Ultradense phosphorus in germanium delta-doped layers

Abstract

Phosphorus (P) in germanium (Ge) delta-doped layers are fabricated inultrahigh vacuum by adsorption of phosphine molecules onto anatomically flat clean Ge(001) surface followed by thermal incorporationof P into the lattice and epitaxial Ge overgrowth by molecular beamepitaxy. Structural and electrical characterizations show that P atomsare confined, with minimal diffusion, into an ultranarrow 2-nm-widelayer with an electrically active sheet carrier concentration of4x10(13) cm(-2) at 4.2 K. These results open up the possibility ofultranarrow source/drain regions with unprecedented carrier densitiesfor Ge n-channel field effect transistors.