Schottky Barrier Photodetectors Research Articles

Micropyramidal Si Photonics–A Versatile Platform for Detector and Emitter Applications

AbstractAnisotropic wet etching of silicon (Si) has been known for decades, but the extraordinary capabilities of this technology to provide highly ordered microphotonic arrays have received limited attention in previous studies. It is shown that these capabilities include: i) a unique self‐terminating etching nature − crucial for achieving uniform arrays over centimeter‐scale wafers, ii) an extraordinary smoothness of the slow‐etching (111) planes, and iii) a precise geometry control including the extent micropyramids or micropyramidal voids are truncated. The combination of these properties transforms this technology into a versatile platform for novel detector and emitter applications in Si photonics. The optical properties of such arrays are studied by finite‐difference time‐domain modeling in two realms represented by different boundary conditions (BCs). Periodic BCs result in Talbot self‐images experimentally observed in this work. Perfectly matched layer BCs describe mesoscale interference effects resulting in the subwavelength focusing properties of micropyramids. Enhancements in the performance of mid‐wave infrared (MWIR) focal plane arrays are demonstrated by monolithic integration of Si micropyramids with silicon‐platinum silicide Schottky barrier photodetectors. Finally, it is shown that Si micropyramidal arrays can be used to enhance light extraction and directionality of quantum sources and infrared scene projectors.

Self-powered Schottky barrier photodetectors based on P3HT:PC61BM bulk heterojunction films

By employing the classic system poly(3-hexylthiophene-2,5-diyl): [6,6]-phenyl-C61-butyric acid methyl ester (P3HT:PC61BM), organic bulk heterojunction films were applied on an indium tin oxide substrate using a one-step spin-coating method, without requiring any complex manufacturing processes, to obtain self-powered photodetectors (PDs) with a simple preparation process. The fullerene material was introduced to create a bulk heterojunction film with proper phase separation and greatly enrich the donor/acceptor dissociation interface, thus improving the high exciton binding energy and short exciton diffusion distance. The built-in electric field formed by the Schottky junction at the interface between the active layer and electrode can enhance the separation of excitons and the transport of charge carriers, realizing optical detection without external energy sources. Moreover, femtosecond transient absorption was employed to investigate the exciton dynamics in organic films and analyze the working mechanism of self-powered detection performance. The long-lived behavior of carriers and the formation of charge transfer states were further verified, which contributed to the enhanced performance of the device. As a result, the self-powered PD-based Schottky bulk heterojunction presents a high light on/off ratio of over 104 (0 V) and fast response speed with rise and decay times of 33 and 36 µs, respectively, under a 532 nm light illumination. These results provide theoretical and experimental verification of this technique for the development of self-powered PDs in the field of organic materials.

Self-powered Schottky barrier photodetector with high responsivity based on homoepitaxial Ga2O3 films by MOCVD

Abstract Ga2O3 is a fast-developing wide band semiconductor for solar-blind ultraviolet (SBUV) photodetectors (PDs) applications. The heterojunction self-powered PDs fabricated from heteroepitaxial Ga2O3 films currently have low responsivity and response speed. In this work, we fabricated Schottky barrier PDs based on homoepitaxially grown high quality Ga2O3 films, which show high performance manifested in high responsivity at different bias voltages. In particular, the device achieves a responsivity of 90.3 mA/W, a photo-to-dark current ratio of 3.2×104 and a detectivity of 3.8×1013 Jones at 0 V. In addition, a response time of superior to 5 ms is achieved. The results demonstrate the advantages of homoepitaxial Ga2O3 films in the field of high-performance devices.

Plasmonic graphene/perovskite Schottky barrier photodetector

Abstract In this paper the performance of a graphene/perovskite Schottky barrier photodetector is investigated theoretically for detecting infrared radiation within the spectral region of 7.5–10 μm. In order to increase the responsivity of the photodetector plasmon–polaritons are excited in the graphene layer within the specified spectral region with the aid of dielectric grating fabricated inside the photodetector structure. The results show that with the increase of the Fermi energy level in the graphene layer the wavelength where plasmon–polaritons are excited is shifted toward shorter wavelengths. This property enables the photodetector for tunable detection. The excitation of plasmon–polaritons localizes the infrared radiation incident on the photodetector to the graphene layer with a full width at half maximum of ≈12.6 nm. This localization increases the absorbance of the graphene layer considerably at peak detection wavelengths where plasmon–polaritons are excited, so that at peak detection wavelengths the absorbance of the graphene layer inside the photodetector is higher than 20 % while without the excitation of plasmon–polaritons the absorbance of the same layer is below 0.05 %. Due to this effect the responsivities of the photodetector at wavelengths where plasmon–polaritons are excited, increase more than 535 times relative to the case where plasmon–polaritons are not excited. Therefore the excitation of plasmon–polaritons not only increases the responsivity of the photodetector significantly but also enables the photodetector for tunable detection by varying the Fermi energy level in the graphene layer.

Enhancing the external quantum efficiency of Schottky barrier photodetectors through thin copper films.

Silicon-based Schottky barrier photodetectors (SBPDs) are a cost-effective alternative to compound semiconductor-based photodetectors by extending the silicon's photodetection range to the near-infrared (NIR) region. However, SBPDs still suffer from low quantum yield due to poor absorption in a metal layer and low emission efficiency of hot electrons. This study investigates the use of thin copper (Cu) films as a means of improving the performance of SBPDs operating in the NIR region. Our results show that thin-film Cu SBPDs present a higher external quantum efficiency (EQE) compared to other metal SBPDs due to their low Schottky barrier height and long mean free path. Notably, at a bias of -3 V, the thinnest Cu SBPDs exhibit an EQE of the order of 1% at 1510 nm.

Highly Efficient Silicon-Based Thin-Film Schottky Barrier Photodetectors

Internal photoemission (IPE) is a promising phenomenon for sub-bandgap photodetection at near-infrared wavelengths using large bandgap semiconductor materials. To improve the photon-to-electron conversion efficiency in silicon-based sub-bandgap Schottky barrier photodetectors (SBPDs), previous studies have mainly focused on subwavelength-scale nanostructures to enhance the electric fields and optical absorption. Here, in a different way from the previous approaches, we theoretically and experimentally demonstrate a rigorous quantum efficiency analysis framework that can quantitatively explain the hot carrier transport processes. Guided by the design principles from the hot carrier loss mechanism analysis, we experimentally demonstrate patternless thin-film SBPDs that can surpass the performance of conventional nanostructured SBPDs, exceeding the external quantum efficiency of 10–3. Our work shows that optical absorption and hot carrier generation are responsible for only a part of the entire IPE process and other transport mechanisms should be carefully considered in a wholistic manner, indicating the importance of quantitative quantum efficiency analysis.

MBE-grown Fe:Pd/ZnSe Schottky-barrier photodetector: Distinguishing blue + UV light levels among white light sources

Blue and ultraviolet radiation is well known to be associated with cataract formation and visual damage. Nowadays, children and teenagers are increasingly exposed to blue light and electromagnetic radiation with even shorter wavelength, which may cause damage to vision due to their frequent use of electronic display devices and participation in disco parties and concerts with illumination by UV light. We developed a Fe:Pd/ZnSe Schottky barrier photodetector that detects blue and UV light with excellent long-wavelength rejection power for green and red light of 4.24 and 5.65 orders, respectively. Its Schottky-barrier height and built-in potential are determined to be 2.48 and 1.17 eV, respectively. Together with the help of a lux meter, this simple and robust photodetector detects the blue light + UV content of different LED light bulbs with accuracy comparable to the much more sophisticated and expensive spectrometer. This compact and efficient blue + UV light detector can help us to increase the awareness of over-exposure to vision damaging radiation.

Ga<sub>2</sub>O<sub>3</sub>-based metal-insulator-semiconductor solar-blind ultraviolet photodetector with HfO<sub>2</sub> inserting layer

Solar-blind photodetector (PD) converts 200–280 nm ultraviolet (UV) light into electrical signals, thereby expanding application range from security communication to missile or fire alarms detections. As an emerging ultra-wide bandgap semiconductor, gallium oxide (Ga<sub>2</sub>O<sub>3</sub>) has sprung to the forefront of solar blind detection activity due to its key attributes, including suitable optical bandgap, convenient growth procedure, highly temperture/chemical/radiation tolerance, and thus becoming a promising candidate to break the current bottleneck of photomultiplier tubes. The Ga<sub>2</sub>O<sub>3</sub>-based solar blind PDs based on various architectures have been realized in the past decade, including photoconductive PDs, Schottky barrier PDs, and avalanche PDs. Till now, the metal-semiconductor-metal (MSM) structure has been widely used in developing photoconductive Ga<sub>2</sub>O<sub>3</sub> solar-blind PDs because of its simple preparation method and large light collection area. Unfortunately, despite unremitting efforts, the performance metric of reported MSM-type Ga<sub>2</sub>O<sub>3</sub> solar-blind PDs still lags behind the benchmark of commercial PMTs. Apparently, lack of solution to the problem has greatly hindered further research and practical applications in this field. One effective strategy for further enhancing the device performance such as detectivity, external quantum efficiency (EQE), and light-to-dark ratio heavily relies on blocking the dark current. In this work, high-quality single crystalline <i>β</i>-Ga<sub>2</sub>O<sub>3</sub> with a uniform thickness of 700 nm is grown by using a metal organic chemical vapor deposition (MOCVD) technique. Then atomic layer deposition (ALD) fabricated ultrathin hafnium oxide (HfO<sub>2</sub>) films (<inline-formula> <tex-math id="Z-20230428020102-1">\begin{document}$ \sim $\end{document}</tex-math><alternatives><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20222222_Z-20230428020102-1.jpg"/><graphic xmlns:xlink="http://www.w3.org/1999/xlink" xlink:href="9-20222222_Z-20230428020102-1.png"/></alternatives></inline-formula>10 nm) are introduced as inserted insulators and passivation layers. The 30 nm/100 nm Ti/Au interdigital electrodes (length: 2800 μm, width: 200 μm, spacing: 200 μm, 4 pairs) are fabricated by sputtering on the top of the film as the Ohmic contacts. Taking advantage of its novel dielectric and insulating properties, the leakage current on Ga<sub>2</sub>O<sub>3</sub> thin film can be effectively inhibited by the inserted ultrathin HfO<sub>2</sub> layer, and thus further improving the performance of PDs. Compared with simple MSM structured Ga<sub>2</sub>O<sub>3</sub> PD, the resulting metal-insulator-semiconductor (MIS) device significantly reduces dark current, and thus improving specific detectivity, enhancing light-to-dark current ratio, and increasing response speed. These findings advance a significant step toward the suppressing of dark current in MSM structured photoconductive PDs and provide great opportunities for developing high-performance weak UV signal sensing in the future.

Band Gap Opening in Borophene/GaN and Borophene/ZnO Van der Waals Heterostructures Using Axial Deformation: First-Principles Study.

One of the topical problems of materials science is the production of van der Waals heterostructures with the desired properties. Borophene is considered to be among the promising 2D materials for the design of van der Waals heterostructures and their application in electronic nanodevices. In this paper, we considered new atomic configurations of van der Waals heterostructures for a potential application in nano- and optoelectronics: (1) a configuration based on buckled triangular borophene and gallium nitride (GaN) 2D monolayers; and (2) a configuration based on buckled triangular borophene and zinc oxide (ZnO) 2D monolayers. The influence of mechanical deformations on the electronic structure of borophene/GaN and borophene/ZnO van der Waals heterostructures are studied using the first-principles calculations based on density functional theory (DFT) within a double zeta plus polarization (DZP) basis set. Four types of deformation are considered: uniaxial (along the Y axis)/biaxial (along the X and Y axes) stretching and uniaxial (along the Y axis)/biaxial (along the X and Y axes) compression. The main objective of this study is to identify the most effective types of deformation from the standpoint of tuning the electronic properties of the material, namely the possibility of opening the energy gap in the band structure. For each case of deformation, the band structure and density of the electronic states (DOS) are calculated. It is found that the borophene/GaN heterostructure is more sensitive to axial compression while the borophene/ZnO heterostructure is more sensitive to axial stretching. The energy gap appears in the band structure of borophene/GaN heterostructure at uniaxial compression by 14% (gap size of 0.028 eV) and at biaxial compression by 4% (gap size of 0.018 eV). The energy gap appears in the band structure of a borophene/ZnO heterostructure at uniaxial stretching by 10% (gap size 0.063 eV) and at biaxial compression by 6% (0.012 eV). It is predicted that similar heterostructures with an emerging energy gap can be used for various nano- and optoelectronic applications, including Schottky barrier photodetectors.

Review of Radiation-Induced Effects on β-Ga2O3 Materials and Devices

β-Ga2O3 has become an ultimate choice of emerging new-generation material for its wide range of compelling applications in power electronics. In this review, we have explored the available radiations in the atmosphere and the effects of radiation on the β-Ga2O3 material and devices. The focus in this review summarizes various studies covering different radiation such as swift heavy ions, protons, neutrons, electrons, Gamma, and X-rays to understand the radiation-induced effects on the structure and their reliable performance in harsh environments. In addition, we focused on the various pre-existing defects in β-Ga2O3 and the emergence of radiation-induced defects that provoke a severe concern, especially from the device performance point of view. This review presents the irradiation-induced effects on the devices such as high-power devices such as Schottky barrier diodes (SBDs), field-effect transistors (FETs), metal-oxide-semiconductor (MOS) devices, and photodetectors. Some key studies including the changes in carrier concentration with a removal rate, Schottky barrier height (SBH), ideality factor, defect dynamics dielectric damage, interface charge trapping, a thermally activated recovery mechanism for charge carriers at elevated temperature, and diffusion length of minority charge carriers. These reports show that β-Ga2O3-based devices could be deployable for space or high-radiation terrestrial applications. These results provide/suggest a better device design based on the radiation degradation studies in the state-of-the-art β-Ga2O3 devices.

Room-temperature plasmonic mid-infrared photodetector based on PtSi/p-Si low Schottky-barrier junction.

In this study, a low Schottky-barrier photodetector with a plasmonic assist using a two-dimensional (2D) nanohole array was demonstrated, which receives mid-infrared (MIR) light at room temperature. In the structural design, it was confirmed that the 2D nanohole-array photodetector has high absorbance in the MIR region using rigorous coupled-wave analysis. The result showed that the nanoholes formed in p-type silicon (p-Si), platinum silicide (PtSi), to form Schottky barriers, and gold (Au), for photocurrent extraction, had high absorbance in the MIR region along with the Fabry-Perot resonance mode toward the depth of the nanohole. The 2D nanohole array, with Au/PtSi/p-Si layers, has high absorbance for illuminating MIR light near 3.46 µm from the backside. The current-voltage characteristics indicated a low Schottky barrier of 0.32 eV, confirming the photoresponsive potential in the MIR photodetection. The photocurrent response to the modulation signal was obtained at room temperature. In addition, signal processing through transimpedance and lock-in amplifiers enabled us to obtain characteristics with high linearity for light intensities in milliwatts. Light acquisition for 2.5-3.8-µm-long MIR wavelength became possible, and applications in gas sensing, including vibrational absorption bands of alkane groups, are expected.

Improving the photoresponse performance of monolayer MoS2 photodetector via local flexoelectric effect

Strain engineering is an effective means of modulating the optical and electrical properties of two-dimensional materials. The flexoelectric effect caused by inhomogeneous strain exists in most dielectric materials, which breaks the limit of the materials’ non-centrosymmetric structure for piezoelectric effect. However, there is a lack of understanding of the impact on optoelectronic behaviour of monolayer MoS2 photodetector via local flexoelectric effect triggered by biaxial strain. In this paper, we develop a probe tip (Pt)-MoS2-Au asymmetric Schottky barrier photodetector based on conductive atomic force microscopy to investigate the impact of flexoelectric effect on the photoresponse performance. Consequently, when the probe force increases from 24 nN to 720 nN, the photocurrent, responsivity and detectivity increase 28.5 times, 29.6 times and 5.3 times at forward bias under 365 nm light illumination, respectively. These results indicate that local flexoelectric effect plays a critical role to improve the photoresponse performance of photodetector. Our approach suggests a new route to improve the performance of photodetectors by introducing local flexoelectric polarization field, offering the potential for the application of strain modulated photoelectric devices.

Influence of the bias voltage on the photoluminescence intensity and spectral responsivity of the GaN Schottky barrier photodetector

The effects of the bias voltage on photoluminescence (PL) intensity and the spectral responsivity are studied for an Au/Ni/undoped GaN/n+-GaN structure Schottky barrier photodetector. Near-band-gap PL of GaN quenches at low reverse bias but enhances at high reverse bias. Under high reverse bias, holes are accumulated in the region of the GaN adjacent to the Ni/Au. Only electrons below empty states at top of valence can be excited to the conduction band in this region, which reduces the absorption of near-band-gap luminescence. The decrease of the spectral responsivity for near the band gap under higher reverse bias also supports this assumption.

Adsorbate-induced enhancement of the spectral response in graphene/silicon-based Schottky barrier photodetectors

The impact of atmospheric adsorbates on the spectral response and response speed of p-type graphene/n-type Silicon (p-Gr/n-Si) based Schottky barrier photodetectors are investigated. Wavelength resolved photocurrent and transient photocurrent spectroscopy measurements conducted under high-vacuum conditions revealed that the atmospheric adsorbates such as O2 and H2O stuck on graphene electrode lead to hole doping in graphene and therefore shift its Fermi level towards higher energy states below its Dirac point. Such a shift in graphene’s Fermi level due to adsorbates increases the zero-bias Schottky barrier height of the p-Gr/n-Si heterojunction from 0.71 to 0.78 eV. Adsorbate induced increment in the barrier height promotes the separation of photo-generated charge carriers at the depletion region and leads to an improvement in the maximum spectral response (e.g., from 0.39 to 0.46 AW−1) and response speed of the p-Gr/n-Si photodetector in the near-infrared region. The experimentally obtained results are expected to give an insight into the adsorbate related variations in the rectification and photo-response characters of the heterojunctions of graphene and other 2D materials with different semiconductors.

Schottky barrier photodetector utilizing tungsten grating nanostructure

Schottky barrier photodetector (PD) (tungsten/nickel/aluminum nitride) based on stacked tungsten gratings is reported in our work. The absorbance of the grating-based structure is obtained using rigorous coupled-wave analysis method. In addition, a responsivity value of 6.164 mA / W is calculated at λ = 559.38 nm based on Fowler’s model. More than three times enhancement in responsivity is achieved as compared with that of bulk structure (without grating) based Schottky barrier PD. In addition, a detectivity value of 33.11 × 1011 cm Hz1/2 / W is obtained. Furthermore, the effect of grating variables and incident angle on responsivity are also demonstrated. In future, the proposed structure can also be used as a plasmonic sensor, absorber, or spectral filter.

III-Nitrides Resonant Cavity Photodetector Devices.

III-nitride resonant cavity-enhanced Schottky barrier photodetectors were fabricated on 2 µm thick GaN templates by radio frequency plasma-assisted molecular beam epitaxy. The optical cavity was formed by a bottom distributed Bragg reflector based on 10 periods of Al0.3Ga0.7N/GaN, an Au-based Schottky contact as top mirror, and an active zone of 40 nm-thick GaN layer. The devices were fabricated with planar geometry. To evaluate the main benefits allowed by the optical cavity, conventional Schottky photodetectors were also processed. The results revealed a planar spectral response for the conventional photodetector, unlike the resonant devices that showed two raised peaks at 330 and 358 nm with responsivities of 0.34 and 0.39 mA/W, respectively. Both values were 80 times higher than the planar response of the conventional device. These results demonstrate the strong effect of the optical cavity to achieve the desired wavelength selectivity and to enhance the optical field thanks to the light resonance into the optical cavity. The research of such a combination of nitride-based Bragg mirror and thin active layer is the kernel of the present paper.

A study of n-doping in self-catalyzed GaAsSb nanowires using GaTe dopant source and ensemble nanowire near-infrared photodetector

This work reports a comprehensive investigation of the effect of gallium telluride (GaTe) cell temperature variation (TGaTe) on the morphological, optical, and electrical properties of doped-GaAsSb nanowires (NWs) grown by Ga-assisted molecular beam epitaxy (MBE). These studies led to an optimum doping temperature of 550 °C for the growth of tellurium (Te)-doped GaAsSb NWs with the best optoelectronic and structural properties. Te incorporation resulted in a decrease in the aspect ratio of the NWs causing an increase in the Raman longitudinal optical/transverse optical vibrational mode intensity ratio, large photoluminescence emission with an exponential decay tail on the high energy side, promoting tunnel-assisted current conduction in ensemble NWs and significant photocurrent enhancement in the single nanowire. A Schottky barrier photodetector (PD) using Te-doped ensemble NWs with broad spectral range and a longer wavelength cutoff at ∼1.2 µm was demonstrated. These PDs exhibited responsivity in the range of 580–620 A W−1 and detectivity of 1.2–3.8 × 1012 Jones. The doped GaAsSb NWs have the potential for further improvement, paving the path for high-performance near-infrared (NIR) photodetection applications.

Epitaxial High-Yield Intrinsic and Te-Doped Dilute Nitride GaAsSbN Nanowire Heterostructure and Ensemble Photodetector Application

Band gap engineering of GaAsSbN nanowires (NWs) grown by Ga-assisted molecular beam epitaxy and demonstration of a Te-doped axial GaAsSbN NW-based Schottky barrier photodetector on p-Si (111) in th...

Au grating on SiC substrate: simulation of high performance plasmonic Schottky barrier photodetector in visible and NIR regions

Plasmonically enhanced light absorption in Schottky barrier photodetectors (PDs) can be achieved by engineering metallic nanostructures. In this context, gold (Au) gratings on titanium (Ti)/silicon carbide (SiC) based Schottky barrier is proposed in this work for photodetection application. Further, the effects of various grating parameters and incident angle on absorbance are demonstrated. The grating based structure is able to provide ~85% incident light absorption leading to a significantly high responsivity value as compared with that of conventional (without metallic grating) structure. High unbiased responsivity values of 4.396 mA W−1 and 2.496 mA W−1 are obtained for Au/Ti/6H-SiC Schottky barrier PD at wavelengths of 694.5 nm and 1035 nm, respectively based on Fowler’s model. In view of advanced properties of SiC, the present work will open new opportunities for plasmonic PDs based on SiC platform.

Narrow-Band 4.3<italic>μ</italic>m Plasmonic Schottky-Barrier Photodetector for CO2 Sensing

Using an embedded platinum silicide (PtSi) grating, a Schottky-barrier photodetector structure for narrow-band detection of mid-infrared (mid-IR) radiation is proposed and designed. Schottky-barrier photodetectors designed for the infrared wavelengths suffer from poor efficiency and photoresponse. We propose a photodetector based on PtSi-Si Schottky junction with increased interface area where hot carriers are more likely to cross the junction in favor of a higher photoresponse. Furthermore, a guided-mode resonance of the presented periodic structure is coupled to its Fabry–Perot resonance to achieve narrow-band absorption. The proposed photodetector absorbs 84% of incident power at a wavelength of 4.3 μm with a full-width half-maximum bandwidth of 94 nm. High photoresponsivity and compatibility with complementary metal oxide semiconductor process render the proposed structure a low-cost photodetector in the mid-IR range for CO2 sensing.