Strong anisotropy and layer-dependent carrier mobility of two-dimensional semiconductor ZrGeTe₄

Layered ZrGeTe₄is 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 ZrGeTe₄from bulk to monolayer were investigated. The bulk and few-layer ZrGeTe₄are predicted as indirect bandgap semiconductors, but the monolayer ZrGeTe₄turns 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 ZrGeTe₄is mechanically stable and anisotropic. In orders of magnitude, the predicted average carrier mobility of ZrGeTe₄(∼10³cm²V^-1s^-1) is between that of graphene (∼10⁵) and MoS₂(∼10²), and the anisotropy of electronic mobility is similar to that of black phosphorus, while hole mobility varies with the numbers of layers.