Concurrent annealing and irradiation of germanium to control dopant diffusion and activation

Germanium (Ge) as material for microelectronic applications has received renewed attention over the past decade. This is due to the advantageous electron and hole mobilities that are higher than those of silicon (Si). However, several obstacles still exist that limit the fabrication of Ge-based nanoelectronic devices. One aspect concerns the limited activation of donor atoms. The deactivation is mainly attributed to the formation of dopant-vacancy clusters whose existence is supported by density functional theory calculations. In this work we discuss experiments on the diffusion of implanted phosphorous (P) and arsenic (As) in Ge under proton irradiation. Continuum theoretical simulations of dopant profiles measured by means of secondary ion mass spectrometry reveal that diffusion under irradiation is much less affected by inactive donor-vacancy clusters than diffusion under annealing only. The suppression of donor-vacancy clusters is caused by interstitials in supersaturation and vacancy concentrations close to thermal equilibrium. Applying the approach of concurrent annealing and irradiation high active doping levels in Ge can be realized even at low processing temperatures.