On the correlation of growth, structural and electrical properties of epitaxial Ge grown on Si by solid source molecular beam epitaxy

We report growth, structural, and electrical properties of epitaxial Ge layers on Si (001) wafers for next generation complementary metal oxide semiconductor devices. The epi-Ge layers were grown by solid source molecular beam epitaxy (MBE) at substrate temperatures (TG) varying from 200 °C to 500 °C. A two-step growth process, where an initial layer of thickness ∼30 nm is grown at a substrate temperature of 250 °C (except those grown below/at 250 °C), and the remaining layer is grown at a higher temperature, was found to be an efficient approach to improve the crystal quality of the Ge layers. The epi-Ge on Si exhibits bulk hole-mobility as high as 736 cm2/V-s at room temperature. Ti/Ge/Ti metal-semiconductor-metal (MSM) back-to-back Schottky diodes, fabricated on these epitaxial Ge layers, show excellent electrical properties. Further, metal oxide semiconductor (MOS) capacitors fabricated with HfO2 as the gate oxide exhibit low leakage current density of 4.7 × 10−2 A/cm2 (at Vg−VFB = 1 V) and mid-gap interface trap density of 5.0 × 1012cm−2eV−1.