Event Dates
From: 22/06/2023 14:00
To: 22/06/2023 16:00
External Speaker
Prof. Matthew Zervos (School of Engineering, University of Cyprus, Cyprus)
Seminar Room: KEEK building, Room 119

Cuprous oxide (Cu2O) is a p-type metal-oxide semiconductor that has a fundamental, direct energy bandgap of 2.1 eV and cubic crystal structure. The native p-type conductivity of Cu2O is related to the occurrence of acceptor-like copper vacancies (VCu). Cu2O has been suggested to be suitable as a solar cell absorber for a long time but but device efficiencies have been limited so far to less than 10%1. Nevertheless, it is an active topic of investigation for the fabrication of solar cells and photocatalysis but also for CO2 reduction. Cu2O has also been used as an archetype for the study of Rydberg excitons with very large principal quantum numbers of n = 25 and giant wavefunction extensions in excess of 2 µm in gem crystals of Cu2O 2. More recently Rydberg exciton-polaritons were detected in a SiO2/Ta2O5/Cu2O/Ta2O5/SiO2 Fabry-Pérot cavity using natural gem Cu2O3.

Here I will describe how it is possible to obtain Cu2O layers that do not contain Cu4O3, CuO or Cu that is critical for the observation of excitons in Cu2O layers but also for the fabrication of solar cells.  Furthermore, I will show that Cu2O layers obtained under optimum conditions exhibit a detailed spectral structure and distinct peaks at 2.75, 2.55 and 2.21 eV corresponding to the blue, indigo and yellow direct transitions of Cu2O as observed by ultrafast pump-probe spectroscopy at room temperature. A lower energy transition at 1.8 eV is attributed to carrier recombination via states located ~ 0.4 eV below the conduction band whose origin remains controversial and is discussed in conjunction with electronic structure calculations as it is very important from an applied and fundamental point of view.   

1 S. Shibasaki et al. Appl Phys Lett 119(24), 242102 (2021).

\2T. Kazimierczuk et al. Nature 514(7522), 343–347 (2014).

3K. Orfanakis et al. Nat Mater 21(7), 767–772 (2022).