Deep-Level Defect Investigation of Si-Doped $\beta$-Ga2O3 Homoepitaxial Films Grown by Halide Vapor Phase Epitaxy

We have electrically investigated deep-level defects in Si-doped
$\beta$
-Ga
2
O
3
homoepitaxial films grown by halide vapor phase epitaxy (HVPE), employing capacitance-voltage (C-V) and steady-state photo-capacitance spectroscopy (SSPC) techniques. The optical bandgap was determined to be ~4.6 eV from Tauc plots. From differential 1/C
²
-V plots, the effective n-type carriers
$(\vert \mathrm{N}_{\mathrm{d}}-\mathrm{N}_{\mathrm{a}}\vert)$
with
$\sim 4.2\mathrm{x}10^{16}\mathrm{cm}^{-3}$
were seen to be almost uniformly distributed. SSPC measurements revealed four positive deep-level defects (T1, T2, T3, T4, and T6) with their optical onsets at ~1.77, ~2.45, ~2.78, ~3.18, and ~3.88 eV below the conduction band and two negative deep-level defects (T5 and T7) with their optical onsets at ~3.67 and ~4.0 eV above the valence band. In particular, the ~3.67 eV and ~4.0 eV levels were found to be significantly enhanced compared to those in undoped
$\beta$
-Ga
2
O
3
substrates and are probably attributable to oxygen vacancies produced by Si doping into
$\beta$
-Ga
2
O
3
epitaxial films during the HVPE growth. In addition, the ~3.88 eV level with precipitous photo-capacitance change is likely associated with dislocations and/or surface defects
$\beta$
-Ga
2
O
3
homoepitaxial films.