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Suppression of non-radiative surface recombination by N incorporation in GaAs/GaNAs core/shell nanowires.

Chen SL, Chen WM, Ishikawa F, Buyanova IA - Sci Rep (2015)

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Chemistry and Biology, Linköping University, 58183, Linköping, Sweden.

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.

No MeSH data available.


Related in: MedlinePlus

(a)–(c) PL spectra of the investigated structures measured at 5 K with the excitation power levels of 4 mW (the solid curves, red) and 55 mW (the dashed curves, blue), respectively. The open circles represent the measured PL lifetimes as a function of emission energy, with the excitation power of 55 mW. (d)–(f) PL spectra of the investigated structures detected at different time delays after an excitation pulse. The arrows indicate the shifts of the peak positions of the LE emission. The vertical dashed lines mark the FE spectral positions.
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f1: (a)–(c) PL spectra of the investigated structures measured at 5 K with the excitation power levels of 4 mW (the solid curves, red) and 55 mW (the dashed curves, blue), respectively. The open circles represent the measured PL lifetimes as a function of emission energy, with the excitation power of 55 mW. (d)–(f) PL spectra of the investigated structures detected at different time delays after an excitation pulse. The arrows indicate the shifts of the peak positions of the LE emission. The vertical dashed lines mark the FE spectral positions.

Mentions: Shown as the solid curves in Fig.1a, b are PL spectra of the GaAs/GaNAs core/shell NWs with [N] = 0.1 and 0.5%, respectively, measured at 5 K with the excitation power (Wexc) of 4 mW (focused to a spot of about 0.5 mm in diameter). For comparison, Fig. 1c also shows the PL spectrum from the GaN0.005As0.995 epilayer measured under the identical excitation conditions (the solid curve). In all structures, the spectra are dominated by a broad asymmetric PL band which originates from localized exciton (LE) recombination within the GaNAs region29. 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 effect1. In principle, structural polytypism in NW structures can further contribute to exciton localization, as was observed in GaAs NWs where excitons could be localized at interfaces between ZB and wurtzite (WZ) phase segments with a type-II band alignment323334. This effect, however, does not seem to have the dominant contribution in the GaNAs NWs studied here, judging from the very similar properties of the LE emission between the NWs and epilayer structures. We should also note that the exact band alignment between ZB and WZ GaNAs is currently unknown. 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 region29. 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). Increasing excitation power, e.g. to 55 mW, leads to a saturation of the LE states. Under these conditions, the PL spectra (shown by the dotted curves in Fig. 1a,b) contain an additional PL component that is located above the high energy cut-off of the LE band and is caused by the FE emission in GaNAs. The same tendency is also observed in the reference GaNAs epilayer (see the dotted curve in Fig. 1c). We note that the FE emission is somewhat broadened in the NW samples. This broadening is likely due to minor variations in the N composition between different NWs forming the studied NW arrays, within 0.07% for the structures with [N] = 0.5%, as was revealed by our previous micro-PL measurements29. The spectral positions of the GaNAs-related FE emission in the investigated structures are indicated in Fig. 1 by the vertical dotted lines.


Suppression of non-radiative surface recombination by N incorporation in GaAs/GaNAs core/shell nanowires.

Chen SL, Chen WM, Ishikawa F, Buyanova IA - Sci Rep (2015)

(a)–(c) PL spectra of the investigated structures measured at 5 K with the excitation power levels of 4 mW (the solid curves, red) and 55 mW (the dashed curves, blue), respectively. The open circles represent the measured PL lifetimes as a function of emission energy, with the excitation power of 55 mW. (d)–(f) PL spectra of the investigated structures detected at different time delays after an excitation pulse. The arrows indicate the shifts of the peak positions of the LE emission. The vertical dashed lines mark the FE spectral positions.
© Copyright Policy - open-access
Related In: Results  -  Collection

License
Show All Figures
getmorefigures.php?uid=PMC4477342&req=5

f1: (a)–(c) PL spectra of the investigated structures measured at 5 K with the excitation power levels of 4 mW (the solid curves, red) and 55 mW (the dashed curves, blue), respectively. The open circles represent the measured PL lifetimes as a function of emission energy, with the excitation power of 55 mW. (d)–(f) PL spectra of the investigated structures detected at different time delays after an excitation pulse. The arrows indicate the shifts of the peak positions of the LE emission. The vertical dashed lines mark the FE spectral positions.
Mentions: Shown as the solid curves in Fig.1a, b are PL spectra of the GaAs/GaNAs core/shell NWs with [N] = 0.1 and 0.5%, respectively, measured at 5 K with the excitation power (Wexc) of 4 mW (focused to a spot of about 0.5 mm in diameter). For comparison, Fig. 1c also shows the PL spectrum from the GaN0.005As0.995 epilayer measured under the identical excitation conditions (the solid curve). In all structures, the spectra are dominated by a broad asymmetric PL band which originates from localized exciton (LE) recombination within the GaNAs region29. 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 effect1. In principle, structural polytypism in NW structures can further contribute to exciton localization, as was observed in GaAs NWs where excitons could be localized at interfaces between ZB and wurtzite (WZ) phase segments with a type-II band alignment323334. This effect, however, does not seem to have the dominant contribution in the GaNAs NWs studied here, judging from the very similar properties of the LE emission between the NWs and epilayer structures. We should also note that the exact band alignment between ZB and WZ GaNAs is currently unknown. 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 region29. 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). Increasing excitation power, e.g. to 55 mW, leads to a saturation of the LE states. Under these conditions, the PL spectra (shown by the dotted curves in Fig. 1a,b) contain an additional PL component that is located above the high energy cut-off of the LE band and is caused by the FE emission in GaNAs. The same tendency is also observed in the reference GaNAs epilayer (see the dotted curve in Fig. 1c). We note that the FE emission is somewhat broadened in the NW samples. This broadening is likely due to minor variations in the N composition between different NWs forming the studied NW arrays, within 0.07% for the structures with [N] = 0.5%, as was revealed by our previous micro-PL measurements29. The spectral positions of the GaNAs-related FE emission in the investigated structures are indicated in Fig. 1 by the vertical dotted lines.

Bottom Line: 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.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.

View Article: PubMed Central - PubMed

Affiliation: Department of Physics, Chemistry and Biology, Linköping University, 58183, Linköping, Sweden.

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.

No MeSH data available.


Related in: MedlinePlus