Analytical and Numerical Investigation of Nanowire Transistor X-ray Detector.

Recently, nanowire detectors have been attracting increasing interest thanks to their advantages of high resolution and gain. The potential of using nanowire detectors is investigated in this work by developing a physically based model for Indium Phosphide (InP) phototransistor as well as by performing TCAD simulations. The model is based on solving the basic semiconductor equations for bipolar transistors and considering the effects of charge distribution on the bulk and on the surface. The developed model also takes into consideration the impact of surface traps, which are induced by photogenerated carriers situated at the surface of the nanowire. Further, photogating phenomena and photodoping are also included. Moreover, displacement damage (DD) is also investigated; an issue arises when the detector is exposed to repeated doses. The presented analytical model can predict the current produced from the incident X-ray beam at various energies. The calculation of the gain of the presented nanowire carefully considers the different governing effects at several values of energies as well as biasing voltage and doping. The proposed model is built in MATLAB, and the validity check of the model results is achieved using SILVACO TCAD device simulation. Comparisons between the proposed model results and SILVACO TCAD device simulation are provided and show good agreement.

Design and Optimization of a Self-Protected Thin Film c-Si Solar Cell against Reverse Bias.

Current mismatch due to solar cell failure or partial shading of solar panels may cause a reverse biasing of solar cells inside a photovoltaic (PV) module. The reverse-biased cells consume power instead of generating it, resulting in hot spots. To protect the solar cell against the reverse current, we introduce a novel design of a self-protected thin-film crystalline silicon (c-Si) solar cell using TCAD simulation. The proposed device achieves two distinct functions where it acts as a regular solar cell at forward bias while it performs as a backward diode upon reverse biasing. The ON-state voltage (VON) of the backward equivalent diode is found to be 0.062 V, which is lower than the value for the Schottky diode usually used as a protective element in a string of solar cells. Furthermore, enhancement techniques to improve the electrical and optical characteristics of the self-protected device are investigated. The proposed solar cell is enhanced by optimizing different design parameters, such as the doping concentration and the layers' thicknesses. The enhanced cell structure shows an improvement in the short-circuit current density (JSC) and the open-circuit voltage (VOC), and thus an increased power conversion efficiency (PCE) while the VON is increased due to an increase of the JSC. Moreover, the simulation results depict that, by the introduction of an antireflection coating (ARC) layer, the external quantum efficiency (EQE) is enhanced and the PCE is boosted to 22.43%. Although the inclusion of ARC results in increasing VON, it is still lower than the value of VON for the Schottky diode encountered in current protection technology.

Boosting the Electrostatic MEMS Converter Output Power by Applying Three Effective Performance-Enhancing Techniques.

This current study aims to enhance the electrostatic MEMS converter performance mainly by boosting its output power. Three different techniques are applied to accomplish such performance enhancement. Firstly, the power is boosted by scaling up the technology of the converter CMOS accompanied circuit, the power conditioning, and power controlling circuits, from 0.35 µm to 0.6 µm CMOS technology. As the converter area is in the range of mm2, there are no restrictions concerning the scaling up of the accompanied converter CMOS circuits. As a result, the maximum voltage of the system for harvesting energy, Vmax, which is the most effective system constraint that greatly affects the converter's output power, increases from 8 V to 30 V. The output power of the designed and simulated converter based on the 0.6 µm technology increases from 2.1 mW to 4.5 mW. Secondly, the converter power increases by optimizing its technological parameters, the converter thickness and the converter finger width and length. Such optimization causes the converter output power to increase from 4.5 mW to 11.2 mW. Finally, the converter structure is optimized to maximize its finger length by using its wasted shuttle mass area which does not contribute to its capacitances and output power. The proposed structure increases the converter output power from 11.2 mW to 14.29 mW. Thus, the three applied performance enhancement techniques boosted the converter output power by 12.19 mW, which is a considerable enhancement in the converter performance. All simulations are carried out using COMSOL Multiphysics 5.4.

Validation and Evaluation of a Behavioral Circuit Model of an Enhanced Electrostatic MEMS Converter.

In this current study, the validation and evaluation of a behavioral circuit model of electrostatic MEMS converters are presented. The main objective of such a model is to accurately find the converter behavior through the proper choice of its circuit elements. In this regard, the model enables the implementation of the electrostatic MEMS converter using commercially available off-shelf circuit elements. Thus, the overall vibration energy harvesting system can be implemented and tested without the need for fabricating the converter. As a result, the converter performance can be verified and evaluated before its fabrication which saves the expenses of fabricating trailed prototypes. To test the model, we apply it to an enhanced converter in which the conventional electrostatic MEMS converter is modified by depositing the tantalum pentoxide, Ta2O5, a high dielectric constant material, on its fingers' sidewalls. Such a deposition technique causes an appreciable increase in the overall converter capacitance and, in turn, the output power, which is boosted from the range of µw to the range of mW. Next, the converter behavioral circuit model, which is based on representing its capacitances variations with respect to the input displacement, x caused by the vibration signal, C-x curve, is built up. The model is qualitatively validated and quantitatively evaluated. The enhanced converter performance is investigated through the interaction of its model with the power conditioning circuit. From the simulation results, it is revealed that the converter behavioral circuit model accurately accomplishes the vibration energy conversion operation. As a result, the specification of the required controlling pulses for the converter operation is accurately determined. Finally, the model accuracy is validated by calibrating its performance with a traditionally simulated and fabricated electrostatic MEMS converter.

Development of solar cell for large area position detection: proof of concept.

Detecting and analyzing a moving body position are helpful in many fields, such as medicine, sports performance, virtual reality and many more. Therefore, researchers try to develop a tool or a system that helps to detect the motion and tracking its position. This paper shows how a Si solar cell can be modified to function as a Position Sensitive Detector (PSD), which could be used as a large area detector in a position detection system. To develop the new detector, we modeled and simulated the modified solar cell by TCAD simulation tools to calculate the detected photocurrent as a function of the position of an incident laser beam sourced by the moving object. Further, an optical position detection system is implemented containing the modified solar cell, a signal amplifier and a microcontroller. The output is then displayed on a Laptop. By measuring the same simulated output photocurrents, it is found that the measured system output matches the simulation results. This proposed position detection system is relatively cheap because it does not contain high precision optical image building components such as lenses and mirrors. Besides, the proposed system could substitute the optical system by using a large area PSD made from a broad array of solar cells. The electronics are also much more straightforward than those in systems based on image processing. So, it has a high-speed response. The error assessment of the proposed system showed a low position detection error of less than 10%.