Strong anisotropy and layer-dependent carrier mobility of two-dimensional semiconductor ZrGeTe ₄

Layered ZrGeTe 4 is a new type of ternary anisotropic semiconductor. The strong in-plane anisotropy may give us another degree of freedom for controlling electrical and optical properties, and designing advanced nanodevices. Using first-principles calculations, physical properties such as band structure, phonon vibration, and carrier mobility of layered ZrGeTe 4 from bulk to monolayer were investigated. The bulk and few-layer ZrGeTe 4 are predicted as indirect bandgap semiconductors, but the monolayer ZrGeTe 4 turns out to be a direct band gap semiconductor with moderate value of 1.08 eV. Electronic structure calculations reveal that the van der Waals interaction is the main reason of causing the transition from indirect band gap to direct one. Phonon calculations demonstrate that the layered ZrGeTe 4 is mechanically stable and anisotropic. In orders of magnitude, the predicted average carrier mobility of ZrGeTe 4 (∼10 3 cm 2 V −1 s −1 ) is between that of graphene (∼10 5 ) and MoS 2 (∼10 2 ), and the anisotropy of electronic mobility is similar to that of black phosphorus, while hole mobility varies with the numbers of layers.