(Invited) Semiconductor/Oxide Composite Nanowires Supplying White Luminescence

Integration of semiconductor and oxides within a monolithically synthesized nanowire system would have strong potential for the future functional devices. We then challenge to fabricate semiconductor/oxide heterostructure nanowire with molecular beam epitaxy combined with wet-oxidation of compound semiconductor heterostructure system.

We fabricate oxide heterostructure nanowire by selective wet oxidation of GaAs/AlGaAs core-shell type nanowire grown on Si substrate. Applying adequate oxidation condition, we obtain GaAs/AlGaOx semiconductor-oxide composite nanowire as illustrated in the Figure. At an adequate condition, the shell AlGaAs was selectively oxidized but the core GaAs remained sue to its large contrast of oxidation rate.

The figure also shows the result of cathodoluminescence measurement on the sample. The contrast in the NW (the panchromatic CL image) reflects the core-shell structure of the NWs. The spectrum acquired from the 1×1μm² area involving the NW is also shown in the figure. The spectrum exhibits a sharp peak at 340 nm and a broad peak extending from approximately 400 nm to 700 nm, probably constituting several overlapped peaks. This spectrum is similar to previously reported spectra of Al₂O₃ nanoparticles. As seen in the figure, the shell layer emitted strong luminescence at 342 nm and 423 nm. Furthermore, the observed emissions were localized, in consistence with luminescence sourced from nanostructured oxides. This suggests the formation of shell oxides with luminescent properties. The observed spectral range varies from violet to a green-yellow regime, possibly reflecting the different arrangements of molecules responsible for the luminescence. In our case, luminescence is observed from ultraviolet (300 nm) to near infrared (700 nm) wavelengths, including the broadened tail of the spectrum.[1] This broad white luminescence might be sourced from the small Ga constituent within the amorphous AlGaOx shell and the wide nanoscale particle size distribution of the shell.

[1] H. Hibi, M. Yamaguchi, N. Yamamoto, and F. lshikawa, Nano Lett. 14, 7024, 2014.