The concepts that will shape the world in the near future, such as quantum technology, sustainable manufacturing and IoT, call for novel material platforms. Amongst the proposed solutions, selective area epitaxy (SAE) is appealing due to its deterministic nature, wide applicability to different crystalline materials and their high quality. Despite the extraordinary progress in the last decades, the community still needs to address key challenges such as scalability, nanoscale engineering and efficient functionalization. 

In this talk, I highlight our recent work on the selective area epitaxy of III-As horizontal 1D nanostructures, hereon nanomembranes (NMs). The investigation of homo-epitaxial growth of GaAs NMs on (100) substrates revealed significant insights into their crystal formation mechanisms. NMs grown by molecular beam epitaxy (MBE) evolve from random crystallites into 1D horizontal nanostructures [1]. They display intermediate facets belonging to high index families and ultimately achieve a triangular cross-section dominated by {111} lateral facets. Surprisingly, their kinetics are strongly affected by their mask geometry. When grown via metalorganic vapor phase epitaxy (MOVPE), the same nanostructures evolve differently [2]. In this case, GaAs NMs grow layer-by-layer due to the lateral propagation of (011) atomic steps on the top flat (100) facet. Semi-empirical models pinpoint the fundamental role of mass transport on the selective mask and highlight key aspects for the nanoscale engineering of functional devices. We applied this knowledge to demonstrate horizontal InAs nanowires as photoconductive THz receivers [3]. These detectors show broadband response and are compatible with gating lasers at telecom wavelengths. Interestingly, InAs nanofaceting dominates the photoconductive lifetime, enabling one to explicitly design receivers with direct or indirect sampling modes. This work clearly demonstrates how control over SAE parameters can directly impact device performance. 

We recently expanded our investigation to GaAs nanomaterials grown by MOVPE on (111)B substrates in order to achieve high aspect ratios. The direct comparison between horizontal and vertical 1D nanostructures manifests fundamental differences in their kinetics. In particular, the sublinear growth of horizontal NMs indicates an unexpected diffusion towards the mask induced by a nucleation-limited regime. These observations open new paths for the engineering of complex nanostructures such as Y-junctions, nanopyramids and mixed vertical/horizontal nanostructures and define a nanoscale synthesis route that is potentially transferrable to earth-abundant substrates.

 

[1] Didem Dede et al., Nanotechnology 33, 485604 (2022)

[2] Nicholas Morgan et al., Crystal Growth & Design 23 (7), 5083 (2023)

[3] Kung Peng et al., Nat Commun 15, 103 (2024)