  In this letter, we report on high performance depletion/enhancement
(D/E)-mode beta-Ga2O3 on insulator (GOOI) field-effect transistors (FETs) with
record high drain currents (ID) of 600/450 mA/mm, which are nearly one order of
magnitude higher than any other reported ID values. The threshold voltage (VT)
can be modulated by varying the thickness of the beta-Ga2O3 films and the
E-mode GOOI FET can be simply achieved by shrinking the beta-Ga2O3 film
thickness. Benefiting from the good interface between beta-Ga2O3 and SiO2 and
wide bandgap of beta-Ga2O3, a negligible transfer characteristic hysteresis,
high ID on/off ratio of 10^10, and low subthreshold swing of 140 mV/dec for a
300 nm thick SiO2 are observed. E-mode GOOI FET with source to drain spacing of
0.9 um demonstrates a breakdown voltage of 185 V and an average electric field
(E) of 2 MV/cm, showing the great promise of GOOI FET for future power devices.
