Cmc21-CdO: Emerging direct band gap semiconductor with ultrahigh mobility and enhanced visible-light optical absorptions

Abstract

In this paper, an unreported polymorph of cadmium oxide with a direct band gap (denoted as Cmc21-CdO) is proposed based on the adaptive genetic algorithm (AGA) crystal structure prediction method. The mechanical, dynamical, and thermodynamic stability are all present in the Cmc21-CdO phase. The Cmc21-CdO is more anisotropic and ductile than ground state B1–CdO according to the anisotropic factor and elastic moduli (B, G, and E), respectively. The calculated optical characteristics show that Cmc21-CdO exhibits higher optical absorption and lower reflectivity versus B1–CdO in visible light, and is more suitable for solar cell applications. Meanwhile, Cmc21-CdO phase has an ultrahigh electron-dominated mobility (7.602 × 104 cm2V−1s−1), which is much larger than B1 phase (0.350 × 104 cm2 V−1 s−1). More interestingly, we discover that Cmc21-CdO will undergo a phase transition in response to compressive stress, whereas under tensile stress, its optical spectrum will be redshifted and its band gaps will decrease.