Obtaining semiconducting properties that meet practical standards for p-type transparent oxide semiconductors is challenging due to the balance between the defects that generate hole and electron carriers. Here, we demonstrate that modulating the individual thermodynamic and kinetic conditions during the growth of p-type oxide SnO films is beneficial in tailoring their semiconducting properties. By tuning the growth temperature and laser fluence for pulsed laser deposition, the hole carrier density dramatically changes from approximately 4 × 10 16 to 6 × 10 18 cm −3 at room temperature. The room-temperature hole mobility (μ) strongly depends on the carrier density (n), and their relationship is like a "volcano-shaped" curve. This suggests the competition between several scattering sources, such as the ionized impurity scattering (μ ∝ n −1 ), and grain boundary and/or dislocation scattering (μ ∝ n 0.5 ) for higher and lower n, respectively. The hole mobility is enhanced to approximately 21 cm 2 V −1 s −1 at room temperature, which is the highest recorded for SnO films to date. These findings provide important guidelines for designing all-oxide transparent electronic devices.

Wide-gap oxides with their valence band maximum (VBM) composed of s orbitals are essential for realizing practical p-type transparent oxide semiconductors. We prepared a new p-type wide-gap oxide, SnNb2O6 foordite, with its VBM composed of Sn 5s orbitals. To discuss carrier generation, we prepared both p-type and n-type SnNb2O6 by controlling the annealing conditions. The carrier mobility and density were 3.8 × 10–1 cm2 V–1 s–1 and 3.7 × 1018 cm–3, respectively, for the p-type sample and 9.9 cm2 V–1 s–1 and 7.5 × 1015 cm–3, respectively, for the n-type sample. The crystal structure of SnNb2O6 foordite consists of two types of alternating layers, Sn and Nb2O6 octahedra, where three nonequivalent oxygen sites exist. Six oxygens in the chemical formula of SnNb2O6 are distributed at the three sites in pairs, where the oxygens in three nonequivalent sites were named O1–O3. Hole and electron carriers were considered to be generated by Sn4+-on-Nb5+ substitutional defects (SnNb ′) and oxygen vacancies of O1 and O2 that are not bonded to Sn (VO1/O2 ••), respectively. Therefore, we concluded that it is essential to control SnNb ′ and VO1/O2 •• to control the semiconducting properties such as the carrier type and carrier density.

Divalent stannous oxide, oxide semiconductor, p-type, oxygen vacancy, EXAFS, Rietveld analysis ABSTRACT: Divalent tin oxides have attracted considerable attention as novel p-type oxide semiconductors, which are essential for realizing future oxide electronic devices. Recently, p-type Sn 2 Nb 2 O 7 and SnNb 2 O 6 were developed; however, enhanced hole mobility by reducing defect concentrations is required for practical use. In this work, we investigate the correlation between the formation of oxygen vacancy (V ! •• ), which may reduce the hole-generation efficiency and hole mobility, and the crystal structure in Sn-Nb complex oxides. Extended X-ray absorption fine structure spectroscopy and Rietveld analysis of x-ray diffraction revealed the preferential formation of V ! •• at the O site bonded to the Sn ions in both the tin niobates. Moreover, a large amount of V ! •• around the Sn ions were found in the p-type Sn 2 Nb 2 O 7 , thereby indicating the effect of V ! •• to the low holegeneration efficiency. The dependence of the formation of V ! •• on the crystal structure can be elucidated from the Sn-O bond strength that is evaluated based on the bond valence sum and Debye temperature. The differences in the bond strengths of the two Sn-Nb complex oxides are correlated through the steric hindrance of Sn 2+ with asymmetric electron density distribution. This suggests the importance of the material design with a focus on the local structure around the Sn ions to prevent the formation of V ! •• in p-type Sn 2+ oxides.