Fabrication and electrical characterization of thermally deposited amorphous Se0.82In0.18 on n-Si (100)

Amorphous (a-) Se_0.82In_0.18 thin films have been deposited onto n-type silicon (n-Si) single crystal, using the three-temperature technique, in the fabricated configuration of Au/a-Se_0.82In_0.18/n-Si/Al. The current density-voltage (J–V) characteristics have been measured at different isotherms in the range of 198–313 K, thus inspecting the conduction mechanisms comparing with Au/a-Se/n-Si/Al heterojunctions. The analysis proved that the forward bias is characterized by two parts: current increasing exponentially with the applied voltage (low voltage bias region, V<0.2 V), and non-exponentially in the higher voltage region (V>0.2 V). At the low bias region, the current was dominated by a multi-tunneling capture-emission process with a rather temperature-independent effect in the temperature range investigated. However, at the high voltage region, the effect of temperature becomes more pronounced with an ohmic character in the range of 198 to 273 K. For temperatures higher than 273 K, and below the glass transition temperature of a-Se_0.82In_0.18 (T _g～330 K), the high voltage region could be subdivided into two parts: an ohmic conduction range that limited at bias voltage of 0.20 V<V<0.46 V, and a space charge limited current region for bias voltage of V>0.46 V. The reverse J–V characteristics showed a deviation from that of the ideal diode behavior, analogous to that of pure a-Se/n-Si heterojunctions.     

Metal and annealing atmospheres dependence of resistive switching in metal/Nb0.7wt%-SrTiO3 interfaces

We investigated the resistance switching (RS) effect of metal/Nb-doped SrTiO₃ interfaces under different treating conditions. Two types of I–V characteristics appeared due to the modification of Schottky-like barrier and the formation of insulating layer. According to X-ray photoelectron spectroscopy analysis, the change in interface potential barrier was contributed to the migration of oxygen vacancies and electrons trapping/detrapping of carriers in the vicinity of interface. Nonlinear fitting is applied to the curves to study the conduction mechanism of metal/NSTO. For “barrier height” style, Schottky emission and Poole–Frenkel (P–F) emission are dominating; for “insulating layer” style, space-charge-limited current, controls the conduction.     

Superconducting current in hybrid heterojunctions of metal-oxide superconductors: Size and frequency dependences

We have detected experimentally considerable deviations of the frequency dependences of the Shapiro step amplitudes and the critical current of Nb/Au/YBa₂Cu₃O_x thin-film hybrid Josephson heterojunctions prepared on YBa₂Cu₃O_x metal-oxide superconductor films with a tilted c axis from the regularities inherent in Josephson junctions of traditional superconductors with an s-symmetry of the order parameter. It is shown that possible formation of “splintered” fluxons with a size λ_s<λ_J due to faceting of the interface and formation of a chain of nanosize 0 and π junctions must be taken into account in describing processes in lumped heterojunctions (whose size L is smaller than the Josephson penetration depth λ_J determined from the averaged value of the critical current density). For heterojunctions with a size λ_s < L < λ_J, a substantial decrease in the maximal amplitude of the first Shapiro step with increasing voltage (Josephson oscillation frequency) is observed at voltages much smaller than the energy gap in niobium (V « Δ_Nb/e); this effect is manifested most strongly when the size L is greater than λ_s. A fractional Shapiro step and a subharmonic detector response have been observed in the current-voltage characteristics of heterojunctions; the dynamic processes responsible for their emergence and indicating the presence of the second harmonic in the current-phase relation are studied. It is shown that the effect of interface faceting on the current-phase relation increases with a heterojunction size L>λ_s.     

Analysis of interface states and series resistance for Al/PVA:n-CdS nanocomposite metal–semiconductor and metal–insulator–semiconductor diode structures

This paper presents the fabrication and characterization of Al/PVA:n-CdS (MS) and Al/Al₂O₃/PVA:n-CdS (MIS) diode. The effects of interfacial insulator layer, interface states (N _ss ) and series resistance (R _s ) on the electrical characteristics of Al/PVA:n-CdS structures have been investigated using forward and reverse bias I–V, C–V, and G/w–V characteristics at room temperature. Al/PVA:n-CdS diode is fabricated with and without insulator Al₂O₃ layer to explain the effect of insulator layer on main electrical parameters. The values of the ideality factor (n), series resistance (R _s ) and barrier height (? _b ) are calculated from ln(I) vs. V plots, by the Cheung and Norde methods. The energy density distribution profile of the interface states is obtained from the forward bias I–V data by taking into account the bias dependence ideality factor (n(V)) and effective barrier height (? _e ) for MS and MIS diode. The N _ss values increase from mid-gap energy of CdS to the bottom of the conductance band edge for both MS and MIS diode.     

I–V characteristics of ZnO/Cu2O thin film n–i–p heterojunction

ZnO/Cu₂O thin film n–i–p heterojunctions were fabricated by magnetron sputtering. The microstructure, optical, and electrical properties of n-type (n‐) ZnO, insulating (i‐) ZnO, and p-type (p‐) Cu₂O films deposited on glass substrates were characterized by X-Ray diffraction (XRD), spectrophotometer, and the van der Pauw method, respectively. XRD results show that the mean grain size of i-ZnO film is much larger than that of n-ZnO film. The optical band gap energies of n-ZnO, i-ZnO, and p-Cu₂O film are 3.27, 3.47, and 2.00 eV, respectively. The carrier concentration of n-ZnO film is two orders of magnitude larger than that of p-Cu₂O film. The current–voltage (I–V) characteristics of ZnO/Cu₂O thin film n–i–p heterojunctions with different i-ZnO film thicknesses were investigated. Results show that ZnO/Cu₂O n–i–p heterojunctions have well-defined rectifying behavior. All ideality factors of these n–i–p heterojunctions are larger than 2.0. The forward bias threshold voltage and ideality factor increase when i-ZnO layer thickness increases from 100 to 200 nm. An energy band diagram was proposed to analyze the I–V characteristics of these n–i–p heterojunctions.     

Photocarrier injection and the I-V characteristics of La0.8Sr0.2MnO3/SrTiO3:Nb heterojunctions

Oxide heterojunctions made of p-type La_0.8Sr_0.2MnO₃ (LSMO) and niobium-doped n-type SrTiO₃ (STO:Nb) have been fabricated by the pulsed laser deposition (PLD) technique and characterized under UV light irradiation by measuring the current-voltage, photovoltaic properties and the junction capacitance. It is shown that the heterojunctions work as an efficient UV photodiode, in which photogenerated holes in the STO:Nb substrate are injected to the LSMO film. The maximum surface hole density Q/e and external quantum efficiency γ are estimated to be 8.3×10¹² cm⁻² and 11% at room temperature, respectively. They are improved significantly in a p-i-n junction of LSMO/STO/STO:Nb, where Q/e and γ are 3.0×10¹³ cm⁻² and 27%, respectively.     

Response of the capacitance and dielectric loss of the SrRuO<Subscript>3</Subscript>/SrTiO<Subscript>3</Subscript>/SrRuO<Subscript>3</Subscript> film heterostructures to variations in temperature and electric field

Three-layer epitaxial heterostructures with a 750-nm-thick intermediate strontium titanate layer between two strontium ruthenate conductive thin-film electrodes have been grown by laser deposition. Photolithography and ion etching have been used to form film parallel-plate capacitors based on the grown heterostructures. The capacitance (C) and dielectric loss tangent (tanδ) of the parallel-plate capacitors have been measured in the temperature range T = 4.2–300 K at an applied bias voltage of up to ±2.5 V and without it. At T > 100 K, the temperature dependence of the dielectric permittivity (ε) of the SrTiO₃ intermediate layer is well approximated by the Curie–Weiss law taking into account the capacitance induced by the penetration of an electric field into the oxide electrodes. At T ≈ 20 K, the dielectric permittivity ε of the SrTiO₃ intermediate layer decreases by approximately 20% in an electric field of 25 kV/cm. The dielectric loss tangent of the film capacitor heterostructures decreases monotonically with a decrease in the temperature in the range from 300 to 80 K and almost does not depend on the electric field strength. However, in the range from 80 to 4.2 K, the dielectric loss tangent increases nonmonotonically (abruptly) with a decrease in the temperature and decreases significantly in an applied electric field.     

Optical and current transport properties of CuO/ZnO nanocoral p–n heterostructure hydrothermally synthesized at low temperature

We demonstrate the synthesis and investigate the electrical and optical characteristics of ‘nanocorals’ (NCs) composed of CuO/ZnO grown at low temperature through the hydrothermal approach. High-density CuO nanostructures (NSs) were selectively grown on ZnO nanorods (NRs). The synthesized NCs were used to fabricate p–n heterojunctions that were investigated by the current density–voltage (J–V) and the capacitance–voltage (C–V) techniques. It was found that the NC heterojunctions exhibit a well-defined diode behavior with a threshold voltage of about 1.52 V and relatively high rectification factor of ～760. The detailed forward J–V characteristics revealed that the current transport is controlled by an ohmic behavior for V≤0.15 V, whereas at moderate voltages 1.46≤V<1.5 the current follows a J? α?exp(βV) relationship. At higher voltages (≥1.5 V) the current follows the relation J? α? V ², indicating that the space-charge-limited current mechanism is the dominant current transport. The C–V measurement indicated that the NC diode has an abrupt junction. The grown CuO/ZnO NCs exhibited a broad light absorption range that is covering the UV and the entire visible parts of the spectrum.     

Dielectric response of a (1000 nm)SrTiO<Subscript>3</Subscript> layer epitaxially grown on (001)La<Subscript>0.67</Subscript>Ca<Subscript>0.33</Subscript>MnO<Subscript>3</Subscript> to temperature variation and electric field

The structure and dielectric characteristics of the (1000 nm)SrTiO₃ spacer in a (001)SrRuO₃ ‖ (001)SrTiO₃ ‖ (001)La_0.67Ca_0.33MnO₃ trilayer heterostructure grown on a (001)(LaAlO₃)_0.3+(Sr₂AlTaO₆)_0.7 substrate have been studied. Both oxide electrodes, as well as the strontium titanate layer, were cube-on-cube epitaxially grown. The unit cell parameter in the SrTiO₃ layer measured in the substrate plane (3.908±0.003 Å) practically coincided with that determined along the normal to the substrate surface (3.909±0.003 Å). The temperature dependence of the real part of the permittivity ?′ of the SrTiO₃ layer in the range 70–180 K fits the relation (?′)^?1 ～ ? ₀ ^?1 C ₀ ^?1 (T-T _C ) well, where C₀ and T_C are the Curie constant and the Curie-Weiss temperature, respectively, for bulk strontium titanate crystals and ?₀ is the free-space permittivity. The data obtained on the temperature dependence of the permittivity of SrTiO₃ films enabled us to evaluate the effective depth of electric field penetration into the manganite electrode (L _e ≈ 0.5 nm) and the corresponding capacitance (C _e ≈1×10^?6 F/cm²) of the interface separating the (001)SrTiO₃ layer from the (001)La_0.67Ca_0.33MnO₃ bottom electrode.     

Effect of SrTiO3 thickness on the capacitance–voltage characteristics of (La,Sr)CoO3/(Pb,La)(Zr,Ti)O3/SrTiO3/LaVO3 epitaxial heterostructures

We report the effect of SrTiO₃ thickness on the capacitance?Cvoltage (C?CV) characteristics of (La,Sr)CoO₃/(Pb,La)(Zr,Ti)O₃/SrTiO₃/LaVO₃ metal?Cferroelectric?Cinsulator?Csemiconductor (MFIS) epitaxial heterostructures. The C?CV measurement of the heterostructure exhibited the asymmetry of capacitance with respect to gate bias. Within the given thickness range (5?C30 nm), the amount of capacitance reduction at positive gate bias and the rapidness of capacitance reduction decreased with increasing SrTiO₃ thickness, which is consistent with the C?CV characteristics of conventional silicon-based MFIS capacitors. These results suggest that quantitative understanding on the electrical behavior of oxide heterostructures is possible with C?CV analysis, with potentially important implications on their device applications.     

Electrical and interface characteristics of nanocrystalline n-Zn0.5Cd0.5S/p-Cu2S heterojunction structure prepared by dip coating

Nanocrystalline of n-Zn_0.5Cd_0.5S/p-Cu₂S heterojunctions were successfully prepared by the dip coating method. The surface morphology and the composition analysis were made by scanning electron microscopy (SEM) and energy dispersive x-ray (EDX) technique, respectively. Temperature dependent current–voltage characteristics of the heterojunctions were measured in the temperature range 300–400 K with a step of 25 K. The current–voltage (I–V) characteristics exhibit electrical rectification behavior. The zero bias barrier height (Φ_B0) and the ideality factor (n) are affected by temperature. Interface states at the n-Zn_0.5Cd_0.5S/p-Cu₂S heterojunction play a crucial role in determining the electrical characteristics of the heterojunction. The high value of n can be ascribed to the presence of an interfacial layer. The energy distribution profile of the density of interface states (N_ss) was extracted from the forward bias I–V measurements using the width of the depletion region deduced from the capacitance -voltage characteristics at high frequency (1MHz).     

Ferroelectric domain structures and polarization switching characteristics of polycrystalline BiFeO3 thin films on glass substrates

We investigated ferroelectric characteristics of BiFeO₃ (BFO) thin films on SrRuO₃ (SRO)/yttria-stabilized zirconia (YSZ)/glass substrates grown by pulsed laser deposition. YSZ buffer layers were employed to grow highly crystallized BFO thin films as well as SRO bottom electrodes on glass substrates. The BFO thin films exhibited good ferroelectric properties with a remanent polarization of 2P_r = 59.6 μC/cm² and fast switching behavior within about 125 ns. Piezoelectric force microscopy (PFM) study revealed that the BFO thin films have much smaller mosaic ferroelectric domain patterns than epitaxial BFO thin films on Nb:SrTiO₃ substrates. Presumably these small domain widths which originated from smaller domain energy give rise to the faster electrical switching behavior in comparison with the epitaxial BFO thin films on Nb:SrTiO₃ substrates.     

Effect of domain wall on the dielectric properties of the BaTiO3/SrTiO3 superlattices

Based on a phenomenological thermodynamical theory, the effect of the domain wall on the dielectric properties of the polydomain BaTiO₃/SrTiO₃ superlattices with 180° electric domains in the BaTiO₃ layer is investigated. Theoretical analysis indicates that complete polarization suppression and the largest dielectric response take place at approximately 72% and 53% of the critical volume fraction of the SrTiO₃ layer for the domain wall energy parameter A=3×10⁷ and 5×10⁷, respectively. The dielectric properties largely depend on both the volume fraction of the SrTiO₃ layer and the domain wall energy parameter. Moreover, the gigantic dielectric response which occurs in single-domain BaTiO₃/SrTiO₃ superlattices cannot appear due to the 180° polydomain state in the BaTiO₃ layer, which is in agreement with the previous prediction. The high domain wall energy parameter results in the stabilization of the paraelectric state in the BaTiO₃ layer, however, the enhancement of the domain wall energy parameter within a certain scale increases the dielectric properties greatly.     

氧非正分La0.9Ba0.1MnO3-δ/SrTiO3:Nb p-n异质结的整流特性研究

利用脉冲激光沉积技术在掺Nb的SrTiO₃衬底上制备了氧非正分La_0.9Ba_0.1MnO_3-δ/SrTiO₃:Nb p-n异质结.在20—300K这一较宽的温度范围内获得了光滑的整流曲线.整流实验表明：该p-n异质结的正向扩散电压V_D随着温度升高在薄膜金属—绝缘转变温度附近出现极大值,表现出与氧正分La_0.9Ba_{0. 关键词： 0.9}Ba_0.1MnO_3-δ薄膜')" href="#">La_0.9Ba_0.1MnO_3-δ薄膜 锰氧化物p-n结 整流性质     

Organic polymer p-n heterostructures for optoelectronics

The photovoltaic effect due to the photogeneration of charge carriers at the interface in organic polymeric p-n-heterostructures based on the developed composites with hole (doped polyimides, conjugated polymers) and electron (doped polyetherimides and carbazolyl-containing polymers) conduction was observed and studied. The best performance was observed for heterostructures with diffuse and developed (bulk) interface. The maximum energy conversion efficiency was found to be 0.5% at λ = 400–650 nm. Components with enhanced photo and thermal stability were used. A weak photovoltaic effect was observed for heterostructures based on conjugated polymers (with a sharp interface). In this case, the rectification (diode) effect was observed for both dark current and photocurrent due to dark and photo injection of carriers from the electrodes at bias voltages across the cell above the injection threshold (V > V _i ). This conclusion is supported by the observation of recombination electroluminescence of the dopant in the n-layer, indicating a full or partial recombination of carriers at the interface. At V < V _i , photocurrent under reverse bias (+A1, ?ITO) is significantly higher than that under forward bias due to an efficient photogeneration of carriers at the interface and separate transport thereof. A sensitivity of about 100 mA/W at λ = 400–500 nm was reached.     

Electronic relaxation of deep bulk trap and interface state in ZnO ceramics

This paper investigates the electronic relaxation of deep bulk trap and interface state in ZnO ceramics based on dielectric spectra measured in a wide range of temperature, frequency and bias, in addition to the steady state response. It discusses the nature of net current flowing over the barrier affected by interface state, and then obtains temperature-dependent barrier height by approximate calculation from steady I--V (current--voltage) characteristics. Additional conductance and capacitance arising from deep bulk trap relaxation are calculated based on the displacement of the cross point between deep bulk trap and Fermi level under small AC signal. From the resonances due to deep bulk trap relaxation on dielectric spectra, the activation energies are obtained as 0.22 eV and 0.35 eV, which are consistent with the electronic levels of the main defect interstitial Zn and vacancy oxygen in the depletion layer. Under moderate bias, another resonance due to interface relaxation is shown on the dielectric spectra. The DC-like conductance is also observed in high temperature region on dielectric spectra, and the activation energy is much smaller than the barrier height in steady state condition, which is attributed to the displacement current coming from the shallow bulk trap relaxation or other factors.     

Post-fabrication annealing effects on the performance of P3HT:PCBM solar cells with/without ZnO nanoparticles

In this study, P3HT:PCBM organic photovoltaic (OPV) devices, with or without ZnO nanoparticles buffer layer between the photoactive layer (P3HT:PCBM) and the cathode (Al top electrode), were fabricated. The devices were annealed at 145 °C either before or after depositing the top electrode. The objective of this study was to investigate the effects of the ZnO buffer layer and pre-/post-fabrication annealing on the general performance of these devices. The short-circuit current density (J_SC), open-circuit voltage (V_OC) and the external quantum efficiency (EQE) of the OPV devices were improved by the insertion of the ZnO layer and post-fabrication annealing. The post-fabrication annealed devices, with or without the ZnO layer, exhibited higher values of J_SC, V_OC and EQE than those of similar devices annealed before depositing the Al metal. This can be attributed to, among other things, improved charge transport across the interface between the photoactive layer and the Al top electrode as a result of post-annealing induced modification of the interface morphology.     

Dielectric and insulating properties of SrTiO3/Si heterostructure controlled by cation concentration

SrTiO3 films with different cation concentration were deposited on Si(001)substrates by oxide molecular beam epitaxy.An amorphous layer was observed at the interface whose thickness depends on the oxygen pressure and the substrate temperature during growth.Although lowering the oxygen vacancy concentration in SrTiO3led to better insulating performance as indicated by the lowered leakage current density of the heterostructure,the dielectric performance was deteriorated because of the thickened interfacial layer that dominated the capacitance of SrTiO3/Si heterostructure.Instead of adjusting the oxygen vacancy concentration,we propose that controlling the film cation concentration is an effective way to tune the dielectric and insulating properties of SrTiO3/Si at the same time.     

The mechanism of efficiency enhancement with proper thickness of DPVBi layer for blue organic light-emitting devices (BOLED)

We report on the fabrication of blue organic light-emitting devices (BOLEDs) with structure: ITO/NPB/DPVBi/Alq₃/LiF/Al. The hole-blocking effect in NPB/DPVBi interface was indirectly demonstrated and deduced by inserting DCJTB layer. In addition, the effect of the device with better J–V characteristics because of the extra DCJTB layer is discussed as well. However, the performance of devices was investigated with various thicknesses of DPVBi layer. The result shows that the device with proper thickness of DPVBi layer generating better electron injection enhances efficiency and luminance for BOLED.     

Asymmetric electrical properties in Pt/Ba0.5Sr0.5Ti0.99Co0.01O3/Nb-doped SrTiO3 capacitors

Ba_0.5Sr_0.5Ti_0.99Co_0.01O₃ (BSTC) thin films have been fabricated with pulsed laser deposition on Nb-doped SrTiO₃ (STN) substrate. In Pt/BSTC/STN capacitor, we systematically investigated the capacitance, leakage current and polarization versus bias voltage characteristics, and found that curves of capacitance versus voltage and leakage current versus voltage were not symmetric, and polarization hysteresis loop exhibited large relaxation of the remnant polarization at negatively poled state. A detailed analysis of capacitance data demonstrated a difference of the built-in voltage between top Pt/BSTC interface (V_b,t=2.5 V) and bottom BSTC/STN interface (V_b,b=1.1 V). Such different built-in voltages lead to the presence of an internal electric field, which results in asymmetric electric characteristics in Pt/BSTC/STN capacitor.