Low Resistance Ohmic Contact on Epitaxial MOVPE Grown β-Ga2O3 and β-(AlxGa1−x)2O3 Films

We report on the realization of record low resistance Ohmic contacts to MOVPE-grown heavily Si-doped
$\beta $
-Ga2O3 and
$\beta $
-(AlxGa1-x)2O3 epitaxial films. Transfer length measurement (TLM) patterns were fabricated on the heavily Si-doped homoepitaxial
$\beta $
-Ga2O3 films with electron concentration (n) ranging from 1.77 to
$3.23\times 10^{20}$
cm−3. Record low specific contact resistance (
$\rho _{c}$
) and total contact resistance (
${\text{R}_{c}}$
) of
$1.62\times 10^{-7}\,\,\Omega $
.cm2 and
$0.023 \Omega $
.mm were realized for
$\beta $
-Ga2O3: Si films with n
$ > 3\times 10^{20}$
cm−3. TLM structures were also fabricated on heavily Si doped coherently strained
$\beta $
-(AlxGa1-x)2O3/
$\beta $
-Ga2O3 (x = 12%, 17% and 22%) films. The film with 12% Al composition (n
$=1.23\times 10^{20}$
cm−3) showed
$\rho _{c}$
of
$5.86\times 10^{-6}\,\,\Omega $
.cm2, but it increased to
$2.19\times 10^{-4}\,\,\Omega $
.cm2 for a layer with a 22% Al composition. Annealing the samples post metal deposition has generally led to a decrease in contact resistance, but for high Al content
$\beta $
-(AlxGa1-x)2O3, the contact resistance did not change significantly after the annealing process. The low contact resistance values measured in this work are the lowest for ultrawide bandgap semiconductors and are very promising for the fabrication of high frequency power devices.