Dear Modassir,

All semicondcutor materials have electrons and holes. But they may be intrinsically n type as the Ga2O3 because of the oxygen deficiency in case of single crystal. In case of fine grained polycrystallied material it may be intrinsic with low intrinsic concentration. In this case the material can act as bipolar that it can act as p- channel or n-channel according to the controlling voltage.

Since Gs2O3 is intrinsically n-type it may be used as n-channel enhancement transistor.

The threshold voltage Vth = VFB - QB/Cox,

VFB= Phi MS - Qi /Cox, PhiMS= Phi M -PhiS, the work function difference between the gate metal and the semicondcutor. Qi is the interface static charge at the oxide semicondcutor interface, QB is the bulk charge for the onset of the conduction at the channel. Cox is the oxide capacitance per unit area.

For the principles of the MOS operation please see the book: Book Electronic Devices

Best wishes