Development of Zn-IV-Nitride Semiconductor Materials and Devices

Author: Shing, Amanda M.

Year: 2016

Degree: Dissertation (Ph.D.)

Advisors: Lewis, Nathan Saul; Atwater, Harry Albert

Committee Members: Faber, Katherine T.; Gray, Harry B.; Goddard, William A., III; Lewis, Nathan Saul; Atwater, Harry Albert

Option: Materials Science

DOI: 10.7907/Z94Q7RXJ

Abstract

This thesis details explorations of the materials and device fabrication of Zn-IV-Nitride thin-films. Motivation in studying this materials series originates from its analgous properties to the III-Nitride semiconductor materials and its potential applications in photonic devices such as solar cells, light emitting diodes, and optical sensors. Building off of initial fabrication work from Coronel, Lahourcade et al., ZnSnxGe1-xN2 thin-films have shown to be a non-phase-segregating, tunable alloy series and a possible earth-abundant alternative to InxGa1-xN alloys. This thesis discusses further developments in fabrication of ZnSnxGe1-xN2 alloys by three-target co-sputtering and molecular beam epitaxy, and the resulting structural and optoelectronic characterization. Devices from these developed alloys are also highlighted.

Initial fabrication was based on the reactive radio-frequency (RF) sputtering technique and was limited to two-target sources and produced nanocrystalline films. Progression to three-target reactive RF co-sputtering for ZnSnxGe1-xN2 (x < 1) alloys is presented, where three-target co-sputtered alloys follow the structural and optoelectronic trends of the initial alloy series. However, three-target co-sputtering further enabled synthesis of alloys having < 10% atomic composition (x < 0.4) of tin, exhibiting non-degenerate doping. The electronic structure of sputtered thin-film surfaces for the alloy series were also characterized by photoelectron spectroscopy to measure their work functions and relative band alignment for device implementation.

Low electronic mobilities, degenerate carrier concentrations, and limited photoresponse may stem from the defective and nanocrystalline nature of the sputtered films. To improve crystalline quality, films were grown by molecular beam epitaxy (MBE). MBE ZnSnxGe1-xN2 films on sapphire and GaN were epitaxially grown, overall displaying single-crystalline quality films, higher electronic mobilities, and lower carrier concentrations. Througout experimentation, devices from both sputter deposited and MBE ZnSnxGe1-xN2 alloys films were constructed. Attempts at solid-state and electrochemical devices are described. Devices exhibited some photoresponse, providing a positive outlook for employment of ZnSnxGe1-xN2 alloys in solar cells or photon sensors.

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