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The optoelectronic properties of two layered copper oxyselenide compounds, with nominal composition Sr2ZnO2Cu2Se2 and Ba2ZnO2Cu2Se2, have been investigated to determine their suitability as p-type conductors. The structure, band gaps and electrical conductivity of pristine and alkali-metal-doped samples have been determined. We find that the strontium-containing compound, Sr2ZnO2Cu2Se2, adopts the expected tetragonal Sr2Mn3SbO2 structure with I4/mmm symmetry, and has a band gap of 2.16 eV, and a room temperature conductivity of 4.8 × 10−1 S cm−1. The conductivity of the compound could be increased to 4.2 S cm−1 when sodium doped to a nominal composition of Na0.1Sr1.9ZnO2Cu2Se2. In contrast, the barium containing material was found to have a small zinc oxide deficiency, with a sample dependent compositional range of Ba2Zn1−xO2−xCu2Se2 where 0.01 < x < 0.06, as determined by single crystal X-ray diffraction and powder neutron diffraction. The barium-containing structure could also be modelled using the tetragonal I4/mmm structure, but significant elongation of the oxygen displacement ellipsoid along the Zn–O bonds in the average structure was observed. This indicated that the oxide ion position was better modelled as a disordered split site with a displacement to change the local zinc coordination from square planar to linear. Electron diffraction data confirmed that the oxide site in Ba2Zn1−xO2−xCu2Se2 does not adopt a long range ordered arrangement, but also that the idealised I4/mmm structure with an unsplit oxide site was not consistent with the extra reflections observed in the electron diffractograms. The band gap and conductivity of Ba2Zn1−xO2−xCu2Se2 were determined to be 2.22 eV and 2.0 × 10−3 S cm−1 respectively. The conductivity could be increased to 1.5 × 10−1 S cm−1 with potassium doping in K0.1Ba1.9Zn1−xO2−xCu2Se2. Hall measurements confirmed that both materials were p-type conductors with holes as the dominant charge carriers. [ABSTRACT FROM AUTHOR]

This work has demonstrated that the single source precursor [nBu3Sn(TenBu)], bearing n-butyl groups and containing the necessary 1 : 1 Sn : Te ratio, facilitates growth of continuous, stoichiometric SnTe thin films. This single source CVD precursor allows film growth at significantly lower temperatures (355–434 °C at 0.01–0.05 Torr) than required for CVD from SnTe powder. This could be advantageous for controlling the surface states in topological insulators. The temperature-dependent thermoelectric performance of these films has been determined, revealing them to be p-type semiconductors with peak Seebeck coefficient and power factor values of 78 μV K−1 and 8.3 μW K−2 cm-1, respectively, at 615 K; comparing favourably with data from bulk SnTe. Further, we have demonstrated that the precursor facilitates area selective growth of SnTe onto the TiN regions of SiO2/TiN patterned substrates, which is expected to be beneficial for the fabrication of micro-thermoelectric generators. [ABSTRACT FROM AUTHOR]

The optoelectronic properties of two layered copper oxyselenide compounds, with nominal composition Sr 2 ZnO 2 Cu 2 Se 2 and Ba 2 ZnO 2 Cu 2 Se 2 , have been investigated to determine their suitability as p-type conductors. The structure, band gaps and electrical conductivity of pristine and alkali-metal-doped samples have been determined. We find that the strontium-containing compound, Sr 2 ZnO 2 Cu 2 Se 2 , adopts the expected tetragonal Sr 2 Mn 3 SbO 2 structure with I 4/ mmm symmetry, and has a band gap of 2.16 eV, and a room temperature conductivity of 4.8 × 10 -1 S cm -1 . The conductivity of the compound could be increased to 4.2 S cm -1 when sodium doped to a nominal composition of Na 0.1 Sr 1.9 ZnO 2 Cu 2 Se 2 . In contrast, the barium containing material was found to have a small zinc oxide deficiency, with a sample dependent compositional range of Ba 2 Zn 1- x O 2- x Cu 2 Se 2 where 0.01 < x < 0.06, as determined by single crystal X-ray diffraction and powder neutron diffraction. The barium-containing structure could also be modelled using the tetragonal I 4/ mmm structure, but significant elongation of the oxygen displacement ellipsoid along the Zn-O bonds in the average structure was observed. This indicated that the oxide ion position was better modelled as a disordered split site with a displacement to change the local zinc coordination from square planar to linear. Electron diffraction data confirmed that the oxide site in Ba 2 Zn 1- x O 2- x Cu 2 Se 2 does not adopt a long range ordered arrangement, but also that the idealised I 4/ mmm structure with an unsplit oxide site was not consistent with the extra reflections observed in the electron diffractograms. The band gap and conductivity of Ba 2 Zn 1- x O 2- x Cu 2 Se 2 were determined to be 2.22 eV and 2.0 × 10 -3 S cm -1 respectively. The conductivity could be increased to 1.5 × 10 -1 S cm -1 with potassium doping in K 0.1 Ba 1.9 Zn 1- x O 2- x Cu 2 Se 2 . Hall measurements confirmed that both materials were p-type conductors with holes as the dominant charge carriers., Competing Interests: There are no conflicts to declare., (This journal is © The Royal Society of Chemistry.)