We have studied the impact of the Al₂O₃ inter-layer on interface properties of HfO₂/InGaAs metal-oxide-semiconductor (MOS) interfaces. We have found that the insertion of the ultrathin Al₂O₃ inter-layer (2 cycle: 0.2 nm) can effectively improve the HfO₂/InGaAs interface properties. The frequency dispersion and the stretch-out of C-V characteristics are improved, and the interface trap density (D_it) value is significantly decreased by the 2 cycle Al₂O₃ inter-layer. Finally, we have demonstrated the 1-nm-thick capacitance equivalent thickness in the HfO₂/Al₂O₃/InGaAs MOS capacitors with good interface properties and low gate leakage of 2.4 × 10⁻² A/cm².

We demonstrate tensile-strained GeSn metal–oxide–semiconductor field-effect transistor (MOSFET) devices on Si(111) substrates using solid phase epitaxy of amorphous GeSn layers. Amorphous GeSn layers are obtained by limiting the adatom surface mobility during deposition. Subsequent annealing transforms the amorphous layer into single-crystalline GeSn by solid phase epitaxy. Single-crystalline GeSn layers with 4.5% Sn and 0.33% tensile strain are fabricated on Si(111) substrates. To verify the structural quality of thin-film GeSn as a channel material, we fabricate ultrathin GeSn p-channel MOSFETs (pMOSFETs) on Si(111). We demonstrate junctionless depletion-mode operation of tensile-strained GeSn(111) pMOSFETs on Si substrates.