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Preparation, Characterization, and Device Applications of Zinc Tin Nitride and Zinc Tin Oxynitride Materials

  • Author(s): Ye, Shenglin
  • Advisor(s): Streit, Dwight C.
  • et al.
Abstract

This dissertation presents a comprehensively theoretical and experimental study on zinc tin nitride and zinc tin oxynitride materials. The purposes of this combinatorial study are to understand the fundamental properties of these two materials, and to examine the potential of these two materials for future optoelectronic applications. These fundamental properties are crystal structure, surface morphology, chemical composition, band structures, and optical as well as electrical properties.

Zinc tin nitride (ZnSnN2) thin films have been synthesized on c-plane sapphire substrates and (0001) GaN templates by the reactive radio-frequency (RF) magnetron sputtering method. The properties are investigated by theoretical calculations and experimental results. In terms of theoretical calculation, the lattice constants a, b and c are calculated by using the density functional theory (DFT) method. These constants are comparable to our experimental results as well as previous calculations. In the case of experimental results, the impacts of substrate temperatures and the ratios of N2/(N2+Ar) on films’ properties are fully characterized by using various kinds of techniques including X-ray diffraction (XRD), Raman spectroscopy, X-ray photoemission spectroscopy (XPS), scanning electron microscopy (SEM), atomic force microscopy (AFM), Hall effect measurement, and UV-Vis-NIR spectrometry. By optimizing the growth conditions, ZnSnN2 thin films with an average grain size larger than reported results have been obtained. Additionally, for the first time, the valence band structure of ZnSnN2 has been investigated by XPS analysis. The result is consistent with our calculated density of states (DOS). The vibrational modes of ZnSnN2 are also studied by Raman spectroscopy. The Schottky-behavior diodes with a structure of ZnSnN2/GaN heterojunctions have been successfully fabricated, using the standard fabricating process for semiconductor devices. Standard electrical measurements such as C-V measurements reveal the height of the Schottky barrier at the interface between ZnSnN2 and GaN, as confirmed by XPS measurement for band alignment of ZnSnN2/GaN heterojunctions.

Zinc tin oxynitride (ZnSn(ON)) thin films have been deposited on corning 1737 glass substrates and SiO2/Si wafers by the reactive RF-magnetron sputtering method. By optimizing the O2 contents in the mixture of total reactive gas, ZnSn (ON) thin films with a Hall mobility of 45 cm2 V-1s-1 and a carrier concentration of 1.63×1018 cm-3 have been obtained. Additionally, for the first time, thin film transistors (TFTs) based on ZnSn(ON) have been successfully fabricated. The mean linear field effect mobility can reach to 39.6 cm2 V-1s-1, which is in a good agreement with the Hall measurements. Preliminary results show that ZnSn(ON) is a promising candidate for next-generation oxynitride channel layers.

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