الفهرس 
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Abstract
Nanowires have ushered in a new era of X-ray detection with their exceptional sensitivity and miniaturized design. These ultra-thin, nanoscale structures possess inherent advantages, such as high surface-to-volume ratios and the ability to efficiently convert X-ray photons into detectable electrical signals. Their small size and flexibility make them ideal candidates for applications requiring compact and portable X-ray devices, while their responsiveness to low-energy X-rays offers improved sensitivity and reduced radiation exposure for patients and operators. As researchers continue to refine and expand upon nanowire-based X-ray detection systems, the potential for more precise and accessible X-ray imaging in various fields becomes increasingly promising. In this thesis, we suggested a proposal a model describe the nanowire detector. In addition, various aspects of process were investigated in Indium Phosphide materials with three types of doping profiles, n-p-n (phototransistor), p-i-n (photodiode) and n+-i-n+ (photoconductor).
The objective of this thesis is to leverage the unique geometry of nanowires (NWs) to investigate charge trapping and enhance the spatial resolution of the nanowire-based detector. To achieve this, a vertical configuration is developed wherein the NWs are aligned vertically. In this configuration, the spatial resolution of the detector is primarily determined by the diameter of the nanowire, and X-rays can be effectively absorbed along the axis of the nanowire. This vertical design not only allows for improved spatial resolution but also offers the potential to scale up the device into a multi-pixel array detector, similar to conventional X-ray detectors. This scalability opens up opportunities for broader applications and advanced imaging capabilities in the field of X-ray detection.
The thesis is divided into five chapters structured as follows.
Chapter 1:
In this chapter, an overview of the X-ray detectors and materials used as nanowire detectors and detection methods used in X-ray detectors is presented. This literature review necessitates the pressing demand for the detection of high-energy radiation, underscoring the critical importance of advancing detection methods.
Chapter 2:
This chapter provides a detailed examination of X-ray detectors, specifically highlighting the differences between direct and indirect types. It also extensively explores X-ray fluorescence (XRF), explaining how it occurs when X-ray photons excite atoms in a material, resulting in the emission of characteristic X-ray fluorescence spectra.
Chapter 3:
In this chapter, an InP nanowire detector photodiode is proposed. To understand the X-ray detection mechanism within this photodiode, an analytical model is introduced. This model not only predicts the current generated by incident X-ray radiation but also offers insights into the collection time and efficiency of the nanowire, especially when surface trap charges are present. To enhance our understanding of the photodiode’s behavior, TCAD SILVACO is utilized for simulating solutions to the electrostatic problem. This involves addressing Poisson’s equation and modeling the processes of charge generation and recombination. To validate and ensure the model’s accuracy, TCAD predictions with experimental data are compared.
Chapter 4:
In this chapter, an extensive analysis of a nanowire photoconductor’s performance characteristics is performed. The examination covered various parameters, including X-ray-induced current, collection time, gain, and the impact of surface trap charges. To accomplish this, TCAD SILVACO is employed for simulating the electrostatic aspects, involving the solution of Poisson’s equation and modeling charge generation and recombination. Additionally, we made use of pyPENELOPE, a Python package that acts as an interface to the PENELOPE Monte Carlo simulation code. This enables us to simulate the transport of photons in matter, offering a comprehensive exploration of photon interactions within our nanowire photoconductor.
Chapter 5:
In this chapter, we present a new InP nanowire (NW) X-ray phototransistor detector and offer essential design guidelines, along with an explanation of its operational principles. We have developed a detailed model that considers critical factors like trap charges and other physical effects relevant to NW structures. This model proves its value in the initial stages of NW detector design. The results from our model shed light on phenomena like charge trapping at surface states, known as photogating and photodoping. In addition to the analytical model, we use the SILVACO TCAD device simulator for validation and to explore phenomena beyond the analytical model’s scope. For example, we study the impact of biasing voltage on the NW phototransistor’s behavior and investigate aspects like leakage current.
Conclusions and Future Work:
To summarize the work, we have incorporated a comparative analysis of the NW phototransistor, photoconductor, and photodiode. Additionally, we have elucidated the disparity pertaining to the collection time and gain transient simulation. Lastly, we propose a prospective framework that aims to address the issue of surface traps and mitigate the occurrence of leakage current as a route of the future work