Showing papers on "Schottky barrier published in 2010"
TL;DR: The results show that the piezo-phototronic effect can enhance the detection sensitivity more than 5-fold for pW levels of light detection.
Abstract: We demonstrate the piezoelectric effect on the responsivity of a metalsemiconductormetal ZnO micro-/nanowire photodetector. The responsivity of the photodetector is respectively enhanced by 530%, 190%, 9%, and 15% upon 4.1 pW, 120.0 pW, 4.1 nW, and 180.4 nW UV light illumination onto the wire by introducing a0.36% compressive strain in the wire, which effectively tuned the Schottky barrier height at the contact by the produced local piezopotential. After a systematic study on the Schottky barrier height change with tuning of the strain and the excitation light intensity, an in-depth understanding is provided about the physical mechanism of the coupling of piezoelectric, optical, and semiconducting properties. Our results show that the piezo-phototronic effect can enhance the detection sensitivity more than 5-fold for pW levels of light detection.
441 citations
TL;DR: The gigantic enhancement in sensitivity of up to 5 orders of magnitude shows that an effective usage of the Schottky contact can be very beneficial to the sensitivity of nanosensors.
Abstract: A Schottky barrier can be formed at the interface between a metal electrode and a semiconductor. The current passing through the metal-semiconductor contact is mainly controlled by the barrier height and barrier width. In conventional nanodevices, Schottky contacts are usually avoided in order to enhance the contribution made by the nanowires or nanotubes to the detected signal. We present a key idea of using the Schottky contact to achieve supersensitive and fast response nanowire-based nanosensors. We have illustrated this idea on several platforms: UV sensors, biosensors, and gas sensors. The gigantic enhancement in sensitivity of up to 5 orders of magnitude shows that an effective usage of the Schottky contact can be very beneficial to the sensitivity of nanosensors.
312 citations
TL;DR: In this article, a model for the internal quantum efficiency of Schottky barrier photodetectors suitable for the detection of optical radiation below the bandgap energy of the semiconductor is presented.
Abstract: Phenomenological models for the internal quantum efficiency of Schottky barrier photodetectors suitable for the detection of optical radiation below the bandgap energy of the semiconductor are presented and discussed. The detection mechanism is internal photoemission from the metal film into the semiconductor substrate. Three detector configurations are considered: the first consists of a thick metal film on a semiconductor substrate forming a single Schottky barrier; the second consists of a thin metal film on a semiconductor substrate also forming a single Schottky barrier; and the third consists of a thin metal film buried in semiconductor and forming two Schottky barriers (one along each metal-semiconductor interface). In the three cases, illumination through the semiconductor substrate is assumed. The two thin-film configurations provide enhanced internal quantum efficiencies due to multiple hot carrier reflections within the metal film, with the double-barrier case providing the greatest enhancement due to emission over two barriers. The models proposed are based on assessing the emission probability of hot carriers as a function of their energy, taking into account multiple reflections within the metal film and energy losses due to internal scattering (e.g., with phonons and cold carriers). The thin-film single-barrier model was tested via comparisons with responsivity measurements reported in the literature for PtSi/p-Si and Pd2Si/p-Si detectors.
265 citations
TL;DR: In this article, a series of CIGS thin film solar cells with differently prepared heterojunctions has been investigated by admittance spectroscopy, capacitancevoltage (CV) profiling, and temperature dependent current-voltage measurements, and the results strongly contradict the common assignment of the N1 response to a donor defect at or close to the heterointerface.
Abstract: A series of Cu(In,Ga)Se2 (CIGS) thin film solar cells with differently prepared heterojunctions has been investigated by admittance spectroscopy, capacitance-voltage (CV) profiling, and temperature dependent current-voltage (IVT) measurements. The devices with different CdS buffer layer thicknesses, with an In2S3 buffer or with a Schottky barrier junction, all show the characteristic admittance step at shallow energies between 40 and 160 meV, which has often been referred to as the N1 defect. No correlation between the buffer layer thickness and the capacitance step is found. IVT measurements show that the dielectric relaxation frequency of charge carriers in the CdS layers is smaller than the N1-resonance frequency at low temperatures where the N1 step in admittance is observed. These results strongly contradict the common assignment of the N1 response to a donor defect at or close to the heterointerface. In contrast, an explanation for the N1 response is proposed, which relates the admittance step to a non-Ohmic back-contact acting as a second junction in the device. The model, which is substantiated with numerical device simulations, allows a unified explanation of characteristic admittance, CV, and IVT features commonly observed in CIGS solar cells.
260 citations
TL;DR: In this article, chemical dopants that modulate the electronic properties of few-layer graphene films synthesized by chemical vapor deposition were systematically modulated by the reduction potential values of dopants.
Abstract: It is essential to control the electronic structure of graphene in order to apply graphene films for use in electrodes. We have introduced chemical dopants that modulate the electronic properties of few-layer graphene films synthesized by chemical vapor deposition. The work function, sheet carrier density, mobility, and sheet resistance of these films were systematically modulated by the reduction potential values of dopants. We further demonstrated that the power generation of a nanogenerator was strongly influenced by the choice of a graphene electrode with a modified work function. The off-current was well quenched in graphene films with high work functions (Au-doped) due to the formation of high Schottky barrier heights, whereas leakage current was observed in graphene films with low work functions (viologen-doped), due to nearly ohmic contact.
244 citations
TL;DR: In this paper, anodic TiO2 nanotube arrays prepared by electrochemical anodization were used to fabricate ultraviolet (UV) photodetectors, which exhibit the highest UV sensitive photoconductance due to the pure anatase phase of the TiO 2.
Abstract: Anodic TiO2 nanotube arrays prepared by electrochemical anodization were used to fabricate ultraviolet (UV) photodetectors. The devices annealed at 450 degrees C exhibit the highest UV-sensitive photoconductance due to the pure anatase phase of the TiO2. The large surface area and one-dimensional nanostructure of the TiO2 nanotubes lead to great photosensitivity (more than 4 orders of magnitude) and fast response with rise time and decay time of 0.5 and 0.7 s, respectively. High responsivity of 13 A/W is found under 1.06 mW/cm(2) UV (lambda = 312 nm) illumination at 2.5 V bias, which is much higher than those of commercial UV photodetectors. The high responsivity mainly comes from the internal gain induced by the desorption of oxygen from the nanotube surfaces and the reduction of the Schottky barrier at TiO2/Ag contact under UV illumination. The devices are promising for large-area UV photodetctor applications.
233 citations
TL;DR: In this article, a high quality n-GaN drift-layer with an electron mobility of 930 cm2 V-1 s-1 was obtained by optimizing the growth conditions by reducing the intensity of yellow luminescence using conventional photoluminescence measurements.
Abstract: Vertical GaN Schottky barrier diodes (SBDs) were fabricated on freestanding GaN substrates with low dislocation density High quality n-GaN drift-layer with an electron mobility of 930 cm2 V-1 s-1 was obtained by optimizing the growth conditions by reducing the intensity of yellow luminescence using conventional photoluminescence measurements The specific on-resistance (RonA) and the breakdown voltage (VB) of the SBDs were 071 mΩ cm2 and over 1100 V, respectively The figure of merit (VB2/RonA) was 17 GW/cm2, which is the highest value among previously reported SBDs for both GaN and SiC
214 citations
TL;DR: In this article, a lateral Schottky-based rectifier called the charge-plasma diode realized on ultrathin silicon-on-insulator was proposed, which utilizes the workfunction difference between two metal contacts, palladium and erbium, and the silicon body.
Abstract: We present a new lateral Schottky-based rectifier called the charge-plasma diode realized on ultrathin silicon-on-insulator. The device utilizes the workfunction difference between two metal contacts, palladium and erbium, and the silicon body. We demonstrate that the proposed device provides a low and constant reverse leakage-current density of about 1 fA/μm with ON/OFF current ratios of around 107 at 1-V forward bias and room temperature. In the forward mode, a current swing of 88 mV/dec is obtained, which is reduced to 68 mV/dec by back-gate biasing.
197 citations
TL;DR: A new principle for controlling the coupling among mechanical, photonic, and electrical properties of ZnO nanowires is described, which could be potentially useful for fabricating piezo-phototronic devices.
Abstract: The localized coupling between piezoelectric and photoexcitation effects of a ZnO micro/nanowire device has been studied for the first time with the goal of designing and controlling the electrical transport characteristics of the device. The piezoelectric effect tends to raise the height of the local Schottky barrier (SB) at the metal−ZnO contact, while photoexcitation using a light that has energy higher than the band gap of ZnO lowers the SB height. By tuning the relative contributions of the effects from piezoelectricity via strain and photoexcitation via light intensity, the local contact can be tuned step-by-step and/or transformed from Schottky to Ohmic or from Ohmic to Schottky. This study describes a new principle for controlling the coupling among mechanical, photonic, and electrical properties of ZnO nanowires, which could be potentially useful for fabricating piezo-phototronic devices.
194 citations
TL;DR: A surface plasmon polariton detector is demonstrated at infra-red wavelengths and holds promise for short-reach optical interconnects and power monitoring applications.
Abstract: A surface plasmon polariton detector is demonstrated at infra-red wavelengths. The device consists of a metal stripe on silicon forming a Schottky contact thereon and supporting surface a plasmon polariton mode that is strongly confined and localised to the metal–semiconductor interface. Detection of optical radiation below the bandgap of silicon (at infrared wavelengths) occurs through internal photoemission. Responsivities of 0.38 and 1.04 mA/W were measured via end-fire coupling to a tapered optical fibre, at room temperature and at a wavelength of 1280 nm, for gold and aluminium stripes on n-type silicon, respectively. The device can be integrated with other structures used in nano-plasmonics, nano-photonics or silicon-based photonics, and it holds promise for short-reach optical interconnects and power monitoring applications.
180 citations
TL;DR: In this paper, a model which describes the bipolar resistive switching in transition-metal oxides is presented, which simultaneously predicts three key features of experimental measurements: the rectifying behavior in high resistance states, abrupt switching, and the existence of bistable resistance states.
Abstract: A model which describes the bipolar resistive switching in transition-metal oxides is presented. To simulate the effect of switching, we modeled results of doping by oxygen vacancies along with variable Schottky barrier and resistor. The model simultaneously predicts three key features of experimental measurements: the rectifying behavior in high resistance states, abrupt switching, and the existence of bistable resistance states. Our model is based on modulation of Schottky barrier formed by variable resistance oxide layer at the metal-oxide interface. Experimental measurements of the $\text{Pt}/{\text{Ta}}_{2}{\text{O}}_{5}/{\text{TaO}}_{x}/\text{Pt}$ structure matched very well with our nonvolatile resistive switching model.
TL;DR: In this article, the photoresponse of a large area infrared photodetector from a thin film of chemically reduced graphene oxide (RGO) sheets was studied and it was found that the photocurrent either increases, decreases, or remains almost zero depending upon the position of the laser spot with respect to the electrodes.
Abstract: We fabricated large area infrared photodetector devices from thin film of chemically reduced graphene oxide (RGO) sheets and studied their photoresponse as a function of laser position. We found that the photocurrent either increases, decreases, or remain almost zero depending upon the position of the laser spot with respect to the electrodes. The position sensitive photoresponse is explained by Schottky barrier modulation at the RGO film-electrode interface. The time response of the photocurrent is dramatically slower than single sheet of graphene possibly due to disorder from the chemical synthesis and interconnecting sheets.
TL;DR: In this article, the photoresponse of a large area infrared photodetector device from a thin film of chemically reduced graphene oxide (RGO) sheets was studied as a function of laser position.
Abstract: We fabricated large area infrared photodetector devices from thin film of chemically reduced graphene oxide (RGO) sheets and studied their photoresponse as a function of laser position. We found that the photocurrent either increases, decreases or remain almost zero depending upon the position of the laser spot with respect to the electrodes. The position sensitive photoresponse is explained by Schottky barrier modulation at the RGO film-electrode interface. The time response of the photocurrent is dramatically slower than single sheet of graphene possibly due to disorder from the chemically synthesis and interconnecting sheets.
TL;DR: In this paper, a Ti/TiO2/Pt oxide diode with excellent rectifying characteristics was fabricated by the asymmetric Schottky barriers at the Ti/ TiO2 (0.13 eV) interfaces.
Abstract: We have fabricated a Ti/TiO2/Pt oxide diode with excellent rectifying characteristics by the asymmetric Schottky barriers at the Ti/TiO2 (0.13 eV) and the TiO2/Pt (0.73 eV) interfaces. Instead of homogeneous conduction, the current transport is governed by the localized oxygen-deficient TiO2 filaments. In addition, the reproducible resistive-switching exists in the same structure, triggered by the forming process. The transition between two modes is ascribed to the destruction of the interface barriers at forming. The rectification stable up to 125 °C and 103 cycles under ±3 V sweep without interference with resistive-switching shows satisfactory reliability of TiO2 diodes for one diode-one resistor memory devices.
TL;DR: In this article, the Schottky barrier height of 0.42 V and ideality factor of 1.6 at room temperature was obtained for a single ZnO nanowire with a response time of ∼55 s.
Abstract: Vertically aligned ZnO nanowires were grown on c-plane sapphire substrate by metal organic chemical vapor deposition technique. The nanowires were single crystalline and structurally uniform and did not exhibit any noticeable defects. Pt/ZnO single nanowire Schottky diodes were fabricated by using e-beam lithography and then characterized by measuring temperature-dependent I−V characteristics. The diode exhibited a low Schottky barrier height of 0.42 V and ideality factor of 1.6 at room temperature. Temperature-dependent hydrogen-sensing measurements were carried out with different hydrogen concentrations. A good sensing characteristic (S ≈ 90%) has been observed at room temperature with a response time of ∼55 s.
Patent•
02 Feb 2010TL;DR: In this article, various structures and methods for improving the performance of trench-shielded power semiconductor devices and the like are described, and the authors also describe various methods to improve the performance.
Abstract: Various structures and methods for improving the performance of trench-shielded power semiconductor devices and the like are described.
TL;DR: In this paper, a zinc oxide (ZnO) nanorod metal-semiconductor-metal ultraviolet detectors with different metal contact were fabricated on glass substrate by a single-step hydrothermal reaction.
Abstract: Lateral zinc oxide (ZnO) nanorod metal-semiconductor-metal ultraviolet detectors with different metal contact were fabricated on glass substrate by a single-step hydrothermal reaction. With the combined effect from a ZnO seed layer and an inactive layer for nanorod growth, ZnO nanorods could grow laterally and aligned between the interdigitated electrodes. When the growth process is terminated, the integration of ZnO nanorods into a function device can be achieved in the meantime. The structure can be modeled as being composed of two same Schottky barriers connected back to back, in series with a resistance of R. The devices are visible-blind and have great response even in mid ultraviolet region. The photodetectors with Ni electrode show better performance both in the aspect of photocurrent and response time, owing to the larger Schottky barrier at the Ni/ZnO interface. By surface coating with polymethyl methacrylate, the response has been further improved. Our approach provides a simple and effective wa...
TL;DR: In this paper, a self-powered ultraviolet photodetector based on a single Sb-doped ZnO nanobelt bridging an Ohmic contact and a Schottky contact was reported.
Abstract: We report a self-powered ultraviolet photodetector based on a single Sb-doped ZnO nanobelt bridging an Ohmic contact and a Schottky contact. The photoresponse sensitivity and the response time of the fabricated device are as high as 2200% and less than 100 ms, respectively. The performance of the device dramatically degrades as the Sb-doping concentration decreases in the ZnO nanobelt. The possible mechanisms have been proposed and discussed.
TL;DR: In this paper, a hydrogen sensor based on a palladium/nanowire Schottky barrier field effect transistor that operates at room temperature is presented, which can reliably detect H2 concentrations in the range from 3 ppm to 5% and has a sensitivity of 6.9%/ppm at 1000 ppm.
Abstract: This work presents the design, fabrication, and characterization of a hydrogen sensor based on a palladium/nanowire Schottky barrier field-effect transistor that operates at room temperature. The fabricated sensor consists of boron-doped silicon nanowire arrays that are contact printed on top of a SiO2/Si substrate with subsequently evaporated Pd contacts. The fabrication process is compatible with post-CMOS and plastic substrate integration as it can be completed at temperatures below 150 ◦ C with good yield and repeatability. The sensor can reliably and reversibly detect H2 concentrations in the range from 3 ppm to 5% and has a sensitivity of 6.9%/ppm at 1000 ppm. A response distinguishable from drift and noise is produced in less than 5 s for H2 concentrations over 1000 ppm and less than 30 s for concentrations over 100 ppm. The sensor settles to 90% of the final signal value in about 1 h at lower concentrations and less than 1 min at 10,000 ppm H2. Drift over an 87-h measurement period is below 5 ppm H2 concentration. © 2009 Elsevier B.V. All rights reserved.
TL;DR: The low density of electronic states in single wall carbon nanotubes is exploited to demonstrate active, electronic modulation of their Fermi level offset relative to n-type silicon in a nanotube-Si Schottky junction solar cell.
Abstract: We exploit the low density of electronic states in single wall carbon nanotubes to demonstrate active, electronic modulation of their Fermi level offset relative to n-type silicon in a nanotube-Si (metal-semiconductor) Schottky junction solar cell. Electronic modulation of the Fermi level offset, the junction interface dipole and a field developed across the depletion layer modifies the built-in potential in the device and its power generation characteristics. As produced (before modulation) devices exhibit ∼8.5% power conversion efficiency (PCE). With active modulation the PCE is continuously and reversibly changed from 4 to 11%.
TL;DR: The Schottky contact based photon detection was demonstrated using CdS (visible light responsive), silicon (indirect n-type oxygen-non-adsorbing), and CuO(indirect p-typeoxy-adsorbbing) nanowire nanosensors as discussed by the authors.
Abstract: The Schottky contact based photon detection was demonstrated using CdS (visible light responsive), silicon (indirect n-type oxygen-non-adsorbing), and CuO (indirect p-type oxygen-adsorbing) nanowire nanosensors. With changing one of the two nanowire-electrode contacts from ohmic to Schottky, detection sensitivities as high as 105% were achieved by the CdS nanowire nanosensor operated at the reverse bias mode of −8 V, which was 58 times higher than that of the corresponding ohmic contact device. The reset time was also significantly reduced. In addition, originally light nonresponsive silicon and CuO nanowires became light responsive when fabricated as a Schottky contact device. These improvements in photon detection can be attributed to the Schottky gating effect realized in the present nanosensor system by introducing a Schottky contact.
TL;DR: In this article, the polarization effect within the AlGaN barrier was incorporated into calculation of the near-surface electrical field ES underneath the Schottky contact metal, which determined the field-dependent characteristics of reverse gate leakage current of high-frequency capacitance-voltage measurement combined with electrostatic analysis is used to estimate ES as a function of reverse bias voltage.
Abstract: In this work, we include the polarization effect within the AlGaN barrier into calculation of the near-surface electrical field ES underneath the Schottky contact metal which determines the field-dependent characteristics of reverse gate leakage current of AlGaN/GaN high electron mobility transistors High-frequency capacitance-voltage measurement combined with electrostatic analysis is used to estimate ES as a function of reverse bias voltage The resultant log(I/ES) versus ES curves over a temperature range from 293 to 453 K agree well with the predicted model of Frenkel–Poole (FP) emission of electrons up to the conductive states of threading dislocations Around zero bias, the reverse polarization-field-induced FP emission current is balanced by a forward defect-assisted tunneling current, both of which follow the same temperature dependent characteristics
TL;DR: In this article, a 2D device simulation for organic thin-film transistors (OTFTs) was carried out to reveal the characteristic difference between staggered and planar structures, and the simulation results indicated that the source electrode of the staggered structure has better ability to supply the current than that of the planar structure.
Abstract: A 2-D device simulation for organic thin-film transistors (OTFTs) was carried out to reveal the characteristic difference between staggered and planar structures. Assuming the OTFT with Schottky barrier contact, the staggered-structure TFT has more current flow, bigger field-effect mobility, and lower contact resistance than the planar structure. The simulation results indicate that the source electrode of the staggered structure has better ability to supply the current than that of the planar structure.
TL;DR: In this article, the Schottky barrier height of high quality metal/MgO/n-Ge junctions with the ultrathin MgO epitaxially grown on Ge was investigated.
Abstract: Fermi level (FL) pinning at the Ge valence band results in a high Schottky barrier height for all metal/n-Ge contacts. The origin of this pinning effect has been ascribed to either metal induced gap states or surface states arise from the native defects at the Ge surface, such as dangling bonds. The discrepancy in the reported results/explanations is mainly due to the lack of an explicit characterization of a high quality metal/Ge or metal/ultrathin oxide/Ge junction, which should be ideally single crystalline, atomically smooth and free of process-induced defects or intermixing. We report the Schottky characteristics of high quality metal/MgO/n-Ge junctions with the ultrathin MgO epitaxially grown on Ge. We find the depinning effect displays a weak dependence on the MgO thickness, indicating the interface states due to the native defects on Ge surface are likely to play the dominant role in FL pinning. © 2010 American Institute of Physics
TL;DR: The currentvoltage characteristics of Schottky barrier diodes formed on GaN(0001) free-standing substrates with net donor concentrations of 7.6×1015-1.4×1017 cm-3 are discussed in this article.
Abstract: The current–voltage characteristics of Schottky barrier diodes formed on GaN(0001) free-standing substrates with net donor concentrations of 7.6×1015–1.4×1017 cm-3 are discussed. The substrates were grown by hydride vapor phase epitaxy. Ni Schottky contacts were directly formed on chemical–mechanical-polished Ga-polar faces of the substrates. Nearly ideal characteristics for both directions were obtained. The ideality factors for forward characteristics are 1.02–1.05, very close to unity. The reverse characteristics agree well with calculations based on thermionic-field emission theory without any fitting parameter.
TL;DR: In this article, the performance of indium tin oxide/molybdenum oxide/fullerene (ITO/MoOx/C60) photovoltaic cells is highly sensitive to the method of depositing MoOx film.
Abstract: We report that the performance of indium tin oxide/molybdenum oxide/fullerene (ITO/MoOx/C60) photovoltaic cells is highly sensitive to the method of depositing MoOx film. The highest open-circuit voltage and short-circuit current are obtained using thermally evaporated MoOx. In contrast, sputtered MoOx produces lower efficiencies. X-ray and ultraviolet photoemission analyses indicate that pristine thermally evaporated MoOx has a high work function of 6.8 eV and Mo6+ oxidation state, whereas argon-sputtered MoOx is characterized by lower work function and coexistence of both Mo6+ and Mo5+ states. The photovoltaic performance of the ITO/MoOx/C60 cells is consistent with MoOx functioning as the Schottky barrier contact.
TL;DR: In this article, an extremely low contact resistivity of 6-7 × 10-9 Ω·cm2 between Ni0.9Pt0.1Si and heavily doped Si is achieved through Schottky barrier engineering by dopant segregation.
Abstract: An extremely low contact resistivity of 6-7 × 10-9 Ω·cm2 between Ni0.9Pt0.1Si and heavily doped Si is achieved through Schottky barrier engineering by dopant segregation. In this scheme, the implantation of B or As is performed into silicide followed by a low-temperature drive-in anneal. Reduction of effective Schottky barrier height is manifested in the elimination of nonlinearities in IV characteristics.
TL;DR: It is shown in this work that nanostructured Schottky diodes have a functionally different response, characteristic of the large electric field induced by the size scale of the array, and are characterized by a low reverse breakdown voltage.
Abstract: There has been significant interest in using electronically contacted nanorod or nanotube arrays as gas sensors, whereby an adsorbate modifies either the impedance or the Fermi level of the array, enabling detection. Typically, such arrays demonstrate the I-V curves of a Schottky diode that is formed using a metal-semiconductor junction with rectifying characteristics. We show in this work that nanostructured Schottky diodes have a functionally different response, characteristic of the large electric field induced by the size scale of the array. Specifically, they are characterized by a low reverse breakdown voltage. As a result, the reverse bias current becomes a strong function of the applied voltage. In this work, for the first time, we model this unique feature by describing the enhancement effect of high aspect ratio nanostructures on the I-V characteristics of a Schottky diode. A Pt/ZnO/SiC nanostructured Schottky diode is fabricated to verify the theoretical equations presented. The gas sensing properties of the Schottky diode in reversed bias is investigated and it is shown that the theoretical calculations are in excellent agreement with measurements.
TL;DR: In this paper, ZnO single-nanowire (NW)-based devices were fabricated on the same nanowire by e-beam lithography so that both sides had Ohmic contact and one side had Schottky contact.
Abstract: In this report, ZnO single nanowire (NW)-based devices were fabricated on the same nanowire by e-beam lithography so that both sides had Ohmic contact and one side had Schottky contact. Information about the mechanism for low-power UV detection by these devices was unambiguously provided by I-V measurements. Adsorption and desorption of oxygen molecules at the NW surface are responsible for the UV detection by the device with Ohmic contacts on both sides. Barrier height modulations and interface states are responsible for UV detection by the device with Schottky contact on one side.