University of Illinois Urbana-Champaign

Metal-assisted chemical etching of β-gallium oxide and its device applications

Huang, Hsien-Chih

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https://hdl.handle.net/2142/117677

Description

Title
Metal-assisted chemical etching of β-gallium oxide and its device applications
Author(s)
Huang, Hsien-Chih
Issue Date
2022-12-01
Director of Research (if dissertation) or Advisor (if thesis)
Li, Xiuling
Doctoral Committee Chair(s)
Li, Xiuling
Committee Member(s)
  • Lee, Minjoo
  • Zhu, Wenjun
  • Rakheja, Shaloo
Department of Study
Electrical & Computer Eng
Discipline
Electrical & Computer Engr
Degree Granting Institution
University of Illinois at Urbana-Champaign
Degree Name
Ph.D.
Degree Level
Dissertation
Keyword(s)
  • β-Ga2O3
  • MacEtch
  • FinFET
  • wide bangap material
  • power electronics
  • plasma-free
Abstract
β-Ga2O3, with an ultra-wide bandgap (UWB) of ~ 4.6 – 4.9 eV and bulk substrate availability, has drawn enormous interest in the power electronics community. So far, the published β-Ga2O3 transistors still suffer from low current density compared to GaN devices. Thus, to further enhance the on-current and gate control, the development of techniques for fabricating β-Ga2O3 vertical structures with high aspect ratio (AR) and smooth surfaces is essential. Nonetheless, dry etch typically damages the surface due to high-energy ions, while most wet etching techniques can only produce very limited aspect ratios. On the other hand, metal-assisted chemical etching (MacEtch) has been demonstrated to produce high aspect ratio nanostructures with smooth sidewalls and could solve the current etching problem of β-Ga2O3. In this thesis, β-Ga2O3 fin arrays by MacEtch with a high aspect ratio and excellent surface quality are demonstrated. The strongly crystal-orientation-dependent etching behaviors are found, and three kinds of vertical structures are formed after the MacEtch process. The Schottky barrier heights (SBHs) between platinum (Pt) and different MacEtch-formed β-Ga2O3 surfaces and sidewalls are found to decrease as the aspect ratio of the β-Ga2O3 structure increases. This behavior is attributed to the varying oxygen composition on the surface after MacEtch, as shown by the XPS and TEM examination. Very little hysteresis has been observed in the capacitance-voltage characteristics of the 3D Pt/ Al2O3/ β-Ga2O3 MOS capacitor structures. Then, β-Ga2O3 FinFETs with MOCVD epitaxial Si-doped channel layer on (010) semi-insulating β-Ga2O3 substrates are fabricated by MacEtch method. A specific on-resistance (Ron,sp) of 6.5 mΩ·cm2 and a 370 V breakdown voltage are achieved. In addition, these MacEtch-formed FinFETs demonstrate DC transfer characteristics with near zero (9.7 mV) hysteresis. The effect of channel orientation on threshold voltage, subthreshold swing, hysteresis, and breakdown voltages are also characterized. The FinFET with channel perpendicular to [102] direction is found to exhibit the lowest subthreshold swing and hysteresis. Finally, the FinFET performance under high temperature and the attempts to further improve device performance, including (AlxGa1-x)2O3 / β-Ga2O3 heterojunction and field-plate structure, are discussed.
Graduation Semester
2022-12
Type of Resource
Thesis
Copyright and License Information
Copyright 2022 Hsien-Chih Huang

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