Modeling and experiments on diffusion and activation of phosphorus in germanium

International audienceWe report on phosphorus diffusion and activation related phenomena in germanium. We have used both conventional thermal processing and laser annealing by pulsed nanosecond Nd:YAG laser. Chemical profiles were obtained by secondary-ion-mass spectroscopy, sheet resistance was estimated by the van der Pauw method, and structural defects were monitored by transmission electron microscopy. Our study covers the temperature range from 440 to 750 °C, and we were able to efficiently simulate the dopant profiles within that temperature range, taking into account a quadratic dependence of the P diffusion coefficient on the free electron concentration. To achieve that we have taken into account dopant activation dependence on temperature as well as dopant pile-up near the surface and dopant loss owing to outdiffusion during the annealing. A combined laser thermal treatment above the melting threshold prior to conventional annealing allowed the elimination of the implantation damage, so we could perceive the influence of defects on both transient dopant diffusion and outdiffusion

Diffusion and activation of phosphorus in germanium

International audienceIn this work we investigate the diffusion and the activation behavior of implanted phosphorus in Ge. We used both conventional thermal processing as well as laser annealing by pulsed ns Nd–YAG laser. Chemical profiles were obtained by secondary-ion-mass spectrometry (SIMS) and sheet resistance was estimated by Van der Pauw method. These measurements demonstrated a box-shaped dopant profile for both conventional and laser annealed samples which are in agreement with other research reports indicating enhanced dopant diffusivity. From these experiments and critical comparison with other studies we conclude about the value of the intrinsic diffusion coefficient and we discuss the validity of the doubly charged vacancy model in simulating our experiments. To more accurately account for these parameters we have also implemented a pileup and a segregation model to simulate the dopant loss due to outdiffusion of phosphorus during the annealing process. In order to understand the influence of defects on transient dopant diffusion as well as on outdiffusion we have also annealed P implanted Ge prior to conventional annealing with laser above melting threshold to eliminate ion implantation defects as these are monitored by transmission electron microscopy

Laser annealing for n+/p junction formation in germanium

International audienceIn the present work we focus our study on laser annealing of implanted with high phosphorus dose p-type germanium wafers using an Nd-YAG laser at 355 nm. Dopant profiles as monitored by SIMS measurements demonstrate dopant profile movement less than 15 nm at junction depth. Germanium (Ge) structural defects were observed by TEM measurements and the roughness of the surface was measured by AFM. The above analysis shows the efficiency of laser annealing in recrystallizing the Ge substrates at lower energy fluences compared to Si and without substantial dopant loss and diffusion