Charge transfer and optical properties of wurtzite-type ZnS/(CdS/ZnS)n (n = 2, 4, 8) superlattices

• Wurtzite ZnS/(CdS/ZnS)n superlattices were prepared at 100 °C by pulsed laser deposition.
• Surface phonon of ZnS and multiple phonons modes of ZnS and CdS were observed.
• The charge transfer of electrons from CdS electron to ZnS holes by excitation energy was found.

ZnS/(CdS/ZnS)n (n = 2, 4, 8) superlattices were deposited on sapphire substrate by pulsed laser deposition (PLD) with alternate cadmium sulfide (CdS) and zinc sulfide (ZnS) crystals at 100 °C. The prepared samples with an average thickness of ∼30 nm for ZnS layer and ∼60 nm for CdS layer have a wurtzite-type structure. Surface phonon of ZnS and multiple phonons modes for ZnS and CdS were observed from Raman spectra. PL spectra show a strong green emission at ∼496 nm, two weak emission bands at ∼400 and ∼577 nm, where the emission band at 400 nm was attributed to the recombination of surface defects states to valence, the emission band at 577 nm as the recombination of Cdi–VCd centers, and the strong emission at ∼496 nm is from the charge transfer of electrons from CdS electron to ZnS holes by excitation energy.

(a) Normalized temperature-dependent PL spectra of ZnS/(CdS/ZnS)4 superlattices from 5 to 300 K and (b) schematic of charge transfer at CdS/ZnS interface.Figure optionsDownload as PowerPoint slide