How does the SAED (Selected Area Electron Diffraction) pattern provide information about the crystal structure of titanium dioxide?5 answersThe SAED pattern of titanium dioxide (TiO2) provides crucial information about its crystal structure. Steinhoff et al. demonstrated that SAED analysis can reveal the crystal structure of TiO2 nanoparticles during wastewater treatment, showing no physicochemical transformation in TiO2-NPs with an anatase/rutile ratio of ∼80/20. Additionally, Walck highlighted the importance of SAED in characterizing materials, emphasizing its role in obtaining dependable results and recording high-quality patterns for diffraction analysis. Furthermore, Nebaba et al. proposed an automated image processing algorithm for SAED images, enhancing the analysis of crystal structures in transmission electron microscopy images. Therefore, by analyzing the diffraction pattern through SAED, researchers can determine the lattice parameters and crystal symmetry of TiO2, aiding in its structural characterization.
How to improve the reverse leakege of the schottky diode?5 answersTo improve the reverse leakage of Schottky diodes, several approaches have been proposed in the literature. One method is the use of oxygen (O2) plasma treatment after mesa etching, which can remove photoresist residue and reduce traps, leading to lower reverse leakage current and higher breakdown voltage. Another approach involves the implementation of edge termination structures, such as "sidewall covering" and "edge capping," which mitigate the edge electric field and suppress nonideal leakage current. Additionally, the use of a p-type NiOx guard ring has been found to reduce reverse leakage and subthreshold leakage current at high temperatures, by increasing the barrier height and passivating defects at the interface. These methods provide valuable routes for developing Schottky diodes with improved reverse leakage characteristics.
What is the role on top contact grid in CIGS solar cells?5 answersThe top contact grid plays a crucial role in CIGS solar cells. It is responsible for collecting the current generated by the solar cell. The top contact grid is typically made up of metallic branches that are placed on top of a transparent front contact. The design and optimization of the top contact grid are important for efficient current transport and overall performance of the solar cell. Different materials, conductivities, and geometries are considered in the design process. The use of a metal grid instead of a transparent conductor oxide (TCO) can increase transparency and absorption, leading to higher efficiency. Additionally, the top contact grid can help reduce resistive losses along the transparent top contact, improving the overall performance of the CIGS solar cell.
1. Why diode is reverse biased in determining the band gap of semi-conductor?5 answersReverse bias is used in determining the band gap of a semiconductor diode because it allows for the measurement of the temperature dependence of the diode voltage drop. By measuring the change in voltage drop at different temperatures, the ideality factor and bandgap energy of the semiconductor can be accurately determined. This method is particularly useful for determining the bandgap of silicon and germanium. The linear variation of the diode terminal voltage with temperature at different fixed forward currents provides the necessary data points for this analysis. This approach offers a simple and accurate way to derive the bandgap using data from a popular experiment, making it suitable for undergraduate laboratories on semiconductors.
What is the relationship between the Schottky effect and thermionic emission?4 answersThe Schottky effect and thermionic emission are closely related in the context of Schottky junctions. The Schottky effect refers to the formation of a potential barrier at the metal-semiconductor interface, which affects the flow of charge carriers. Thermionic emission, on the other hand, is a process where charge carriers overcome the potential barrier and escape from the metal into the semiconductor. The extraction of parameters in Schottky contacts, such as barrier height and ideality factor, often involves the use of thermionic emission models. Different parameter extraction methodologies, such as the Cheung-Cheung's method, have been examined for their effectiveness in determining barrier heights. Additionally, the choice of thermionic emission model, such as the surface recombination velocity-based models, can impact the accuracy of parameter extraction.
Why is the response of a Schottky photodetector higher when using back illumination?5 answersStep 1:
Back illumination increases the response of a Schottky photodetector due to the effect of the built-in electric field caused by Schottky contacts, which leads to a reduction in electron-hole recombination rate and an increase in free carrier density, resulting in faster response times and higher photocurrent. Additionally, the excitation of surface plasmons at the metal-semiconductor junction intensifies the electromagnetic field, leading to increased light absorption and higher photocurrent. Furthermore, the motion of photo-generated carriers under back illumination enhances the photocurrent, contributing to the higher response of the Schottky photodetector.
Step 3:
Back illumination increases the response of a Schottky photodetector due to the effect of the built-in electric field caused by Schottky contacts, which leads to a reduction in electron-hole recombination rate and an increase in free carrier density, resulting in faster response times and higher photocurrent. Additionally, the excitation of surface plasmons at the metal-semiconductor junction intensifies the electromagnetic field, leading to increased light absorption and higher photocurrent. Furthermore, the motion of photo-generated carriers under back illumination enhances the photocurrent, contributing to the higher response of the Schottky photodetector.