Si-based Detectors Research Articles

Patterned 3D-graphene for self-powered broadband photodetector

The remarkable ultra-wideband energy capabilities of zero-bandgap two-dimensional (2D) graphene have made it an outstanding material for photon absorption and charge carrier generation across a broad spectrum. However, atomically thick 2D-graphene only exhibits a light absorption efficiency of 2.3%, posing a challenge for graphene-based photodetectors to harness photon energy effectively. This study utilized plasma-enhanced chemical vapor deposition technology and a mask to create in situ patterned 3D-graphene/Si-based Schottky heterojunctions. The porous structure and natural nano-resonant cavities of the 3D-graphene enhanced the probability of light absorption, while the curved and sharp edges and corners of the patterned 3D-graphene concentrated the local electromagnetic field and induced localized surface plasmon resonance. Both theoretical and experimental analyses confirmed the improved light absorption mechanisms and charge transfer of photogenerated carriers under the built-in electric field. The photodetector based on the patterned 3D-graphene/Si Schottky structure exhibits excellent broadband response characteristics spanning from 380 to 1550 nm, with responsivity and specific detectivity of 68.47 A/W and 1.43 × 1012 Jones at a wavelength of 1550 nm. Furthermore, the photodetector demonstrated ultrafast microsecond-level response times (116/120 μs rise/fall times) along with exceptional stability and reliability. The potential applications of as-fabricated photodetector include logic devices such as “AND” and “OR” gates and information encryption. This research holds valuable scientific significance for the design of future optoelectronic devices and provides crucial insights and technical support for developing high-performance Si-based graphene detectors.

Near-infrared imaging via upconversion in Er3+:CaF2 crystal with dual wavelength excitation.

We propose a system for imaging 1510 nm near-infrared (NIR) wavelength via upconversion (UC) luminescence in an Er3+-doped CaF2 crystal. Er3+ ions are excited from the ground to the excited state levels by an 800-nm pre-excitation wavelength, followed by the promotion of these ions to a higher energy level by the NIR excitation wavelength. Relaxation of these excited ions gives rise to 540 nm UC luminescence in the visible region, enabling the detection of the 1510 nm NIR wavelength. Using this UC scheme, 1510 nm was successfully imaged. Our system enables imaging of NIR wavelengths using low-cost optics and readily available Si-based detectors that are sensitive only to visible wavelengths, opening new possibilities for detection and imaging of NIR wavelengths.

Solar blind avalanche photodetector based on a n-β-Ga2O3/n-Si heterojunction via an introduction of AlN buffer layer for interface lattice and band Engineering

The ultrawide-band gap semiconductor Ga2O3 as a photodetector heteroepitaxially grown on Si is expected to be widely used for weak solar-blind signal detections because the optical filters typically used in Si-based UV detectors can be avoided. Photodetectors fabricated from Ga2O3/Si are promising for multi-color detection (Ga2O3-based for UV and Si-based for visible/IR) and are more compatible with traditional Si-based electronic circuits. This paper proposes an n-type semiconductor-barrier-n-type semiconductor (n/B/n) with a unipolar barrier β-Ga2O3/AlN/n-Si heterostructure as a solar-blind avalanche photodetector. Introducing the AlN buffer layer eliminates the native amorphous SiOx layer, reduces lattice mismatch between β-Ga2O3 and Si, and improves the quality of β-Ga2O3 crystallization. Embedding AlN increases the conduction band shift of β-Ga2O3/Si, limits electron migration, reduces device dark current, and increases the reverse breakdown voltage. The β-Ga2O3/AlN (150 nm)/n-Si heterostructure has a high responsivity of 131.3 A/W with a detectivity of 2.9 × 1015 Jones, and an ultrahigh UV/visible (Rpeak/R400nm) rejection ratio of 5.2 × 105 at −55 V. The avalanche gain can also reach 2.7 × 104 at an 85 V reverse bias. This work provides an effective strategy for constructing a high-performance avalanche solar-blind-UV/visible/IR as a multi-color photodetector on one “chip” of a Si-based integrated circuit.

Enhancing radiation-hardness of Si-based diodes: An investigation of Al-doping effects in Si using I–V measurements

The impact of radiation on Si-based detectors garnered interest due to the observed degradation in their stability in high-radiation environments. In this study, we examined the effects of 3 MeV proton irradiation on both undoped and Al-doped n-Si diodes using I–V technique. The results revealed a decline in current trends for both types of diodes post-irradiation. This decrease was attributed to defects created by proton irradiation, which acted as recombination or trapping centres. However, the Al-doped n-Si diodes experienced a lesser decline in measured current, hinting at the radiation suppression effect of Al doping in Si. Additionally, Al-doped n-Si diodes displayed minimal changes in their diode parameters after irradiation, and their conduction mechanism remained unchanged. These results suggested that Al-doped n-Si diodes had superior stability compared to their undoped counterparts, implying that the presence of Al enhanced the diodes' resistance to radiation. The radiation suppression effect of Al seemed to stem from its ability to produce defects that improve Si's radiation-hardness, thereby mitigating the introduction of additional instability-causing defects during proton irradiation. Thus, incorporating Al was recommended for research aiming to improve the radiation resistance of Si.

Characterization of the Performance of a Thin Si-based Timepix3 Detector at 10-30 keV Electron Energies.

Characterization of the Performance of a Thin Si-based Timepix3 Detector at 10-30 keV Electron Energies.

Wide-field-of-view optical detectors for deep ultraviolet light communication using all-inorganic CsPbBr3 perovskite nanocrystals.

Optical wireless communication (OWC) links suffer from strict requirements of pointing, acquisition, and tracking (PAT) between the transmitter and receiver. Extending the narrow field-of-view (FoV) of conventional light-focusing elements at the receiver side can relax the PAT requirements. Herein, we use all-inorganic CsPbBr3 nanocrystals (NCs) to extend various optical concentrators' FOV to 60°, regardless of the original FOV values of the concentrators. Given the robustness of UV light against communication channel misalignment, the used CsPbBr3 NCs provide another advantage of converting transmitted UVC light into a green color that matches the peak absorption of the widely available Si-based detectors. We evaluated the feasibility of the reported wide FoV optical detectors by including them in deep UV OWC systems, deploying non-return-to-zero on-off keying (NRZ-OOK) and orthogonal-frequency division multiplexing (OFDM) modulation schemes. The NRZ-OOK and OFDM schemes exhibit stable communication over the 60° FoV, providing data transmission rates of 100 Mb/s and 71.6 Mb/s, respectively, a unique capability to the reported design.

Up-converted photorefractive optical transient detection with femtosecond laser pulses.

We report on experimental demonstration of optical transient detection (OTD) based on photorefractive two-wave mixing of femtosecond pulses. The demonstrated technique also combines nonlinear-crystal-based OTD with up-conversion from infrared into the visible range. The approach enables measurement of phase changes of a dynamic signal in the infrared using GaP- or Si-based detectors while suppressing stationary background. Experimental results reveal existence of the relation between input phases in the infrared and output phases in the visible wavelength range. We further present experimental evidence of additional merits of up-converted transient phase analysis under noisy conditions, such as residual continuous-wave emission affecting the ultrashort pulses from the laser.

Improved epitaxy of CsI(Tl) film on Si substrate buffered by graphene for X-ray detection

The growth of the CsI(Tl) scintillators deposited on glass substrates with proper wavelength matching the mainstream semiconductor circuits is crucial for X-ray imaging industry. But the coupling loss between the scintillators and silicon based photo sensors has limited the performance. So fabricating CsI(Tl) films on monocrystalline silicon is greatly important for next-generation high performance X-ray image devices. However, the lattice and thermal mismatch between CsI(Tl) and Si always deteriorates the morphology and structure, and thus degrades the property of the CsI(Tl) scintillation converters. Here, by utilizing crystalline graphene(Gr) as a buffer layer, the van der Waals epitaxial growth of CsI(Tl) film on Si(111) substrate is reported and its advanced applications are demonstrated. The introduced graphene buffer layer extremely frees the stress between CsI(Tl) and Si substrate. Therefore, the CsI(Tl) films show perfect micro-columnar and crystalline structures, and then, exhibit much higher light output and signal to noise ratio, and better modulation transfer functions and a bar pattern X-ray image compared to that on bare Si(111) substrate. This facile method not only lays the foundation for the epitaxy of the alkali halide crystals, including CsI(Tl), onto Si-based detectors and its applications in radiation detection, but also may broaden a new perspective of deposition of CsI(Tl) scintillators into flexible substrates.

Perovskite colloidal quantum-dot enhanced graphene/silicon heterojunction with improved ultraviolet response

Silicon (Si) is a mature semiconductor detection material because of its appropriate bandgap, high reliability, and low-cost manufacturing process. However, the detection range of Si-based photodetectors is mainly restricted to visible and near-infrared (NIR) ranges. Broadening the detection range of Si-based detectors to ultraviolet (UV) could ignite numerous applications, including flame detection, defense safety, and environmental monitoring. Here, the obtained perovskite colloidal quantum dots (QDs) with high quality are integrated with a Si/graphene heterojunction to broaden and improve response. By the electrical coupling mechanism between graphene and QDs, the built-in potential in detectors is maximized. As a result, the devices exhibit a high UV responsivity of 0.33 A W−1 at 210 nm, 0.73 A W−1 at 400 nm, and a superior detectivity of nearly 1012 Jones under the UV region. Aside from that, the performance of devices under visible and NIR ranges is also dramatically improved compared to that of the one without perovskite QDs.

The high-performance linear scan imaging system of terahertz Si-based blocked-impurity-band detector

Terahertz (THz) Si-based blocked-impurity-band (BIB) detector is becoming the overwhelming choice for applications in space-based instruments, airborne, and imaging systems. A high-performance linear scan imaging system based on the THz Si-based BIB detector is designed. Through the optimized design of cryogenic Dewar and a suitable optical system, the imaging system reduces background stray radiation, and then improves the THz imaging performance of the detector. At the temperature of 4.2 K and the bias of 2.6V, the blackbody peak responsivity of the Si-based BIB detector is 23.77A/W, while the dark current is 4.72×10−11 A and the corresponding responsivity non-uniformity is less than 6.8%. Moreover, the experiment results show that the noise equivalent temperature difference (NETD) of the whole system reaches 10mK, and the spatial resolution reaches 50 µm. This work is beneficial to the larger scale array integrated BIB imaging system.

The Anti-Reflection Coating Design for the Very-Long-Wave Infrared Si-Based Blocked Impurity Band Detectors

An anti-reflection coating on a back-illuminated 128 × 128 array Si-based blocked impurity band (BIB) detector in a very-long-wave infrared range was designed in this work. The reflectance and transmittance spectra of ZnS films with different thicknesses on intrinsic Si substrates were studied with a FDTD simulation and experiment. Compared to bare Si substrate, the reflectance of Si coated with 1.5, 2.0, 2.5, and 3.0 μm thick ZnS significantly decreased, while the transmittance increased in the range of 10.0~25.0 μm band. The transmittance enhancement ratio reached approximately 32%, 32%, 28%, and 29%, respectively. It was evidenced that the enhanced transmission at a specific wavelength was caused by the effective interference cancellation effect. Then, a 2.0 μm thick ZnS thin film was deposited on the backside of the 128 × 128 array Si-based BIB detector. The spectral responsivity of the detector increased significantly. Additionally, the blackbody responsivity increased by approximately 36%, suggesting that the ZnS film is an ideal anti-reflection material for VLWIR detectors in the range of 10.0~25.0 μm band.

High sensitivity of room-temperature terahertz photodetector based on silicon

SummarySilicon (Si) is the most important semiconductor material broadly used in both electronics and optoelectronics. However, the performance of Si-based room temperature detectors is far below the requirements for direct detection in the terahertz (THz) band, a very promising electromagnetic band for the next-generation technology. Here, we report a high sensitivity of room temperature THz photodetector utilizing the electromagnetic induced well mechanism with an SOI-based structure for easy integration. The detector achieves a responsivity of 122 kV W−1, noise equivalent power (NEP) of 0.16 pW Hz−1/2, and a fast response of 1.29 μs at room temperature. The acquired NEP of the detector is ∼2 orders lower in magnitude than that of other types of Si-based detectors. Our results pave the way to realize Si-based THz focal plane arrays, which can be used in a wide range of applications, such as medical diagnosis, remote sensing, and security inspection.

Demonstration of SWIR Silicon-Based Photodetection by Using Thin ITO/Au/Au Nanoparticles/n-Si Structure.

Plasmonic photodetection based on the hot-electron generation in nanostructures is a promising strategy for sub-band detection due to the high conversion efficiencies; however, it is plagued with the high dark current. In this paper, we have demonstrated the plasmonic photodetection with dark current suppression to create a Si-based broadband photodetector with enhanced performance in the short-wavelength infrared (SWIR) region. By hybridizing a 3 nm Au layer with the spherical Au nanoparticles (NPs) formed by rapid thermal annealing (RTA) on Si substrate, a well-behaved ITO/Au/Au NPs/n-Si Schottky photodetector with suppressed dark current and enhanced absorption in the SWIR region is obtained. This optimized detector shows a broad detection beyond 1200 nm and a high responsivity of 22.82 mA/W at 1310 nm at −1 V, as well as a low dark current density on the order of 10−5 A/cm2. Such a Si-based plasmon-enhanced detector with desirable performance in dark current will be a promising strategy for realization of the high SNR detector while keeping fabrication costs low.

Wavelength Modulation Characteristics of Metal Gratings on Si-Based Blocked-Impurity-Band (BIB) Terahertz Detectors.

In this work, the wavelength selection characteristics of metal gratings on Si-based blocked-impurity-band (BIB) detectors in the terahertz band were studied by performing experiments and a finite difference time domain (FDTD) simulation. The transmission spectra of metal gratings with different periods on 130 μm intrinsic Si substrates were measured. When the metal grating period increased from 16 to 20 to 32 μm, the peak position of the spectrum moved from 21.71 to 24.50 to 36.59 μm, which is in good agreement with the FDTD simulation results. The structure with the period of 32 μm shows the best wavelength selective transmission characteristics. Then, the bare Si-based BIB devices and metal grating/Si-based BIB hybrid devices with different thicknesses of blocking layers of 2 and 5 μm were fabricated. By covering different periods of metal gratings for the devices with a thicker blocking layer of 2 μm, we obtained more effective wavelength selection characteristics and stronger response spectra enhancement ratios that were about 1.3, 2.4, or 1.9 times. This was mainly due to the localized optical field enhancement effect of the plasmons resonance in metal gratings, which decays exponentially in a vertical direction. Our results demonstrate a new approach for the Si-based BIB detector to realize multiband selective detection applications.

An Alternative to Compound Semiconductors Using a Si-Based IR Detector

Though infrared (IR) photodetection is popular, it faces several problems. First, the main materials, compound semiconductors, require high temperature, low pressure, and high energy consumption facilities. Second, compound semiconductor elements are rare on earth. Third, compound semiconductors are difficult to integrate with Si-based integrated circuit (IC) manufacturing process. To overcome these problems, we utilized a Si-based Schottky junction and internal photoemission to break the detection limit of a Si photodetector. The spectral detection limit extends from 1100 nm, the bandgap wavelength of Si, to ca. 1600 nm, the Schottky barrier wavelength of the metal/Si junction. The Schottky junction is composed by Ag and n-type Si through simple thermal evaporation. The light incident direction, metal thickness, and device temperature were analyzed. As a result, under normal temperature and pressure, the Schottky barrier height of the Ag/Si junction is 0.742 eV. The detection limit is 1670 nm. If the 1550-nm laser is a detected light source illuminating from the metal film, the responsivity is 0.02122 mA/W. If the same detected light source illuminates from the Si substrate, the responsivity improves to 0.04567 mA/W due to the light absorption enhancement. Furthermore, if the metal thickness is increased to 100 nm, the responsivity increases to 1.242 mA/W, which is about 585.3% of the original value. In addition, the influence of the temperature on the electric properties of the devices indicates that a Ag/Si Schottky device could be a candidate for temperature detection.

Calibration of a versatile multi-energy soft x-ray diagnostic for WEST long pulse plasmas.

A compact multi-energy soft x-ray diagnostic is being installed on the W Environment in Steady-state Tokamak (WEST), which was designed and built to test ITER-like tungsten plasma facing components in a long pulse (∼1000 s) scenario. The diagnostic consists of a pinhole camera fielded with the PILATUS3 photon-counting Si-based detector (≲100 kpixel). The detector has sensitivity in the range 1.6-30 keV and enables energy discrimination, providing a higher energy resolution than conventional systems with metal foils and diodes with adequate space and time resolution (≲1 cm and 2 ms). The lower-absorption cut-off energy is set independently on each one of the ∼100 kpixels, providing a unique opportunity to measure simultaneously the plasma emissivity in multiple energy ranges and deduce a variety of plasma parameters (e.g., Te, nZ, and ΔZeff). The energy dependence of each pixel is calibrated here over the range 3-22keV. The detector is exposed to a variety of monochromatic sources-fluorescence emission from metallic targets-and for each pixel, the lower energy threshold is scanned to calibrate the energy dependence. The data are fit to a responsivity curve ("S-curve") that determines the mapping between the possible detector settings and the energy response for each pixel. Here, the calibration is performed for three energy ranges: low (2.3-6 keV), medium (4.5-13.5 keV), and high (5.4-21 keV). We determine the achievable energy resolutions for the low, medium, and high energy ranges as 330eV, 640eV, and 950 eV, respectively. The main limitation for the energy resolution is found to be the finite width of the S-curve.

Lithium source for focused ion beam implantation and analysis

We present a new Li source for focused ion beam applications. Based on an AuSi eutectic alloy, Li is added as an impurity to minimize effects from degradation when exposed to air. We show the source is stable over the course of an hour and spot sizes ≲10 nm can be achieved. The Li beam can achieve hundreds of nanometer ranges in semiconductors with minimal damage being generated along the path length. The source performance is evaluated through a high-resolution ion beam induced charge collection experiment on an Si-based detector. Further application of the source for ion beam analysis is numerically explored; the example investigated is based on probing a semiconductor heterostructure through a Rutherford backscattering experiment, where the Li beam can reveal information that is inaccessible with either low energy or high energy He projectiles used as probes.

Blocked impurity band very long wavelength infrared detector

Blocked impurity band (BIB) detector is a derivative of the impurity band conduction (IBC) detector. It can detect low-energy photons whose energy is much smaller than the band gap of the semiconductor through the electronic transition on the impurity band. The detection wavelength of the BIB detector is mainly determined by the substrate and doped impurities which can cover the range of 5–300 μm. Owing to the advantages of long detection wavelength, high detection rate and good radiation resistance, BIB detectors have been extensively studied and are widely used in various large-scale astronomical infrared detection platforms. Presently, Si-based BIB detectors are developing rapidly, but the development of Ge-based and GaAs-based BIB detectors is relatively slow. BIB detectors play an irreplaceable role in promoting the development of astronomy and related sciences. Developed countries such as Europe and the United States have invested a lot in scientific research on BIB detectors. With the development of China’s economy and technology, Chinese researchers hope eagerly that the domestic BIB detector can be put into use as soon as possible. Herein, in order to help the related researchers to quickly understand the BIB detector, the device physical model, preparation methods, testing methods and development status have been discussed, and the involved working mechanism and key device technology are also explored.

The High-Performance Imaging Verification of Si:P Blocked Impurity Band Detector for Very-Long-Wave-Infrared Spectral Range

Very-long-wave-infrared (VLWIR) photodetectors have attracted great attention from scientists worldwide in the ground and space-based detections, imaging and early warning. However, the application of VLWIR photodetectors on earth is limited by the difficulty of establishing a high spatial-resolution fine imaging system with high-performance detector and large size optical lens. In this work, the VLWIR Si-based blocked-impurity-band (BIB) detector is fabricated and its high-performance imaging system is constructed. The CVD growth progress is optimized by enhancing the doping concentration of absorption layer, and shortening the transition length between blocking and absorption layers. At the temperature of 4.2K, the blackbody responsivity of Si-based BIB detector reaches 20.78A/W and the Noise Equivalent Power is $8.7\times 10^{-16}\text{W}$ /Hz1/2 at 2.6V. Based on the high performance Si-based BIB detector, an imaging verifying system is set up to detect different room-temperature objects. Its spatial and temperature resolution reaches $250~\mu \text{m}$ and 10mK, respectively. Our results indicate that with suitable optical imaging system, the BIB detector is more effective than the infrared detector of commercial thermal infrared imager in detecting room temperature or low temperature objects like metal. Our work is helpful for the further research on the large scale array integrated BIB imaging and detection system used on earth for explosives detection, biological nondestructive detection as well as security check.

Study on the fabrication process and photoelectric performances of si-based blocked-impurity-band detector

The structural model and fabrication process of the Si-based blocked-impurity-band (BIB) detector were proposed. The numerical simulation of phosphorus ion implantation and rapid thermal annealing was investigated. Various implantation conditions were analyzed to meet the requirements of good electrical contact. Moreover, the carrier activation effect of phosphorus ion implantation and rapid thermal annealing was demonstrated by Hall test. Then the relationship between blackbody responsivity and annealing temperature was analyzed. According to the measurement results, the blackbody responsivity and response wavelength range of Si-based BIB detector we fabricated can reach 2.2A/W and 5–45 μm, respectively. Our work shows that the good electrical contact can improve the blackbody responsivity. It provides an effective method to fabricate Si-based BIB detector with good performances.