Polarization discontinuity driven two dimensional electron gas at A$_2$Mo$_3$O$_8$/B$_2$Mo$_3$O$_8$ (A, B : Zn,Mg,Cd) interfaces

We prospose a novel heterostructure system consisting of compounds with chemical formula A$_2$Mo$_3$O$_8$ (A, B : Zn,Mg,Cd) that can host a two dimensional electron/hole gas (2DEG/2DHG). We study spontaneous polarization and piezoelectric properties of these compounds using first principles methods and Berry phase approach. We show that these kind of heterostructures are very stable due to extreamly low interfacial strain. The formation of a 2DEG/2DHG has been investigated in case of Zn$_2$Mo$_3$O$_8$/Mg$_2$Mo$_3$O$_8$ and polarization discontinuity has been found to be driving mechanism. The sheet carrier densities and charge localization in these kind of heterostrcutures have been found to be of the same order of magnitude in other well known system that hosts 2DEG through similar mechanism, such as AlN/Al(Ga)N or ZnO/Zn(Mg)O. In addition to conventional applications of a 2DEG, these materials hold promise to exciting pioneering technolgy such as piezo-phototronics using solar radiation, as they are also capable of absorbing a significant fraction of it due to low optical gap of $\sim$ 2 eV