Abstract
A Ge MOS device with an ultralow equivalent oxide thickness of ∼ 0.5 nm and acceptable leakage current of 0.5 A/cm 2 is presented in this paper. The superior characteristics can be attributed to a tetragonal HfO 2 with a higher k value k∼ 31 and comparable bandgap. In addition, a Ge MOS device with tetragonal phase HfO 2 t-HfO 2 also shows a lower leakage current and better thermal stability. The mechanisms for t-HfO 2 formation may be explained by the little Ge diffusion from Ge substrate and oxygen deficiency, which are obtained by in~situ interfacial layer (IL) formation and high-k processes. The IL with k∼ 13 can be formed by in situ H 2 O plasma treatment. Moreover, a Ge MOS device with the IL grown by H 2 O plasma shows smaller interface trap density and hysteresis effects due to a high composition of Ge +4 . © 2014 IEEE.