Evolution of vacancy like defects in heavily doped GaAs

N-type doping of GaAs is a self-limiting process where a carrier concentration in the
level of 1019 cm-3 is difficult to achieve. By means of ion implantation sequences with
precisely defined energy, homogenizing the distribution profile of dopants, followed
by non-equilibrium thermal annealing using intense light pulses, a highly doped ntype
GaAs with electron concentration easily exceeding the level of 5×1019 cm-3 was
obtained. Although, the absolute achieved carrier concentration has been
exceptionally large a peculiar variations of its magnitude across the samples
thickness have been observed, which we will regard to the incomplete
recrystallization processes. Moreover, we will discuss the effect of intense pulsed
laser melting and flash lamp annealing on defects distribution and electrical
activation efficiency in chalcogenide-implanted GaAs investigated by means of
positron annihilation spectroscopy, transport measurements, as well as
electrochemical capacitance-voltage techniques. Using positron beams, delivered by
the large scale facility ELBE at HZDR, as a sensitive probe of open volumes and
dedicated DFT calculations, we will highlight the capability of nanosecond pulsed
laser melting to control the type and density of defect complexes across the depth,
e.g. S or Te substitutions of As atoms associated to Ga vacancy, playing a crucial
role for donor deactivation. The distribution of defects and carriers will be discussed
considering the depth distribution of implanted elements and the solidification
velocity during recrystallization. The ultra-doped n-type GaAs is a potential candidate
for plasmonic and photonic applications. The proposed model for the donor-vacancy
formation during the PLM process of highly doped semiconductors is potentially
transferable to the group IV elements and groups III-V compound semiconductors.