First-principles study on SrSnO3 as a transparent conductive oxide

As a wide band gap semiconductor with perovskite structure, SnSnO3 is regarded as a promising candidate of transparent conductive oxides owing to its superior properties like high transparency, non-toxicity and low price etc. In this work, the electronic structures of SrSnO3 were obtained through first-principles calculations based on HSE06 hybrid functional. Especially, we investigated the defect formation energies and transition levels of the intrinsic and external defects in SrSnO3. The intrinsic defects including the anti-site defects (SrSn and SnSr), the vacancy defects (VSr, VSn, and VO), and the interstitial defects (Sri, Sni and Oi) were considered while the external doping defects involving Li, Na, K, Al, Ga, In substituting at Sr site, Al, Ga, In, P, As, Sb substituting at Sn site, and N, P substituting at O site were taken into account. Subsequently, the suitable doping elements and the corresponding experimental preparation environments were pointed out. Furthermore, we discussed the mechanism on its conductance according to the energy positions of the band edges. Our calculated results demonstrated that SrSnO3 is an indirect-type semiconductor with the fundamental band gap of 3.55 eV and the optical band gap of 4.10 eV and then have a good visible light transmittance. Its valence band maximum (VBM) mostly comes from O-2p states while its conduction band minimum (CBM) mainly originates from Sn-5s states. In consistent with the delocalized Sn-5s states at CBM, the electron effective masses are light and isotropic, which is beneficial to n-type conductance. The n-type intrinsic defects SnSr and Vo have lower defect formation energy than the p-type intrinsic defects under O-poor condition while the n-type and p-type defects with low defect formation energy are almost equal under O-rich condition. Moreover, the transition levels of both SnSr and Voare deep. Therefore, SrSnO3 cannot have a good conductance without external doping. Our calculation also demonstrated that it is hard to produce an efficient p-type external doping owing to the compensation effect by VO, on the other hand, As or Sb substituting at Sn site can result in an effective n-type external doping due to their low defect formation energies and shallow transition levels. Based on the low energy positions of VBM (-7.5 eV) and CBM (-4.0 eV) of SrSnO3, we explained the reason why it is easy to realize a n-type conductance while it is hard to produce a high-performance p-type conductance, which follows the doping rules for wide band gap semiconductors. Finally, Sb-doped SrSnO3 is proposed as a promising candidate for n-type transparent conductive materials.