Technical Description: There exists a poorly understood semiconductor family closely related to the (In,Ga)N family where the column III element is replaced by an ordered cation sublattice composed of equal numbers of Zn and column IV (Si, Ge, Sn) atoms. While the Si- and Ge-containing members have been synthesized, the narrow band-gap member based on Sn -- key to realizing photon absorption and emission in the visible wavelength portion of the spectrum -- has not, limiting the application prospects of this family whose band-gap range is very similar to that of (In,Ga)N. This project is focused on growth and characterization of high-quality single-crystal thin films of zinc tin nitride and the determination of its fundamental optical and electrical properties, particularly with respect to the influence of defects and disorder. Thin films are grown using a plasma-assisted molecular beam epitaxy technique. Crystallinity and microstructure are evaluated using in-situ reflection high energy diffraction as well as x-ray diffraction and both electron and scanning probe microscopy tools; stoichiometry is evaluated using energy dispersive spectrometry calibrated using ion beam analysis. Optical properties are evaluated using optical absorption and photoluminescence spectroscopy, and electrical characteristics are measured using Hall effect techniques.
Non-technical Description: Many inorganic semiconductor alternatives to silicon solar cells contain indium, an element only three times more abundant than silver and a commodity experiencing significant increases in demand. The II-IV-nitride family in contrast is synthesized from earth-abundant elements for which there already exists significant recycling infrastructure, making it of interest both from economic and environmental perspectives for optoelectronic applications such as photovoltaics and solid state lighting. High-quality samples of new materials also provide important opportunities in the broader semiconductor community to improve our understanding of thin film growth processes, and the nature and role of defects in determining fundamental material properties. Educating students in contemporary issues in semiconductor synthesis and characterization, as well as photovoltaics, provides them with important skills highly relevant to the semiconductor industry and the realization of next-generation devices. Exposing high school students to basic solar cell fabrication provides a valuable pathway to encouraging them to consider careers in science and engineering, while at the same time providing them insight into limitations of current photovoltaic technology.
