Papers by Keyword: Heterojunction

Abstract: We prepared n-type nanocrystalline iron disilicide (NC-FeSi₂)/intrinsic (i) ultrananocrystalline diamond/amorphous carbon composite (UNCD/a-C)/p-type Si heterojunctions and evaluated as photodiodes. UNCD/a-C and NC-FeSi₂ films were deposited by coaxial arc plasma deposition and pulsed laser deposition, respectively. The capacitance-voltage and current-voltage characteristics of heterojunctions were measured at room temperature. The inserted i-UNCD/a-C layer to form pin heterojunctions reduced the capacitance and dark current as compared with those in the case of pn heterojunctions. The build-in potential of heterojunctions was estimated to be 1.2 eV. The prepared heterojunctions showed typical rectifying action and a response for an illumination with a 6 mW, 1.31 μm laser. The recombination process is the predominant mechanism of current transport in the heterojunctions. The dynamic resistance area product and detectivity were 1.54 × 10³ Ω cm² and 5.0 × 10⁸ cmHz^1/2/W at-1 V. The evident improvement in the device performance was demonstrated, which should be due to the reduction of dark current by i-UNCD/a-C layer.

Abstract: In this work, n-type β-FeSi₂/intrinsic Si/p-type Si heterojunctions were prepared by facing-targets direct-current sputtering. We measured their current-voltage characteristics at low temperatures ranging from 300 K down to 50 K and investigated their ideality factor, saturation current and series resistance using thermionic emission theory and Cheung’s method. From thermionic emission theory, the ideality factor and saturation current density were calculated from the slope of the linear part from the forward lnJ-V and the straight line intercept of lnJ-V at zero voltage, respectively. When the temperature decreased from 300 K down to 50 K, the ideality factor increased from 1.12 to 11.13, whereas the saturation current density decreased from 2.09 × 10^-6 A/cm² to 1.06 × 10^-9 A/cm². Using Cheung’s method, we plotted the relations of dV/d(lnJ)-J and H(J)-J in order to estimate the series resistance from the slope of both plots. In addition, we estimated the ideality factor from a y-axis intercept of the dV/d(lnJ)-J plot. The series resistances from both plots were consistent with each other and increased with the decreasing temperature. The ideality factor estimated by Cheung’s method was in agreement with that obtained from estimation by thermionic emission theory.

Abstract: (001)-oriented LiNbO₃ (LN) ferroelectric films were grown on (100)-oriented n-type Si substrates using 15 nm-thick ZnO layers as buffers by pulse laser deposition technique and the LN/ZnO/n-Si heterojunctions were fabricated. Obvious photoswitching characteristics to white light were observed when the reverse voltages were applied on the LN/ZnO/n-Si heterojunction. High performance was exhibited, such as a large ON/OFF ratio, short photoresponse time, steady ON or OFF states, and well reversible. The results were discussed in terms of the band diagrams of the LN/ZnO/Si heterojunctions in this work.

Abstract: Photoresponse characteristic from efficient exciton dissociated heterojunction based on copper phthalocyanine (CuPc) and fullerene (C60) layers was observed the different spectrum responses under positive and negative biases. The nanostructures of CuPc and C60 thin films were fabricated between transparent indium tin oxide (ITO) and aluminum (Al) electrodes. The 100 nm thick of CuPc and C60 layers were deposited on patterned ITO glass substrates by thermal evaporation with quartz thickness monitor. Photoresponses of the fabricated devices were investigated by current measuring as a function of wavelength in range of 400 to 700 nm. Measured current in Al/C60/CuPc/ITO structure when applied negative voltage to ITO electrode is higher than that of positive voltage case. Under monochromatic light, the photoresponse characteristic of Al/C60/CuPc/ITO structure under negative bias shows dominate response current peak at around 450 nm and double peaks in range of 500-700 nm originated from C60 and CuPc layers, respectively. These two response characteristics can be described by the combination of responses from Al/C60/ITO and Al/CuPc/ITO structures. The response current characteristics of Al/C60/ITO and Al/CuPc/ITO structures also agree with the optical absorptions of C60 and CuPc layers, respectively. By applying positive bias to Al/C60/CuPc/ITO structure, the photoresponse characteristic has only one peak at about 450 nm that is similar to the response in Al/C60/ITO structure only. This indicates that under positive bias, the photocurrent only from C60 layer can be observed.

Abstract: We fabricated the copper oxide (Cu₂O or Cu₃O₄)/perovskite CH₃NH₃PbI₃ heterojunction solar cells via ultrasonic spray deposition technique. Perovskite CH₃NH₃PbI₃ thin films were sprayed directly from precusor solution onto a copper oxide pre-coated ITO substrate. We analyzed the properties of the as-deposited perovskite thin films. The surface morphologies of Perovskite CH₃NH₃PbI₃ thin films were examined by optical microscope, and their crystallinities were confirmed by X-ray diffraction measurements. Large CH₃NH₃PbI₃ crystal with grain size of ~20μm was observed. The solar cells device achieved a conversion efficiency of 4.13%.

Abstract: Nanocrystalline Si:Er (nc-Si:Er) films were sputtered on p-Si (100) substrates and diffused with phosphorus to form PN heterojunction diodes. The I-V properties of these diodes were characterized. And the properties of diodes without Er were compared with n-nc-Si:Er/p-Si. It was found that n-nc-Si:Er/p-Si diodes had better characteristics. Solar cells based on n-nc-Si:Er/i-nc-Si/p-Si were fabricated and characterized. The photoelectrical conversion efficiency of 18.13% for n-nc-Si:Er/i-nc-Si/p-Si solar cell was achieved.

Abstract: AgBr nanoparticle decorated mesoporous Bi₂WO₆ architectures was fabricated via a facile precipitation-deposition process. As-prepared AgBr/Bi₂WO₆ heterojunction was characterized by XRD, FE-SEM and HR-TEM. The photocatalytic activities of the samples were evaluated by the photodegradation of methyl orange (MO) under visible light irradiation. The results showed that AgBr nanoparticles decrodation great improved the photocatalytic activity of Bi₂WO₆. The 2.0at%AgBr/Bi₂WO₆ sample exhibited the best photocatalytic activity for decolorization of MO.Furthermore, the mechanism of enhanced photocatalytic activity for hierarchical AgBr/Bi₂WO₆ heterojunction was also discussed.

Abstract: The physical and electrical properties of p⁺-Si/n-4H-SiC and n⁺-Si/n-4H-SiC heterojunctions fabricated by using surface-activated bonding (SAB) were investigated by scanning electron microscopy (SEM), current-voltage (I-V) and breakdown characteristics measurements at raised ambient temperatures. The I-V characteristics for the reverse bias voltages of the two junctions were compared with the expectations based on Frenkel-Poole, and trap-assisted tunneling models. The results of calculations using the trap-assisted tunneling model were close to the measurements.

Abstract: Si wafers were directly bonded to 6H-SiC wafers without the formation of an intermediate layer. Heterojunctions of n-Si/n-SiC and p-Si/n-SiC exhibited ohmic and rectifying characteristics, respectively, as expected based on their band lineups. Band bending of Si at the bonded interface was observed for Si/semi-insulating 6H-SiC heterointerfaces. This band bending can be explained by either heterojunction formation based on Anderson’s model or the existence of negative charge with a density of ~2 × 10¹⁰ cm⁻² at the Si/SiC interface.

Abstract: Heterojunction photocatalyst containing one dimensional nanostructures exhibits interesting size, shape and material-dependent photocatalytic properties compared to single-component counterpart. In this work, we develop a simple two-step strategy to WO₃/TiO₂ heterojunction based on WO₃ nanorods and TiO₂ nanoparticles. The as-obtained heterojunction features core-shell morphology and has the advantage of extended solar light response, enhanced chemical stability and easy recyclability. As such, it exhibits high photocatalytic activity toward organic pollutants degradation including rodamine B dye and gaseous acetaldehyde.