Si Photodetectors Research Articles

Wavelength-Tunable Multispectral Photodetector With Both Ultraviolet and Near-Infrared Narrowband Detection Capability

The development of high-performance multispectral photodetector with narrowband and tunable spectral sensitivity is of importance but remains highly challenging to date. Here, we have reported on the fabrication of a Si Au/n-type Si/Au photodetector with tunable narrowband sensitivity not only in ultraviolet but also in near-infrared region, which is related to the controlled charge collection narrowing (CCN) mechanism. What is more, the negative response peak of the device can be readily tuned from 365 to 605 nm, and the positive response peak can be modulated from 938 to 970 nm when the bias varies from 0.1 to −0.1 V. In particular, the full-width at half-maximum is as small as 92 and 117 nm when the negative and positive response peaks approach the ultraviolet short wavelength end and near-infrared long wavelength end, respectively. The opposite polarity of the device responses in ultraviolet-visible and near-infrared regions renders the present Si photodetector potentially important in future multiple band optoelectronic systems.

Fast Wafer-Level Characterization of Silicon Photodetectors by Photoluminescence Imaging

Photoluminescence imaging (PLI) technique is conventionally used in silicon (Si) photovoltaics (PV) for device characterization and inline quality control, providing substantial assistance for a wafer-level process monitoring from as-cut wafers to fully fabricated devices. Surprisingly, employing this method has not spread outside PV, and thus, its potential remains largely unknown in other fields. In this case study, a fully processed Si photodetector wafer, consisting of photodiodes with various sizes, has been chosen as an example to explore the potential of PLI beyond PV. First, we show that the standard PLI measurement is able to provide a high-resolution full-wafer luminescence image of the complete devices only within a couple of seconds. The image reveals various types of inhomogeneities present in the devices, such as furnace contamination and other processing-induced defects. The measured data are then converted to an effective lifetime image followed by benchmarking with a conventionally measured recombination lifetime map obtained by microwave-detected photoconductance decay (<inline-formula> <tex-math notation="LaTeX">$\mu $ </tex-math></inline-formula>-PCD), demonstrating further superiority of PLI in terms of the spatial resolution and the measurement time. Finally, correlation with diode leakage current and photoresponse measurements show that PLI is able to provide useful information on the final device performance without a need for traditional electrical contact measurements. While this study has focused on Si photodetectors, the results imply that PLI also has potential in other semiconductor devices for fast wafer-level process monitoring purposes as well as for a single device characterization either before or after wafer dicing.

Hybrid Silicon‐Polymer Photodetector Engineered Using Oxidative Chemical Vapor Deposition for High‐Performance and Bias‐Switchable Multi‐Functionality

AbstractBlack silicon (b‐Si) featured by anti‐reflective surfaces is extensively studied to realize highly sensitive photodetectors. The key to augmenting the light‐detection capability of b‐Si is to facilitate charge extraction while limiting undesired recombination events at surface defects. To this end, oxidative chemical vapor deposition (oCVD) is leveraged to form a highly conformal and conductive (3000 S cm−1) organic transport layer, poly(3,4‐ethylenedioxythiophene) (PEDOT), on b‐Si nanostructures. The oCVD PEDOT instrumentally extracts photo‐induced charges, through which b‐Si photodetectors implementing oCVD PEDOT achieve a superior photo‐detectivity of 1.37 × 1013 Jones. Furthermore, by engineering the pore dimension of b‐Si, a mode‐tunable Si photodetector is contrived, where the functions of broad‐band and visible‐blinded modes are switched facile by a bias polarity. The unprecedented device paves the way for extending the applications of Si detectors toward novel sensory platforms such as night‐vision, motion tracking, and bio‐sensing.

Patterning of Wafer-Scale MXene Films for High-Performance Image Sensor Arrays.

As a rapidly growing family of 2D transition metal carbides and nitrides, MXenes are recognized as promising materials for the development of future electronics and optoelectronics. So far, the reported patterning methods for MXene films lack efficiency, resolution, and compatibility, resulting in limited device integration and performance. Here, a high-performance MXene image sensor array fabricated by a wafer-scale combination patterning method of an MXene film is reported. This method combines MXene centrifugation, spin-coating, photolithography, and dry-etching and is highly compatible with mainstream semiconductor processing, with a resolution up to 2µm, which is at least 100 times higher than other large-area patterning methods reported previously. As a result, a high-density integrated array of 1024-pixel Ti3 C2 Tx /Si photodetectors with a detectivity of 7.73 × 1014 Jones and a light-dark current ratio (Ilight /Idark ) of 6.22 × 106 , which is the ultrahigh value among all reported MXene-based photodetectors, is fabricated. This patterning technique paves a way for large-scale high-performance MXetronics compatible with mainstream semiconductor processes.

Visible‐Blind ZnMgO Colloidal Quantum Dot Downconverters Expand Silicon CMOS Sensors Spectral Coverage into Ultraviolet and Enable UV‐Band Discrimination

Selective spectral detection of ultraviolet (UV) radiation is highly important across numerous fields from health and safety to industrial and environmental monitoring applications. Herein, a nontoxic, visible-blind, quantum dot (QD)-based sensing scheme that expands the spectral coverage of silicon complementary metal-oxide-semiconductor (CMOS) sensors into the UV, enabling efficient UV detection without affecting the sensor performance in the visible and UV-band discrimination, is reported. This scheme uses zinc magnesium oxide (ZnMgO) QDs with compositionally tunable absorption across UV and high photoluminescence quantum yield in the visible. The efficient luminescence and large Stokes shift of these QDs are exploited herein to act as an efficient downconverting material that enhances the UV sensitivity of Si-photodetectors (Si-PDs). A Si-PD integrated with the QDs results in a ninefold improvement in photoresponsivity from 0.83 to 7.5mA W-1 at 260nm. Leveraging the tunability of these QDs, a simple UV-band identification scheme is further reported, which uses two distinct-bandgap ZnMgO QDs stacked in a tandem architecture whose spectral emission color depends on the UV-band excitation light. The downconverting stack enables facile discrimination of UV light using a standard CMOS image sensor (camera) or by the naked eye and avoids the use of complex optics.

Ultraviolet-Visible-Near Infrared Broadband Photodetector Based on Electronspun Disorder ZnO Nanowires/Ge Quantum Dots Hybrid Structure

Ultraviolet-visible-near infrared broadband photodetectors have significant prospects in many fields such as image sensing, communication, chemical sensing, and day and nighttime surveillance. Hybrid one-dimensional (1D) and zero-dimensional (0D) materials are attractive for broadband-responsive photodetectors since its unique charges transfer characteristics and facile fabrication processes. Herein, a Si/ZnO nanowires/Ge quantum dots photodetector has been constructed via processes that combined electrospinning and spin-coating methods. A broadband response behavior from ultraviolet to near-infrared (from 250 to 1550 nm) is observed. The responsivity of the hybrid structure increases around three times from 550 to 1100 nm compared with the pure Si photodetector. Moreover, when the photodetector is illuminated by a light source exceeding 1100 nm, such as 1310 and 1550 nm, there is also a significant photoresponse. Additionally, the ZnO NWs/Ge quantum dots heterostructure is expected to be used in flexible substrates, which benefits from electrospinning and spin-coating processes. The strategy that combines 1D ZnO NWs and 0D solution-processed Ge QDs nanostructures may open a new avenue for flexible and broadband photodetector.

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.

Strain—Engineered Asymmetrical Si/Si1–xGex IR-Photo-Detector: Theoretical Reliability and Experimental Feasibility Studies

This paper reports the prospect of strained Si/Si1-xGex nano-scale p++-i-n++ photo-detector in the infrared (IR) wavelength region (1000nm-2200nm). The proposed device is capable of offering high photo-responsivity and quantum efficiency at 1600 nm wavelength in comparison to the unstrained conventional Si based pin photo-detector device. The authors have developed a Quantum Modified Drift Diffusion Model to analyze the nano-scale properties of strained Si photo-detector device. The analysis reveals that the strained Si based pin photo-detector offers high photo responsivity 0.67 A/W at 1600nm wavelength and quantum efficiency 0.60 at the same wavelength compared to the conventional unstrained Si based photo-detector. The enhancements of the photo electric characteristics of the Si photo device are obtained by incorporating selective amount of Ge into the Si active region. The electrical properties in the strained Si semiconductor at room temperature (300K), have made this material more attractive for being used as a photodetector. Due to the incorporation of this Ge layer, in-plane biaxial strain is produced in the active region. This phenomenon enhances the out-of-plane mobility of charge carriers. In this current research, in-plane strain is used to boost up the outplane mobility depending on the geometrical structure of the active region. The validity of the proposed model is established by comparing the simulated data with the corresponding experimental results. The authors also report the reliability study of the proposed device in details. Further, the authors have developed a 4x4 array type photo-detector based on the strained Si structure and the results are compared with the corresponding single array type photo-detector. In case of the 4x4 array type photo detector, the photo electric characteristics i.e. photo responsivity and quantum efficiency increase to 0.74 A/W and 0.69 respectively at 1600nm wavelength. In IR wavelength region, the designed photo-sensor depicts a significant improvement of performance compared to the available photo-detector in published research work. The proposed photo-detector can play an important role in Biomedical, Defence and Agro industries. According to the authors’ knowledge, this is the first report on strain engineered nano scale asymmetrical Si/Si1-xGex based photo-detector array.

Correlation between deep-level defects and functional properties of β-(SnxGa1-x)2O3 on Si photodetectors

Heterogeneous integration of β-(SnxGa1−x)2O3 (TGO) UV-C photodetectors on silicon substrates by molecular beam epitaxy is demonstrated. Multimodal electron microscopy and spectroscopy techniques reveal a direct correlation between structural, compositional, and optical properties of TGO and the functional properties of the photodetectors. Wavelength dispersive x-ray spectroscopy results accurately determine Sn concentrations (x) in the region of 0.020, and room temperature cathodoluminescence (CL) hyperspectral imaging shows changes in the CL emission intensity in TGO compared with a Ga2O3 sample with no Sn. Alloying Ga2O3 with Sn is shown to quench the red emission and enhance the blue emission. The increase in blue emission corresponds to the rise in VGa-related deep acceptors responsible for the high gain observed in the TGO detectors. A Ga2O3 nucleation layer is shown to improve the TGO surface quality and give better device properties compared to TGO grown directly onto the Si substrate, including a higher specific detectivity on the order of 1012 Jones.

Enhancing the ultraviolet response of silicon photodetectors using Yb3+-doped CsPbCl2Br nanocrystals glass with self-crystallization inhibited by ZnO

All-inorganic CsPbX3 (X = Cl, Br, I) perovskite nanocrystals (NCs) are the most promising next generation photoelectric materials owing to their excellent properties. Although embedding perovskite NCs into a glass matrix improves their stability, different applications require perovskite nanocrystal glasses (PNGs) with different properties. In this work, we controlled the network structure of the precursor glass by changing the content of ZnO (3.8–11.4 mol. %) in the raw materials, thus inhibiting the direct precipitation of CsPbCl2Br NCs in the glass (i.e., the self-crystallization process), and obtained samples with local emission and high transmittance. In addition, we incorporated rare-earth (RE) Yb3+ into a CsPbCl2Br PNG to achieve efficient ultraviolet (UV) to near-infrared quantum cutting emissions and boost the UV response of silicon photodetectors (PDs). Finally, after combining the Yb3+-doped CsPbCl2Br PNG on the Si PDs, the responsivity of the latter increased to 0.014 A/W at 320 nm, which is 14 times higher than that of the bare Si PDs. Moreover, Si PDs based on Yb3+-doped CsPbCl2Br PNG exhibited excellent photocurrent stability.

Investigation on dark current and photoresponsivity of flexible single-crystal semiconductor photodetectors on plastic substrates

High-performance flexible photodetectors have drawn increasing attentions, and the dark current and photoresponsivity are the major performance parameters. Investigations on the influence factors and operation mechanisms of the dark current and photoresponsivity for the flexible photodetectors are highly desirable. In this paper, flexible single-crystal Si and Ge photodetectors on polyethylene terephthalate (PET) substrates were fabricated and characterized. The transferred single-crystal Si and Ge nanomembranes on PET substrates showed good crystal quality by x-ray diffraction and Raman spectroscopy. Based on the experimental and modeling results, the performance dependences on semiconductor materials, doping concentrations, dimensions of the intrinsic region, incident light wavelength and power were presented. The influential factors and the operation mechanisms for the performance dependence were discussed by analyzing the electric field distribution, energy band distribution, recombination rate, absorption coefficient, penetration depth and photogeneration rate based on the device model. The results provided useful guidelines to design high performance flexible single-crystal semiconductor photodetectors.

Ultrawide-bandgap (6.14 eV) (AlGa)2O3/Ga2O3 heterostructure designed by lattice matching strategy for highly sensitive vacuum ultraviolet photodetection

One judiciously designed strategy of utilizing an ultrathin but conductive Ga2O3:Si nanolayer to prepare (AlGa)2O3 crystalline film is demonstrated. Benefiting from the existence of Ga2O3:Si nanolayer, a high-quality (Al0.68Ga0.32)2O3 sesquioxide film with 68 at.% aluminum was epitaxially grown on sapphire substrates, which was characterized by high-resolution transmission electron microscopy, X-ray photoelectron spectroscopy and X-ray diffraction. Its bandgap was broadened to 6.14 eV, and a vacuum ultraviolet (VUV) (AlGa)2O3/Ga2O3:Si photodetector was subsequently fabricated. The detector exhibits a pretty high on-off ratio of about 103, an open-circuit voltage of 1.0 V and a responsivity of 8.1 mA W−1 at 0 V bias voltage. The performances imply that the proposed strategy is valuable for improving the quality and also adjusting the bandgap of (AlGa)2O3 sesquioxides, which is expected to facilitate their application in VUV photodetection.

Sub-bandgap absorption and photo-response of molybdenum heavily doped black silicon fabricated by a femtosecond laser.

Molybdenum (Mo)-doped black silicon (Si) is obtained by using femtosecond laser irradiation. The concentration of Mo atoms at the depth from 10 to 200 nm has exceeded 1019cm-3. In contrast, the carrier concentration in the Mo-doped layer is lower than 1015cm-3. The surface morphologies with ripple and conical spike microstructures are formed by changing the pulsed laser fluences. The Mo-doped Si samples exhibit a sub-bandgap (1100∼2500nm) absorptance of more than 60% at a wavelength of 1310 nm. A Mo-doped Si photodetector is made, and the responsivity of the device for 1310 nm is up to 76 mA/W at a -10V bias.

Achieving high-responsivity near-infrared detection at room temperature by nano-Schottky junction arrays via a black silicon/platinum contact approach

A room temperature sub-bandgap near-infrared ( λ &gt; 1100 nm ) Si photodetector with high responsivity is achieved. The Si photodetector features black Si made by wet etching Si (100), Si/PtSi nano-Schottky junction arrays made from black Si/Pt contacts, and chemical and field-effect passivation of black Si. Responsivities are 147.6, 292.8, and 478.2 mA/W at reverse voltages of − 1.0 , − 1.5 , and − 2.0 V for 1550 nm light, respectively, with corresponding specific detectivities being 9.79 × 10 8 , 1.88 × 10 9 , and 2.97 × 10 9 cm · Hz 1 / 2 / W . This work demonstrates a practical room temperature sub-bandgap near-infrared Si photodetector that can be made in a facile and large-scale manner.

Preparation of nanostructured cerium-doped MnS/Si heterojunction photodetector by chemical spray pyrolysis: Influence of doping concentration

We report on the preparation of MnS/Si and cerium-doped MnS /Si heterojunction photodetectors by spray pyrolysis technique. The effect of doping concentration on the structural, optical and electrical properties of the MnS film was investigated. X–ray diffraction (XRD) data show that the pure MnS film was crystalline with mixed α-MnS and γ-MnS phases and the doped films exhibited poor crystallinity. Scanning electron microscope (SEM) results illustrate that the film doped with 1 wt% Ce has nanowires morphology, while the other films have spherical grains morphology. Energy dispersive x-ray (EDX) and elemental mapping showed the presence of cerium, magnesium and sulfur elements. The optical transmittance of the film decreases as doping concentration increase. The optical energy gap of decreased from 2.8 eV to 2.58 eV after cerium doping with 3 wt%. Raman spectra of pure MnS and Ce-doped MnS films revealed the presence of vibration mode at 365 and 635 cm−1. The electrical resistivity and mobility of the film after doping with different contents of Ce were measured. The figures of merit of the MnS:Ce/Si heterojunction photodetector as a function of doping concentration were investigated. The current-voltage characteristics under dark and illuminated conditions were investigated. The maximum responsivity was 0.71 A/W at 350 nm for the Mn:Ce (1 wt%)/Si photodetector.

Efficient Er/O Doped Silicon Photodiodes at Communication Wavelengths by Deep Cooling

AbstractWide band infrared photodetectors have found a wide range of applications in sensing, communication, and spectral analysis. However, the commonly used infrared photodetectors are based on Ge and III‐V semiconductors which are not complementary metal‐oxide‐semiconductor (CMOS) compatible and therefore have limited applications. There is a huge demand for silicon‐based infrared photodetectors due to its low‐cost and compatibility with CMOS processes. Nevertheless, the spectral bandwidth of Si photodetectors is limited to wavelengths below 1.1 µm. Several approaches are developed to extend Si photodetection bandwidth to communication wavelengths. Er/O doped Si is a promising approach which, however, suffers from low infrared responsivities at room temperature when the samples are treated with the standard rapid thermal annealing (RTA). In this work, a novel deep cooling process to treat Er/O doped silicon waveguide photodiodes is applied. In comparison with RTA process, the deep cooling process reduces the defect concentration in silicon by two orders of magnitude, resulting in a two‐orders‐of‐magnitude reduction in leakage current density and an enhanced photoresponsivity to 100 mA W−1 at 1510 nm. The 3dB bandwidth of the silicon waveguide photodiode reaches 30 kHz. The device performance can be further improved by optimizing the deep cooling condition and Er/O doping concentration.

Energy Down-Conversion Cs3Cu2Cl5 Nanocrystals for Boosting the Efficiency of UV Photodetector

Zero-dimension (0-D) lead halide perovskite nanocrystals (NCs) have attracted a sight of interest in the field of optoelectronic devices due to their outstanding properties, such as high photoluminescence quantum yield (PLQY) and size- and composition-controlled tunable emission wavelengths. However, the toxicity of lead (Pb) element in the lead perovskite NCs is the bottleneck for the commercial application of perovskite NCs. Herein, we report a facile ligand-assisted synthesis to achieve lead-free Cs3Cu2Cl5 NCs with a high PLQY of ∼70% and good stability against environmental oxygen/moisture as a promising down-conversion material. It has good merits of high PLQY and large Stokes shift (∼300 nm) originated from the effect of Jahn–Teller distortion and self-trapped excitons (STEs). Furthermore, the Cs3Cu2Cl5 NCs embedded composite films (NCCFs) were utilized to enhance the ultraviolet (UV) response of silicon (Si) photodetectors. External quantum efficiency (EQE) measurements show that the UV response can be greatly improved from 3.3 to 19.9% @ 295 nm based on NCCFs combined with Si photodiodes. Our work offers an effective approach to develop highly efficient and stable lead-free Cs3Cu2Cl5 NCs for the application in the solar-blind UV photodetector.

Integrated all-Si traveling-wave optical modulators and photodetectors operating beyond 40 GHz

We present high-speed, traveling-wave (TW) Si Mach–Zehnder modulators and Si sub-bandgap photodetectors (SBPD) monolithically integrated on an Si-only photonics platform without incorporation of Ge epitaxial growth process. Through constructing a detailed equivalent circuit model on the components, we design the device structure and TW electrodes for operating the device with bandwidth beyond 40 GHz. The experimental results show the 3-dB bandwidths of the Si modulator and photodetectors are 35 and 44 GHz, respectively, generally agreeing well with our design. The measured photoresponsivity of the SBPD varies from 0.1 A / W to nearly 1 A / W, depending on the bias voltage. These two components potentially can be utilized for an integrated optical transceiver operating for 50 Gbit / s data transmission.

Solution processed transparent anatase TiO2 nanoparticles/MoO3 nanostructures heterojunction: high performance self-powered UV detector for low-power and low-light applications.

Ultraviolet (UV) photodetectors are considered as the major players in energy saving technology of the future. Efforts are needed to further develop such devices, which are capable of operating efficiently at low driving potential as well as with weak illumination. Herein, we report an all-oxide, highly transparent TiO2/MoO3 bilayer film, with nanoparticulate anatase TiO2 as the platform, fabricated by a simple solution based method and demonstrate its use in UV photodetection. Photoconductivity measurement with 352 nm light reveals the self-powered UV detection capability of the device due to the built-in potential at the bilayer interface. The device exhibits a high photoresponsivity (46.05 A W−1), detectivity (2.84 × 1012 Jones) and EQE (16 223%) even with a weak illumination of 76 μW cm−2, at a low bias of only −1 V. The self-powered performance of the bilayer device is comparable to that of commercial Si photodetectors as well as other such UV detectors reported based on metal oxide heterojunctions. The improved and faster photoresponse shown by the device is due to the formation of an effective heterojunction, as evidenced by XPS, electrochemical and I–V studies. It can be further attributed to the better charge transport through the densely aligned nanostructures, reduced recombination and the better mobility of anatase TiO2 nanoparticles. The performance is best-in-class and proves the potential of the transparent heterojunction to be used in highly responsive, self-powered UV detectors for low bias, low light applications.

Improved of the ZnO:ZrO &lt;sub&gt;2&lt;/sub&gt; Composite Fibers (Fs)/ &lt;i&gt;n&lt;/i&gt;-Si Photodetector for Long-Term Reliable, Self-Powered and Highly Sensitive Properties

Improved of the ZnO:ZrO &lt;sub&gt;2&lt;/sub&gt; Composite Fibers (Fs)/ &lt;i&gt;n&lt;/i&gt;-Si Photodetector for Long-Term Reliable, Self-Powered and Highly Sensitive Properties