Direct Band Gap Semiconductors with Two- and Three-Dimensional Triel-Phosphide Frameworks (Triel=Al, Ga, In)

Recently, several ternary phosphidotrielates and -tetrelates have been investigated with respect to their very good ionic conductivity, while less focus was pointed towards their electronic structures. Here, we report on a novel series of compounds, in which several members possess direct band gaps. We investigated the known compounds Li3AlP2, Li3GaP2, Li3InP2, and Na3InP2 and describe the synthesis and the crystal structure of novel Na3In2P3. For all mentioned phosphidotrielates reflectance UV-Vis measurements reveal direct band gaps in the visible light region with decreasing band gaps in the series: Li3AlP2 (2.45 eV), Li3GaP2 (2.18 eV), Li3InP2 (1.99 eV), Na3InP2 (1.37 eV), and Na3In2P3 (1.27 eV). All direct band gaps are confirmed by quantum chemical calculations. The unexpected property occurs despite different structure types. As a common feature all compounds contain EP4 tetrahedra, which share exclusively vertices for E=In and vertices as well as edges for E=Al and Ga. The structure of the novel Na3In2P3 is built up by a polyanionic framework of six-membered rings of corner-sharing InP4 tetrahedra. As a result, the newly designed semiconductors with direct band gaps are suitable for optoelectronic applications, and they can provide significant guidance for the design of new functional semiconductors. New family of direct band gap semiconductors. The new compound Na3In2P3 is a semiconductor with a direct band gap of 1.27 eV and exhibits a three-dimensional polyanionic framework of corner-sharing InP4 tetrahedra. Additionally, the related phosphidotrielates Li3AlP2, Li3GaP2, Li3InP2 and Na3InP2, which are all built up by triel phosphorus tetrahedra as well, have been proven to be semiconductors as well, with direct band gaps ranging from of 1.37 eV to 2.45 eV.+ image