Ultra-dense phosphorus in germanium delta-doped layers

TL;DR

This paper reports the fabrication of ultra-dense phosphorus delta-doped layers in germanium, achieving minimal diffusion and high carrier concentration, which could enable advanced ultra-narrow source/drain regions in Ge transistors.

Contribution

It introduces a novel fabrication method for ultra-dense phosphorus delta-doped layers in germanium with minimal diffusion and high electrical activity.

Findings

Confined P atoms in 2-nm-wide layers with minimal diffusion.

Achieved sheet carrier concentration of 4x10^13 cm^-2 at 4.2 K.

Potential for ultra-narrow source/drain regions in Ge FETs.

Abstract

Phosphorus (P) in germanium (Ge) delta-doped layers are fabricated in ultra-high vacuum by adsorption of phosphine molecules onto an atomically flat clean Ge(001) surface followed by thermal incorporation of P into the lattice and epitaxial Ge overgrowth by molecular beam epitaxy. Structural and electrical characterizations show that P atoms are confined, with minimal diffusion, into an ultra-narrow 2-nm-wide layer with an electrically-active sheet carrier concentration of 4x10^13 cm-2 at 4.2 K. These results open up the possibility of ultra-narrow source/drain regions with unprecedented carrier densities for Ge n-channel field effect transistors.