Localized Self-Assembly of InAs Nanowire Arrays on Reusable Si Substrates for Substrate-Free Optoelectronics

We present a low-cost and scalable approach for the synthesis of wafer-scale InAs nanowire (NW) arrays on photo-lithographically patterned, reusable Si wafers using a localized selfassembly (LSA) epitaxial growth technique. Conventional i-line lithography is used to define arrays of 500 nm diameter pores through 50 nm thick SiO2 layers, which serve as the LSA mask. A two-step, flowrate-modulated growth sequence is implemented to optimize selective-area self-assembly of NW arrays with over 80% yield and excellent control over the placement of one NW, with a mean diameter of 130 nm, inside each 500 nm pore. As-grown NW arrays are delaminated from the growth substrate, enabling fabrication of flexible membrane devices as well as reuse of Si wafers and growth masks while preserving the template pattern fidelity. Reuse of Si substrates for III-V epitaxy is demonstrated with and without pre-growth substrate restoration treatments. In both cases, the yield of NWs on reused wafers is comparable to that achieved in the original growth run. Without substrate restoration procedures, the remnant base segments of NWs on parent wafers act as preferential sites for regrowth of vertical NWs. Transmission electron microscopy analysis reveals that the InAs lattice is coherently extended from the remnant NW base segments during regrowth. The delaminated InAs NW arrays are transferred to carrier wafers for the fabrication of substrate-free photodetectors through the use of an anchoring procedure, which preserves the original NW position and orientation. Under broadband illumination, the NW array-based photodetectors produce a photo-to-dark current ratio of 102, demonstrating the utility of the fabrication procedure employed. This work establishes a low-cost route toward III-V semiconductor-based flexible optoelectronics via LSA epitaxial growth of NW arrays on reusable Si wafers.

Automated summary

We present a low-cost and scalable approach for the synthesis of wafer-scale InAs nanowire (NW) arrays on photo-lithographically patterned, reusable Si wafers using a localized selfassembly (LSA) epitaxial growth technique. The NW arrays can be delaminated and reused for the fabrication of flexible devices. The reuse of Si substrates for III-V epitaxy is also demonstrated.