Expanding the Capabilities of GaAs Nanowires as a Platform for Hexagonal SiGe

The development of a laser based on silicon (Si) represents a pivotal milestone in advancing the commercial viability and widespread adoption of photonic circuits. One of the most promising pathway is the recently developed coaxial hexagonal silicon germanium (hex-SiGe) quantum well (QW) shells around wurtzite (WZ) gallium arsenide (GaAs) nanowires (NWs) for which efficient direct band gap emission was shown.¹ However, studies have highlighted the limitations of the core/multi-shell NW system that notably restricts its lasing capabilities. These challenges include: the limitation of phase control induced by the formation of I3 defects,^2,3 the presence of Si concentration gradients in high-Si shells attributed to strain between the GaAs core and SiGe shell, as well as a recently discovered aspect ratio limitation in WZ GaAs NWs ascribed to a dynamic variation of the growth conditions.⁴<br/>Here, we report on the crystal phase control of GaAs NWs down to the monolayer regime opening up new pathways for superlattices as well as high aspect ratios GaAs NWs. To achieve this, Ga pulses are executed by momentarily halting the As supply, leading to an accumulation of Ga atoms within the catalyst particle. This process leads to the increase of the contact angle of the catalyst particle enabling a controlled transition from the WZ phase to the zinc blende (ZB), and then back to the WZ phase. By finetuning this process, WZ/ZB superlattices with varying WZ segment length have been grown, which can be used as a template for axial SiGe QWs. Furthermore, by using the ZB inclusion as a marker during the growth process, we successfully carried out a detailed investigation into the evolution of the NW growth, considering its diameter, length, and the pulse frequency. With this study, we showed the growth of high aspect ratio GaAs NWs with high crystal phase purity expanding the platform capabilities of GaAs NWs for the next generation hex-SiGe.<br/><br/><b>*presenting & corresponding author: Marvin Marco Jansen *e-mail: [email protected]</b><br/><br/><b>References:</b><br/>1. Peeters, W. H. J. <i>et al.</i> Direct bandgap quantum wells in hexagonal Silicon Germanium. <i>Nat Commun</i> <b>15</b>, 5252 (2024).<br/>2. Fadaly, E. M. T. <i>et al.</i> Unveiling Planar Defects in Hexagonal Group IV Materials. <i>Nano Lett</i> <b>21</b>, 3619–3625 (2021).<br/>3. Vincent, L. <i>et al.</i> Growth-Related Formation Mechanism of I3-Type Basal Stacking Fault in Epitaxially Grown Hexagonal Ge-2H. <i>Adv Mater Interfaces</i> <b>9</b>, (2022).<br/>4. Peeters, W. H. J. <i>et al.</i> Onset of uncontrolled polytypism during the Au-catalyzed growth of wurtzite GaAs nanowires. <b>020401</b>, 1–6 (2024).