Cu₂O quantum dots emitting visible light grown by atomic layer deposition

This paper reports the fabrication of the Cu₂O quantum dots (QDs) emitting a controlled wavelength in the visible spectral range prepared by atomic layer deposition (ALD). Cu₂O thin film layers formed on the Al₂O₃ surface showed large density of islands via Volmer–Weber growth mode, which resulting in QD formation. As the number of ALD cycles was increased from 60 to 480, the spatial density and mean diameter of the Cu₂O QDs increased systematically from 4.02 × 10¹¹/cm² to 2.56×10¹²/cm² and from 2.1 to 3.2 nm, respectively. The absorption spectral results indicated that the electron energy transition in the Cu₂O QDs was a direct process with the optical band gaps decreasing from 2.71 to 2.15 eV with increasing QD size from 2.1 to 3.2 nm because of the quantum confinement effect. The Cu₂O QDs showed broad emission peaks composed of multiple elementary emission spectra corresponding to the Cu₂O QD ensembles with a different size distribution. As the size of Cu₂O QDs decreased, the shoulder peaks at the higher energy side developed due to the quantum confinement effect.