Abstract
III-V semiconductor nanowires (NWs) such as GaAs NWs form an interesting artificial materials system promising for applications in advanced optoelectronic and photonic devices, thanks to the advantages offered by the 1D architecture and the possibility to combine it with the main-stream silicon technology. Alloying of GaAs with nitrogen can further enhance performance and extend device functionality via band-structure and lattice engineering. However, due to a large surface-to-volume ratio, III-V NWs suffer from severe non-radiative carrier recombination at/near NWs surfaces that significantly degrades optical quality. Here we show that increasing nitrogen composition in novel GaAs/GaNAs core/shell NWs can strongly suppress the detrimental surface recombination. This conclusion is based on our experimental finding that lifetimes of photo-generated free excitons and free carriers increase with increasing N composition, as revealed from our time-resolved photoluminescence (PL) studies. This is accompanied by a sizable enhancement in the PL intensity of the GaAs/GaNAs core/shell NWs at room temperature. The observed N-induced suppression of the surface recombination is concluded to be a result of an N-induced modification of the surface states that are responsible for the nonradiative recombination. Our results, therefore, demonstrate the great potential of incorporating GaNAs in III-V NWs to achieve efficient nano-scale light emitters.
Highlights
The spectra are dominated by a broad asymmetric PL band which originates from localized exciton (LE) recombination within the GaNAs region[29]
This emission mechanism is common for dilute nitrides where alloy disorder leads to strong fluctuations in the conduction band edge enhanced by the giant bandgap bowing effect[1]
In addition to the LE band, the PL spectra from the GaAs/GaN0.005As0.995 core/shell NWs contain a much weaker ‘plateau’-like emission band within the 1.41–1.45 eV spectral range which stems from excitonic transition within the GaAs core region[29]. Since this weak emission only has a minor contribution in the PL spectra, it will not be further discussed in this paper. (In the case of the epilayer structure, the high-energy PL lines at 1.493 and 1.515 eV are related to free-to-acceptor (e, A0) and free exciton (FE) transitions from the GaAs substrate, respectively35)
Summary
The energy transfer between the localized states does not contributes to the dynamics of the deeply localized excitons as τ LE does not depend on Edet at the low energy side of the LE band Under these conditions, τ LE saturates at around 5.2 ns in the GaAs/GaNAs NW structures, which is similar to the saturation value of 4.6 ns in the reference GaN0.005As0.995 epilayer. Τ LE saturates at around 5.2 ns in the GaAs/GaNAs NW structures, which is similar to the saturation value of 4.6 ns in the reference GaN0.005As0.995 epilayer The FE decays can be fitted by a bi-exponential function of the form
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