  Recently, a covalent-like quasi-bonding was unveiled for the inter-chain
interaction in a promising semiconductor, few-layer Tellurium. Such quasi-bond
offers comparable bond lengths and strengths with those of a typical Te-Te
covalent bond, which may lead to much easier transformations between the
quasi-bonds and the covalent bonds. Here, we show a few structural
phase-transitions among four Te allotropes in few-layer Te under charge doping.
In particular, the semiconducting {\alpha}-phase can transform into a
smaller-bandgap {\beta}-phase, even-smaller-bandgap {\gamma}-phase and then
metallic {\delta}-phase in a Te bilayer. In a tri-layer, a metallic chiral
{\alpha}+{\delta} phase is more stable under initial electron doping, leading
to the appearance of chirality. Variations of electronic structures aside,
these transitions are accompanied by the emergence or elimination of inversion
centers ({\alpha}-{\beta}, {\alpha}-{\gamma}, {\alpha}-{\alpha}+{\delta}),
structural anisotropy ({\alpha}-{\gamma}, {\gamma}-{\delta}) and chirality
({\alpha}-{\alpha}+{\delta}), which could result in substantial changes in
optical and other properties. In light of this, this work opens the possibility
toward building mono-elemental electronic and optoelectronic heterostructures
or devices. It also offers a platform for studying relations between charge
doping and electric/optical properties.
