Photoelectronic properties of the Zn x Cd1−x In2S4 system

Summary Photoelectrical investigations on the Zn _x Cd_1−x In₂S₄ system have been carried our particularly with respect to the high residual conductivity and the long-relaxation-time properties. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Photoelectric effect in some alloys in the region of absorption edges

Summary Photoelectric effect in alloys using the transmission method in the energy range (17.8÷138) keV, at energies in the region of absorption edges of the various elements in the alloys, have been measured and compared with the respective theoretical estimates.     

Detection of Mn pinned level in Cd1−x Mn x Se monocrystals by the photoconductivity technique

Summary The photoconductivity of the magnetic semiconductor compound Cd_1−x Mn _x Se has been studied at 300 K and at 77K for the first time for several Bridgman-grown single crystals. With this technique it was possible to detect the Mn 3d level. Experimental data found in this investigation reveal that the Mn 3d level is pinned at 1.9 eV below the bottom of the conduction band,i.e. it is independent of temperature and insensitive to the amount of manganese. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Photoconductivity of Cu x Ag1−x Cd2InTe4

Summary The prominent photoelectric parameters of the semiconducting solid solutions Cu _x Ag_1−x Cd₂InTe₄ are reported. From the spectral dependence of photoconductivity at room temperature and at 77 K the energy gaps and their thermal coefficients are obtained. The detectivityD ^*, the photocurrent gainG and the carrier lifetime are measured and the carrier mobility is deduced. In order to improve theD ^* characteristics, the analysis of its parameters is also performed. Paper presented at the ?V International Conference on Ternary and Multinary Compounds?, held in Cagliari, September 14–16, 1982.     

Structural,optical and electrical properties of sulfur-incorporated amorphous carbon films

Amorphous carbon–sulfur (a-C:S) composite films were prepared by vapor phase pyrolysis technique. The structural changes in the a-C:S films were investigated by electron microscopy. A powder X-ray diffraction (XRD) study depicts the two-phase nature of a sulfur-incorporated a-C system. The optical bandgap energy shows a decreasing trend with an increase in the sulfur content and preparation temperature. This infers a sulfur incorporation and pyrolysis temperature induced reduction in structural disorder or increase in sp ² or π-sites. The presence of sulfur (S 2p) in the a-C:S sample is analyzed by the X-ray photoelectron spectroscopy (XPS). The sp ³/sp ² hybridization ratio is determined by using the XPS C 1s peak fitting, and the results confirm an increase in sp ² hybrids with sulfur addition to a-C. The electrical resistivity variation in the films depends on both the sulfur concentration and the pyrolysis temperature.     

聚苯胺-碳纳米管复合体的制备及其光响应

纳米尺寸导电材料对功能分子材料及分子器件的作用越来越显得重要.采用原位乳液聚合法制备聚苯胺 碳纳米管复合体，SEM和TEM照片显示复合管的直径为60—70nm，聚苯胺的包裹层厚度约25—30nm.x射线衍射及热分析表明纳米复合管的结晶性能增强，热稳定性得到提高.光电响应试验表明复合管的光吸收增强，光电流增大，说明聚苯胺 碳纳米复合管薄膜受光照射后发生了光诱导电荷分离现象. 关键词： 聚苯胺 碳纳米管 复合纳米管 光电流     

Theoretical analysis of trapping and recombination of photogenerated carriers in amorphous silicon solar cells

We have made theoretical studies on the trapping and recombination of photogenerated carriers in hydrogenated amorphous silicon (a-SiH) p-i-n solar cells. We discuss in detail the following points: 1) The limitations of the assumptions in the previous analysis. It has been clarified that the single-level Shockley-Read-Hall model for carrier recombination and the treatment of trap occupation in terms of quasi-Fermi levels are inadequate for exact analysis. 2) The superlinear dependence of carrier recombination rate on the free-carrier density which can explain the enhancement of photo-induced changes ina-SiH under high intensity light. 3) The estimation of capture cross section of the tail states ina-SiH. We show that the charged and neutral tail states have rather small capture cross sections of less than 10^–16 cm² and of less than 10^–19 cm², respectively. 4) The effect of the recombination of photogenerated (PG) carriers at the p/i and the n/i interfaces. We estimate the recombination velocityS of PG carriers at these interfaces to be about 10³ cm/s. It has been also clarified that the decrease inS is effective to improve the cell performance, especially the open circuit voltage.     

Electrical properties and degradation behavior of hydrogenated amorphous Si alloys for solar cells

The electrical properties and the degradation behavior of hydrogenated amorphous silicon alloys (a-Si_1–x A _x : H, with A=C, Ge, B, P) in designs of pin, pip, nin, and MOS structures are investigated by measuring the dark and light I(V) characteristics and the spectral response as well as the space-charge-limited current (SCLC), the time of flight (TOF) of carriers and the field effect (FE). These investigations give an overview of our recent work combined with new results emphasizing the physics of the a-Si:H pin solar cells. We discuss the stabilizing influence on the degradation behavior achieved by profiling the i layers of the pin solar cells with P and B. Two kinds of pin solar cells, namely glass/SnO₂/p(C)in/metal and glass/metal/pin/ITO, are investigated and an explanation of their different spectral response behavior is given. SCLC measurements lead to the conclusion that trapping is also involved in the degradation mechanism, as is recombination. TOF experiments on a-Si_1–x Ge _x : H pin diodes indicate that the incorporation of Ge widens the tail-state distribution below the conduction band. FE measurements showed densities of gap states of about 5×l0¹⁶cm^–3eV^–1.     

Design and optimization of a nano-antenna hybrid structure for solar energy harvesting application

A novel hybrid structure with high responsivity and efficiency is proposed based on an L-shaped frame nano-antenna(LSFNA) array for solar energy harvesting application. So, two types of LSFNAs are designed and optimized to enhance the harvesting characteristics of traditional simple electric dipole nano-antenna(SEDNA). The LSFNA geometrical dimensions are optimized to have the best values for the required input impedance at three resonance wavelengths of λres = 10 μm,15 μm, and 20 μm. Then the LSFNAs with three different sizes are modeled like a planar spiral-shaped array(PSSA).Also, a fractal bowtie nano-antenna is connected with the PSSA in the array gap. This proposed hybrid structure consists of two main elements:(I) Three different sizes of the LSFNAs with two different material types are designed based on the thin-film metal–insulator–metal diodes that are a proper method for infrared energy harvesting.(II) The PSSA gap is designed based on the electron field emission proposed by the Fowler–Nordheim theory for the array rectification. Finally,the proposed device is analyzed. The results show that the PSSA not only has an averaged 3-time enhancement in the harvesting characteristics(such as return loss, harvesting efficiency, etc.) than the previously proposed structures but also is a multi-resonance wide-band device. Furthermore, the proposed antenna takes up less space in the electronic circuit and has an easy implementation process.     

Microwave control of directed transport in asymmetric antidot structures

It is shown that a polarized microwave radiation creates directed transport in an asymmetric antidot superlattice in two dimensional electron gas. A numerical method is developed that allows to establish the dependence of this ratchet effect on several parameters relevant for real experimental studies. It is applied to the concrete case of a semidisk Galton board where the electron dynamics is chaotic in the absence of microwave driving. The obtained results show that strong currents can be reached at a relatively low microwave power. This effect opens new possibilities for microwave control of transport in asymmetric superlattices.     

Structural, electrical, electronic and optical properties of melanin films

We present thick, uniform and rather flat melanin films obtained using spray deposition. The morphology of the films was investigated using Scanning Electron Microscopy (SEM) and Atomic Force Microscopy (AFM). Temperature-dependent electrical resistance of melanin thin films evidenced a semiconductor-like character and a hysteretic behavior linked to an irreversible process of water molecule desorption from the melanin film. X-ray Photoelectron Spectroscopy (XPS) was carried out to analyze the role of the functional groups in the primary and secondary structure of the macromolecule, showing that the contribution of the 5,6-dihydroxyindole-2-carboxylic acid (DHICA) subunit to the molecule is about 35%. Comparison of the optical absorption of the thick (800nm) and thin (80nm) films showed a spectral change when the thickness increases. From in vacuum photoconductivity (PC) measured at controlled temperatures, we suggest that the melanin films exhibit a possible charge transport mechanism by means of delocalized states along the stacked planar secondary structure.     

Structural, optical and electrical properties of amorphous silicon thin films prepared by sputtering with different targets

Amorphous silicon (a-Si) films were prepared by sputtering method with polycrystalline and monocrystalline silicon targets. Structural, optical and electrical properties of the a-Si films have been systematically studied. The deposition power is from 100 to 200 W. Compared with the a-Si films deposited by using monocrystalline silicon target, the a-Si films prepared with polycrystalline silicon target exhibit better growth property, similar optical band gap, and own the highest mobility of 1.658 cm²/Vs, which make a good match with the optimal window of optical band gap for a-Si solar cells. The results indicated that the polycrystalline silicon target is superior to the monocrystalline silicon target when used to prepare a-Si films as the intrinsic layer in a-Si solar cells.     

Structural, optical, and electrical properties of p-type NiO films and composite TiO2/NiO electrodes for solid-state dye-sensitized solar cells

p-Type nickel oxide thin films were prepared by sol-gel method, and their structural, optical and electrical properties were investigated. The Ni(OH)₂ sol was formed from nickel (II) acetate tetrahydrate, Ni(CH₃COO)₂·4H₂O, in a mixture of alcohol solution and poly(ethylene glycol), and deposited on an ITO substrate by spin coating followed by different heat treatments in air (50-800 °C). The formation and composition of NiO thin film was justified by EDX analysis. It is found that the thickness of the NiO film calcined at 450 °C for 1 h is about 120 nm with average particle size of 22 nm, and high UV transparency (∼75%) in the visible region is also observed. However, the transmittance is negligible for thin films calcined at 800 °C and below 200 °C due to larger particle size and the amorphous characteristics, respectively. Moreover, the composite electrode comprising n-type TiO₂ and p-type NiO is fabricated. The current-voltage (I-V) characteristics of the composite TiO₂/NiO electrode demonstrate significant p-type behavior by the shape of the rectifying curve in dark. The effect of calcination temperature on the rectification behavior is also discussed.     

Anisotropy of optical,electrical, and photoelectrical properties of amorphous hydrogenated silicon films modified by femtosecond laser irradiation

Two types of independent anisotropic structures have been formed simultaneously in amorphous hydrogenated films by applying a femtosecond laser pulse to them, i.e., a structure with a period of several micrometers to several tens of micrometers and a structure with a period of several hundred nanometers. The formation mechanisms of these strictures are different, which allows us to orient them relative to each other in a desirable way. Both structures independently influence the optical properties of the modified films, which causes the diffraction of transmitted light and making the films polarization-sensitive. The conductivity of the modified films correlates with the mutual orientation of the anisotropic structures, whereas no interrelation between the photoconductivity and optical performance of the modified films has been observed.     

Electrical and optical properties of chemically deposited conducting glass for SIS solar cells

Thin layers of conducting glass (SnO₂:F) of 3 ohm per square sheet resistance were chemically deposited on borosilicate glass for potential applications in SIS solar cells. The layers exhibit 90% optical transmission at the solar maximum (0.5 μm). In an optical investigation of the conducting glass at room temperature, a direct allowed transition at 4.1 eV was observed. Indirect allowed transition was also observed with an energy gap of 2.65 eV and an assisting phonon of 0.05 eV. These observations were supported by reflectance data obtained by an integrating sphere. A technique of making ohmic contacts with SnO₂:F layers is also described.     

A physics-based analytical model for bulk heterojunction organic solar cells incorporating monomolecular recombination mechanism

We present an analytical model for bulk heterojunction organic solar cells incorporating the physics of recombination in the transport equations. Monomolecular recombination process is considered to be the dominant mechanism and treated explicitly. The proposed analytical model shows good agreement with the experimental data as well as with the numerical simulations. The improvements over the previous models are also presented to show the importance of considering the recombination process. The model can be used to find device characteristics such as current–voltage characteristic, efficiency etc. of bulk heterojunction organic solar cells avoiding the mathematical complexities of numerical models.     

非晶FezZn1-xO薄膜的结构、磁性和电性能：

采用射频共溅射方法制备了FezZn1-xO（x=0．80,0．86,0．93）非晶薄膜,该薄膜具有较强的室温铁磁性,制备态的Fe093Zn0．07O的饱和磁化强度Ms可达333．29emu／cm3,磁性能是各向同性的．与多晶的FezZn1-xO（z≤20％）不同的是样品出现了明显的异常霍尔效应（AHE）,样品均为n型半导体,载流子浓度约为10^19-10^20cm^-3．退火后的样品在低温222K下存在着电阻极小值现象．薄膜的低温电阻导电机理属于自旋依赖的电子变程跃迁机理,上述实验结果表明高Fe含量的非晶FeZnO体系有作为新型自旋电子学器件材料的可能．     

Effects of electron-beam irradiation on structural,electrical, and optical properties of amorphous indium gallium zinc oxide thin films

High-energy electron-beam irradiation of indium gallium zinc oxide (IGZO) films improved the short-range arrangement. The increase in band gap was used as an indication of such improvement. X-ray diffraction confirmed that the films treated with a DC voltage of 2–4.5 kV for duration of up to 35 min are in the amorphous state or nanocrystalline phase. Higher energy electron-beam irradiation led to increased conductivity, which mainly comes from the drastic increase in electron concentration. Electron-beam treatment could be a viable route to improve the contact resistance between the source/drain and channel layer in thin-film transistor devices.