Nanoscale measurements of phosphorous-induced lattice expansion in nanosecond laser annealed germanium

International audienceLaser Thermal Annealing (LTA) at various energy densities was used to recrystallize and activate amorphized germanium doped with phosphorous by ion implantation. The structural modifications induced during the recrystallization and the related dopantdiffusion were first investigated. After LTA at low energy densities, the P electrical activation was poor while the dopant distribution was mainly localized in the polycrystalline Ge resulting from the anneal. Conversely, full dopant activation (up to 1 1020 cm3) in a perfectly recrystallized material was observed after annealing at higher energy densities. Measurements of lattice parameters performed on the fullyactivated structures show that P doping results in a lattice expansion, with a perpendicular lattice strain per atom Ps = +0.7 0.1 Å3. This clearly indicates that, despite the small atomic radius of P compared to Ge, the “electronic contribution” to thelattice parameter modification (due to the increased hydrostatic deformation potential in the conduction band of P doped Ge) is larger than the “size mismatch contribution” associated with the atomic radii. Such behavior, predicted by theory, is observedexperimentally for the first time, thanks to the high sensitivity of the measurement techniques used in this work