Cryomilled Group IV elements (Silicon & Germanium) for optoelectronic applications

Abstract

Group IV elements such as silicon and germanium are elemental semiconductors and lead to the evolution of modern electronic applications. Synthesis of contamination-free nanoparticles of these materials in bulk quantity becomes an important aspect because the contaminations could substantially change the electrical properties. With this in motivation, the thesis is focused on synthesis of nanoparticles of Si and Ge by cryomilling. Following this we have explored the optoelectronic applications. Thesis is organized in eight chapters and a brief description of each chapter is given here. Chapter 1 introduces the research topic and briefly explains the work performed in this thesis. Chapter 2 provides the literature review on synthesis methods of Si nanostructures. Chapter 3 explains the experimental methods used to synthesize Si and Ge nanoparticles and process methods to fabricate optoelectronic devices. Chapter 4 presents our work on the synthesis of Si nanoparticles by cryomilling. Cryomilling is a type of ball milling in which the powders are milled at cryogenic temperature to avoid the inadvertent reactions, which has been used in this work to synthesis Si and Ge nanoparticles. The dynamics of the ball motion during the cryomilling process has been understood for the efficient synthesis of nanoparticles. Initially, p-type and n-type Si nanoparticles have been synthesized by the cryomilling process. The phase and structural characterizations reveal the polycrystalline particles containing both amorphous and crystalline grains. One-step simple etching process has been proposed to obtain the nanocrystals. Photoluminescence studies of this nanocrystals show the luminescence at UV range, and the efficiency has been estimated. The particles were functionalized to enhance the colloidal and oxidation stability. In chapter 5, the optimized synthesis parameters of Si have been employed on germanium to obtain nano crystals, which belongs to the same group (group IV). Ge ink has been further synthesized using functionalization process. In chapter 6, the application of doped Si nanoparticles has been explored by incorporating the particles in organic-inorganic hybrid solar cells. The device efficiency has been improved, and the effect of various dopant states on device performance has been studied. Solution-processed semiconductors are promising candidates for next-generation optoelectronic devices. In chapter 7, spray coating and inkjet printing methods are used to fabricate semiconducting diodes using Si and Ge nanoparticles. Si nanocrystals obtained from the etching process have been sandwiched in TiO2/CuI semiconductor device using a spray coating process. The reason behind the improved current flow in the diode, due to the addition of Si nanocrystals and the mechanism has been explored. Ge ink obtained from the functionalization step has been inkjet printed on Si to obtain Si-Ge heterostructure. The major problem of coffee-stain effect during the inkjet printing has been suppressed, and the current- voltage characteristics of the device showed the diode behavior. Chapter 8 summarizes the thesis work and explains the future scope of the thesis