Ternary metal-oxy-chalcogenides are emerging as next-generation layered semiconductors beyond binary metal-chalcogenides (i.e., MoS 2 ). Among ternary metal-oxy-chalcogenides, especially Bi 2 O 2 Se has been demonstrated in field-effect transistors and photodetectors, exhibiting ultrahigh performance with robust air stability. The growth method for Bi 2 O 2 Se that has been reported so far is a powder sublimation based chemical vapor deposition. The first step for pursuing the practical application of Bi 2 O 2 Se as a semiconductor material is developing a gas-phase growth process. Here, we report a cracking metal−organic chemical vapor deposition (c-MOCVD) for the gas-phase growth of Bi 2 O 2 Se. The resulting Bi 2 O 2 Se films at very low growth temperature (∼300 °C) show single-crystalline quality. By taking advantage of the gas-phase growth, the precise phase control was demonstrated by modulating the partial pressure of each precursor. In addition, c-MOCVD-grown Bi 2 O 2 Se exhibits outstanding electrical and optoelectronic performance at room temperature without passivation, including maximum electron mobility of 127 cm 2 /(V•s) and photoresponsivity of 45134 A/W.

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The realization of ternary, single-layer transition metal dichalcogenides has suggested a promising strategy to develop two-dimensional (2D) materials with alternative features. In this study, we design and investigate Janus aluminum monochalcogenide monolayers, Al 2 X X (X/X = O, S, Se, and Te) by using first-principles methods. Starting from binary constituents, the ternary structures are optimized without any constraint and ground-state configurations are obtained. The stability of these systems is tested by performing phonon spectra analysis and ab initio molecular dynamics simulations and all Al 2 X X monolayers other than AlTeO are confirmed to be dynamically stable. Mechanical properties are examined by calculating Young's modulus and Poisson's ratio and subsequently compared with binary counterparts. Monolayers of Al 2 X X have a brittle character but oxygenation makes them less stiff. The electronic structure is also analyzed and variation of the band gap with the type of chalcogen atoms is revealed. It is found that different from their binary counterparts, Al 2 X O monolayers are direct band-gap semiconductors. Additionally, modification of the electronic structure in the presence of biaxial compressive or tensile strain is investigated by taking into account possible indirect-direct band-gap transitions. Our results not only predict stable 2D ternary Al 2 X X structures but also point out them as promising materials for optoelectronic applications.