Deposition and Characterization of AlN and GaN Thin Films by Plasma-Enhanced Atomic Layer Deposition

  • Author / Creator
    Motamedi, Pooyan
  • III-nitride semiconductors have a combination of structural characteristics and engineering properties that give them a unique place among semiconductors. The fact that they have the same crystal structure makes it possible to deposit alloys with fine-tuned band gaps from infrared to ultraviolet wavelengths. Such alloys have applications in general lighting, UV detectors, and laser diodes. In addition, piezoelectric sensors and actuators are an attractive area of application for AlN. GaN has a high breakdown field and carrier mobility, which make it a promising choice for high power/high frequency applications. While metal-organic chemical vapor deposition and reactive sputtering have been successfully used for deposition of micron-thick III-N films, they are not suitable for deposition on high aspect ratio surface features, or when thickness control at the atomic level is required. Atomic layer deposition (ALD) offers the perfect solution for such applications. Plasma-enhanced ALD makes it possible to deposit crystalline films at lower temperatures. Employing this method for deposition of crystalline AlN and GaN thin films at low temperatures is the subject of this thesis. AlN and GaN films were deposited on various substrates using nitrogen plasma and metal-organic precursors. Comprehensive experiments were carried out to optimize the deposition parameters. Both AlN and GaN films were found to be structurally comparable to the films deposited at much higher temperatures using conventional methods. GaN films deposited on sapphire have the desirable (001) preferential orientation, high mass density, high electron mobility, and optical properties close to the bulk values. In addition to deposition of AlN and GaN, several interesting phenomena were observed and investigated to varying degrees, in light of the available means. Substrate temperature was found to have a profound role in determination of the structure and properties of GaN films. A likely change in the growth mechanism was observed at higher growth temperatures. It was found that the growth of GaN starts epitaxially, but a shift to the three-dimensional growth occurs afterwards. In-situ ellipsometry was employed to investigate the evolution of optical properties of the films during growth, and the results are in good agreement with structural observations.

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  • Degree
    Doctor of Philosophy
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