Exploring optoelectronic properties of ZnO monolayers originated from NaCl- and GeP-like polymorphs: A first-principles study

Exploring the cost-effective and environment-friendly two-dimensional materials for miniaturized portable device applications has received remarkable attention in recent years. In this article, we explore two new atomically thin polymorphs of ZnO derived from the pressure-driven rock salt (NaCl) and GePPhases. These 2D ZnO structures are originated from the 110-facet of NaCland GeP-like ZnO polymorphs employing a vacuum 20 angstrom separation. The energy stability, structural parameters, electronic structure, and optical spectra of these 2D ZnO polymorphs have been comprehensively studied from first-principles calculations. The two monolayers of ZnO exhibited energetic stability as large as their bulk counterparts. Similarly, following their bulk counterparts, both monolayers are found semiconductors of indirect bandgap nature with Eg of 1.06 and 2.55 eV as estimated theoretically for NaCl-and GeP-types of ZnO monolayers, respectively. The two monolayers demonstrated optical absorption as high as 35.61 x 10(4) cm(-1) and 30.26 x 10(4) cm(-1) for NaCl-ZnO and GeP-ZnO respectively. Moreover, NaCl-ZnO yields transparency over infrared, visible, and UV light regions below the energy of 8.0 eV, whereas GeP-ZnO possesses transparent nature below similar to 12 eV of the electromagnetic spectrum. Overall, these ZnO monolayers exhibit relatively small optical reflection, considerable refraction, and significant absorption indicating that a large portion of incident UV light is absorbed by these monolayers. This study is believed to unveil the potential of these two monolayers of ZnO for nanoscale electronic, optoelectronic, and photovoltaic applications. \