The p-Type Conductivity of Stannate Perovskite System

Abstract

Thin films of the transparent oxide semiconductor with a p-type conduction are fabricated by the impurity doping method in the stannate Perovskite system. Ba1-xNaxSnO3 (x = 0.04 ~ 0.1) thin films were grown by the pulsed laser deposition method and their physical properties were measured. All of films are epitaxially grown with a good crystallinity. Images of the transmission electron microscopy reveal that Na impurity atoms do not severely distort the crystal structure of the host material. Microscopy images of surfaces of films confirm that there is no Na segregation and surfaces of films are smooth enough. Its p-type conduction is indirectly confirmed by the almost ideal characteristic curves of the BNSO-BLSO pn junction. Furthermore, its p-type conductivity is directly verified by the high temperature Hall measurement data, namely the positive Hall coefficients. The 4 % doped BNSO film shows the high p-type mobility of 77 cm2/V∙s with a carrier concentration about 6.9 × 1014 cm-3 around 200 C. Despite the existence of threading dislocations in the film, revealed by the TEM image, there is no dislocation scattering effect, similar to the cases of the p-type Ge and GaN. Temperature dependences of the hole concentration indicate that hole carriers are largely trapped in localized states at the low temperature due to disorder of the system. Optical measurement confirms the disordered nature by showing the Drude peak shift in the optical conductivity and the Urbach tail state in the optical absorption and reveals that disorder originates from the deep level character of the Na doping. The observed high hole mobility seems closely related to the A-site doping in the Perovskite system. SrSn1-xRuxO3 films (0.1 ≤ x ≤ 0.3) were grown by the pulsed laser deposition method. X-ray diffraction measurement exhibits that all of the films maintain a single phase over the doping range and lattice constants of the system monotonously decrease as the Ru doping increases. Hall measurement data indicates that the conduction of this system is mediated by hole carriers. Transport measurement shows that this system undergoes the metal-insulator transition depending on the Ru doping rate and their resistivities dramatically decrease as the Ru doping increase. Furthermore, its corresponding mobility values vary from 0.1~20 cm2/V∙s, depending on the Ru doping rate. Optical measurement suggests that there are mid-gap states, which are varying depending on the Ru doping rate. Magnetic measurement data confirms that mid-gap states with a Mott-Hubbard gap are mainly composed by the Ru 4d character like as the SrRuO3 and the ferromagnetic ordering is closely related with the relative magnitude of correlations (U) and the bandwidth (W), the metal-insulator transition, which is consistent with the above mentioned mid-gap model. The p-type conductivity of the SrSn1-xRuxO3 system is closely related to the p-type conduction of SrRuO3 at the room temperature, which is originated from the dispersive p-d hybridized valence band and the flat eg conduction band.