Abstract
In the past decade, beta-phase gallium oxide (β-Ga2O3) has attracted extensive research asan ultra-wide bandgap semiconductor material owing to its outstanding material properties and
cost advantage of large-size bulk crystals over SiC (silicon carbide) and GaN (gallium nitride).
The literature review shows the development of vertical β-Ga2O3 MOSFETs is in an early
phase, and it is challenging to implement normally-off enhancement-mode (E-mode) β-Ga2O3
MOSFETs since the absence of p-type doping causes no inversion layer. In this dissertation,
two novel vertical β-Ga2O3 MOSFETs were designed and simulated in Sentaurus TCAD to
achieve E-mode operation, and their device performance was investigated with different
structure parameters, temperatures, and applications. The first proposed transistor is a current
aperture vertical β-Ga2O3 MOSFET with a trench gate. The transistors with a depth of trench
gate recess (Gr) greater than or equal to 130 nm realize E-mode operation, and MOSFET with
Gr = 130 nm obtains better performance than the reported E-mode planar gate vertical β-Ga2O3
MOSFET with high current density, low specific on-resistance, high breakdown voltage, and
good thermal stability. The second proposed E-mode vertical trench gate β-Ga2O3 MOSFET
has an interlayer-based channel along the sidewall of the trench. It achieves higher on-current
density, lower specific on-resistance, and better thermal stability than the first proposed
MOSFET, while breakdown voltage and on/off current ratio remain similar. Both MOSFETs
were applied to simulate a switching circuit with excellent switching performance at room
temperature, and the second one achieved outstanding dynamic characteristics at high
temperatures. The second MOSFET gained high efficiency and conversion ratio in a boost
converter circuit. The proposed vertical β-Ga2O3 MOSFETs exhibit great potential as a highspeed
power switch in high-voltage and high-temperature applications.