Space Charge Limited Current Mechanism Research Articles

Electrical transport mechanisms and photovoltaic behavior of 2-(2-furanylmethylene) propanedinitrile/p-Si heterojunction

Au/2-(2-furanylmethylene) propanedinitrile/p-Si heterojunction was fabricated using conventional thermal evaporation technique. Current density–voltage (J–V) characteristics of the heterojunction were investigated at different temperatures. Tunneling conduction mechanism in the lower voltage range was identified from the forward bias (J–V) characteristics. The calculated value of the change of built-in voltage with respect to the absolute temperature is (−1.88 × 10−3 V K−1). At higher voltages, a space charge limited current (SCLC) mechanism controlled by an exponential trapping distribution above the valence band edge was observed. The total concentration of traps was found to be 8.077 × 1021 m−3. Under reverse bias, the conduction mechanism is due to thermally generated carriers in the lower voltage range and the Poole–Frenkel effect is observed in the higher voltage range. The heterojunction showed a photovoltaic behavior under illumination with an open-circuit voltage of 0.19 V and a short-circuit current density of 102.7 mA m−2.

Radiation effects on floating rings of voltage terminating structure in Si p-on-n detectors

In the 1990s a suggestion was put forward that the space charge limited current mechanism is responsible for stabilization of the I–V characteristics in irradiated Si p-on-n detectors. This mechanism is switched on in the case of high concentration of radiation induced deep traps which via holes accumulation will reduce the electric field in the regions of breakdown. The present study shows that voltage terminating structure (VTS) consisting of the floating p+ rings as a main element for stabilization of I–V characteristics in nonirradiated detectors is still active being irradiated to the fluence beyond space charge sign inversion. This characteristic of VTS can be accounted for by the double peak electric field distribution in heavily irradiated detectors and the punch-through mechanism of current flow between the floating p+ rings in the silicon bulk with high concentration of deep traps. It is shown that VTS operates as a potential divider up to the fluence of 1×1015neq/cm2 and it is at higher fluences that the detector stability is maintained only by the space charge limited current mechanism.

Bipolar resistive switching behavior with high ON/OFF ratio of Co:BaTiO3 films by acceptor doping

The bipolar resistive switching characteristics have been investigated in the Co:BaTiO3 films deposited by sol-gel method. It has been demonstrated that such devices can be used as resistive random access memory cells without required electroforming. Ohmic transport and space charge limited current mechanism are dominant during the resistive switching. The ON/OFF ratio between the resistance at the high and low resistance states is more than 106, better than other perovskite films. The high ratio should be attributed to acceptor doping into the n-type semiconductor. The results imply that the ON/OFF ratio can be enhanced by controlling doping type and concentration in those insulating oxides.

Polarity Reversion of the Operation Mode of HfO<SUB>2</SUB>-Based Resistive Random Access Memory Devices by Inserting Hf Metal Layer

The reversion of polarity within bipolar resistive switching operation occurs in Pt/HfO2/TiN and Pt/Hf/HfO2/TiN resistive random access memory devices. This reversion of voltage polarity is the result of interface generation which induces a conduction mechanism transformation from Poole-Frenkel emission to space charge limited current mechanism. To prove the reversion of polarity, this study uses curve fitting of I-V relations to verify the conduction mechanism theoretically and physical analysis to verify the oxygen ion distribution practically. The proposed Pt/Hf/HfO2/TiN devices exhibit good resistive switching characteristics, such as good uniformity, low voltage operation, robust endurance (10(3) dc sweep), and long retention (3 x 10(4) s at 85 degrees C).

Characterization of Al/p-Si/n-AgGaSe2/Au thin films heterojunction device

Crystalline Al/p-Si/n-AgGaSe2/Au heterojunction device was fabricated by depositing AgGaSe2 thin films at temperature 473 K, onto p-type single crystal silicon wafers with surface orientation (111) and glass substrates. The crystalline nature and the chemical composition of the deposited AgGaSe2 films have been confirmed using both X-ray diffraction (XRD) and energy dispersive X-ray spectrometer (EDX) techniques. The dark current–voltage characteristics of the heterojunction diode have been investigated at various temperatures to elucidate the electrical conduction mechanisms. It was found that at forward bias voltages ≤100 mV, the current is controlled by the thermionic emission mechanism, whereas, at bias voltages higher than 100 mV, the current is controlled by the space charge limited current mechanism. The reverse current mechanism of the diode is controlled by the carrier generation–recombination process in the depletion region. The photovoltaic parameters were determined from the current–voltage characteristics under illumination. The built-in potential, effective carrier concentration and barrier height were also evaluated from the C–V measurement.

InGaN metal-insulator-semiconductor photodetector using Al2O3 as the insulator

In this paper, an InGaN metal-insulator-semiconductor (MIS) photodetector with an ultra-thin Al2O3 insulation layer deposited by atomic layer deposition (ALD) was studied. A high photoelectric responsivity of 0.25 A/W and a spectral responsivity rejection ratio of about three orders of magnitude at 1 V reverse bias were achieved for this MIS photodetector. The dominant carrier transport mechanism in the InGaN MIS photodetectors is submitted to the space charge limited current (SCLC) mechanism at high field and exhibits an Ohmic-like conduction at low electric field. The results indicate that the ultra-thin Al2O3 film deposited by the ALD technique can act as an excellent insulation dielectric for the InGaN photodetectors.

Carrier Transport Mechanisms in Metal-Insulator–Metal Au/Ba0.8Sr0.2TiO3/ ZrO2/ Ba0.8Sr0.2TiO3/Pt Thin Film Heterostructures

ABSTRACTBa0.8Sr0.2TiO3/ZrO2 heterostructured thin films are deposited on Pt/Ti/SiO2/Si substrates by a sol-gel process. The current versus voltage (I-V) measurements of metal-insulator-metal (MIM) devices using the above multilayered thin film as the dielectric have been taken in the temperature range of 310 to 410K. The electrical conduction mechanisms contributing to the leakage current at different field regions have been studied in this work. Various models are used to know the different leakage mechanisms contributing to the conduction current in these devices. It is observed that Poole-Frenkel mechanism is the dominant conduction process in the high field region with a deep trap level energy (φt) of 1.31 eV whereas space charge limited current (SCLC) mechanism and Ohmic conduction process are contributing to the leakage current in the medium and low field regions respectively. The estimated shallow trap level (Et) for SCLC mechanism is 0.26 eV whereas the activation energy (Ea) for the electrons in the Ohmic conduction process is about 0.07 eV. An energy band diagram is given to explain the various leakage mechanisms in different field regions for these heterostructured thin films.

Field Dependent Electrical Conduction in Metal-Insulator-Metal Devices using Alumina-Silicone Nanolaminate Dielectrics

ABSTRACTHybrid alumina-silicone nanolaminate films were synthesized by plasma enhanced chemical vapor deposition (PECVD) process. PECVD allows digital control over nanolaminate construction, and may be performed at low temperature for compatibility with flexible substrates. These materials are being considered as dielectrics for application such as capacitors in thin film transistors and memory devices. In this work, we present the temperature dependent current versus voltage (I-V) measurements of the nanolaminate dielectrics in the range of 200- 310 K to better asses their potential in these applications. Various models are used to know the different conduction mechanisms contributing to the leakage current in these nanolaminate films. It is observed that space charge limited current (SCLC) mechanism is the dominant conduction process in the high field region whereas Ohmic conduction process is contributing to the leakage current in the low field region. The shallow electron trap level energy (Et) of 0.16 eV is responsible for SCLC mechanism whereas for Ohmic conduction process the activation energy (Ea) for electrons is about 0.22 eV. An energy band diagram is given to explain the dominance of various conduction mechanisms in different field regions in these nanolaminate films.

Field Dependent Carrier Transport Mechanisms in Metal-Insulator–Metal Devices with Ba0.8Sr0.2TiO3/ ZrO2 Heterostructured Thin Films as the Dielectric

ABSTRACTBa0.8Sr0.2TiO3/ZrO2 heterostructured thin films with different individual layer ZrO2 thicknesses are deposited on Pt/Ti/SiO2/Si substrates by a sol-gel process. The current versus voltage (I-V) measurements of the above multilayered thin films in metal-insulator-metal (MIM) device structures are taken in the temperature range of 310 to 410K. The electrical conduction mechanisms contributing to the leakage current at different field regions have been studied in this work. Various models are used to know the different conduction mechanisms responsible for the leakage current in these devices. It is observed that Poole-Frenkel mechanism is the dominant conduction process in the high field region with deep electron trap energy levels (φt) whereas space charge limited current (SCLC) mechanism is contributing to the leakage current in the medium field region with shallow electron trap levels (Et). Also, it is seen that Ohmic conduction process is the dominant mechanism in the low field region having activation energy (Ea) for the electrons. The estimated trap level energy varies from 0.2 to 1.31 eV for deep level traps and from 0.08 to 0.18 eV for shallow level traps whereas the activation energy for electrons in ohmic conduction process varies from 0.05 to 0.17 eV with the increase of ZrO2 sub layer thickness. An energy band diagram is given to explain the dominance of the various leakage mechanisms in different field regions for these heterostructured thin films.

Nano-crystalline p-ZnGa2Te4/n-Si as a new heterojunction diode

In this communication, ZnGa2Te4 thin film was prepared by thermal evaporation technique on n-Si substrate. P-ZnGa2Te4/n-Si heterojunction diode was fabricated. The structure of ZnGa2Te4 thin film was checked by XRD pattern and confirmed by AFM micrographs. The dark current–voltage characteristics of the heterojunction diode were investigated to determine the electrical parameters and conduction mechanism as a function of forward and reverse biasing conditions in the range (−10V to 10V) at temperature interval (303–423K). The conduction mechanism was controlled by thermionic emission, space charge limited (SCLC) and trap-charge limited current (TCLC) mechanisms. The basic parameters such as the series resistance Rs, the shunt resistance Rsh, the ideality factor n and the barrier height ϕb of the diode, the total density of trap states N0 and the exponential trapping distribution Po were determined. The obtained results showed that ZnGa2Te4 is a good candidate for the applications of electronic devices.

Optical absorption and charging effect in nano-crystalline Ge/SiNx multilayers

Nanocrystalline Ge (nc-Ge)/SiNx multilayers and sandwiched structures were fabricated by thermally annealing amorphous Ge/SiNx layered films at 600°C. The evolution of microstructure before and after annealing was studied by various characterization techniques, which reveals the formation of nc-Ge after annealing. The tunable optical absorption and band gap were observed by changing the grain size of nc-Ge. The study on carrier transport behavior of nc-Ge/SiNx MLs indicated that the transport process was dominated by space-charge limited current mechanism. Furthermore, the charging storage effect in SiNx/nc-Ge/SiNx floating gate structures was demonstrated due to both the electron and hole injection processes.

DC conduction mechanism and dielectric properties of Poly (methyl methacrylate)/Poly (vinyl acetate) blends doped and undoped with malachite green

Cast thin films of Poly (methyl methacrylate)/Poly (vinyl acetate) blends of different concentrations undoped and doped with malachite green have been prepared and subjected to both dc electrical conduction and dielectric spectroscopy measurements. The analysis of dc electrical conduction data showed that the space charge limited current mechanism has been dominant for Poly (vinyl acetate) while Schottky–Richardson conduction mechanism prevailed for the Poly (methyl methacrylate) and blended samples. The values of field lowering constant β and the thermal activation energy ΔE involved in the dc conduction were reported, which provide another support for the suggested Schottky–Richardson mechanism. The increase in current for the blend sample doped with malachite green has been attributed to the formation of charge transfer complexes inside the polyblend matrix. The dielectric constant as a function of temperature for all samples have been calculated which are affected by the composition ratio and the addition of dye. The relaxation peak that appeared in the dielectric loss curve at 347 K for the doped blend sample is related to local dipoles that are present in the dye material. The obtained relaxation process spectra present in the investigated samples were analyzed with the well-known model of Havriliak–Negami.

Leakage current mechanisms in high performance alumina-silicone nanolaminate dielectrics

Alumina-silicone nanolaminates deposited by plasma-enhanced chemical vapor deposition were explored as dielectrics in metal-insulator-metal capacitors. Temperature-dependent current versus voltage (I-V) measurements were used to investigate the conduction mechanisms contributing to the leakage current in these structures. It is observed that space charge limited current mechanism is the dominant conduction process in the high field region. The estimated shallow trap level energies (Et) are 0.16 eV and 0.33 eV for 50% and 83.3% Al2O3 nanolaminates, respectively.

Research on the field emission mechanism of nano-structured carbon film

The field emission (FE) characteristics of nano-structured carbon films (NSCFs) are investigated. The saturation behaviour of the field emission current density found at high electric field E cannot be reasonably explained by the traditional Fowler—Nordheim (F—N) theory. A three-region E model and the curve-fitting method are utilized for discussing the FE characteristics of NSCFs. In the low, high, and middle E regions, the FE mechanism is reasonably explained by a modified F—N model, a corrected space-charge-limited-current (SCLC) model and the joint model of F—N and SCLC mechanism, respectively. Moreover, the measured FE data accord well with the results from our corrected theoretical model.

Electrical transport properties of manganite powders under pressure

We have measured the electrical resistance of micrometric to nanometric powders of the La5/8−yPryCa3/8MnO3 (LPCMO with y=0.3) manganite for hydrostatic pressures up to 4kbar. By applying different final thermal treatments to samples synthesized by a microwave assisted denitration process, we obtained two particular grain characteristic dimensions (40nm and 1000nm) which allowed us to analyze the grain size sensitivity of the electrical conduction properties of both the metal electrode interface with manganite (Pt/LPCMO) and the intrinsic intergranular interfaces formed by the LPCMO powder, conglomerate under the only effect of external pressure. We also analyzed the effects of pressure on the phase diagram of these powders. Our results indicate that different magnetic phases coexist at low temperatures and that the electrical transport properties are related to the intrinsic interfaces, as we observe evidences of a granular behavior and an electronic transport dominated by the Space Charge limited Current mechanism.

Interface-dependent resistance switching in Nd0.7Sr0.3MnO3 ceramics

Interface-dependent electric-pulse-induced resistance switching effect (EPIR) in Nd0.7Sr0.3MnO3 ceramics was studied. The results reveal that the EPIR effect originates from the interface between the electrodes and the bulk, and the EPIR ratio as well as the high and low resistance states can be strongly influenced by applying a large electrical field on the sample for different intervals. Also, the pulse parameters have great effect on the stability of EPIR and the optimal pulse width, pulse amplitude and read bias are obtained. Based on the space charge limited current mechanism together with the theory of interfacial charge-trapped state, the interface-dependent resistance switching effect is discussed.

The electrical and magnetic properties of epitaxial orthorhombic YMnO3 thin films grown under various oxygen pressures

Orthorhombic YMnO3 thin films were epitaxially grown on bare and LaNiO3 buffered (001)–SrTiO3 substrates by pulsed laser deposition under various oxygen pressures from 5 to 30Pa. The crystal structure and microstructure of these films have been characterized by both X-ray diffractions and transmission electron microscopy. The leakage current, modeled as the space charge limited current (SCLC) mechanism, decreased significantly with the increase of oxygen content. It is further found that the magnetic property of films is greatly enhanced in YMnO3 films grown under high oxygen pressure, which can be explained decreased oxygen vacancies. In addition, bipolar switching behavior was obtained only in the films grown under 30Pa oxygen pressure, which is attributed to the decrease of voltage-driven oxygen vacancy migration.

Electrical characterization of the organic semiconductor Ag/CuPc/Au Schottky diode

This paper reports on the fabrication and investigation of a surface-type organic semiconductor copper phthalocyanine (CuPc) based diode. A thin film of CuPc of thickness 100 nm was thermally sublimed onto a glass substrate with preliminary deposited metallic electrodes to form a surface-type Ag/CuPc/Au Schottky diode. The current-voltage characteristics were measured at room temperature under dark conditions. The barrier height was calculated as 1.05 eV The values of mobility and conductivity was found to be 1.74 × 10−9 cm2 (V · s) and 5.5 × 10−6 Ω−1 · cm−1, respectively. At low voltages the device showed ohmic conduction and the space charge limited current conduction mechanisms were dominated at higher voltages.

Thickness Dependence of Electrical Properties for High-k SrTa2O6 Thin Films Fabricated by Sol–Gel Method

The interface between SrTa2O6 thin films and Pt electrodes, and defects in SrTa2O6 thin films were investigated through the study of thickness dependence. High dielectric constant of about 109 and low leakage current density of about 10-8 A/cm2 were obtained for the 150 nm SrTa2O6 thin film. These values are comparable with metal organic chemical vapor deposition (MOCVD) derived SrTa2O6 thin films. Space-charge limited current mechanism predominated in the 113 and 150 nm SrTa2O6 thin films. Higher Ti concentration was found in the layer close to the bottom interface of 113 and 150 nm SrTa2O6 thin films. From these results, we suggest a two-layered model for these two thin films. The anomalous dispersion of loss tangent and Poole–Frenkel predominated leakage current was found in 75 nm SrTa2O6 thin film. This may be induced by higher Ti concentration not only in the layer close to the bottom interface, but also in the whole thin film.

Analysis of current–voltage characteristics of Al/p-ZnGa 2Se 4/n-Si nanocrystalline heterojunction diode

The polycrystalline ZnGa 2Se 4 thin film was prepared by thermal evaporation technique on n-Si wafer followed by annealing at 700 K. Then, the Al/p- ZnGa 2Se 4/n-Si/Al heterojunction diode was fabricated. XRD pattern shows that the annealed ZnGa 2Se 4 film has a polycrystalline structure. AFM images indicate that the ZnGa 2Se 4 film is formed of nanoparticles. The dark current–voltage characteristics of the heterojunction diode at various temperatures have been investigated to determine the electrical parameters and conduction mechanism. The Al/p-ZnGa 2Se 4/n-Si/Al diode shows a rectification ratio of 2.644 × 10 2 at ±2 V at room temperature. It was found that at forward bias voltages ≤0.5 V, the conduction mechanism of the diode is controlled by the thermionic emission mechanism, while at bias voltages higher than 0.5 V, it is controlled by the space charge limited current mechanism. The series resistance R s , the ideality factor n and the barrier height ϕ b values of the diode are determined by performing different plots from the forward current–voltage characteristics. The reverse current mechanism of the diode is controlled by the carrier generation–recombination process in the depletion region. The obtained results show that the Al/p-ZnGa 2Se 4/n-Si/Al heterojunction is a good candidate for the electronic device applications.