title: New avenues to an old material: controlled nanoscale doping of germanium.
abstract: We review our recent research into n-type doping of Ge for nanoelectronics and integrated photonics. We demonstrate a doping method in ultra-high vacuum to achieve high electron concentrations in Ge while maintaining atomic-level control of the doping process. We integrated this doping technique with ultra-high vacuum scanning tunneling microscope lithography and femtosecond laser ablation micron-scale lithography, and demonstrated basic components of donor-based nanoelectronic circuitry such as wires and tunnel gaps. By repetition of controlled doping cycles we have shown that stacking of multiple Ge:P two-dimensional electron gases results in high electron densities in Ge (>10(20) cm(-3)). Because of the strong vertical electron confinement, closely stacked 2D layers - although interacting - maintain their individuality in terms of electron transport. These results bode well towards the realization of nanoscale 3D epitaxial circuits in Ge comprising stacked 2DEGs and/or atomic-scale Ge:P devices with confinement in more dimensions.
authors: School of Physics, University of New South Wales, Sydney, NSW 2052, Australia. giordano.scappucci@unsw.edu.au
authors: Giordano
authors: G
authors: Scappucci
authors: Giovanni
authors: G
authors: Capellini
authors: Wolfgang M
authors: WM
authors: Klesse
authors: Michelle Y
authors: MY
authors: Simmons