Polycrystalline Ge Nanosheets Embedded in Metal-Semiconductor Heterostructures Enabling Wafer-Scale 3D Integration of Ge Nanodevices with Self-Aligned Al Contacts

The ability to stack nanosheet transistors is an important prerequisite for the realization of vertically monolithic 3D integrated circuits enabling higher integration densities of functions and novel circuit topologies that relax miniaturization constraints. In this respect, a wafer-scale platform is presented embedding high-quality nanoscale polycrystalline Ge channels into monolithic metal-semiconductor heterostructures. Thereto, a fabrication scheme comprising a combination of flash lamp annealing, crystallizing ultra-thin amorphous Ge nanosheets, and a thermally induced Al-Ge exchange reaction is demonstrated, facilitating the formation of self-aligned Al leads enabling sharp Al-Ge heterojunctions. The high quality of the obtained polycrystalline Al-Ge-Al heterostructure nanosheets is confirmed by mu-Raman, scanning transmission electron microscopy, energy-dispersive X-ray spectroscopy, and electron backscatter diffraction measurements. Embedded in back- and top-gate field-effect transistor architectures, the electrical transport in polycrystalline Al-Ge-Al heterostructures is systematically analyzed. Enabling a complementary metal-oxide-semiconductor compatible wafer-scale accessibility of high-quality polycrystalline Ge with self-aligned Al contacts, the proposed platform significantly contributes to the development of a broad spectrum of emerging 3D integrated Ge nanodevices.

Automated summary

The study presents a wafer-scale platform embedding high-quality nanoscale polycrystalline Ge channels, demonstrating self-aligned Al leads and sharp Al-Ge heterojunctions. The high-quality polycrystalline Al-Ge-Al heterostructure nanosheets enable the development of novel circuit topologies and contribute to the advancement of integrated circuits.