(Invited) GaAs Related Nanowires on Si for Large Area and Functional Electron-Photon Conversion
Authors: Ishikawa Fumitaro 
Published: December 2024

Wafer scale growth and material exploration of GaAs-related heterostructure nanowires were carried out by self-catalyzed molecular beam epitaxy on Si(111) substrate, showing functional electron-photon conversion. GaAs has high mobility and photoelectric conversion efficiency with a possible formation of heterostructure with related compounds, enabling its application of functional opto-electronic devices such as solar cells, lasers, as well as transistors. The integration of GaAs heterostructure nanowires on Si can thus be promising for those applications on the developed Si platform, and the exploration of unexplored materials can extend the future prospects of the material system.
GaAs/AlGaAs core-shell nanowires were grown over a 2-inch Si wafer by a single process of molecular beam epitaxy, which was carried out without specific pre-treatment such as film deposition, patterning, and etching. The outermost Al-rich AlGaAs shells form a native oxide surface protection layer, which provides efficient passivation with elongated carrier lifetime. The 2-inch Si substrate sample exhibits a dark-colored feature due to the light absorption of the nanowires where the reflectance in the visible wavelengths is less than 2%. Homogeneous, optically luminescent, and adsorptive GaAs-related core-shell nanowires were prepared over the wafer, showing the prospect for large-scale III–V heterostructure devices.
Introduction of nitrogen and bismuth into GaAs-related heterostructure nanowires extends the tunability of the band gap and lattice constant, as well as showing lasing operation at telecommunication wavelengths, photon up-conversion, and characteristic nanostructure formation applicable to quantum structures. We have grown GaInNAs or GaNAsBi, dilute nitride semiconductor systems that can extend the operating wavelength to the near-infrared regime while maintaining lattice matching with GaAs. From the sample grown on patterned substrate, we observed the clear formation of the regular three-layered quantum well structure within the nanowire shell. The sample shows the room temperature photoluminescence from the samples. Varying the concentration of the nitrogen at the GaInNAs shell up to 3%, the emission wavelength approaches 1.28 μm of the telecommunication wavelengths.
Besides, we found the formation of rolled-up cylindrical membranes stemming from the strain deformation-induced delamination of a film-like nanowires array composed of coalesced GaAs nanowires embedded in AlOx with a buried GaAs/AlAs core-shell structure. The delamination of the nanowires array film is driven by natural oxidation resulting from prolongated exposure to ambient atmosphere. Investigations of the structural and chemical characteristics of the individual nanowires in the array provide an analytical description of the oxidation mechanism leading to the formation of the rolled-up structures. The rolled up membrane can be easily transferred to the other substrate by simply shaking off those existing on the sample surface. The cylindrical membranes maintain the optical properties of the core GaAs nanowires surrounded by native oxide. The results show the prospects for area-saving semiconductor devices with advanced nanoscale optical functions.