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.