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Germanium (Ge) has been considered as a promising alternative channel material owing to higher carrier mobility than that of Si. Replacing substrate or channel material with other material with high mobility is an imperative option. With conventional complementary metal-oxide-semiconductor (CMOS) devices approaching its physical limit, performance enhancement is hard to realize for high-speed semiconductor devices with silicon (Si) as the channel material. By comparing two different oxidation methods, the results show that the OPO is an effective way to increase the interface layer quality which is contributing to the improved effective mobility of Ge pMOSFETs. A thicker Al 2O 3 block layer in the OPO process leads to a higher mobility in Ge transistors. Ge pMOSFETs with OPO exhibit a higher I ON/ I OFF ratio (up to four orders of magnitude), improved subthreshold swing, and enhanced carrier mobility characteristics as compared with PPO devices. The PPO treatment leads to a positive threshold voltage ( V TH) shift and a lower I ON/ I OFF ratio, implying a poor interface quality.
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The quality of the dielectric/Ge interface layer was characterized by X-ray photoelectron spectroscopy and transmission electron microscopy. PPO and OPO were carried out on an Al 2O 3/n-Ge (001) substrate followed by a 5-nm HfO 2 gate dielectric in situ deposited in an ALD chamber. A comparison study on electrical performance of Ge pMOSFETs with a GeO x passivation layer formed by ozone post oxidation (OPO) and plasma post oxidation (PPO) is performed.