  Two-dimensional (2D) elemental semiconductors have great potential for device
applications, but their performance is limited by the lack of efficient doping
methods. Here, combining molecular beam epitaxy, scanning tunneling
microscopy/spectroscopy, X-ray photoelectron spectroscopy, and density
functional theory calculations, we investigate the evolution of the structural
and electronic properties of 2D selenium/tellurium films with increased Se
dosages on graphene/6H-SiC(0001) substrates. We found that Se atoms form
isovalent dopants by replacing surface Te atoms, which introduces efficient
electron doping and lowers the work function of Te films. With the Se dosage
increasing, two types of elemental 2D crystalline Se structures, trigonal Se
and Se8 molecular assembly films, are obtained on ultrathin Te films, which are
distinct from the amorphous Se acquired by depositing Se directly on
graphene/6H-SiC(0001). Our results shed light on tuning the electronic
properties of 2D elemental semiconductors by isovalent doping and constructing
heterostructures of isovalent 2D elemental materials.
