Valerio Piazza

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We outline the growth mechanismand shape evolution of GaAsnanoridges by selective area MOVPE with three well-identified, distinctstages of growth. Selective area epitaxy at the nanoscale enables fabricationofhigh-quality nanostructures in regular arrays with predefined geometry.Here, we investigate the growth mechanisms of GaAs nanoridges on GaAs(100) substrates in selective area trenches by metal-organicvapor-phase epitaxy (MOVPE). It is found that pre-growth annealingresults in the formation of valley-like structures of GaAs with atomicterraces inside the trenches. MOVPE growth of GaAs nanoridges consistsof three distinct stages. Filling the trench in the first stage exhibitsa step-flow growth behavior. Once the structure grows above the masksurface, it enters the second stage of growth by forming {101} sidefacets as the (100) flat top facet progressively shrinks. In the thirdstage, the fully formed nanoridge begins to overgrow onto the maskwith a significantly reduced growth rate. We develop a kinetic modelthat accurately describes the width-dependent evolution of the nanoridgemorphology through all three stages. MOVPE growth of fully formednanoridges takes only about 1 min, which is 60 times faster than inour set of molecular beam epitaxy (MBE) experiments reported recently,and with a more regular, triangular cross-sectional geometry definedsolely by the {101} facets. In contrast to MBE, no material loss dueto Ga adatom diffusion onto the mask surface is observed in MOVPEuntil the third stage of growth. These results are useful for thefabrication of GaAs nanoridges of different dimensions on the samesubstrate for various applications and can be extended to other materialsystems.

AMER CHEMICAL SOC2023

Nanoscale Mapping of Light Emission in Nanospade-Based InGaAs Quantum Wells Integrated on Si(100): Implications for Dual Light-Emitting Devices

Akshay Balgarkashi, Titouan Charvin, Didem Dede, Anna Fontcuberta i Morral, Wonjong Kim, Raphaël François Lemerle, Jean-Baptiste Leran, Nicholas Paul Morgan, Valerio Piazza, Nicolas Tappy

III-V semiconductors outperform Si in many optoelectronics applications due to their high carrier mobility, efficient light emission and absorption processes, and the possibility to engineer their band gap through alloying. However, complementing Si technology with III-V semiconductors by integration on Si(100) remains a challenge still today. Vertical nanospades (NSPDs) are quasi-bi-crystal III-V nanostructures that grow on Si(100). Here, we showcase the potential of these structures in optoelectronics application by demonstrating InGaAs heterostructures on GaAs NSPDs that exhibit bright emission in the near-infrared region. Using cathodoluminescence hyperspectral imaging, we are able to study light emission properties at a few nanometers of spatial resolution, well below the optical diffraction limit. We observe a symmetric spatial luminescence splitting throughout the NSPD. We correlate this characteristic to the structure's crystal nature, thus opening new perspectives for dual wavelength light-emitting diode structures. This work paves the path for integrating optically active III-V structures on the Si(100) platform.

AMER CHEMICAL SOC2022

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Selective area epitaxy (SAE) provides the path for scalable fabrication of semiconductor nanostructures in a device-compatible configuration. In the current paradigm, SAE is understood as localized epitaxy, and is modelled by combining planar and self-assembled nanowire growth mechanisms. Here we use GaAs SAE as a model system to provide a different perspective. First, we provide evidence of the significant impact of the annealing stage in the calculation of the growth rates. Then, by elucidating the effect of geometrical constraints on the growth of the semiconductor crystal, we demonstrate the role of adatom desorption and resorption beyond the direct-impingement and diffusion-limited regime. Our theoretical model explains the effect of these constraints on the growth, and in particular why the SAE growth rate is highly sensitive to the pattern geometry. Finally, the disagreement of the model at the largest pitch points to non-negligible multiple adatom recycling between patterned features. Overall, our findings point out the importance of considering adatom diffusion, adsorption and desorption dynamics in designing the SAE pattern to create pre-determined nanoscale structures across a wafer. These results are fundamental for the SAE process to become viable in the semiconductor industry.

IOP Publishing Ltd2022