Ultraviolet Photodetector Applications Research Articles

Zinc Oxide Nanorods/Reduced Graphene Oxide for Schottky Junction Ultraviolet Photodetector Application

Zinc Oxide Nanorods/Reduced Graphene Oxide for Schottky Junction Ultraviolet Photodetector Application

Heteroepitaxial growth of Ga2O3 thin films on nickel-nanodot-induced buffer layers for solar-blind ultraviolet photodetector applications

Heteroepitaxial growth of gallium oxide (Ga2O3) thin films has been conducted on nickel (Ni)-nanodot-induced buffer layers using a mist chemical vapor deposition. The separation degree and droplet size of the Ni nanodots on sapphire substrates were controlled through a thermal annealing process, thereby being used as templates for the Ga2O3 thin-film growth. The growth of the inverted cone-shaped ε-Ga2O3 polymorph was observed on the nanodots while the α-Ga2O3 polymorph was grown on the sapphire substrate without nanodots, ultimately a thin film with a mixture of ε and α polymorphs can be achieved. By comparing photoresponses of metal–semiconductor–metal photodetectors fabricated on the thin film with the mixed polymorphs and on a single-crystalline α-Ga2O3 film, a promising template for using solar-blind photo-detecting applications has been verified.

Multilayered BCST/PZT thin films on GaN substrate for ultraviolet photodetector applications

In the realm of photodetection, there has been growing interest in Ferroelectric/semiconductors heterostructures due to the interfacial charge coupling resulting from ferroelectric polarization. In this study, we created a thin film consisting of alternating layers of Ba0.86Ca0.14Ti0.9Sn0.1O3 and PbZr0.52Ti0.48O3 (referred to as BCST/PZT) using a sol-gel growth method on a (0001) GaN/c-sapphire template. Our objective was to examine the impact of these films on the optoelectronic properties of ferroelectric/GaN heterojunctions. Our findings indicate that the BCST/PZT multilayer films possess improved ferroelectric properties. Furthermore, the multilayer structure demonstrates outstanding optoelectronic performance compared to the individual BCST/GaN or PZT/GaN structures, particularly within the 1 V to 3 V bias range. Notably, the multilayer thin film/GaN devices exhibit a responsivity of 121.4 mA/W and a detectivity of 1.44 × 1011 Jones under a 1 V bias voltage. In contrast to other GaN-based materials documented in the literature, our straightforward sol-gel techniques yielded devices exhibiting UV photodetection characteristics that are either comparable to or superior than those reported.

Phase Transition and Bandgap Engineering of MgSnO Thin Films for Solar-Blind Ultraviolet Photodetector Applications

Phase Transition and Bandgap Engineering of MgSnO Thin Films for Solar-Blind Ultraviolet Photodetector Applications

Fabrication and photo-responsive characteristics of GeO2 doped SnO2/porous Si film for ultraviolet photodetector application

In this manuscript, tin oxide (SnO2) and Germanium dioxide (GeO2) doped SnO2/porous silicon (Si) film/s were fabricated using combined co-precipitation and laser pulsed deposition methods for ultraviolet photodetector/s application. X-ray diffraction (XRD) study indicated the occurrence of high crystalline film/s, wherein nanoparticle diameters of 85 and 50 nm were attained using field emission scanning electron microscopy (FE-SEM). The attained optical bandgap for un-doped SnO2 layer was found to be 3.8 eV which was found to be increased to deeper ultraviolet region (4.2 eV) after GeO2 doping. Further, a considerable photo-current value of 148 μA was attained at 396 nm for the GeO2-doped SnO2 photodetector. This in turn was noticed to significantly increased to 165 μA at deeper UV light (365 nm). The recovery time of the un-doped SnO2 photodetector was found to be 710 ms, while adding 25% of GeO2 as dopant resulted in lower recovery rate (615 ms). Along with the robustness and steadiness of the proposed geometry, it reveals an approachable path for cost-effective optoelectronic system.

Pulsed laser deposition of lead-free Cs3Cu2Br5 thin films on GaN substrate for ultraviolet photodetector applications

Recently, intensive attention has been paid to the development of copper halide perovskites (CsCuX, X = I, Br, and Cl) due to their suitable band gaps, large light absorption, environmental stability, eco-friendliness, and low cost. Although CsCuBr possesses a much larger band gap than CsCuI perovskites, there have been few reports about CsCuBr due to its poor stability in the ambient environment. In this study, high-quality Cs3Cu2Br5 thin films with good stability were prepared on GaN substrates by pulse laser deposition (PLD) for the first time. The morphology, crystal structure, and photoelectric properties of the Cs3Cu2Br5 thin films were systematically studied. Moreover, a self-powered UV photodetector based on Cs3Cu2Br5/n-GaN heterojunction was fabricated. The heterojunction device exhibits two clear dominant responses in the UV region located at 270 nm and 360 nm, with the corresponding detectivities of 5.29 × 1011 cm·Hz1/2W−1 and 3.35 × 1011 cm·Hz1/2W−1. Besides, the photoresponse mechanism of the Cs3Cu2Br5/GaN photodetector has been studied by Anderson model. Our results suggest that lead-free Cs3Cu2Br5 thin films prepared by PLD could be a potential candidate for stable and environment-friendly optoelectronic devices, such as UV detectors and light emitting devices.

Growth of bulk BiOBr single crystals for the characterization of intrinsic semi-conductive properties and application in ultraviolet photodetectors

High-quality bulk BiOBr crystal with mm size is obtained by a space-confined chemical vapor transport strategy, & its intrinsic semi-conductive properties are characterized. It is fabricated into two-terminal UV photodetectors, which exhibit good UV detection performance.

Synthesis of single-crystalline ZnO nanoflowers for a superhigh-sensitivity ultraviolet photodetector application

The high-performance, low-cost and simple ultraviolet photodetectors are very promising in some applications. Here, single-crystalline zinc oxide (ZnO) nanoflowers were prepared by combining a facile hydrothermal method with post-annealing treatment, we built an ultraviolet photodetector with an active area of 0.36 cm2 using the as-prepared ZnO nanoflowers. The results showed that under 365 nm light illumination with a light intensity of 77 μW/cm2, the sensitivity, response time, decay time, responsivity and gain of the device were 19991.3 (−0.1 V), 16.4 s, 37.6 s, 9.0 A/W (5 V) and 30.6 (5 V), respectively, indicating that a ZnO nanoflowers UV photodetector with superhigh sensitivity was achieved.

Superior UV photodetector performance of TiO2 films using Nb doping

Titanium dioxide (TiO2) is one of the excellent materials used for photodetector applications due to its high photoactive nature. In this research, highly sensitive ultra-violet (UV) photodetectors with high detectivity and external quantum efficiency (EQE) are developed by depositing Nb-doped TiO2 (TNO) films onto a Si/SiO2 substrate at different Nb concentrations. The doping effect of Nb on the electronic structure and photodetector performance of TiO2 films has been investigated. The charge compensation mechanism due to Nb-doping has been explained using X-ray photoelectron spectroscopy. Lower doping concentrations of Nb5+ result in creating a Ti vacancy and an excess electron per Nb atom, contributing to the enhanced photocurrent. The metal-semiconductor-metal (M-S-M) structure of the device generates an ohmic-contact and the Si/SiO2 layer assisted toward reducing the surface recombination. All these factors cause an enhancement in the photocurrent, detectivity, and EQE of the TNO photodetector. Finally, the optimized TNO film grown using 1.0 at.% Nb shows improved photodetector properties and is suitable for ultra-sensitive UV photodetector applications.

Characterization of budding twigs of flower-type zinc oxide nanocrystals for the fabrication and study of nano-ZnO/p-Si heterojunction UV light photodiode

In this work, we focused on the study of the structural and optical properties of chemical precipitation-derived special shape (budding twigs of flower-type) ZnO nanostructures for optoelectronic and photodetection applications. The structural and optical properties of the budding twigs of Jasminum flower-like ZnO nanocrystals have been studied and discussed in detail from the XRD, HRTEM, UV–Vis, and photoluminescence spectra. The grown ZnO nanocrystals have been coated on the p-Si substrate to fabricate nano-ZnO/p-Si heterojunction photodiode. The junction properties of the fabricated photodiode were examined by measuring ultraviolet (UV)-light-dependant (λ ~ 366 nm) and dark condition current (I)–voltage (V) as well as capacitance (C)–voltage (V) characteristics. The photodetection properties of the diode in the UV light region have been examined. The diode has well-defined rectifying behavior with a photoresponsivity and external photodetection efficiency of 0.065 and 21.5%, respectively. The observed barrier height and donor concentration under dark condition were ≈ 0.25 eV and 2 × 1017 cm−3, respectively. The change in heterojunction capacitance, barrier height, the depletion width, and other parameters of the heterojunction photodiode under UV illumination has been discussed. The qualities of the device demonstrate that it tends to be used for UV photodetection applications in nano-optoelectronic and photonic devices.

Hybrid Device Architecture Using Plasmonic Nanoparticles, Graphene Quantum Dots, and Titanium Dioxide for UV Photodetectors.

In this work, a nanoscale device architecture is demonstrated for a UV photodetector application on sapphire (0001), incorporating the plasmonic hybrid nanoparticles (HNPs), graphene quantum dots (GQDs), and titanium oxide (TiO2) for the first time. The hybrid GQDs/TiO2/HNPs photodetector exhibits the photocurrent of 1.58 × 10-5 A under the 1.64 mW/mm2 of 275 nm illumination at 10 V, which is around two order increase from the bare TiO2 device. The proposed architecture demonstrates a low dark current of ∼1 × 10-10 A at 10 V and thus the device demonstrates an excellent photo to dark current ratio along with the improved rise and fall time on the order of several hundred millisecond. The enhanced performance of device architecture is attributed to the efficient utilization of localized surface plasmon resonance (LSPR) induced hot carriers as well as scattered photons from the plasmonic HNPs that are fully encapsulated by the photoactive TiO2 layers. Furthermore, the addition of GQDs on the TiO2 can offer an additional photon absorption pathway. The proposed hybrid architecture of GQDs/TiO2/HNPs demonstrates the integration of the photon absorption and carrier transfer properties of plasmonic HNPs, GQDs, and TiO2 for an enhanced ultraviolet (UV) photoresponse. The photocurrent enhancement mechanisms of the hybrid device architecture are thoroughly investigated based on the finite-difference time domain (FDTD) simulation along with the energy band analysis. This work demonstrates a great potential of the hybrid device architecture for high-performance UV photodetectors.

Highly Sensitive and Tunable Self-Powered UV Photodetectors Driven Jointly by p-n Junction and Ferroelectric Polarization.

Ferroelectric (FE) materials are thought to be promising materials for self-powered ultraviolet (UV) photodetector applications because of their photovoltaic effects. However, FE-based photodetectors exhibited poor performance because of the weak photovoltaic effect of FE depolarization field (Edp) on the separation of photo-generated carriers. In this work, self-powered photodetectors based on both Edp and built-in electric field at the p-n junction (Ep-n) were designed to obtain enhanced device performance. A NiO/Pb0.95La0.05Zr0.54Ti0.46O3 (PLZT) heterojunction-based device is constructed to take advantage of energy level alignments that favor electron extraction. The device exhibits a tunable performance upon varying the polarization direction of PLZT. The NiO/PLZT heterojunction-based device with the PLZT layer in the poling down state shows a higher responsivity [R = (1.8 ± 0.12) × 10-4 A/W] and detectivity [D* = (3.69 ± 0.2) × 109 Jones], a faster response speed (τr = 0.34 ± 0.03 s, τd = 0.36 ± 0.02 s), and a lower dark current [Idark = (1.3 ± 0.19) × 10-12 A] under zero bias than the PLZT-based device because of the synergistic effects of Edp and Ep-n. Moreover, under weak-light illumination (0.1 mW/cm2), it exhibits even higher R [(6.3 ± 1.2) × 10-4 A/W] and D* [(1.29 ± 0.26) × 1010 Jones] values, which surpass those of most previously reported FE-based self-powered photodetectors. Our work emphasizes the role of the coupling effect between Ep-n and Edp in the photovoltaic process of NiO/PLZT heterojunction-based devices and provides an effective way to promote the self-powered UV photodetector applications.

Ag Nanowire-Plasmonic-Assisted Charge Separation in Hybrid Heterojunctions of Ppy-PEDOT:PSS/GaN Nanorods for Enhanced UV Photodetection.

The surface states, poor carrier life, and other native defects in GaN nanorods (NRs) limit their utilization in high-speed and large-gain ultraviolet (UV) photodetection applications. Making a hybrid structure is one of the finest strategies to overcome such impediments. In this work, a polypyrrole (Ppy)-poly(3,4-ethylenedioxythiophene):poly(styrenesulfonate) (PEDOT:PSS)/GaN NRs hybrid structure is introduced for self-powered UV photodetection applications. This hybrid structure yields high photodetection performance, while pristine GaN NRs showed negligible photodetection properties. The ability of the photodetector is further boosted by functionalizing the hybrid structure with Ag nanowires (NWs). The Ag NWs-functionalized hybrid structure exhibited a responsivity of 3.1 × 103 (A/W), detectivity of 3.19 × 1014 Jones, and external quantum efficiency of 1.06 × 106 (%) under a UV illumination of λ = 382 nm. This high photoresponse is due to the huge photon absorption rising from the localized surface plasmonic effect of a Ag NWs network. Also, the Ag NWs significantly improved the rising and falling times, which were noted to be 0.20 and 0.21 s, respectively. The model band diagram was proposed with the assistance of X-ray photoelectron spectroscopy to explore the origin of the superior performance of the Ag NWs-decorated Ppy-PEDOT:PSS/GaN NRs photodetector. The proposed hybrid structure seems to be a promising candidate for the development of high-performance UV photodetectors.

Effect of sputter pressure on UV photodetector performance of WO3 thin films

Tungsten trioxide (WO3) is a promising material for ultra-violet (UV) photodetector applications. In this research, high sensitivity and external quantum efficiency (EQE) of UV photodetector test-device is fabricated by the deposition of WO3 films through sputtering at 10 mTorr sputter pressure. The effect of sputter pressure on the crystallinity and morphology as well as the photodetector performance of WO3 films is studied. Here, the thickness of the WO3 films is decreased from 225 nm to 95 nm as the sputter pressure is increased from 10 mTorr to 20 mTorr due to the low deposition rate upon accumulation of argon ions. The crystallinity and surface roughness are found to be high for WO3 film deposited at 10 mTorr as an effect of Ostwald ripening. The SiO2 layer on Si substrates acts as a passivation to inhibit the surface recombination and the ohmic-contact between WO3 and Ti electrode is helped to enhance the photocurrent. The higher crystallinity, tailored grain size, and surface roughness of WO3 films assist to achieve high responsivity and EQE by minimizing the overall impedance. Therefore, WO3 films deposited at 10 mTorr sputter pressure is suitable for UV photodetector applications with good stability and higher photodetector performance.

Diode parameters and ultraviolet light detection characteristics of n-type silicon/p-type nanocrystalline diamond heterojunctions at different temperatures

n-Type silicon (Si)/p-type boron (B)-doped ultrananocrystalline diamond (UNCD) heterojunctions were manufactured through coaxial arc plasma deposition, and were examined in terms of the diode parameters and ultraviolet (UV) photodetection at different temperatures. The structure of the deposited films was examined by Raman spectroscopy and a field emission scanning electron microscope. The Raman spectra revealed two wide peaks centered at the positions of 1345 cm−1 and 1585 cm−1 that represented the D and G peaks, respectively. At 300 K, the current density-voltage characteristics showed a considerable high leakage current, which was reduced over two orders of magnitude at 150 K. The ideality factor (n) increased from 2.82 at 300 K to 6.37 at 150 K. In parallel, the barrier height was reduced from 0.75 eV at 300 K to 0.43 eV at 150 K. Through Norde’s approach, the series resistance values were found to be 4.33 kΩ at 300 K and 277.52 kΩ at 150 K, which increased by decreasing the temperature because of the increased n and the lack of carrier mobility in the B-doped UNCD/a-C:H films. Although a small UV response was observed at 300 K, the photocurrent at 150 K was over two orders of magnitude above the dark current at zero voltage. The detectivity values at 0 V were 2.37 × 109 Hz1/2 cm/W and 1.34 × 1010 Hz1/2 cm/W at 300 K and 150 K, respectively. This research proposed a comprehensive study on the n-type Si/p-type UNCD heterojunctions as candidate photodiodes for UV photodetection applications.

Morphology Effect of 1D ZnO Nanostructures Designed by Hydrothermal and Thermal Annealing for Fast Ultraviolet Photodetector Applications

ZnO nanorods are grown on a ZnO seed layer using the hydrothermal method and subsequently annealed at temperatures of 400–800 °C. The ZnO nanorods annealed at 400 °C exhibit a morphology similar to that of the unannealed ZnO nanorods. However, the tips of the ZnO nanorods gradually become rounded and their density and diameter increase with an increase in the annealing temperature. The intensity of the near‐band‐edge emission increases gradually with an increase in the annealing temperature from 400 to 600 °C but decreases sharply in the case of nanorods annealed at 800 °C. With respect to the deep‐level emissions, broad yellow, orange, and green emissions are observed. Further, the low‐temperature photoluminescence spectrum measured at 12 K of the ZnO nanorods annealed at 600 °C contains a donor‐bound exciton emission, as well as emissions related to the donor–acceptor pair (DAP) transition and the first‐order and second‐order longitudinal optical phonon replicas of the DAP transition. Finally, with respect to the photoresponse, the dark current and photocurrent of the nanorods decrease and their photosensitivity increases with the increase in the annealing temperature.

Influence of Al doping on the crystal structure, optical properties, and photodetecting performance of ZnO film

The structural, optical, and electrical properties of undoped and Al-doped ZnO films deposited on p-Si (001) substrate were studied using DC-unbalanced magnetron sputtering. This study is motivated by the absence of detail reports concerning the orbital states inducing the optical bandgap (Eg) blueshift. Besides, the influences of Al on the possible modification of point defect and the photodetecting performance are highlighted to offer guidelines for better development in ZnO-based photodetector. It was found that the Al doping reduced the grain size. The doping increased the lattice parameters and slightly decreased the local-symmetry distortion at ZnO4. From the absorbance spectra, the doping increased Eg of ZnO film (3.28–3.36 eV), induced by the Burstein-Moss effect. From the density-functional calculation, the Burstein-Moss effect induced Eg from the valence band maximum (VBM) to Fermi level located above the lowest Zn 4s conduction state. From the photoluminescence spectra, the undoped film showed the transitions from O vacancy, Zn interstitial, and free-exciton states to the VBM. The doped film showed the transitions from Zn interstitial to O interstitial and few Zn vacancy states at the cost of O vacancies. Moreover, the energy level of free-exciton states slightly decreased. Notably, O interstitials increased the lattice parameters. From the electrical properties, the doping enhanced the ultraviolet-region photo-to-dark-current ratio up to 3.044 V, leading to the photodetecting sensitivity enhancement. This study emphasizes the significant effect of Al doping on the optical absorbance, point-defect evolution, and photodetecting performance of ZnO film for low-voltage ultraviolet photodetector applications.

First-principle investigation of monoclinic (AlxInyGa1−x−y)2O3 quaternary alloys

First-principle density functional theory calculations were performed to explore electronic and structural properties of β-(AlxInyGa1−x−y)2O3 quaternary alloys with both Al-content (x) and In-content (y) ranging from 0% to 18.75%. The β-(AlxInyGa1−x−y)2O3 quaternary alloys exhibit indirect band gap property with the bandgap energy varying from 4.432 to 5.171 eV. Electron effective masses are also presented for β-(AlxInyGa1−x−y)2O3 quaternary alloys, showing a general reduction with In-content increases but a general increment with Al-content increases in the material. Further analysis indicates the possibility of achieving lattice-matched or near-lattice-matched β-(AlxInyGa1−x−y)2O3/β-Ga2O3 structures system, which is critical for high performance field effect transistor and deep ultraviolet photodetector applications. Our work shows that the β-(AlInGa)2O3 alloys with proper tuning of Al- and In-content have strong potential to be used as part of the epitaxial layers for β-Ga2O3-based material system.

Facile synthesis of ZnS quantum dots at room temperature for ultra-violet photodetector applications

Zinc sulfide (ZnS) quantum dots (QDs) were synthesized using a facile, low-cost and environmentally friendly method at room temperature and ambient pressure. The structural, optical and electrical properties of the as-prepared ZnS QDs were investigated. The monodispersed crystalline ZnS QDs with an average size of 3.8 nm has been prepared, an absorption peak at 292 nm in the ultra-violet (UV) range was observed. The maximum responsivity (R) and detectivity (D*) of the ZnS QDs based photodetector under 365 nm UV light illumination were 5.8 A W−1 and 1.97 × 1013 Jones, respectively, which shows important potential application in UV detection.

Fabrication and Characterization of Ni-Doped ZnO Nanorod Arrays for UV Photodetector Application

In this work, the structure morphologies, lattices, and optical properties of zinc oxide (ZnO) nanorods (NRs) with various amounts of nickel (Ni) dopants were investigated and explored. The 100 nm ZnO seed layer was grown on the Corning glass substrate by the radio frequency (RF) magnetron sputtering technique, and the chemical bath deposition (CBD) method was used to grow NR arrays. It was found that the Ni concentration of the sample is 1.06 at% by EDX spectra examination. All the NRs exhibited a hexagonal wurtzite structure and preferentially grew along the c-axis on the substrate. Additionally, the ultraviolet (UV) photodetectors (PDs) with Ni-doped ZnO (NZO) NRs based on metal-semiconductor-metal (MSM) structure were fabricated through a photolithography process. Then, such a sample was annealed at 500 °C to obtain good performance and reduced oxygen vacancy (∼560 nm). The results showed that the NZO NRs were with an excellent photosensitivity for UV PD applications and a faster rise/decay time than pure ZnO. Furthermore, with a 3 V applied bias and 380 nm UV illumination, the sensitivities of the fabricated ZnO PDs with different Ni contents (0, 4, and 8 mM) were 71.45, 393.04, and 238.75, respectively.