Study of band alignment type in Janus HfSe2/Ga2SeS and HfSeS/GaSe heterostructures

Abstract

Motivated by the successful preparations and excellent properties of Janus monolayers, we construct the van der Waals (vdW) heterostructures HfSe2/Ga2SeS, and HfSeS/GaSe. Their electronic features and the type of band alignment are investigated. We find that the HfSe2/Ga2SeS exhibits the similar electronic properties to HfSe2/GaSe. Both heterostructures own type-I band alignment, in which both valence band maximum (VBM) and conduction band minimum (CBM) are provided by HfSe2 layer. However, the HfSeS/GaSe heterostructure owns type-II band alignment, in which the electrons and holes are located within the HfSeS layer and the layer of GaSe, respectively. This means that the HfSeS/GaSe heterostructure can facilitate the effective separation of the photo-generated hole and electron pairs. The band offsets of valence bands are 0.09 eV, 0.26 eV and 0.17 eV for HfSe2/GaSe, HfSe2/Ga2SeS, and HfSeS/GaSe heterostructures. The small band offsets indicate the band alignment can easily be modulated by some external means. Thus, the external electric field and interlayer coupling effect are considered to modulate the electronic properties of those heterostructures. They can simultaneously tune the band gap and induce the band alignment transition between type-I and type-II. These results indicate that HfSe2/GaSe and Janus HfSe2/GaSe heterostructures have great applications in nanoelectronic device.