Increasing Illumination Intensity Research Articles

Light and magnetic field double modulation on the resistive switching behavior in BaTiO3/FeMn/BaTiO3 trilayer films

An obvious resistive switching (RS) was observed in BaTiO/3FeMn/BaTiO3 (BFB) trilayer films under different conditions. The RS effect was enhanced in light irradiation and restrained in magnetic field. The ratio of high resistance to low resistance of samples annealed at 500 °C is larger than 1500, and the samples showed a good stability. SET and RESET voltages decrease with increasing illumination intensity, but the ON/OFF ratio showed an inverse tendency. Conduction mechanisms in low resistance and high resistance were determined to be Ohmic and space charge limited conduction (SCLC) mechanism, respectively. A redistribution of oxygen vacancies and bound magnetic polaron (BMP) were used for explanation of the mechanism of RS behavior in this system under light irradiation and magnetic field, respectively.

Synthesis and characterization of pure and graphene (Gr)-doped organic/polymer nanocomposites to investigate the electrical and photoconductivity properties of Au/n-GaAs structures

Abstract In the present study, Schottky diodes (SDs) were produced with and without interlayer to evaluate synthesis and characterization of pure and graphene (Gr)-doped organic/polymer nanocomposites on the electrical (i.e. ideality factor (n), saturation current (Io), barrier height (ФBo), shunt (Rsh) and series (Rs) resistances) and photoconductivity (i.e. photocurrent (Iph), responsivity (R), photoconductivity sensitivity (Sph), photosensitivity) parameters of Au/n-GaAs devices. Electrical parameters of Au/n-GaAs (MS) type (D1), Au/pure PVA/n-GaAs (MPS) type (D2) and Au/Gr-doped PVA/n-GaAs (MPS) type (D3) structures have been obtained to the current-voltage (I-V) measurements using thermionic emission (TE) theory, Cheung's method and modified Norde's methods and, moreover, compared each other. The resistance (Ri) for these SDs was additionally calculated from Ohm's law as function of voltage for each diode. Experimental research indicate that there is an increase in Rsh value and a decrease in Rs value and rectifier rate (RR = IF/IR) for Gr-doped PVA structure according to the pure PVA structure, when the values of Rs and Rsh are compared between each other. Also, the ΦBo values for D2 and D3 type SDs is lower than that of D1 type SDs. The value of Rs for Gr-PVA interlayer 286 times lower than without interlayer. Therefore, it can be said that the PVA (pure and Gr-doped) interfacial layer effectively modified the barrier height (BH) according to without interlayer. As photoconductivity properties for SDs, the Iph values in the reverse bias increased with illumination intensities (50–200 W). On the other hand, it is clear that there are an increase for D2 and D3 and a decrease for D1 with increasing illumination intensities in the R and Sph values. So, they are sensitive to illumination intensities and exhibit a photoconductivity effect. As a result, Gr-doped PVA interlayer substantially got better the quality and performance of Au/PVA/n-GaAs SDs.

Influence of Irradiation Time on Structural, Morphological Properties of ZnO-NRs Films Deposited by MW-CBD and Their Photodiode Applications

Microwave-assisted chemical bath deposition (MW-CBD) was used to deposit zinc oxide nanorods (ZnO-NRs) films by using different microwave irradiation time. The films exhibit a good crystallinity having a hexagonal wurtzite phase formation. Although the dominant preferred orientation was not observed for the ZnO-5 and ZnO-10, ZnO-8 showed (002) preferred orientation. The emission scanning electron microscope (FESEM) showed almost randomly oriented hexagonal nanorods on the surface. A slight decrease in the length of the observed hexagonal nanorods due to the increase in the irradiation time was observed, changing from 550 nm to 300 nm. The p-Si/n-ZnO-NRs heterojunction photodiodes were fabricated. The current-voltage characteristics of these photodiodes were investigated under dark and different illumination intensity. An increase in the reverse current with increasing illumination intensity confirmed that the fabricated photodiodes exhibited a photoconducting behavior. In addition, the barrier height and series resistance values of the photodiodes were determined from capacitance-voltage measurements.

Organic semiconductor photosensors

Coumarin doped with poly(3-hexylthiophene)/p-Si photodiodes were prepared by the drop-casting technique. The current–voltage characteristics of the prepared diodes with the structure of Al/P3HT:Coumarin/p-Si/Al diodes were investigated under dark and various illumination intensities using both I–V and C–V methods. Using both illuminated DC and transient I–V and C–V measurements, the photocurrents are shown to depend on light intensity with the P3HT:Coumarin ratio influencing photoresponsivity. The photocurrents increase with increasing illumination intensity. C–V measurements show that the capacitance of the diode depends on voltage, frequency and illumination, indicating the existence of a continuous distribution of interface states that can be described in terms of organic-organic polymer blend domains in additional to the well studied metal-semiconductor interface states. The best responses were found to be for the diode having 10% Coumarin weight. These results suggest that the Al-p-Si/P3HT:Coumarin/Al diode can be used as a photosensor.

A new shape memory alloy film/p-Si solar light four quadrant detector for solar tracking applications

Shape memory alloys (SMAs) are promising materials for industrial and electronic actuators applications. The Cu-Al-Mn-Ni shape memory alloy was coated as a Schottky contact on p-Si substrate to fabricate a four quadrant sensor using a vacuum coating system. A front illuminated shape memory film-p-type silicon -based four-quadrant solar light Schottky sensor was fabricated using the various metal contact masks. The electrical and photoresponse properties of Cu-Al-Mn-Ni/p-Si diode were investigated. These properties of the diode were analyzed under in a wide range of frequencies and illumination intensities. The reverse current of the diode increases with increasing illumination intensities. This result confirms that the diode exhibits both photoconducting and photovoltaic behavior. The forward bias current of the diode increases exponentially with voltage confirming rectification behavior. Electronic parameters such as ideality factor, barrier height and series resistance of the diode were determined from I-V characteristics and Cheung’s functions. The transient photocurrent, photocapacitance and photoconductance measurements indicate that the diode is very sensitive to illumination. Also, the admittance measurements of the diode exhibited a decrease in capacitance and increase in conductance with increasing frequency. The frequency dependence of capacitance and conductance is attributed to the presence of interface states. It is evaluated that Cu-Al-Mn-Ni/p-Si shape memory alloy film/p-Si based four quadrant detector can be used in solar tracking applications.

Single crystal ruthenium(II) complex dye based photodiode

The electrical and photoresponse properties of Ruthenium(II) complex dye based on photodiode were analyzed by current, capacitance and conductance measurements performed in a wide illumination intensity and frequency range. It was observed that the reverse current increases with increasing illumination intensity. The results confirm that the photodiode exhibits a photoconducting behavior. Also, the transient photocurrent, photocapacitance and photoconductance of the photodiode were investigated as a function of time. It was observed that the values of these parameters increase after illuminating and reach back to original value after turning off the illumination. In addition, the interface states and series resistance of the photodiode were determined from capacitance/conductance–voltage measurements. The value of these parameters decreases with increasing frequency. The obtained experimental results suggest that the photodiode with Ruthenium/Ru(II) complex thin film could be used in various optoelectronic devices and applications.

N-(CdMgTe/CdTe)/(p-(CdTe/ZnCdTe/ZnTe)/p-GaAs heterostructure diode for photosensor applications

High quality n-(CdMgTe:I/n-CdTe:I)/(p-CdTe:N/p-ZnCdTe:N/p-ZnTe:N)/p-GaAs heterojunction diodes have been fabricated by molecular beam epitaxial growth. The illumination effect on the complex impedance and conductivity of heterostructure diode was investigated. The illumination intensities were taken up to the 200 mW/cm2 with frequency range of 42 Hz to 1 MHz. The observed real and imaginary parts of the complex impedance were strongly dependent on the illumination frequency. The inverse relation was observed between the illumination intensity and the complex impedance. The relaxation mechanism of the diode was analyzed by the Cole–Cole plots. The radius of the Cole–Cole curve decreases with increasing illumination intensity. This suggests a mechanism of illumination dependent on the relaxation process. It is also found that the conductivity increases linearly with increasing the illumination intensity. We can conclude that the new design heterostructure diode in our work is a good candidate in photodetector and optoelectronic applications.

Graphene controlled organic photodetectors

Drop casting deposition technique was used to fabricate graphene oxide doped methylene blue (GO doped MB) photodiode, Al/p-Si/GO doped MB/Au. The effects of illumination on the current–voltage (I–V) characteristics of the Al/p-Si/GO doped MB/Au Schottky diode for optical sensing applications were explored. The reverse current of the diode in the reverse bias increases with the increasing illumination intensities. The obtained trends for both ideality factor and barrier height are in agreement, suggesting that they are both affected by GO doping. The photosensitivity of the photodiodes was investigated. The highest photosensitivity was observed for the diode having 0.03 GO:MB ratio with Iphoto/Idark ratio of 8.67×103 at 100mW/cm2 under 10V. The rectification ratio was of the order of 104. In addition, the capacitance–voltage (C–V) and conductance–voltage (G–V) measurements of the diode were studied in the frequency range of 10kHz–1MHz. The measured values of the capacitance decrease with the increasing frequency. The decrease in capacitance was explained on the basis of interface states. The photoelectrical properties of Al/p-Si/GO doped MB/Au devices indicate that the prepared diodes can be used both as a photodiode and a photocapacitor in optoelectronic device applications.

Photoresponse and photocapacitor properties of Au/AZO/p-Si/Al diode with AZO film prepared by pulsed laser deposition (PLD) method

The electrical and photoresponse properties of Au/nanostructure AZO/p-Si/Al diode were investigated. Al-doped ZnO (AZO) thin films were deposited via pulsed laser deposition method on silicon substrate. Structural properties of the films were performed by using transmission electron microscopy and X-ray powder diffraction (XRD). The XRD patterns showed that the AZO films are polycrystalline with hexagonal wurtzite structure preferentially oriented in (002) direction. Electrical and photoresponse properties of the diode were analyzed under in a wide range of frequencies and illumination intensities. It is observed that the reverse current of the diode increases with increasing illumination intensity. This result confirms that the diode exhibits both photoconducting and photovoltaic behavior. Also, the transient photocurrent, photocapacitance and photoconductance measured as a function of time highly depend on transient illumination. In addition, the frequency dependence of capacitance and conductance is attributed to the presence of interface states.

Electrical and photoresponse properties of Al/graphene oxide doped NiO nanocomposite/p-Si/Al photodiodes

The electrical and photoconducting properties of Al/graphene oxide doped NiO nanocomposite/p-Si/Al photodiodes with various graphene oxide contents were investigated by using current–voltage, transient photocurrent, photocapacitance and photoconductance measurements at various illumination intensities in the range of 10–100 mW/cm2. Graphene oxide doped NiO nanocomposite thin films were prepared by sol–gel spin method. Experimental results indicate that the reverse current of the photodiodes increases with the increasing illumination intensity. The value of transient photocurrent, photocapacitance and photoconductance measured as a function of time increases after illuminating and returns to original value after turning off the illumination. In addition, the frequency-dependent capacitance and conductance measurements was performed to indicate the existence of interface states. The obtained results suggest that the fabricated diode can be used as a photodiode in optoelectronic applications.

Organic photodetector with coumarin-adjustable photocurrent

Drop casting technique was used to fabricate Al/p-Si/coumarin doped fullerite/Al diodes. The effects of coumarin doping on the photoresponse properties of the diodes were investigated. The forward bias current of the diodes increases exponentially with voltage confirming rectification behavior. The reverse current of the diodes increases with increasing illumination intensities. The photocurrent of the diodes is higher than the dark current. The obtained m value indicates that the photocurrent exhibited a linear photoconducting behavior. The coumarin doped fullerite diodes indicate a non-ideal behavior with obtained ideality factors. The obtained barrier height value of the Al/p-Si/coumarin doped fullerite/Al diode is comparable to that of the conventional Al/p-Si (ϕb=0.58eV) Schottky diode. The measured values of the capacitance decrease with the increasing frequency. The decrease in capacitance was explained on the basis of interface states. It was concluded that the obtained barrier height and interface state density values of the diode are modified doping fullerite with coumarin. The obtained results suggest that the fabricated diodes could be used as an optical sensor in various optoelectronic applications.

Illumination and Voltage Dependence of Electrical Characteristics of Au/0.03 Graphene-Doped PVA/n-Si Structures via Capacitance/Conductance-Voltage Measurements

Au/n-Si (MS) structures with a high dielectric interlayer (0.03 graphene-doped PVA) are fabricated to investigate the illumination and voltage effects on electrical and dielectric properties by using capacitance-voltage (C-V) and conductance-voltage (G/ω-V) measurements at room temperature and at 1 MHz. Some of the main electrical parameters such as concentration of doping atoms (ND), barrier height (ϕB(C - V)), depletion layer width (WD) and series resistance (Rs) show fairly large illumination dispersion. The voltage-dependent profile of surface states (Nss) and resistance of the structure (Ri) are also obtained by using the dark-illumination capacitance (Cdark-Cill) and Nicollian-Brews methods, respectively. For a clear observation of changes in electrical parameters with illumination, the values of ND, WD, ϕB(C - V) and Rs are drawn as a function of illumination intensity. The values of ND and WD change almost linearly with illumination intensity. On the other hand, Rs decreases almost exponentially with increasing illumination intensity whereas ϕB(C - V) increases. The experimental results suggest that the use of a high dielectric interlayer (0.03 graphene-doped PVA) considerably passivates or reduces the magnitude of the surface states. The large change or dispersion in main electrical parameters can be attributed to generation of electron-hole pairs in the junction under illumination and to a good light absorption. All of these experimental results confirm that the fabricated Au/0.03 graphene-doped PVA/n-Si structure can be used as a photodiode or a capacitor in optoelectronic applications.

Plasmon-induced dynamics of H2 splitting on a silver atomic chain

Localized surface plasmon resonances (LSPR) supported in metal nanostructures can be efficiently harnessed to drive photocatalytic reactions, whose atomic scale mechanism remains a challenge. Here, real-time dynamics of H2 photosplitting on a linear silver atomic chain, upon exposure to femtosecond laser pulses, has been investigated using time-dependent density functional theory. The wavelength dependent H2 splitting process is strongly coupled to LSPR excitation in silver chain. We identify that hot electrons produced in the silver chain by plasmon excitation are transferred to the antibonding state of the adsorbed H2 and trigger H2 dissociation, consistent with experimental observations. Increasing illumination intensity and the length of atomic chain promote H2 splitting, thanks to stronger LSPR. Dynamic electronic response can be quantitatively described within the present approach, providing insights towards a complete fundamental understanding on plasmon-induced chemical reactions at the microscopic scale.

A novel photodiode based on Ruthenium(II) complex containing polydentate pyridine as photocatalyst

Ruthenium(II)-complex thin film, bearing pyridine-based tridentate was deposited on p-Si substrate by spin coating technique. The I–V measurements across the junction showed rectifying behavior. The reverse bias current of the heterojunction diode increased with increasing illumination intensity. The sensitivity to the light of I–V characteristics was attributed to the photocatalytic effect of Ruthenium(II)-complex. Ruthenium(II)-complex thin film exhibited a transparency higher than 70% in the visible part of the spectrum. The band gap of Ruthenium(II)-complex film was calculated to be 4.42eV. The reflectance data can be analyzed to determine optical constants such as refractive index and dielectric constant. The results indicate that Ruthenium(II)-complex can be used in fabrication of high photosensitive diodes.

Graphene–cobalt phthalocyanine based on optoelectronic device for solar panel tracking systems

The photoconducting properties of graphene–cobalt phthalocyanine organic semiconductor photodiodes were investigated. GO doped cobalt phthalocyanine (CoPc) thin films were prepared with various graphene oxide (GO) contents. The electrical properties of the diodes were analyzed by using current–voltage and capacitance/conductance–voltage measurements. The reverse current of the diodes increases with the increasing illumination intensity. The transient photocurrent, photocapacitance, and photoconductance measurements of the diodes were also investigated. The photocurrent, capacitance and conductance increase after illuminating and returns to original value after turning off the illumination. Graphene–cobalt phthalocyanine based on optoelectronic device exhibited both a photodiode and photocapacitor behavior under solar light illuminaton.

Analysis of the Junction Properties of C/GaSe<sub>0.5</sub>S<sub>0.5</sub>/C Back-to-Back Schottky-Type Photodetectors

In this paper, a C/GaSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> /C metal-semiconductor-metal photodetector is suggested and described. The device is explored by means of current-voltage and capacitance-voltage (C-V) characteristics under different photoexcitation intensities. It was observed that the design of the back-to-back Schottky device has reduced the dark current of the normal Ag/GaSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> /C Schottky diode by 13 times and increased the photosensitivity from 3.8 to ~2.1×10 <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</sup> . The device exhibited a barrier height of 0.842 eV in the dark. The barrier height is reduced via photoexcitation. In addition, the C/GaSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> /C device exhibited an ON/OFF switching property from low injection OFF to high injection ON at specific biasing voltages. This voltage decreased with the increasing illumination intensity. On the other hand, the C-V characteristics of the device, which was recorded for an ac input signal with 100 MHz at different levels of photoexcitation shifted up when the intensity of light was increased. When the same measurement was repeated at signal frequency of 1.6 GHz, the C-V characteristics reflected a different level of capacitance response. These features of C/GaSe <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> S <sub xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">0.5</sub> /C photodetectors nominate the device to be used as multipurpose optical switches being suitable to store different levels of electromagnetic energy at microwave frequencies.

Influence of illumination intensity on the electrical characteristics and photoresponsivity of the Ag/ZnO Schottky diodes

In this article, the ZnO thin films were grown by RF-magnetron sputtering on ITO glass substrates. The Schottky diodes with the configuration of Ag/ZnO/ITO have been fabricated and it has been observed that the diodes exhibit a good rectification. The structural and optical properties of the ZnO films were investigated by X-ray diffractometry and spectrophotometry. The current–voltage (I–V) characteristics of the Ag/ZnO diode were measured under various illuminations. We use the forward bias current–voltage measurements to determine the electrical parameters such as ideality factor, barrier height and series resistance of the diode. The Ag/ZnO Schottky diode exhibits a non-ideal behavior due to the interfacial layer, the interface states and the series resistance. It is found that the barrier height and ideality factor values are strong functions of illumination intensity. The results show that the ideality factor and the barrier height decrease with increasing illumination intensity. The values of Rs obtained from Cheung and Norde methods are decreased with increasing illumination intensity. Photoresponse characteristics of the diode have been analyzed and it is clear that the diode shows a fast response. It is evaluated that the prepared diodes can be used as optoelectronic devices.

A novel type heterojunction photodiodes formed junctions of Au/LiZnSnO and LiZnSnO/p-Si in series

Lithium–zinc–tin–oxide thin films were prepared by sol gel method. The structural and optical properties of the films were investigated. The optical band gaps of the LiZnSnO films were found to be 3.78eV for 0at.% Li, 3.77eV for 1at.% Li, 3.87eV for 3at.% Li and 3.85eV for 5at.% Li, respectively. Au/LiZnSnO/p-Si/Al photodiodes were fabricated using a lithium–zinc–tin–oxide (LZTO, Li–Zn–Sn–O) layer grown on p-Si semiconductor. The electrical characteristics of the photodiodes were analyzed by current–voltage, capacitance–voltage and conductance–voltage measurements. The reverse current of the diodes increases with both the increasing illumination intensity and Li content. It was found that the Li-doped ZTO photodiodes exhibited a better device performance than those with an undoped ZTO.

Electrical and photoconducting properties of nanorod in based spinel compound/p-Si photodiode by sol–gel spin coating technique

A new Schottky diode (InFe2O4/p-Si/Al) was fabricated using the sol–gel spin coating technique. The current–voltage (I–V) characteristics of the Schottky diode were investigated under various illumination intensities. The value of ideality factor (n) and zero-bias barrier height (ΦB0) for all illuminations was determined by using the forward-bias I–V measurements, and were found to be about 4.20 and 0.72 eV, respectively. The reverse current of the diode in the reverse bias increases with the increasing illumination intensities. Also, the photocurrent under illumination is higher than the dark current. In addition, the capacitance–voltage (C–V) and conductance–voltage (G–V) measurements of the diode were studied in the frequency range of 10 kHz–1 MHz. The measured values of the C decrease with the increasing frequency. The decrease in capacitance was explained on the basis of interface states. To obtain the real C and G of the diode, the measured values of C and G were corrected to eliminate the effect of series resistance. The obtained results suggest that the diode can be used as a photodiode in optoelectronic applications.

Dielectric and Photo-Dielectric Properties of TlGaSeS Crystals

The room temperature, dark and photo-dielectric properties of the novel crystals TlGaSeS are investigated in the frequency, intensity and biasing voltage having ranges of ~ 1–120 MHz, 14–40 klux and 0–1 V, respectively. The crystals are observed to exhibit a dark high frequency effective dielectric constant value of ~ 10·65 × 103 with a quality factor of ~ 8·84 × 104 at ~ 120 MHz. The dielectric spectra showed sharp resonance– antiresonance peaks in the frequency range of ~ 25–250 kHz. When photoexcited, pronounced increase in the dielectric constant and in the quality factor values with increasing illumination intensity are observed. Signal amplification up to ~ 33% with improved signal quality up to ~ 29% is attainable via photoexcitation. On the other hand, the illuminated capacitance–voltage characteristics of the crystals reflected a downward shift in the voltage biasing and in the built-in voltage of the device that is associated with increase in the uncompensated carrier density. The increase in the dielectric constant with increasing illumination intensity is ascribed to the decrease in the crystal's resistance as a result of increased free carrier density. The light sensitivity of the crystals, the improved dielectric properties and the lower biasing voltage obtained via photoexcitation and the well-enhanced signal quality factor of the crystals make them promising candidates for optical communication systems.