Ultra-doping germanium with atomic precision: nanowires, 2DEGs, and possibly 3D epitaxial circuits

CIC nanoGUNE Seminars

Giordano Scappucci, University New South Wales, Newport, UK
nanoGUNE seminar room, Tolosa Hiribidea 76, Donostia - San Sebastian
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Ultra-doping germanium with atomic precision: nanowires, 2DEGs, and possibly 3D epitaxial circuits (Attention: Tuesday) There is a race internationally to achieve n-doping of germanium at high concentrations and with sharp profiles. For nanoelectronics, low resistivity and abrupt n-type source/drain contacts are required to integrate the high mobility Ge n-channel into the Si platform [1]. For photonics, new exciting approaches towards the development of a Si-compatible laser rely on heavy n-doped Ge as a gain medium [2]. Here, I demonstrate a doping method for Ge based on a combination of gas phase doping in ultra-high vacuum and molecular beam epitaxy to achieve the highest n-dopant concentrations while maintaining atomic-level control of the doping process. By integrating this technique with STM atomic-scale lithography and laser ablation micron-scale lithography, a radical new fabrication route towards atomic-scale donor-based devices in Ge is demonstrated [3]. This technology has proven successful to embed P-doped planar nanodevices, such as 1D wires and tunnel gaps, in a Ge crystal, opening an entire new playground where the quantum behavior of highly confined electrons in Ge can be studied. The demonstration of highly confined 2DEGs in Ge, their patterning into planar nanodevices with an atomically flat surface, and the possibility to stack an arbitrary number of 2DEGs in a high quality crystal environment [4], pave the way for STM patterning of three dimensional (3D) epitaxial circuits, where atomic-level control over donor positioning is achieved in all three spatial dimensions. [1] R. Pillarisetty, Nature 479, 324 (2011). [2] D. Liang, J. E. Bowers, Nature Photonics 4, 511(2010). [3] G. Scappucci et al., Nano Letters 11, 2272 (2011) [4] G. Scappucci et al., Nanotechnology 22, 375203 (2011).