  Impurity spins in crystal matrices are promising components in quantum
technologies, particularly if they can maintain their spin properties when
close to surfaces and material interfaces. Here, we investigate an attractive
candidate for microwave-domain applications, the spins of group-VI Impurity
spins in crystal matrices are promising components in quantum technologies,
particularly if they can maintain their spin properties when close to surfaces
and material interfaces. Here, we investigate an attractive candidate for
microwave-domain applications, the spins of group-VI $^{125}$Te$^+$ donors
implanted into natural Si at depths as shallow as 20~nm. We show that surface
band-bending can be used to ionise such near-surface Te to spin-active Te$^+$
state, and that optical illumination can be used further to control the Te
donor charge state. We examine spin activation yield, spin linewidth,
relaxation ($T_1$) and coherence times (\ttwo) and show how a zero-field
3.5~GHz `clock transition' extends spin coherence times to over 1~ms, which is
about an order of magnitude longer than other near-surface spin systems.
