Bridged oxide nanowire device fabrication using single step metal catalyst free thermal evaporation

Abstract

In this study, indium-tin-zinc-oxide (ITZO) and Zn doped In₂O₃ nanowires were directly grown as bridged nanowires between two heavily doped silicon (Si) electrodes on an SOI wafer using single step vapor-solid-solid (VSS) growth method. SEM analysis showed highly dense and self aligned nanowire formation between the Si electrodes. Electrical and UV response measurements were performed in ambient condition. Current-voltage characteristics of devices exhibited both linear and non-linear behavior. This was the first demonstration of bridged ITZO and Zn-doped In₂O₃ nanowires. Our results show that bridged nanowire growth technique can be a potential candidate for high performance electronic and optoelectronic devices.

Fig. 1. SOI wafer patterning flow diagram: (a) unprocessed SOI wafer, (b) after the deposition of photoresist, (c) photomask patterning photoresist, (d) after photolithography, (e) patterning Si device layer using hot KOH or reactive ion etching, (e) after the growth of nanowires between heavily doped Si electrodes (bridged nanowires).

Fig. 2. Metal-oxide nanowire growth steps: (a) heavily doped patterned SOI wafer with surface orientations before the nanowire growth process, (b) first, the powders tend to deposit on the edge of Si electrodes because of high surface energy of some sites, (c) these powders behave like a seed catalyst layer and nanowires start to grow from these site. (d) Completed growth process results in bridged nanowires between heavily doped Si electrodes.

Fig. 3. (a) Low magnification SEM image of Si electrodes on SOI wafer for first ITZO device. (b) ITZO nanowires are seen both on Si electrode sides and gap between Sii electrodes. (c) High magnification SEM image of a gap between Si electrodes on a SOI wafer. (d) High magnification SEM images of bridged ITZO nanowires that grown between Si electrodes. As seen from the SEM images, only 6 ribbon shaped nanowire are connected to two the Si electrodes.

Fig. 4. XRD analysis result of (a) ZnO (PDF 01-089-1397), (b) SnO₂ (PDF 01-070-4175), (c) In₂O₃ (PDF 00-044-1087), (d) the first bridged ITZO nanowire device, (e) the second bridged ITZO Nanowire device, (f and g) EDX analysis result of first ITZO nanowire.

Fig. 5. (a) Illustration of ribbon shaped nanowire calculated using SEM images. (b) Equivalent circuit of the bridged ITZO nanowire device.

Fig. 6. Current–voltage characteristic of bridged ITZO nanowire under dark and UV (365 nm) light. The device showed very little response to UV light because of its high conductivity.

Fig. 7. (a) Low magnification SEM image of Si electrodes and ITZO nanowires between them on a SOI wafer for second ITZO device. (b) Medium and, (c) high magnification SEM images of ITZO nanowires between Si electrodes. (d and e) EDX analysis of bridged ITZO nanowire for the second category of devices.

Fig. 8. Current–voltage curves of second ITZO nanowire device in dark and under UV light.

Fig. 9. (a) Low and (b) high magnification SEM images of bridge Zn doped In₂O₃ nanowire devices. Clearly seen from the images that high dense nanowires grown on the vertical walls of Si electrode' and not on the planar surface. (c) and (d) show EDX analysis results of Zn doped In₂O₃.

Fig. 10. XRD analysis result of (a) In₂O₃ (PDF 00-044-1087), (b) bridged Zn doped In₂O₃ nanowire. Arrows show the peaks shift through the higher two theta values.

Fig. 11. (a) Current–voltage characteristic of bridged Zn doped In₂O₃ nanowire device in dark and under UV light (365 nm). (b) Comparison of current–voltage characteristic of second bridged ITZO and Zn doped In₂O₃ devices.