Metal-oxide-semiconductor capacitors on GaAs with high-k gate oxide and amorphous silicon interface passivation layer

We demonstrate the electrical properties of metal-oxide-semiconductor capacitors on molecular beam epitaxial GaAs in situ passivated with ultrathin amorphous Si ($a$ -Si) layer and with ex situ deposited ${\mathrm{HfO}}_2$ gate oxide and TaN metal gate. Minimum thickness of the Si interface passivation layer of 1.5 nm is needed to prevent the Fermi level pinning and provide good capacitance-voltage characteristics with equivalent oxide thickness of 2.1 nm and leakage current of $⩽1.0\mathrm{mA}∕{\mathrm{cm}}^2$ . Transmission electron microscopy analysis showed that the Si layer was oxidized up to 1.4 nm during ex situ processing while the interface between the GaAs and $a$ -Si remained atomically sharp without any sign of interfacial reaction.