Search Results (16)

Both CuI and CuI:Zn semiconductor thin films, along with MSM-structured UV photodetectors, were prepared on flexible mica substrates at low temperature (150 °C) by a wet chemical method. The two CuI-based films exhibited a polycrystalline phase with an optical bandgap energy close to 3.0 eV. Hall effect measurements indicated that the CuI thin film sample had p-type conductivity, while the CuI:Zn thin film sample exhibited n-type conductivity, with the latter showing a higher carrier mobility of 14.78 cm²/Vs compared to 7.67 cm²/Vs for the former. The I-V curves of both types of photodetectors showed asymmetric rectification characteristics with rectification ratios at ±3 V of 5.23 and 14.3 for the CuI and CuI:Zn devices, respectively. Flexible CuI:Zn devices exhibited significantly better sensitivity, responsivity, and specific detectivity than CuI devices both before and after static bending tests. It was found that, while the optoelectronic performance of flexible CuI-based photodetectors degraded under tensile stress during static bending tests, they still exhibited good reproducibility and repeatability in their photoresponses. Full article

Oxygen vacancies (V_o) can significantly degrade the electrical properties of indium oxide (In₂O₃) thin films, thus limiting their application in the field of ultraviolet detection. In this work, the V_o is effectively suppressed by adjusting the Trimethylindium (TMIn) flow rate (f_TMIn). In addition, with the reduction of the f_TMIn, the background carrier concentration and the roughness of the film decrease gradually. And a smooth In₂O₃ thin film with roughness of 0.44 nm is obtained when the f_TMIn is 5 sccm. The MSM photodetectors (PDs) are constructed based on In₂O₃ thin films with different f_TMIn to investigate the opto-electric characteristics of the films. The dark current of the PDs is significantly reduced by five orders from 100 mA to 0.28 μA with the reduction of the f_TMIn from 50 sccm to 5 sccm. In addition, the photo response capacity of PDs is dramatically enhanced. The photo-to-dark current ratio (PDCR) increases from 0 to 2589. Finally, the PD with the f_TMIn of 5 sccm possesses a record-high responsivity of 2.53 × 10³ AW⁻¹, a high detectivity of 5.43 × 10⁷ Jones and a high EQE of 9383 × 100%. Our work provides an important reference for the fabrication of high-sensitivity UV PDs. Full article

β-Ga₂O₃ photodetectors have the advantages of low dark current and strong radiation resistance in UV detection. However, the limited photocurrent has restricted their applications. Herein, MSM UV photodetectors based on (In_xGa_1−x)₂O₃ (x = 0, 0.1, 0.2, 0.3) by a sol-gel method were fabricated and studied. The doping of indium ions in Ga₂O₃ leads to lattice distortion and promotes the formation of oxygen vacancies. The oxygen vacancies in (In_xGa_1−x)₂O₃ can be modulated by various proportions of indium, and the increased oxygen vacancies contribute to the enhancement of electron concentration. The results show that the amorphous In_0.4Ga_1.6O₃ photodetector exhibited improved performances, including a high light-to-dark current ratio (2.8 × 10³) and high responsivity (739.2 A/W). This work provides a promising semiconductor material In_0.4Ga_1.6O₃ for high-performance MSM UV photodetectors. Full article

In this paper, high-performance UV photodetectors have been demonstrated based on indium oxide (In₂O₃) thin films of approximately 1.5–2 μm thick, synthesized by a simple and quick plasma sputtering deposition approach. After the deposition, the thin-film surface was treated with 4–5 nm-sized platinum (Pt) nanoparticles. Then, titanium metal electrodes were deposited onto the sample surface to form a metal–semiconductor–metal (MSM) photodetector of 50 mm² in size. Raman scattering spectroscopy and scanning electron microscope (SEM) were used to study the crystal structure of the synthesized In₂O₃ film. The nanoplasmonic enhanced In₂O₃-based UV photodetectors were characterized by various UV wavelengths at different radiation intensities and temperatures. A high responsivity of up to 18 A/W was obtained at 300 nm wavelength when operating at 180 °C. In addition, the fabricated prototypes show a thermally stable baseline and excellent repeatability to a wide range of UV lights with low illumination intensity when operating at such a high temperature. Full article

Developing non-toxic, semiconductor-doped heterojunction materials for optoelectronic applications on the surface of a flexible substrate is a viable strategy for meeting the world’s energy needs without introducing any environmental issues. In this paper, Ti:TiO₂/ZnO nanocomposites were prepared by heat treatment and utilized as an active layer in UV photodetectors. First, a ZnO seed layer was deposited by radio frequency (RF) sputtering on polytetrafluoroethylene (PTFE) substrates. Then, TiO₂/ZnO thin films (TFs) were successfully grown by combining volumetric mixtures of TiO₂ and ZnO at the ratios of 1:7, 1:3, 3:5, and 1:1 via the chemical bath deposition (CBD) method. The morphological, elemental, and topographical analyses of the grown TFs were investigated through SESEM, EDX, and AFM spectroscopy, respectively. XRD patterns illustrated the presence of the unified (002) peak of the Ti/ZnO hexagonal wurtzite structure in all prepared samples, with intensities indicating a very strong preferential crystallinity with increasing TiO₂ ratios. Enhanced diffuse reflectance curves were obtained by UV–Vis spectroscopy, with allowed indirect energy bandgaps ranging from 3.17 eV to 3.23 eV. FTIR characterization revealed wider phonon vibration ranges indicating the presence of Ti–O and Zn–O bonds. Metal–semiconductor–metal (MSM) UV photodetectors were fabricated by thermally evaporating Ag electrodes on the grown nanocomposites. The volumetric ratio of TiO₂/ZnO impacted the photodetector performance, where the responsivity, photosensitivity, gain, detectivity, rise time, and decay time of 0.495 AW⁻¹, 247.14%, 3.47, 3.68 × 10⁸ jones, 0.63 s, and 0.99 s, respectively, were recorded at a ratio of 1:1 (TiO₂:ZnO). Based on the results, the heterostructure nanocomposites grown on PTFE substrates are believed to be highly promising TF for flexible electronics. Full article

Transparent Ga and In co-doped ZnO (ZnO:Ga-In) semiconductor thin films were deposited on Corning glass substrates by the sol-gel spin-coating process. The ZnO:Ga-In thin films were used as the sensing layer of metal–semiconductor–metal (MSM)-type ultraviolet (UV) photodetectors (PDs). In this study, the optoelectronic characteristics of ZnO:Ga-In MSM PDs with symmetrical interdigital electrodes (Al–Al) and asymmetrical interdigital electrodes (Al–Au) were compared. The as-prepared ZnO:Ga-In thin films were polycrystalline, and they had a single-phase hexagonal wurtzite structure and high transparency (~88.4%) in the visible region. The MSM-PDs with asymmetric electrodes had significantly reduced dark current (9.6 × 10⁻⁵ A at 5 V) according to the current-voltage (I-V) characteristics and higher photoresponse properties than those of the MSM-PDs with symmetric electrodes, according to the current-time (I-t) characteristics. In addition, the Al–Au devices were self-powered without an applied bias voltage. The photocurrent was 6.0 × 10⁻⁵ A; the sensitivity and responsivity were 0.25 and 0.03 mA/W, respectively, under UV illumination. Full article

Metal–semiconductor–metal (MSM) configuration of perovskite photodetectors (PPDs) suggests easy and low-cost manufacturing. However, the basic structures of MSM PPDs include vertical and lateral configurations, which require the use of expensive materials such as transparent conductive oxides or/and sophisticated fabrication techniques such as lithography. Integrating metallic nanowire-based electrodes into the perovskite photo-absorber layer to form one-half of the MSM PPD structure could potentially resolve the key issues of both configurations. Here, a manufacturing of solution-processed and self-powered MSM PPDs with embedded silver nanowire electrodes is demonstrated. The embedding of silver nanowire electrode into the perovskite layer is achieved by treating the silver nanowire/perovskite double layer with a methylamine gas vapor. The evaporated gold layer is used as the second electrode to form MSM PPDs. The prepared MSM PPDs show a photoresponsivity of 4 × 10⁻⁵ AW⁻¹ in the UV region and 2 × 10⁻⁵ AW⁻¹ in the visible region. On average, the devices exhibit a photocurrent of 1.1 × 10⁻⁶ A under white light (75 mW cm⁻²) illumination with an ON/OFF ratio of 83.4. The results presented in this work open up a new method for development and fabrication of simple, solution-processable MSM self-powered PPDs. Full article

In this work, Ga₂O₃ films were deposited on sapphire substrates using a plasma-enhanced atomic layer deposition system with trimethylgallium precursor and oxygen (O₂) plasma. To improve the quality of Ga₂O₃ films, they were annealed in an O₂ ambient furnace system for 15 min at 700, 800, and 900 °C, respectively. The performance improvement was verified from the measurement results of X-ray diffraction, X-ray photoelectron spectroscopy, and photoluminescence spectroscopy. The optical bandgap energy of the Ga₂O₃ films decreased with an increase of annealing temperatures. Metal-semiconductor-metal ultraviolet C photodetectors (MSM UVC-PDs) with various Ga₂O₃ active layers were fabricated and studied in this work. The cut-off wavelength of the MSM UVC-PDs with the Ga₂O₃ active layers annealed at 800 °C was 250 nm. Compared with the performance of the MSM UVC-PDs with the as-grown Ga₂O₃ active layers, the MSM UVC-PDs with the 800 °C-annealed Ga₂O₃ active layers under a bias voltage of 5 V exhibited better performances including photoresponsivity of 22.19 A/W, UV/visible rejection ratio of 5.98 × 10⁴, and detectivity of 8.74 × 10¹² cmHz^1/2W⁻¹. Full article

In this paper, 100 nm-thick zinc oxide (ZnO) films were deposited as a seed layer on Corning glass substrates via a radio frequency (RF) magnetron sputtering technique, and vertical well-aligned Fe-doped ZnO (FZO) nanorod (NR) arrays were then grown on the seed layer-coated substrates via a low-temperature solution method. FZO NR arrays were annealed at 600 °C and characterized by using field emission scanning microscopy (FE-SEM) and X-ray diffraction spectrum (XRD) analysis. FZO NRs grew along the preferred (002) orientation with good crystal quality and hexagonal wurtzite structure. The main ultraviolet (UV) peak of 378 nm exhibited a red-shifted phenomenon with Fe-doping by photoluminescence (PL) emission. Furthermore, FZO photodetectors (PDs) based on metal–semiconductor–metal (MSM) structure were successfully manufactured through a photolithography procedure for UV detection. Results revealed that compared with pure ZnO NRs, FZO NRs exhibited a remarkable photosensitivity for UV PD applications and a fast rise/decay time. The sensitivities of prepared pure ZnO and FZO PDs were 43.1, and 471.1 for a 3 V applied bias and 380 nm UV illumination, respectively. Full article

The effects of Mg on the microstructural, optical, and electrical properties of sol-gel derived ZnO transparent semiconductor thin films and the photoelectrical properties of photodetectors based on Mg_xZn_1−xO (where x = 0 to 0.3) thin films with the metal-semiconductor-metal (MSM) configuration were investigated in this study. All the as-synthesized ZnO-based thin films had a single-phase wurtzite structure and showed high average transmittance of 91% in the visible wavelength region. The optical bandgap of Mg_xZn_1−xO thin films increased from 3.25 to 3.56 eV and the electrical resistivity of the films rose from 6.1 × 10² to 1.4 × 10⁴ Ω·cm with an increase in Mg content from x = 0 to x = 0.3. Compared with those of the pure ZnO thin film, the PL emission peaks of the MgZnO thin films showed an apparent blue-shift feature in the UV and visible regions. The photo-detection capability was investigated under visible, UVA, and UVC light illumination. Linear I-V characteristics were obtained in these ZnO-based photodetectors under dark and light illumination conditions, indicating an ohmic contact between the Au electrodes and ZnO-based thin films. It was found that the pure ZnO photodetector exhibited the best photoconductivity gain, percentage of sensitivity, and responsivity under UVA illumination. Under UVC illumination, the photoconductivity gain and percentage of sensitivity of the MgZnO photodetectors were better than those of the pure ZnO photodetector. Full article

The fabrication of a single pixel sensor, which is a fundamental element device for the fabrication of an array-type pixel sensor, requires an integration technique of a photodetector and transistor on a wafer. In conventional GaN-based ultraviolet (UV) imaging devices, a hybrid-type integration process is typically utilized, which involves a backside substrate etching and a wafer-to-wafer bonding process. In this work, we developed a GaN-based UV passive pixel sensor (PPS) by integrating a GaN metal-semiconductor-metal (MSM) UV photodetector and a Schottky-barrier (SB) metal-oxide-semiconductor field-effect transistor (MOSFET) on an epitaxially grown GaN layer on silicon substrate. An MSM-type UV sensor had a low dark current density of 3.3 × 10⁻⁷ A/cm² and a high UV/visible rejection ratio of 10³. The GaN SB-MOSFET showed a normally-off operation and exhibited a maximum drain current of 0.5 mA/mm and a maximum transconductance of 30 μS/mm with a threshold voltage of 4.5 V. The UV PPS showed good UV response and a high dark-to-photo contrast ratio of 10³ under irradiation of 365-nm UV. This integration technique will provide one possible way for a monolithic integration of the GaN-based optoelectronic devices. Full article

AlGaN semiconductors are promising materials in the field of ultraviolet (UV) detection. We fabricated AlGaN/GaN UV metal–semiconductor–metal (MSM) photodiodes with two back-to-back interdigitated finger electrodes comprising reduced graphene oxide (rGO). The rGO showed high transparency below the wavelength of 380 nm, which is necessary for a visible-blind photodetector, and showed outstanding Schottky behavior on AlGaN. As the photocurrent, dark current, photoresponsivity, detectivity, and cut-off wavelength were investigated with the rGO/AlGaN MSM photodiodes with various Al mole fractions, systematic variations in the device characteristics with the Al mole fraction were confirmed, proving the potential utility of the device architecture combining two-dimensional materials, rGO, and nitride semiconductors. Full article

ZnO, Al-doped ZnO (AZO), and Ga-doped ZnO (GZO) semiconductor thin films were deposited on glass substrates via a sol-gel spin-coating process for application in a photoconductive ultraviolet (UV) detector. The doping concentrations of Al and Ga were 1.0 at % in the precursor solutions. In this study, the microstructural features and the optical and electrical properties of sol-gel-derived ZnO, AZO, and GZO thin films were compared, and the performance of ZnO-based UV photodetectors under ultraviolet A (UVA) light were measured. Experimental results confirmed the synthesis of single-phase nanocrystalline ZnO-based thin films and the successful substitution of Al and Ga into Zn sites in ZnO crystals. The results also demonstrated that the optical transmittance and electrical properties of ZnO thin films could be improved by Al and Ga doping. UV photodetectors based on ZnO-based thin films, having a metal-semiconductor-metal (MSM) configuration, were fabricated with Al inter-digitated electrodes. All photodetectors showed an ohmic nature between semiconductor and electrode contacts and exhibited a sharp increase in photocurrent under illumination with UVA light. We found that the MSM UV photodetector based on the GZO semiconductor thin film exhibited the best UV response (I_UVA/I_dark) of 73.3 and the highest photocurrent responsivity of 46.2 A/W under UVA light (power density ~0.825 mW/cm²) at 5 V bias. Full article

The UV-to-visible rejection ratio is one of the important figure of merits of GaN-based UV photodetectors. For cost-effectiveness and large-scale fabrication of GaN devices, we tried to grow a GaN epitaxial layer on silicon substrate with complicated buffer layers for a stress-release. It is known that the structure of the buffer layers affects the performance of devices fabricated on the GaN epitaxial layers. In this study, we show that the design of a buffer layer structure can make effect on the UV-to-visible rejection ratio of GaN UV photodetectors. The GaN photodetector fabricated on GaN-on-silicon substrate with a step-graded Al_xGa_−xN buffer layer has a highly-selective photoresponse at 365-nm wavelength. The UV-to-visible rejection ratio of the GaN UV photodetector with the step-graded Al_xGa_1−xN buffer layer was an order-of-magnitude higher than that of a photodetector with a conventional GaN/AlN multi buffer layer. The maximum photoresponsivity was as high as 5 × 10⁻² A/W. This result implies that the design of buffer layer is important for photoresponse characteristics of GaN UV photodetectors as well as the crystal quality of the GaN epitaxial layers. Full article

In this study, high-density single crystalline Ga-doped ZnO (GZO) nanorods were grown on glass substrate by the hydrothermal method. The structural and optoelectronic properties of Ga-doped ZnO nanorods were studied. The microstructure of the GZO was studied by scanning electrical microscope (SEM). The structural characteristics of the GZO were measured by X-ray diffraction (XRD). It was found that the peaks related to the wurtzite structure ZnO (100), (002), and (101) diffraction peaks. The (002) peak indicates that the nanorods were preferentially oriented in the c-axis direction. The existence of Ga was examined by energy diffraction spectra (EDS), indicating the Ga atom entered into the ZnO lattice. The optical properties of the GZO were measured by photoluminescence spectra. It was found that all GZO nanorod arrays showed two different emissions, including UV (ultraviolet) and green emissions. GZO nanorod metal-semiconductor-metal (MSM) ultraviolet (UV) photodetectors (PD) were also fabricated. The photo-current and dark-current constant ratio of the fabricated PD was approximately 15.2 when biased at 1 V. Full article