We propose material conversion of compound semiconductor GaAs nanowires for its extension of their functions and structures. As utilized for the oxidation technique of AlGaAs within GaAs-based vertical cavity surface emitting lasers for the electrical and optical confinement, such kind of material conversion enables functions which cannot be utilized without the introduction of contrastive materials. If we can convert nanoscale materials with keeping its structure, which can widely extend the tunability of wide range of materials properties such as electric, dielectric, as well as mechanical properties. Recently, we proposed precise selective oxidations to GaAs/AlGaAs heterostructure, enabling the synthesis of semiconductor/oxide composite GaAs/AlGaOx and full-oxide and finely structurally controlled GaO/AlGaOx nanowires. Characteristically, the composite nanowire provide specific white luminescence, which cannot be achievable for conventional compound semiconductors without the material conversion for nanoscale oxides[1,2] To further develop the material conversion technique for GaAs nanowires, we investigate two-step materials conversion consisting of the thermal treatment within liquid In, and nitrogen gas flow under atmospheric pressure. By the technique, we show the conversion of GaAs nanowire constituents to In, oxygen, as well as silicon from the substrate, eventually forming Ga(In)As and In(Si)O nanowires.

We used GaAs nanowires having about 100 nm diameter with 5mm length on Si substrate, synthesized by molecular beam epitaxy. The conversion was carried out in a furnace introducing nitrogen gas under atmospheric pressure. During the conversion, the nanowires were dipped into a custom-made qualz pod with In melt, which was weighted down with qualz cap. By heating the sample up to 600oC for an hour, we observe the introduction of In into the GaAs nanowire. We then carry out the heating without using the pod but just pasting the In onto the substrate surface having GaAs nanowires. As a result, the wire was converted from GaAs nanowire to InO with the constituent of substrate Si. These results suggest a possible technique realizing the introduction of wide range functionalities into the optically active and electrically high-speed compound semiconductor GaAs nanowires.

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

[2] F. Ishikawa and N. Yamamoto, ECS transactions, 69, (In press), 2015.