Metal work function engineering on epitaxial (100)Ge and (110)Ge metal-oxide-semiconductor devices

Abstract

Capacitance-voltage characterization of epitaxial n-type (100)Ge and (110)Ge metal-oxide-semiconductor capacitors (MOSCs) was performed using two work function Al and Pt gate metals to evaluate the orientation effect on flat-band voltage (VFB) shift, Fermi level pinning factor (S), and interface induced defects (Dit). These epitaxial (100)Ge/AlAs/GaAs and (110)Ge/AlAs/GaAs heterostructures were grown in-situ using two separate molecular beam epitaxy (MBE) chambers. A VFB shift of >700 mV, S > 0.5, and Dit value of ~ 6 × 1011 cm−2 eV−1 in the energy range of 0.05 eV to 0.3 eV below the conduction band, have been demonstrated from epitaxial n-type (100)Ge and (110)Ge surfaces, which are comparable to the reported bulk Ge MOS-C values, suggesting a robust MOS-C developed process as well as device quality epitaxial (100)Ge and (110)Ge layers on GaAs substrates using an AlAs intermediate buffer. Thus, the metal work function engineering on device-quality MBE grown crystallographically oriented Ge materials, can offer a promising path for extending the performance and application of Ge-based field-effect transistors for low-power devices.