Encapsulation strategies for III-V core-shell nanowires grown on nanopatterned substrates by selective area epitaxy

Semiconductor nanowires (NWs) are a 1-D material system of high-purity, crystalline materials with radii of tens of nanometers and lengths up to several microns. At such small length scales, material combinations that would normally be incompatible are stable. Quantum mechanical effects can also be engineered at this scale. Group III-V materials-based NWs are a favorable system to act as a base for infrared optoelectronics.

In this work, indium arsenide (InAs)-based core-shell NWs are grown by molecular beam epitaxy (MBE), a high-purity method for NW growth. NW nucleation on a silicon (Si) (111) substrate was controlled by opening nanoscale windows in a dielectric film coated on the substrate. Two different types of semiconductor shells, indium aluminum arsenide (InAlAs) and gallium antimonide (GaSb), were grown to modify the NW's light emission properties.

We observed NW brightness to decrease significantly when exposed to an ambient environment. Therefore, strategies to protect the NWs were explored. The NWs were coated with thin dielectric films of varied thicknesses. For dielectric films around 60 nm, the light-emitting properties immediately showed a ten-fold increase. Further investigations revealed this was caused partially by increased absorption of the laser that was used to excite electrons in the materials and partially from improved management of the heat generated during testing. Finally, the NWs’ optical properties were tested over time in a high humidity chamber. We observed that the NWs that had been encapsulated with dielectric film(s) showed drastically increased resistance to environmental degradation.