ZnO:Al/p-Si heterokavşakların kapasitans-voltaj ve akım-voltaj karakteristik özellikleri

In the modern world, finding new alternative energy sources is a vital issue for many reasons. One reason is that traditional energy sources like coal, gas, and oil are not renewable sources and they will eventually be depleted. Another important reason is that burning of fossil fuels cause air and water contamination. Additionally, one of the most important another reason is that the electricity generated from fossil fuels has led to high concentrations of harmful gases like carbon monoxide, carbon dioxide, etc. in the atmosphere, which increase the average temperature on the planet, which is known as the global warming. Clean and renewable energy sources like solar energy, wind energy and hydrogen fuel energy can be considered as an alternative. This kind of energy resources cause fewer emissions, reduce pollution and stand out as a viable source of clean and limitless energy. In this study, we will focus on the solar energy as one of the most promising sources of alternative energy. Among renewable energy, solar energy is the most abundant one that can supply the energy needed by the world's population. It has also an advantage for isolated places to where they are away from the grid. Electricity from sun has no damage to environment since there is no toxicity and waste products. It can be categorized as the cleanest and most abundant source of energy Transparent conducting oxide (TCO) films have much interest in recent years. The optical and electrical properties of the films have been improved over the years. TCO's have been widely used in various industry areas such as optoelectronics, display industry, solar cells, with their desirable optical and electrical properties. In2O3, SnO2 and ZnO are metal oxides that widely used as transparent conductive oxide (TCO) materials ZnO has received much attention over the past few years because it has a wide range of properties that depend on doping, including a range of conductivity from metallic to insulating (including n-type and p-type conductivity), high transparency, high piezoelectricity, wide-bandgap semiconductivity, room-temperature ferromagnetism, huge magnetooptic and chemical-sensing effects, non-toxicity, high resistivity control, high chemical, mechanical and thermal stability together with its abundance in nature which makes it a lower cost material. These characteristics have made ZnO thin films very attractive for promising applications in solar cells, gas sensors, transducers, luminescent materials, transparent conductors, heat mirrors and semiconductor heterojunctions. Un-doped ZnO films which have poor electrical properties due to the low carrier concentration, showed high conductivity due to defects like oxygen vacancies and Zn interstitial. Its electrical properties are significantly affected by adsorption of O2, CO2, hydrocarbons, S-containing compounds, and water. Doping of ZnO with aluminum (ZnO:Al) can increase film conductivity. Aluminum-doped zinc oxide (ZnO:Al) has attracted much attention because of its low cost, good optical and electronic properties, heat stability, non-toxicity and high transparency in the near-infrared (IR) and invisible regions (90 %) ZnO films have been used as solar cell electrodes, gas sensors and optical devices. For fabrication of ZnO films various techniques have been used such as sputtering, chemical vapor deposition, spray pyrolsis, sol-gel etc. Among these, the sol–gel process presents an easy way to integrate ZnO devices into the Si technology, since it offers the possibility of excellent compositional control, multicomponent oxide layers of many compositions on substrate, simplicity, homogeneity, lower crystallization temperature and low production costs. Sol-gel process can be used to fabricate almost any single or multi-component oxide coating. Such coatings have been deposited on glass to provide coloration, anti-reflection, selective reflection, electrochromism and photochromism, selective absorption, wave guiding, reduced friction, anti-soiling reduced adhesion, transparent conductors, electro-optics, Ferro-electrics, sensors, and dye lasers. Deposition of ZnO films on p/n type substrates provides to produce heterojunction which are generally used for fabrication of solar cells. Recently n-ZnO/p-Si heterojunctions has received much attention for electronical applications. The biggest advantage of these heterojunctions is to combine the large binding energy of ZnO thin films and the inexpensiveness of Si substrates. In this work Al doped n-ZnO/p-Si heterojuntions were fabricated by sol-gel dip coating process. P type Si (100) wafers and glasses were used as the substrates. The structural and electrical properties of ZnO:Al thin films and heterojunction properties of ZnO:Al/p-Si were investigated with respect to effects of Al doping concentration and process parameters (i.e. thermal treatment temperature and ambient). After the coating process, characterization of the ZnO:Al thin films and ZnO:Al/p-Si heterojunctions were made by X-Ray diffractomerter, scanning electron microscopy, surface profilometer, dispensible four point resistivity probe and a semiconductor characterization system (SCS). Structural properties investigation by X-ray diffraction method showed that the films were in the form of hexagonal wurzite and tetragonal structure. The XRD patterns of the ZnO:Al films on p type si substrate had (100), (002) and (101) diffraction peaks were in accordance with literature. SEM images show that ZnO:Al films had granular nanostructure. The increasing of the termal treatment temperature caused an increase on crystalline size. The annealing ambient tended to change the crystalline size of the thin films. The thicknesses of the thin films are in the range of 150-500 nm and the certain decrease was detected while the annealing temperature was increased. Electrical resistivity changed with respect to Al doping concentration, annealing ambient and temperature. Minimum resistivity were detected at 1.2 at.% Al concentration. ZnO:Al/p-Si heterojunction properties were analysed by current-voltage (I-V) measurements and capacitance-voltage (C-V) depend on the Al dopand concentrations and annealing temperatures. Most of the ZnO:Al/p-Si heterojunctions exhibited diode-like rectifying behavior. Under UV illumination the photoelectric behavior observed for the diodes. In this study the 1.2 at.% Al doping concentration, vaccum ambient and 700°C annealing temperature are the optimum process parameters to produce heterojunction.