From radical-enhanced to pure thermal ALD of gallium and aluminium nitrides

Sourish Banerjee

    Research output: ThesisPhD Thesis - Research UT, graduation UT

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    Abstract

    To continue the miniaturization trend of Silicon (Si)-based microelectronic devices in an era when we have almost fully-exploited the physical capabilities of Si, other semiconductors such as gallium nitride (GaN) and aluminium nitride (AlN) (collectively (Al)GaN) are currently being investigated. These can potentially complement Si, since in their monocrystalline form, have superior material properties to Si. Examples include direct and wider bandgap, high electron mobility and high breakdown field. Thus, combining the mature Si-based process technology with such superior (Al)GaN material properties on one platform enables microelectronic devices, in accordance with the ‘More-than-Moore’ philosophy. Exploring polycrystalline and thin film (i.e., sub-micron) (Al)GaN must also be pursued, since that broadens their applications; enabling utilization in sensors, thin film transistors (TFT), as passivation layers, etc. Atomic layer deposition (ALD) is a highly relevant technique for (Al)GaN, since the technique promises atomic-level thickness control, coupled with superb film conformality and spatial uniformity. Reports of (Al)GaN ALD are only appearing recently in the literature, suggesting the increasing relevance of this field.

    This thesis investigated ALD of polycrystalline (Al)GaN, using conventional Si-technology and industrially accepted precursors. A variety of activation techniques, from thermal, to plasma, and the novel hot-wire activation were explored. Some important obtained research results were: (a) Identification of a chemical route which enables pure thermal ALD of GaN, (b) Preparation of novel GaCN composite layers with high refractive indices, (c) Selectively depositing GaN on specially-terminated substrates, (d) Tuning (Al)GaN polycrystallinity and optical properties with plasma composition and investigating the underlying causes, (e) Investigating the role of precursor-generated radicals on (Al)GaN growth, and (f) Identifying the discontinuous nature of sub-10 nm AlN with electrical and optical techniques. In conclusion, the results obtained and the suggested future work are expected to advance the state-of-the-art of Al(GaN) ALD.
    Original languageEnglish
    QualificationDoctor of Philosophy
    Awarding Institution
    • University of Twente
    Supervisors/Advisors
    • Gravesteijn, Dirk J, Supervisor
    • Kovalgin, Alexey Y., Supervisor
    Award date11 Sep 2019
    Place of PublicationEnschede
    Publisher
    Print ISBNs978-90-365-4825-0
    DOIs
    Publication statusPublished - 11 Sep 2019

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