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Deep Level Defects in Advanced III-Nitride Semiconductors: Presence, Properties and Impact of Proton Irradiation

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2016, Doctor of Philosophy, Ohio State University, Electrical and Computer Engineering.
The development of the next generation GaN-based electronic and optoelectronic devices primarily depends on the capability of growing high quality novel materials and improving device reliability to support new functionalities. Essential to both is a comprehensive understanding of the electrically active crystalline defects, as these defects may introduce deep states in the bandgap, thus substantially impacting material properties and device performance. To date, in spite of large amounts of research on defects in III-nitrides, there is still an extraordinary gap of knowledge. Thus, the goal of this dissertation has been to explore the presence and properties of defect states in a wide range of state-of-the-art III-nitride materials, and investigate their role in device level degradation, particularly, under high energy proton irradiation as intended for space communication applications. To enable these objectives, a set of capacitance-based measurements, including deep level transient/optical spectroscopy (DLTS/DLOS) that facilitate the quantitative characterization of deep states throughout the 3.4 eV GaN bandgap, have been performed on a variety of materials, such as non-polar m-plane GaN, NH3MBE grown p-type GaN, proton irradiated n-type and p-type GaN. Systematically varied growth, irradiation and annealing conditions allowed for methodical investigation of defect behaviors and properties, thus shedding light on the defect physical sources and atomic configurations. Specifically, by comparing simultaneously grown c-/m-plane GaN, substantial impacts of the growth surface on the defect formation were revealed, as both external and native defects formed with much higher concentrations in m-plane GaN. M-plane growth also created traps at EC - 0.14 eV, EC - 0.20 eV and EC - 0.66 eV that were absent in c-plane GaN, among which the EC - 0.14 eV and EC - 0.66 eV states closely correlated with V/III ratio (and/or oxygen content). In proton irradiation study, monotonic but differential concentration increases were observed for almost all pre-existing traps, along with the generation of “new” states at EC - 0.13 eV and EC - 0.16 eV. Systematically controlled thermal annealing led to differential responses for individual irradiation induced traps, suggestive of different introduction/reduction mechanisms linked to their physical origins. In addition, a specially devised p+/p-/n+ diode structure enabled the quantitative characterization of defects in p-GaN. Significant impacts of growth method (NH3MBE vs. MOCVD) and proton irradiation were observed, and possible origins for major p-GaN traps were discussed. Moreover, how these defects affect materials electrical and optical properties, and ultimately the device performance, were carefully examined where possible. Particularly, the proton irradiation induced defect states at the materials level have been correlated with the primary degradation mode at device level (i.e., threshold voltage instability). Not only the sub-linear evolution of VT as a function of proton fluence can be well modeled using experimentally measured GaN buffer trap energy and introduction rate, but also changing buffer designs substantially altered the VT evolution, clearly demonstrating the role of GaN buffer traps in causing VT shift. An analytic model was developed and suggested particular material and structural optimization path to mitigate such degradation, among which, scaling down the barrier thickness has been demonstrated as one of the most effective approaches for improving the radiation hardness of AlGaN/GaN HEMT.
Steven Ringel (Advisor)
Siddharth Rajan (Committee Member)
Roberto Myers (Committee Member)
Betty Anderson (Committee Member)
243 p.

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Citations

  • Zhang, Z. (2016). Deep Level Defects in Advanced III-Nitride Semiconductors: Presence, Properties and Impact of Proton Irradiation [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1449497825

    APA Style (7th edition)

  • Zhang, Zeng. Deep Level Defects in Advanced III-Nitride Semiconductors: Presence, Properties and Impact of Proton Irradiation. 2016. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1449497825.

    MLA Style (8th edition)

  • Zhang, Zeng. "Deep Level Defects in Advanced III-Nitride Semiconductors: Presence, Properties and Impact of Proton Irradiation." Doctoral dissertation, Ohio State University, 2016. http://rave.ohiolink.edu/etdc/view?acc_num=osu1449497825

    Chicago Manual of Style (17th edition)