Purdue University Graduate School
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posted on 2021-03-12, 15:31 authored by Jinhyun NohJinhyun Noh

Beta-gallium oxide (β-Ga2O3) is an emerging wide bandgap semiconductor for next generation power devices which offers the potential to replace GaN and SiC. It has an ultra-wide bandgap (UWBG) of 4.8 eV and a corresponding Ebr of 8 MV/cm. β-Ga2O3 also possesses a decent intrinsic electron mobility limit of 250 cm2/V·s, yielding high Baliga’s figure of merit of 3444. In addition, the large bandgap of β-Ga2O3 gives stability in harsh environment operation at high temperatures.

Although low-cost large-size β-Ga2O3 native bulk substrates can be realized by melt growth methods, the unique property that (100) surface of β-Ga2O3 has a large lattice constant of 12.23 Å allows it to be cleaved easily into thin and long nano-membranes. Therefore, β-Ga2O3 FETs on foreign substrates by transferring can be fabricated and investigated before β-Ga2O3 epitaxy technology becomes mature and economical viable. Moreover, integrating β-Ga2O3 on high thermal conductivity materials has an advantage in terms of suppressing self-heating effects.

In this dissertation, structural and material innovations to overcome and improve critical challenges are summarized as follows: 1) Top-gate nano-membrane β-Ga2O3 FETs on a high thermal conductivity diamond substrate with record high maximum drain current densities are demonstrated. The reduced self-heating effect due to high thermal conductivity of the substrate was verified by thermoreflectance measurement. 2) Local electro-thermal effect by electrical bias was applied to enhance the electrical performance of devices and improvements of electrical properties were shown after the annealing. 3) Thin thermal bridge materials such as HfO2 and ZrO2 were inserted between β-Ga2O3 and a sapphire substrate to reduce self heating effects without using a diamond substrate. The improved thermal performance of the device was analyzed by phonon density of states plots of β-Ga2O3 and the thin film materials. 4) Nano-membrane tri-gate β-Ga2O3 FETs on SiO2/Si substrate fabricated via exfoliation have been demonstrated for the first time. 5) Using the robustness of β-Ga2O3 in harsh environments, β-Ga2O3 ferroelectric FETs operating as synaptic devices up to 400 °C were demonstrated. The result offers the potential to use the novel device for ultra-wide bandgap logic applications, specifically neuromorphic computing exposed to harsh environments.


Degree Type

  • Doctor of Technology


  • Electrical and Computer Engineering

Campus location

  • West Lafayette

Advisor/Supervisor/Committee Chair

Peide Ye

Additional Committee Member 2

Dallas Morisette

Additional Committee Member 3

Na Lu

Additional Committee Member 4

Peter Bermel