  Understanding the origin of unintentional doping in Ga2O3 is key to
increasing breakdown voltages of Ga2O3 based power devices. Therefore,
transport and capacitance spectroscopy studies have been performed to better
understand the origin of unintentional doping in Ga2O3. Previously unobserved
unintentional donors in commercially available (-201) Ga2O3 substrates have
been electrically characterized via temperature dependent Hall effect
measurements up to 1000 K and found to have a donor energy of 110 meV. The
existence of the unintentional donor is confirmed by temperature dependent
admittance spectroscopy, with an activation energy of 131 meV determined via
that technique, in agreement with Hall effect measurements. With the
concentration of this donor determined to be in the mid to high 10^16 cm^-3
range, elimination of this donor from the drift layer of Ga2O3 power
electronics devices will be key to pushing the limits of device performance.
Indeed, analytical assessment of the specific on-resistance (Ronsp) and
breakdown voltage of Schottky diodes containing the 110 meV donor indicates
that incomplete ionization increases Ronsp and decreases breakdown voltage as
compared to Ga2O3 Schottky diodes containing only the shallow donor. The
reduced performance due to incomplete ionization occurs in addition to the
usual tradeoff between Ronsp and breakdown voltage. To achieve 10 kV operation
in Ga2O3 Schottky diode devices, analysis indicates that the concentration of
110 meV donors must be reduced below 5x10^14 cm^-3 to limit the increase in
Ronsp to one percent.
