Breakthrough in Nanowire Crystal Phase Control
Jülich, 19. October 2020
Researches of the Peter Grünberg Institute developed a pathway to control the crystal phase of GaAs nanowires (NWs) on silicon surfaces.
This discovery represents a major advance in the field of NW crystal phase engineering as the crucial basis for application of NWs in advanced laser devices and single-photon sources. The results are published in ACS Applied Nano Materials.
In recent years, nanowires (NWs) featured enormous potential for advanced nano-optoelectronic applications. With their high aspect ratio (diameters of about 100 nanometers and length of multiple micrometers), these nanostructures yield exciting emission and absorption properties, which are flexible and particularly suited for integrated photonics with low-threshold lasers and single-photon emitters for quantum computing directly on silicon chips.
Since the first published work on molecular beam epitaxy (MBE) of self-catalyzed GaAs ND by Fontcuberta I Moral in 2008, scientists around the world focused their work on controlling the crystal phase of these ND. GaAs ND grow in wurtzite (WZ) and zincblende (ZB) crystal structure, both configurations have different mechanical, electrical and optical properties. Previously, the growth of phase-pure WZ GaAs ND required the use of a foreign catalyst such as gold, but this contaminates the GaAs ND and significantly affects the optical and electrical properties. Apart from this approach, the growth of phase-pure WZ GaAs ND by self-catalyzed MBE has been impossible.
In early 2020, Panciera et al. discovered that the preferred crystal structure of GaAs ND (either WZ or ZB) is related to the stabilization of a specific contact angle regime during MBE growth. This finding paved the way for phase control of self-catalyzed GaAs ND. Building on this preliminary work, researchers at the Peter Grünberg Institute at Forschungszentrum Jülich developed a comprehensive kinetic growth model, which was calibrated using more than 600 individually studied NDs to quantify the time evolution of nanowire length and contact angle. The growth model was applied to dynamically modify the Ga flux during growth, thereby controlling and stabilizing the contact angle in a range that favors the growth of phase-pure WZ GaAs ND. Extensive analysis of the samples by transmission electron microscopy demonstrated the growth of self-catalyzed GaAs ND with 99-100% phase-pure WZ crystal structure on pre-patterned substrates for the first time in the world.
The developed model and associated growth strategy of phase-pure ND are not limited to self-catalyzed GaAs ND, but can be applied to the synthesis of phase-pure ND from various III/V material systems. The results represent a major advance in the field of ND growth and provide the critical foundation for the application of ND in advanced lasers and single photon sources for quantum communications.
“Phase-Pure Wurtzite GaAs Nanowires Grown by Self-Catalyzed Selective Area Molecular Beam Epitaxy for Advanced Laser Devices and Quantum Disks” by Marvin M. Jansen, Pujitha Perla, Mane Kaladzhian, Nils von den Driesch, Johanna Janssen, Martina Luysberg, Mihail I. Lepsa, Detlev Grützmacher and Alexander Pawlis