The modification of the characteristics of ZnO nanofibers by TCNQ doping content

In this study, the electrical properties of an Al/p-Si metal/semiconductor photodiodes with Tetracyanoquinodimethane–Polyvinyl chloride (TCNQ–PVC) and PVC–TCNQ:ZnO interfacial layers were investigated. Growing of the interfacial layers on p-Si were fulfilled using electrospinning method as a fiber form. Al metallic and ohmic contacts were deposited via physical vapor deposition method. Scanning electron microscopy (SEM) pictures of the devices were captured to examine the morphology of the structure. Within the scope of electrical characterization, I–V measurements of the Al/PVC–TCNQ/p-Si and Al/PVC–TCNQ:ZnO/p-Si devices were accomplished both in the dark and under illumination conditions. Various device parameters, such as ideality factor and barrier height values were determined from I–V characteristics. Although the ideality factor values were obtained as 8.47 and 6.85 for undoped and ZnO-doped Al/PVC–TCNQ/p-Si diodes, the barrier height values were calculated as 0.84 for both devices. When a comparison was made between ZnO doped and undoped Al/PVC–TCNQ/p-Si diodes, it was evaluated that the rectification and photoresponse properties of the heterojunction diode was improved with ZnO dopant.

     

Effect of ZnO layer thickness upon optoelectrical properties of NiO/ ZnO heterojunction prepared at room temperature

In this work, p-NiO/n-ZnO heterostructures were successfully prepared at room temperature using RF sputtering technique. The influence of ZnO layer thickness on the performance of the heterojunction was investigated. The deposited ZnO layers have a hexagonal Wurtzite structure with preferable growth orientations along (002) and (103) for thinner films. Increasing the thickness results in more crystallographic orientation randomness. The current–voltage measurements of the realized heterojunctions showed a clear rectifying behavior. The measured ideality factor varies from 2.5 to 1.6 according to the thickness of ZnO layer. The series resistance of the device is enlarged with increasing ZnO thickness. The deduced parameters from the I–V characteristics suggest that 200 nm is the optimal thickness of the ZnO layer according to our experimental conditions. We attribute the relatively better performance of this thickness to achieving reasonable compensation between serial resistance and ideality factor. The best heterojunction was tested and successfully used as a UV detector.     

Series resistance determination of Au/Polypyrrole/p-Si/Al structure by current–voltage measurements at low temperatures

The current–voltage (I–V) characteristics of Polypyrrole(PPy)/p-Si/Al structure have been investigated as a function of temperature. A modified Norde function combined with conventional forward I–V method has been used to extract the junction parameters including the ideality factor, barrier height and series resistance. Norde function has been compared with the Cheung functions and it has been seen that there is a good agreement with both method for the barrier height values. However, the values of series resistance have very different especially towards to the lower temperatures. This is attributed to non-ideal I–V characteristics of the Au/PPy/p-Si/Al structure and non-pure Thermionic emission theory due to the low temperature effects.     

Properties of PEDOT:PEG/ZnO/p-Si heterojunction diode

The zinc oxide (ZnO) and poly(3,4-ethylenedioxythiophene) bis-poly(ethyleneglycol) (PEDOT:PEG) films were deposited on p-Si substrate by sputter and spin coating methods, respectively. An organic/inorganic heterojunction diode having PEDOT:PEG/ZnO on p-Si substrate was fabricated. The barrier height (BH) and the ideality factor values for the device were found to be 0.82 ± 0.01 eV and 1.9 ± 0.01, respectively. It has been seen that the value of BH is significantly larger than those of conventional Au/p-Si metal–semiconductor contacts. The PEDOT:PEG/ZnO/p-Si heterostructure exhibits a non-ideal I–V behavior with the ideality factor greater than unity that could be ascribed to the interfacial layer, interface states and series resistance. The modified Norde's function combined with conventional forward I–V method was used to extract the parameters including the barrier height and series resistance. At the same time, the physical properties of ZnO and PEDOT:PEG films deposited by sputter and spin coating technique, respectively, were investigated at room temperature. The obtained results indicate that the electrical parameters of the diode are affected by structural properties of ZnO film and PEDOT:PEG organic film.     

Current–voltage characteristics and inhomogeneous barrier height analysis of Au/poly(o-toluidine)/p-Si/Al heterojunction diode

Thin films of poly(o-toluidine) (POT) with amorphous structure were prepared onto the surface of p-Si single crystal by spin coating technique. The electrical conduction mechanisms and related parameters of the Au/POT/p-Si/Al heterojunction diode were investigated using current–voltage (I–V) characteristics in temperature range 298–378 K. The device showed rectifying behavior. At relatively low forward applied voltages; the current through the junction has been analyzed on the bases of the standard thermionic emission theory. The ideality factor decreases with increasing temperature, whereas the barrier height increases. This behavior could be elucidated in terms of inhomogeneity model of barrier heights. In addition, the values of series resistance, ideality factor and effective barrier height at zero-bias are determined at different temperatures by using Cheung’s functions. At relatively high forward bias voltages, analysis of the double logarithmic I–V characteristics indicates that transport through the device is controlled by a space-charge-limited current process characterized by single trap of distribution in which the related parameters are estimated. Data analysis in reverse direction showed that the current can be described in terms of Poole–Frenkel mechanism at low applied voltage and in terms of Schottky mechanism at higher applied voltage.     

ZnO/Si solar cell fabricated by spray pyrolysis technique

The ZnO/Si heterojunctions have been prepared by depositing n-ZnO films doped with aluminium on p-Si by spray pyrolysis method. Heterojunction solar cells were fabricated using the configuration Al/ZnO/Si/In. The electrical properties of the heterojunction are investigated by means of current–voltage measurements in the temperature range 295–375 K. The cells show the rectifying behaviour characterized by the current–voltage (I–V) measurement under a dark condition, while photoelectric effects have been exhibited under the illumination. As a result, the conversion efficiency of the fabricated cell of about 6.6% was obtained.     

Fabrication and electrical characterization of p-Cu2O/n-ZnO heterojunction

The conducting metal oxide (ZnO, Cu2O) films were used for fabrication of p-n heterojunction by rf sputtering and electrodeposition techniques respectively. The as synthesized films were characterized by X-ray diffraction (XRD), scanning electron microscope (SEM), UV spectroscopy and electrical techniques. The electrical properties of the p-Cu2O/n-ZnO heterojunction were examined using the current-voltage measurements. The current-voltage (I-V) result showed that potential barrier was higher than the turn-on voltage, which was attributed to the presence of the interface defect states. The PN junction parameters such as ideality factor, barrier height, and series resistance were determined using conventional forward bias current-voltage characteristics. The annealing of Cu2O increase the crystallinity size and which enhance the photo current from 1.6 mA/cm2 to 3.7 mA/cm2. The annealing of respective film resulted in a decrease of these parameters with an increase in efficiency of solar cell from 0.14% to 0.3% at 350 degrees C.     

基于MEMS制作n-Zn0/p-Si异质结及特性

基于MEMS技术在P型<100>晶向双面抛光单晶硅片上制作c型硅杯,在C型硅杯上表面扩散P+,采用磁控溅射法在扩散区上制备择优取向为<0002>晶向的n-ZnO薄膜,形成n-ZnO/P-Si异质结.采用HP4280A型C-V特性测试仪分析n-ZnO/p-Si异质结的C-V特性,该异质结为突变结.采用HP4145B型半导体参数测试仪分析n-ZnO/p-si异质结,I-V特性,结果给出,n-ZnO/p-Si异质结在正向偏压下,电流随外加偏压按指数函数增加,反向电流不饱和,采用突变异质结的正反向势垒能带结构对其,I-V特性进行分析.     

Fabrication and characterization of DBM/p-Si heterojunction solar cell

Hybrid organic/inorganic solar cell was fabricated by depositing a thin film of p-N,N dimethylaminobenzylidenemalononitrile (DBM) onto p-Si substrate. DBM is a donor–acceptor disubstituted benzenes dye known as molecular rotors and highly polar molecular compounds. Its powder has a polycrystalline structure, while nano-crystallite rods are formed in the as-deposited film. The dark current density–voltage (J–V) characteristics of Au/DBM/p-Si/Al heterojunction device measured at different temperatures ranging from 291 to 353 K have been investigated. The operating conduction mechanisms, the series and shunt resistances, the rectification ratio, the ideality factor, the effective barrier height, and the total trap concentration were determined. The capacitance–voltage (C–V) characteristics indicated that the junction is of abrupt nature. The built-in voltage and the carrier concentration distributed through the depletion region were estimated. Under illumination, the DBM/p-Si cell showed photovoltaic properties and the photovoltaic parameters were evaluated.     

Fabrication of a n-ZnO/p-Si heterojunction diode by ultra-high vacuum magnetron sputtering

Heterojunction diodes of n-type ZnO were fabricated on a p-type Si(100) substrate using an ultra-high vacuum radio frequency magnetron sputtering method at room temperature. A short-time post-annealing process was performed to prevent inter-diffusion of Zn, dopants, and Si atoms. The post-annealing process at 600 °C enhanced the crystallinity of ZnO films and produced a high forward to reverse current ratio of the heterojunction diode with a barrier height of approximately 0.336 eV. A thin SiO_x layer at the interface of the ZnO film and Si substrate appeared distinctly at the 600 °C annealing, however the post-annealing at 700 °C showed an a-(Zn_2xSi_1 − xO₂) structure caused by diffusion of silicon into the ZnO film. In the n-ZnO/p-Si sample annealed at 700 °C, a rapid change in the barrier height was considered due to the effect of the dopant segregation from the substrate and deformation of the a-SiO_x structure.     

Passivation and antireflection AZO:H layer in AZO:H/p-Si heterojunction solar cells

In this work, aluminum-doped zinc oxide (AZO)/p-Si heterojunction solar cells were prepared by sputtering of ~120 nm AZO thin films in Ar or Ar–H₂ atmosphere on textured p-Si wafers, and the effects of hydrogen incorporation on the solar cell performance were investigated. Results showed that the performance of AZO/p-Si heterojunction solar cells was improved with the increase of hydrogen volume concentration from 0 to 23 %. The AZO:H/p-Si heterojunction solar cells prepared in Ar–23 % H₂ exhibited a short-circuit current density of 29 mA/cm² and a conversion efficiency of 2.84 %. The reflectance measurement indicated that the reflectance of p-Si surface in the range of 400–1,100 nm decreased from 13 to 4 % after AZO:H films coating; and the capacitance–voltage measurement indicated that the density of defect states at AZO/p-Si interface was decreased after hydrogen incorporation. Passivation and antireflection functions can be realized in AZO:H films deposited in Ar–H₂, which opens a novel route to prepare cost-effective AZO/p-Si heterojunction solar cells.     

PLD法制备ZnO/Si异质结的I-V特性研究

用脉冲激光沉积法分别在不同电阻率的p型和n型Si( 100)衬底上制备了不掺杂ZnO薄膜,相应制成n-ZnO/p-Si和n-ZnO/n-Si异质结器件.利用X射线衍射和原子力显微镜对ZnO薄膜进行的结构和形貌测试表明,薄膜结晶情况良好,具有高度的c轴择优取向,表面颗粒大小、分布均匀.对器件的I-V特性测试表明,在无光条件下,制备的n-ZnO/p-Si异质结漏电流很低,而n-ZnO/n-Si同型异质结漏电流要稍大一些;随衬底电阻率的增大,上述器件的阈值电压变小;器件在光照下的漏电流明显比无光条件下的要大.     

Temperature effects on the electrical characteristics of $$\mathrm{Al}/\mathrm{PTh}-\mathrm{SiO}_{2}/\mathrm{p\hbox {-}Si}$$ structure

The temperature-dependent current–voltage (\(I\text {--}V\)) and capacitance–voltage (\(C\text {--}V\)) characteristics of the fabricated Al/p-Si Schottky diodes with the polythiopene–SiO\(_{2}\) nanocomposite (\(\hbox {PTh--SiO}_{2}\)) interlayer were investigated. The ideality factor of \(\hbox {Al}/\hbox {PTh--SiO}_{2}/{p}\text {-Si}\) Schottky diodes has decreased with increasing temperature and the barrier height has increased with increasing temperature. The change in the barrier height and ideality factor values with temperature was attributed to inhomogeneties of the zero-bias barrier height. Richardson plot has exhibited curved behaviour due to temperature dependence of barrier height. The activation energy and effective Richardson constant were calculated as 0.16 eV and \(1.79 \times 10^{-8} \hbox {A\,cm}^{-2} \,\hbox {K}^{-2}\) from linear part of Richardson plots, respectively. The barrier height values determined from capacitance–voltage–temperature (\(C\text {--}V\text {--}T\)) measurements decrease with increasing temperature on the contrary of barrier height values obtained from \(I\text {--}V\text {--}T\) measurements.     

Effect of annealing temperature on ZnO:Al/p-Si heterojunctions

Al-doped, zinc oxide (ZnO:Al) films with a 1.2 at.% Al concentration were deposited on p-type silicon wafers using a sol-gel dip coating technique to produce a ZnO:Al/p-Si heterojunction. Following deposition and subsequent drying processes, the films were annealed in vacuum at five different temperatures between 550 and 900 °C for 1 h. The resistivity of the films decreased with increasing annealing temperature, and an annealing temperature of 700 °C provided controlled current flow through the ZnO:Al/p-Si heterojunction up to 20 V. The ZnO:Al film deposited on a p-type silicon wafer with 1.2 at.% Al concentration was concluded to have the potential for use in electronic devices as a diode after annealing at 700 °C.     

Nitrogen effect on spin-coated ZnO-based p–n homojunctions: structural,optical and electrical characteristics

In this work, ZnO:Al–N/ZnO:Al and ZnO:Ag–N/ZnO:Al homojunctions were deposited by means of spin coating method using precursors obtained by sol gel chemistry. The optical, structural and electrical properties of spin coated undoped and M-doped ZnO thin films (M?=?Al, Ag–N and Al–N) using ammonium hydroxide as a nitrogen source are reported. The films showed the wurtzite type structure with a c-axis (002) preferential orientation. The films showed a surface morphology consisting of wrinkles, which were constituted of nanocrystals in the range of ～?20 nm. The thin films were highly transparent in the visible region of the electromagnetic spectrum. The optical band gap of the films was close to 3.30 eV. Hall Effect measurements indicated that undoped and Al doped ZnO thin films showed an n-type conductivity, whereas ZnO:Al–N and ZnO:Ag–N thin films exhibited p-type conductivity, probably related to the formation of dual acceptor complexes related to nitrogen. Two types of p–n homojunctions (ZnO:Al–N/ZnO:Al and ZnO:Ag–N/ZnO:Al) were fabricated by means of sol–gel spin-coating method. In both cases, a rectifying behavior was observed, as revealed by current–voltage measurements.     

Carrier transport mechanisms and photovoltaic characteristics of Au/toluidine blue/n-Si/Al heterojunction solar cell

Toluidine blue (TB)/n-silicon heterojunction solar cell was fabricated by depositing TB film on n-silicon wafer using thermal deposition technique. X-ray diffraction patterns of the TB film show presence of crystals with size 30 nm dispersed in amorphous matrix. The current–voltage–temperature performance of Au/TB/n-Si/Al device was studied in dark and under illumination conditions. The device showed diode behavior. The diode parameters such as ideality factor, barrier height, series and shunt resistance were determined using a conventional I–V–T characteristics. The analysis of the diode characteristics in forward bias direction confirmed that the transport mechanisms of the Au/TB/n-Si/Al solar cell at applied potential?<?0.1 V is thermionic emission and at high electric field?>?0.1 V is Ohmic conduction. The operating conduction mechanisms in reverse bias direction are Pool–Frenkel effect followed by Schootky field lowering mechanism. The small value of activation energy in reverse bias direction indicates that the conduction process is expected to be by tunneling of electrons between nearest-neighbor sites and it is temperature independent. The photo conduction characteristics of the diode suggests its application as a solar cell.     

Growth and properties of aligned ZnO nanowires and their applications to n-ZnO/p-Si heterojunction diodes

Aligned n-ZnO nanowires were synthesized via simple thermal evaporation process by using metallic zinc powder in the presence of oxygen on p-silicon (Si) substrate. The as-synthesized aligned ZnO nanowires were characterized in terms of their structural and optical properties by scanning electron microscopy (SEM), transmission electron microscopy (TEM), X-ray diffraction process (XRD) and room-temperature photoluminescence (PL) properties. The detailed structural and optical studies revealed that the as-grown nanowires are single crystalline with the wurtzite hexagonal phase and exhibit good optical properties. From application point of view, the as-grown aligned n-ZnO nanowires on p-Si substrates were used to fabricate heterojunction diodes. The fabricated heterojunction diodes exhibited good electrical (I-V) properties with the turn-on voltage of approximately 1.0 V. A temperature-dependant (from 25 degrees C approximately 130 degrees C), I-V characteristics for the fabricated device was also demonstrated in this paper. The presented results demonstrate that the simply grown aligned n-ZnO nanowires on p-Si substrate can be efficiently used for the fabrication of efficient heterojunction devices.     

Electrical characterization of the polyaniline/p-silicon and polyaniline titanium dioxide tetradecyltrimethylammonium bromide /p-silicon heterojunctions

Au/PANI/p-Si/Al and Au/PANI TiO₂ TTAB/p-Si/Al heterojunctions have been fabricated by spin coating of soluble polyaniline (PANI) and PANI titanium dioxide (TiO₂) tetradecyltrimethylammonium bromide (TTAB) on the chemically cleaned p-Si substrates. The thicknesses of the polymeric films have been determined by a profilometer. The current-voltage (I-V) characteristics of the heterojunctions have been obtained in the temperature range of 98-258 K. These devices have showed the rectifying behavior such as diode. The I-V characteristics of the devices have been analyzed on the basis of the standard thermionic emission theory at low forward bias voltage regime. It has been shown that the values of ideality factor decrease while the values of barrier height increase with increasing temperature. This temperature dependence has been attributed to the presence of barrier inhomogeneities at the organic/inorganic semiconductor interface. Furthermore, analysis of the double logarithmic I-V plots at higher forward bias voltages at all temperatures indicates that transport through the organic thin film is explained by a space-charge-limited current process characterized by exponential distribution of traps within the band gap of the organic film. The total concentration of traps has been found to be 3.52 × 10¹⁴ cm^− 3 and 3.14 × 10¹⁵ cm^− 3 for PANI and PANI TiO₂ TTAB layer, respectively.     

Investigation of PtSi/p-Si Schottky barrier height using I-V-T technique

Both forward and reverse I-V characteristics of PtSi/p-Si Schottky diodes at different temperatures have been studied in detail. The PtSi/ p-Si Schottky diode shows ideal I-V characteristics with an ideality factor between 1.0 and 1.05, The barrier heights of PtSi/p-Si diodes obtained from forward and reverse I-V-T show a consistent value. The barrier heights measured from the I-V-T Technique are compared with those measured from an optical method. The barrier height measured by the optical method (0.235 eV) is higher than that measured by I-V-T (0.205 eV). Hot holes scattered at PtSi grain boundaries may raise the higher barrier height obtained in the optical measurement. The barrier height of PtSi/p-Si diodes is decreased if the formation temperature for PtSi is increased. Transmission electron microscopy results show that the PtSi is likely to form texture if the formation temperature is higher than 450°C. The decrease of barrier height is due to the formation of PtSi texture at high temperature.     

Temperature dependant characteristics of zinc oxide nanorods based heterojunction diode

Temperature-dependant characteristics of heterojunction diode made by n-ZnO nanorods grown on p-silicon substrates has been characterized and demonstrated in this paper. ZnO nanorods were grown onto the silicon substrate via simple thermal evaporation process by using metallic zinc powder in the presence of oxygen at approximately 550 degrees C without the use of any metal catalysts or additives. The as-grown ZnO nanorods were characterized in terms of their structural and optical properties. The detailed structural studies by XRD, TEM, HRTEM and SAED revealed that the grown nanorods are well-crystalline with the wurtzite hexagonal phase and preferentially grown along the [0001] direction. The as-grown n-ZnO nanorods grown on p-Si substrate were used to fabricate p-n heterojunction diode. The fabricated p-n junction diode attained almost similar turn-on voltage of approximately 0.6 V. The values of turn-on voltage and least current are same with the variations of temperature (i.e., 27 degrees C, 70 degrees C and 130 degrees C).