Observation and enhancement through alkali metal doping of p-type conductivity in the layered oxyselenides SrZnOCuSe and BaZnOCuSe

• Published in: Journal of materials chemistry. C, Materials for optical and electronic devices Materials for optical and electronic devices, 2024-11, Vol.12 (43), p.17574-17586
• Main Authors: Malik, Zahida, Broadley, Sarah, Herkelrath, Sebastian J. C, Newbrook, Daniel W, Kemp, Liam, Rutt, George, Gál, Zoltán A, Blandy, Jack N, Hadermann, Joke, Davies, Daniel W, Smyth, Robert D, Scanlon, David O, Huang, Ruomeng, Clarke, Simon J, Hyett, Geoffrey
• Format: Article
• ISSN: 2050-7526; 2050-7534
• DOI: 10.1039/d4tc02458c

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. 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.