Material and Photonic Engineering on Lead Selenide Nanocrystal Films for Mid-infrared Emitter Development

Abstract

Lead selenide (PbSe) is a IV-VI semiconductor material and is known to have a high absorption coefficient. This property comes from its narrow band gap (0.27eV) and strong interaction with light within the material. This means that it efficiently absorbs a significant amount of light relative to its thickness. The high absorption coefficient makes it a promising material also for solar cell absorbers, as it efficiently converts light into electrical current over a broad wavelength range. Research on PbSe has been ongoing for nearly a century, with continuous advancements in understanding its properties and potential applications. The full extent of its physical properties remains underutilized in practical devices. Despite significant advancements in recent technologies, there is still considerable potential for improving the performance and cost-efficiency of miniaturized MIR gas sensing systems. This thesis aims to develop a narrowband mid-infrared emitter by leveraging photonic engineering techniques applied to lead selenide (PbSe) nanocrystals. A key challenge lies in the inherently low radiative efficiency of PbSe, particularly at room temperature, where non-radiative processes, most notably Auger recombination tend to dominatecarrier dynamics. The first chapter of the thesis presents an overview of the properties of Lead Selenide (PbSe) and High Contrast Gratings (HCG) in the context of mid-infrared photodetection. It examines various PbSe growth techniques, emphasizing the relevance of the Chemical Bath Deposition method. Furthermore, it introduces a novel approach known as Oriented Attachment, underscoring its role in improving the material characteristics of PbSe. Chapter two of the thesis focused on deposition PbSe using Chemical Bath Deposition method, which allow the cost-effective and scalable fabrication of MIR photonic devices. In this study, I employed the water bath method to grow uniform PbSe nanocrystals using the Oriented Attachment technique on amorphous substrates. Different parameters were varied during the growth process and their effects were critically analysed. In chapter three, I studied about the annealing effects on PbSe sample. After annealing with nitrogen at different temperatures, photo luminesce significantly improved.Surface morphologies before and after the annealing of PbSe thin films were studied by Scanning Electron Microscope (SEM) and X-Ray Diffraction (XRD). The chapter four of this thesis explores the nanostructure design simulated using RSoft software, followed by the fabrication methods applied to lead selenide samples which includes the photolithography process. This work contributes to the goal of developing compact, cost-effective, low-power, and highly efficient on-chip MIR narrowband emitter for chemical sensing applications. This work explores methods to enhance PbSe film quality, along with the design and fabrication of photonic structures on PbSe samples, potentially improving the performance of PbSe-based MWIR sensingplatforms. Additionally, the potential future work aimed at enhancing the performance of PbSe emitters and photodetectors will be discussed in the concluding section of the thesis.