Formation of metal–semiconductor nanowire heterojunctions by nanosecond laser irradiation

Laser nano-joining has emerged as a preferred technique for better device performance as it can result in stronger mechanical contacts and enhance the electrical properties between nanocomponents. It is often used to bond metallic nanostructures, but there is little information available on the applicability of the corresponding processes for creating hybrid bonds between metal and semiconductor nanomaterials. In this article, we show that Nd:YAG nanosecond (ns) laser irradiation is an effective tool for use in the nano-joining of metal–semiconductor nanowire (NW) combinations. We show that photothermal, electron–hole pair creation and plasmonic effects combine to facilitate nano-joining with Nd:YAG ns laser radiation, producing similar interfacial structures to those occurring under femtosecond laser irradiation. We find that Nd:YAG laser irradiation is effective in the production of bonds between Ag–TiO2 and Ag–CuO NW structures but that the detailed mechanism involved in the creation of these bonds depends on the bandgap energy of the semiconductor NW. Direct heating of the semiconductor through photoexcitation of excitons and electron transfer to the conduction band is significant in the Nd:YAG laser nano-joining of low bandgap materials such as CuO. Coupling of surface plasmon resonance energy to electrical carriers in the semiconductor NW at the Ag-semiconductor interface is found to be important in all hybrid systems, including those involving a wide bandgap material such as TiO2. Since the Nd:YAG ns laser is widely available, these results suggest that nano-joining of heterogeneous materials with ns laser pulses is a practical alternative to joining with ultrashort laser radiation.