Ge metal oxide semiconductor field effect transistors with optimized Si cap and HfSiO2 high-k metal gate stacks

High mobility metal-oxide-semiconductor-field-effect-transistors (MOSFETs) are demonstrated on high quality epitaxial Si0.75Ge0.25 films selectively grown on Si (100) substrates. With a Si cap processed on Si0.75Ge0.25 channels, HfSiO2 high-k gate dielectrics exhibited low C-V hysteresis (<10 mV), interface trap density (7.5 × 1010), and gate leakage current (∼10−2A/cm2 at an EOT of 13.4 Å), which are comparable to gate stack on Si channels. The mobility enhancement afforded intrinsically by the Si0.75Ge0.25 channel (60%) is further increased by a Si cap (40%) process, resulting in a combined ∼100% enhancement over Si channels. The Si cap process also mitigates the low potential barrier issues of Si0.75Ge0.25 channels, which are major causes of the high off-state current of small band gap energy Si0.75Ge0.25 pMOSFETs, by improving gate control over the channel.