Thickness effects on properties of GaInNAs quantum dots grown by molecular-beam epitaxy with nitrogen plasma source

Abstract

Self-assembled GaInNAs quantum dots (QDs) were grown on a GaAs (001) substrate by solid-source molecular-beam epitaxy equipped with a radio-frequency nitrogen plasma source. The GaInNAs QD growth characteristics were investigated using atomic-force microscopy (AFM) and photoluminescence (PL) measurements. The growth experiment was conducted using indium and nitrogen compositions of 50% and ∼1%, respectively, at different nominal thicknesses of 3 monolayers (MLs) to 6 MLs. AFM images suggest the onset of QD formation at ∼3 MLs and QD coalescence at ∼6 MLs. The highest PL intensity at low temperature (5 K) was obtained from the sample with nominal thickness of 5 ML, consistent with the highest QD density observed from AFM measurement. Under the present experimental conditions, GaIn0.5N0.01As QDs of 5–6 MLs gave the best optical property in terms of the lowest full width at half maximum and highest PL intensity. The reduced barrier potential of a strain-compensated layer (SCL) of GaNAs inserted between the substrate and GaInNAs QD layer was able to extend the PL emission wavelength by more than 140 nm compared to the sample without the GaNAs SCL.