  The efficient integration of transition metal dichalcogenides (TMDs) into the
current electronic device technology requires mastering the techniques of
effective tuning of their optoelectronic properties. Specifically, controllable
doping is essential. For conventional bulk semiconductors, ion implantation is
the most developed method offering stable and tunable doping. In this work, we
demonstrate n-type doping in MoSe2 flakes realized by low-energy ion
implantation of Cl+ ions followed by millisecond-range flash lamp annealing
(FLA). We further show that FLA for 3 ms with a peak temperature of about 1000
{\deg}C is enough to recrystallize implanted MoSe2. The Cl distribution in
few-layer-thick MoSe2 is measured by secondary ion mass spectrometry. An
increase in the electron concentration with increasing Cl fluence is determined
from the softening and red shift of the Raman-active A_1g phonon mode due to
the Fano effect. The electrical measurements confirm the n-type doping of
Cl-implanted MoSe2. A comparison of the results of our density functional
theory calculations and experimental temperature-dependent micro-Raman
spectroscopy data indicates that Cl atoms are incorporated into the atomic
network of MoSe2 as substitutional donor impurities.
