Semiconductor researchers are trying to use Germanium -based semiconductor material along with Silicon to increase the switching speed of MOSFETs and also to use optical link for intra-chip and inter chip communications. The Germanium Tin (GeSn) -based metal oxide semiconductor field effect transistor is explored as channel material to increase switching speed of MOSFET and also to support optical communications. Researchers are trying to come out with a process to deposit layer of germanium-Tin on silicon, which can be integrated into present chip making equipment. The challenges to grow a thin layer of GeSn on silicon includes limited solubility of Sn in Ge (0.5%), its compositional fluctuations, Sn segregation, and large lattice mismatch (>4%).
The researchers of Belgium-based Imec, and Japan-based AIST could achieve a new solid phase epitaxial deposition process to integrate a Germanium-Tin (GeSn) metal-oxide semiconductor field-effect transistor (MOSFET) devices on Silicon. They claim to have demonstrated operation of depletion-mode junctionless GeSn pMOSFET on silicon, an important step toward achieving tensile strain in MOSFET devices, and increasing their mobility.
The achievements claimed by researchers include:
1. Ultrathin (>10µm) single-crystalline GeSn layers on silicon substrates showing tensile strain, attractive for strain engineering of Ge channels.
2. Reducing the difference between the direct and indirect band transition, resulting in acquisition of a direct band gap group IV material.
3. The new method enables the development of GeSn with high Sn concentrations .
4. By decreasing the channel thickness with reactive ion etching (RIE) from ~30 to ~10 nm, the researchers improved the on/off ratio by more than one order of magnitude.
5. Hole depletion in the ultrathin (~10 nm) GeSn layers on silicon resulted in good transfer characteristics with an on/off ratio of 84.
In the future, researchers to focus on optimizing the GeSn MOSFET on silicon devices to further increase the channel mobility.
The details of the results is going to be presented at the Solid State Devices and Materials (SSDM) conference in Fukuoka, Japan on September 25, and to be published in Applied Physics Express 2013.
TEM image of NiGeSn metal S/D MOSFET.