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Pure CuI and Zn-substituted CuI (CuI:Zn) semiconductor thin films, and metal-semiconductor-metal (MSM) photodetectors were fabricated on glass substrates by a low-temperature solution process. The influence of Zn substitution concentration (0–12 at%) on the microstructural, optical, and electrical characteristics of CuI thin films and its role in improving the optoelectronic performance of CuI MSM photodetectors were investigated in this study. Incorporation of Zn cation dopant into CuI thin films improved the crystallinity and increased the average crystalline size. XPS analysis revealed that the oxidation state of Cu ions in all the CuI-based thin films was +1, and the estimated values of [Cu]/[I] for the CuI:Zn thin films were lower than 0.9. It was found that the native p-type conductivity of polycrystalline CuI thin film was converted to n-type conductivity after the incorporation of Zn ions into CuI nanocrystals, and the electrical resistivity decreased with increases in Zn concentration. A time-resolved photocurrent study indicated that the improvements in the optoelectronic performance of CuI MSM photodetectors were obtained through the substitution of Zn ions, which provided operational stability to the two-terminal optoelectronic device. The 8 at% Zn-substituted CuI photodetectors exhibited the highest response current, responsivity, and EQE, as well as moderate specific detectivity. [ABSTRACT FROM AUTHOR]

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. [ABSTRACT FROM AUTHOR]

• Transparent Ga 2 O 3 semiconductor thin films were deposited by magnetron sputtering. • Results indicated the 1% oxygen flow ratio film had device quality characteristics. • Device with Ni-Ni symmetrical electrodes had good photoresponse characteristics. • Self-powered device realized by using paired Ni-Al asymmetric metal contacts. Gallium oxide (Ga 2 O 3) thin films were deposited on quartz substrates under different oxygen flow ratios (O 2 /[O 2 +Ar], 0%−5%) by radio-frequency (RF) magnetron sputtering technique followed by thermal annealing at 900 °C for 2 h under N 2 atmosphere. The influence of the oxygen concentration on the structural and optical characteristics of Ga 2 O 3 thin films was investigated. The Ga 2 O 3 thin films prepared under an oxygen flow ratio of 1% exhibited optimum crystal quality and the lowest oxygen vacancy (V O) concentration according to X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and photoluminescence (PL) investigations. All as-prepared polycrystalline Ga 2 O 3 thin film samples exhibited high average transmittance above 87.8% in the visible spectral region and the 0% and 1% thin films had optical bandgap energies of about 4.9 eV. We also fabricated metal−semiconductor−metal (MSM) photodetectors based on 1% Ga 2 O 3 thin films by employing pairs of Ni−Ni symmetrical or Ni−Al asymmetrical interdigitated electrodes. The Ni−Ni photodetector had a high on/off current ratio (I on /I off > 105), a responsivity of 88.7 mA/W, and specific detectivity of 4.81×1010 J at 10 V bias under ultraviolet light-C (UVC) illumination, and the Ni−Al photodetector exhibited self-driven behavior along with short rise and fall times (0.45 s and 0.69 s, respectively). [ABSTRACT FROM AUTHOR]

Ultraviolet (UV) irradiation-assisted thermal annealing is used for the fabrication of Mg doped InZnO (MIZO) semiconductor thin films and metal-semiconductor-metal (MSM) type photodetectors on alkali-free glasses at a low temperature of 300 °C. In this study, the effects of UV irradiation time on the structural features and the optical and electrical properties of sol-gel derived MIZO thin films were investigated, and the photoresponse properties of MIZO photodetectors fabricated using UV-assisted thermal annealing (UV-TA) and conventional thermal annealing (CTA) were compared. The molar ratio of In:Zn was fixed at 3:2, and the Mg content was maintained at 20 at% ([Mg]/[In+Zn]) in the precursor solution. After a spin-coating and drying procedure was performed twice, the dried sol-gel films were heated on a hotplate at 300 °C and exposed to UV irradiation in ambient air. The UV irradiation time was adjusted to 1, 2, 3, and 4 h. All annealed MIZO thin films had a dense microstructure, uniform film thickness, and flat surface and exhibited good optical transmittance (> 86.0%). The mean resistivity decreased with increasing irradiation time, and the samples irradiated for 4 h exhibited the lowest mean resistivity of 4.4×10 2 Ω-cm. Current-voltage (I-V) characteristics showed that the MIZO photodetectors operated in the photoconductive mode. Under illumination with UVC light, the MIZO photodetectors exhibited an I light -to-I dark ratio of 7.7 × 10 2 and had a photoresponsivity of 5.0 A/W at a bias of 5 V. [ABSTRACT FROM AUTHOR]

In this study, a p-type wide-bandgap oxide semiconductor CuGaO 2 thin film was grown on quartz substrate by sol-gel method. The authors report the influence of annealing temperature on the phase transformation, structural features, and electrical properties of sol-gel derived Cu-Ga-O thin films. At relatively low annealing temperatures (≤900 °C), the films are a mixture of CuGa 2 O 4 , CuGaO 2 , and CuO phases. At relatively high annealing temperatures (≥925 °C), the majority phase in the films is delafossite CuGaO 2 . All as-prepared Cu-Ga-O thin films exhibited p-type conductivity, as confirmed by Hall measurements. The mean electrical resistivity of the Cu-Ga-O films decreased from 3.54×10 4 Ω-cm to 1.35×10 2 Ω-cm and then increased slightly to 3.51×10 2 Ω-cm when the annealing temperature was increased from 850 °C to 950 °C. We found that annealing the Cu-based oxide thin films at 925 °C produced nearly phase-pure CuGaO 2 thin films with good densification. Such thin films exhibited the best electrical properties: a mean electrical resistivity of 1.35×10 2 Ω-cm, and a mean hole concentration of 1.60×10 16 cm −3 . In addition, we also fabricated and characterized MSM-type CuGaO 2 UV photodetectors on quartz substrates. [ABSTRACT FROM AUTHOR]

The n-type zinc-tin oxide (ZTO) and p-type nickel oxide (NiO) semiconductor thin films were prepared by the sol-gel spin coating process. The influence of 4 at% Mg and Cu doping on the microstructural, optical, and electrical characteristics of NiO thin films and physical properties of ZTO thin film were investigated. In addition, bi-layered ZTO/NiO thin films were grown onto Corning glasses to develop a visible light transparent p-n heterojunction ultraviolet (UV) photodetector. Mg doping slightly enhances the visible transparency and enlarges the optical bandgap energy, while Cu doping decreases the visible transparency and narrows the optical bandgap energy. The electrical properties of NiO sol-gel thin films were improved through Mg and Cu doping. According to the current-voltage (I–V) characteristic curves, the n-ZTO/p-NiO:Mg photodetector had the highest rectification ratio of 11.7 and on-to-off current ratio of 18.3 at 5 V bias. Under UV illumination, the three kinds of devices all exhibited a self-powered nature, while the Mg- and Cu-doped NiO devices had better photoresponse characteristics than the undoped NiO device. It was found that the Mg-doped NiO devices displayed the best photoconductivity gain and sensitivity, and acceptable response speed and responsivity, with applied reverse bias of 1 V. [Display omitted] • n-ZTO and p-NiO semiconductor films were prepared via sol-gel spin-coating process. • Results of XRD, SEM, XPS confirmed the incorporation of Mg and Cu into NiO films. • Fabrication of p-n heterojunctions for developing oxide based UV photodetectors. • The n-ZTO/p-NiO based heterojunction was adopted in self-powered UV photodetectors. • NiO:Mg device exhibited the best photosensing characteristics than those of others. [ABSTRACT FROM AUTHOR]

Solar-blind ultraviolet (UV) photodetectors with an amorphous zinc−tin oxide (a-ZTO) sensing layer have been fabricated on alkali-free glass substrates by a sol-gel method and spin coating technique. The as-prepared a-ZTO semiconductor thin films are highly transparent (>88.5%) in the visible region and exhibit moderate electrical properties at room temperature. The effects of changes in the asymmetry ratio of the line-width of a pair of Al interdigitated electrodes on the photoelectrical characteristics of solution-processed a-ZTO metal−semiconductor−metal (MSM) UV photodetectors was investigated. These photodetector devices had good photosensing properties, and their current-voltage (I–V) characteristic exhibited obvious rectification behavior under UV light illumination when operated at bias voltages of -3 V–3 V. Experimental results showed that the responsivity and specific detectivity of the a-ZTO MSM photodetectors increased with increases in the asymmetry ratio of a pair of Al interdigital electrodes. The a-ZTO MSM UV photodetector operated at 3 V bias voltage had the best responsivity of 7.42 mA/W and the highest specific detectivity of 6.35 × 107 J when the asymmetry ratio of electrodes was 10:1. • The a-ZTO films are highly transparent and exhibit moderate electrical properties. • Increasing asymmetry ratio of electrodes reduce resistance of detectors in dark. • I–V curves of devices exhibit obvious rectification behavior under UV illumination. • Performance of a-ZTO photodetectors were enhanced by increasing asymmetry ratio. • Low bias-voltage driving a-ZTO photodetectors fabricated by sol-gel spin-coating. [ABSTRACT FROM AUTHOR]

Highlights: [•] Transparent GZO, GZO:B, GZO:Al semiconductor films were prepared by sol–gel method. [•] The GZO:Al films had the lowest resistivity and the highest Hall mobility. [•] All ZnO-based UV photodetectors operated in the photoconductive mode. [•] The GZO:Al detector had the highest responsivity of 3.22A/W at a bias of 5V. [ABSTRACT FROM AUTHOR]

ZnO, Ga-doped ZnO (GZO), In-doped ZnO (IZO), and Ga–In co-doped ZnO (GIZO) nanowire arrays were grown on a template of sapphire/p-GaN thin film by low-temperature hydrothermal method for fabricating self-powered p-GaN/n-ZnO heterojunction ultraviolet (UV) photodetectors. The authors investigated the effects of Ga or In single doping and Ga–In co-doping on the microstructural features and optical properties of hydrothermally synthesized ZnO nanowires and conducted a comparison study on the photosensing characteristics and photoelectrical response performances of four kinds of p-n heterojunction UV photodetectors. X-ray diffraction (XRD) examination showed that the as-synthesized ZnO-based nanowire arrays had a single-phase hexagonal wurtzite structure and exhibited a preferential orientation along the (002) plane. Scanning electron microscope (SEM) observation evidenced that the type of dopants modified the morphology and average diameter of the nanowires. The average diameter of ZnO-based nanowires was in the range of 61–101 nm. Room-temperature photoluminescence (PL) spectra revealed that these as-synthesized ZnO-based nanowires had high crystalline quality. The current-voltage (I–V) curves of heterojunction photodetectors based on p-GaN thin film/n-ZnO based nanowire arrays exhibited a rectification characteristic in darkness and under UV illumination. Under UV illumination, the GIZO device had the best photosensing characteristics of all the devices under 5 V bias. The light-to-dark current ratio was close to 6.0 at 5 V bias and the turn-on voltage was lower than 1.8 V. The presented p-GaN/n-GIZO heterojunction UV photodetector realized superior photoresponse performance at zero-bias voltage as compared to single-doped and un-doped ZnO devices. • ZnO-based nanowire arrays were synthesized by low-temperature hydrothermal method. • Results of XRD, PL, EDS confirm the incorporation of Ga and In into ZnO nanowires. • Fabrication of p-n heterojunctions for developing high performance photodetectors. • GIZO device exhibited the best photosensing characteristics than those of others. • The p-GaN/n-GIZO heterojunction was adopted in self-powered UV photodetectors. [ABSTRACT FROM AUTHOR]

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 MgxZn1−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 MgxZn1−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. [ABSTRACT FROM AUTHOR]