Implantation-induced damage in Ge: strain and disorder profiles during defect accumulation and recovery

We present an experimental study of structural lattice damage in Ge induced by ion implantation. From the strain and disorder profiles, calculated from x-ray diffraction and ion channelling experiments we have investigated the defect accumulation as a function of ion fluence, mass, energy and current density as well as the damage recovery and recrystallization of the implanted region upon annealing. The damage accumulation process can be divided into three different regimes, based on the ion fluence. In the lowest fluence regime, the strain and the defect fraction are linearly proportional to the ion fluence, and the number of defects in the implanted layer is directly related to the deposited energy that is converted into the creation of vacancies. In the second regime, the damage accumulation process is more efficient, due to the increased defect density in the implanted layer. The third fluence regime starts at the critical fluence for amorphization, and this value has been determined for a wide range of ion masses and energies. The recovery study of the implantation-induced damage has revealed two distinct annealing steps. Rapid thermal annealing at temperatures as low as 100 degrees C results in the removal of isolated defects, which are present in the low-fluence implanted samples, as well as in the tail of the implantation profile of heavily damaged samples. Annealing at 350 degrees C results in the recrystallization of amorphous Ge at the amorphous-crystalline interface at a rate of 14 +/- 3 nm min(-1). Although Ge amorphizes at much lower fluences than Si, the influence of the studied implantation parameters on the damage accumulation process is comparable for both group IV semiconductors. This extended experimental overview of implantation-induced structural damage partly fills the large knowledge gap on implantation-related issues in Ge, and provides relevant and complementary information for defect studies in Ge and, in general, for any study using implanted Ge.