Studies showed that the uniaxial compressive strain is also promising for improving the mobility of Ge pMOSFETs.

With the low thermal budget device fabrication process, the strain in channel region was maintained, which substantially boosted the transistor performance. It was reported that, by optimizing the growth condition and controlling the film thickness precisely, fully strained Ge channel could be pseudomorphically grown directly on Si and silicon-on-insulator (SOI).

Nonetheless, the development of defect-free SiGe buffer with smooth surface on Si raised a major challenge for Ge devices. A great deal of efforts were devoted to demonstrating biaxially strained Ge-based ultrathin quantum well (QW) pMOSFETs, which have exhibited the advantages of confining hole in the undoped quantum well, eliminating dopant impurity scattering, and accommodating very high strain in channel. Theoretical and experimental results proved that in order for Ge channel transistors to have significantly improved mobility and driving current over their Si and SiGe channel competitors, compressive strain is essential.

Germanium (Ge) has been attracting tremendous research interests for future pMOSFET applications due to it possesses the higher hole mobility over Si.

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