to terahertz (THz) due to its gapless surface state and narrow bulk bandgap. However, the low responsivity of TCIs‐based photodetectors limits their further applications. In this regard, a high‐performance photodetector based on SnTe, a recently developed TCI, working in a broadband wavelength range from deep UV to mid‐IR with high responsivity is reported. By taking advantage of the strong light absorption and small bandgap of SnTe, photodetectors based on the as‐grown SnTe crystalline nanoflakes as well as specific short channel length achieve a high responsivity (71.11 A W^?1 at 254 nm, 49.03 A W^?1 at 635 nm, 10.91 A W^?1 at 1550 nm, and 4.17 A W^?1 at 4650 nm) and an ultra‐broad spectral response (254–4650 nm) simultaneously. Moreover, for the first time, a durable flexible SnTe photodetector fabricated directly on a polyethylene terephthalate film is demonstrated. These results prove the great potential of TCIs as a promising material for integrated and flexible optoelectronic devices.     

Thin-film optical sensors with silicon-compatible materials

Antireflection filters based on multilayer stacks of dielectric and polysilicon films on monocrystalline silicon combined with charge collection in different (poly)Si layers can be used to realize sensors with a programmable spectral response controlled by weighted summing of the photocurrents detected in the polysilicon and the substrate. Thus, employing both interference and selective absorption of light yields increased photoelectric efficiency and improved flexibility of spectral control and enables on-chip integration of the detector(s) with the signal conditioning and processing circuits. The potential of thin-film color sensors has been evaluated for this purpose. However, for practical implementation of such structures the problems associated with the realization of reliable photodetectors in polysilicon must also be considered. Phosphorus passivation of the grain-boundary states has been employed to yield polysilicon photodiodes with improved electrical characteristics and reliable light and color detection. We present the design methods of thin-film color sensors employing silicon-compatible materials only. The measurement results of a fabricated structure fully demonstrate that such sensors can be realized with good spectral selectivity.