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Advanced polarization engineering of III-nitride heterostructures towards high-speed device applications

Nath, Digbijoy N
http://rave.ohiolink.edu/etdc/view?acc_num=osu1376927078

Abstract Details

2013, Doctor of Philosophy, Ohio State University, Electrical and Computer Engineering.
This thesis explores polarization-engineering in III-nitride heterostructures towards next generation high-speed GaN-based transistors. GaN-based devices have found a wide range of useful applications such as high-speed RF transistors in wireless technology and as blue/green light emitters in opto-electronics. Due to superior material and electrical properties, GaN-based transistors offer much higher output power with increased efficiency than its rival technologies can offer. However, with aggressive scaling of device dimensions, conventional AlGaN/GaN HEMTs are now reaching the limit of their high-speed performance (maximum cut-off frequency, fT) due to LO phonon-limited saturation velocity (~1-2x107 cm/s) of electrons in GaN. To enable a high-power III-nitride device technology in the THz regime, unconventional transport mechanism and advanced channel engineering need to be explored. This thesis seeks to explore three approaches towards this – alternative channel material (InxGa1-xN) for higher intrinsic electron velocity, lower dimensional transport (1D transistors), and unconventional tunnel-injected ballistic transport in a hot electron transistor. The electron velocity in InxGa1-xN (x~0.25) is theoretically estimated to be at least 50-100% higher than in GaN which can lead to substantial increase in fT; however, achieving high quality InxGa1-xN with high In-composition presents significant epitaxial challenges. In the first part of this thesis, MBE growth of high composition InGaN is investigated, and a comprehensive growth diagram is developed. Lower dimensionality can be promising for superior electron transport including better noise figure. Conventional approaches to nanowire fabrication including both top-down and catalysis-mediated bottom-up approaches have their own limitations. Besides, it has always been a challenge to achieve dense arrays of nanowire transistors required for technological applications. In the next part of the thesis, self-defined arrays of nanowires or 1-D channel transistors are demonstrated in vicinal N-polar GaN-based heterostructure by using polarization-engineering. High current densities up to 150 mA/mm is achieved in dense arrays (>105 nanowires/cm) of self-defined 1D transistors. In the final part, a unipolar III-nitride device - tunnel-injected hot electron transistor (THETA) - is investigated which can theoretically provide fT > 1 THz by exploiting ballistic transport of electrons over a thin base layer. However, all unipolar III-nitride vertical devices have been always found to suffer from unacceptably high leakage current densities. A comprehensive investigation in to such vertical leakage mechanism is presented and is attributed to a ternary alloy-mediated percolation-based transport. By eliminating ternary alloys as leakage barrier, III-nitride THETA is demonstrated for the first time with output modulation in common-emitter configuration with a current transfer ratio up to 0.80 at 6 eV base-emitter bias.
Siddharth Rajan (Advisor)
Steven Ringel (Committee Member)
Wu Lu (Committee Member)
William Brantley (Committee Member)
Electrical Engineering
III-nitride, GaN, hot electron, transistor, MBE, epitaxy

Recommended Citations

Citations

  • Nath, D. N. (2013). Advanced polarization engineering of III-nitride heterostructures towards high-speed device applications [Doctoral dissertation, Ohio State University]. OhioLINK Electronic Theses and Dissertations Center. http://rave.ohiolink.edu/etdc/view?acc_num=osu1376927078

    APA Style (7th edition)

  • Nath, Digbijoy. Advanced polarization engineering of III-nitride heterostructures towards high-speed device applications. 2013. Ohio State University, Doctoral dissertation. OhioLINK Electronic Theses and Dissertations Center, http://rave.ohiolink.edu/etdc/view?acc_num=osu1376927078.

    MLA Style (8th edition)

  • Nath, Digbijoy. "Advanced polarization engineering of III-nitride heterostructures towards high-speed device applications." Doctoral dissertation, Ohio State University, 2013. http://rave.ohiolink.edu/etdc/view?acc_num=osu1376927078

    Chicago Manual of Style (17th edition)

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