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Breakthrough in Nanowire Crystal Phase Control

Jülich, 19th 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 the 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.

Crystal schemeFigure 1. a) Schematic of the NW growth model. b) Time evolution of the Ga flux required for the WZ stabilized growth of phase-pure NWs. The blue curve was obtained from our model, while the red curve corresponds to the measured Ga flux (BEP).

Since, the first published work on molecular beam epitaxy (MBE) of self-catalyzed GaAs nanowires by Fontcuberta I Moral in 2008, many efforts were performed by researchers all around the world to engineer the crystal phase of the as-grown NWs. For example, GaAs NWs grow in wurtzite (WZ) and zincblende (ZB) crystal phase, both exhibiting different mechanical, electrical and optical properties. Previously, the growth of phase-pure WZ GaAs NWs required the use of a foreign catalyst, such as gold, which contaminates the GaAs NW and significantly spoils optical and electrical properties of such NWs. Apart from this approach, the growth of phase-pure WZ GaAs NWs by self-catalyzed MBE was so far impossible.

At the beginning of 2020, Panciera et al. discovered that the preferred crystal structure of GaAs NWs (either WZ or ZB) is linked to the stabilization of specific contact angle regimes during growth, paving the way for phase control in self-catalyzed GaAs NWs. Building on this knowledge, researches from the Peter Grünberg Institut at the Research Center Jülich developed a comprehensive kinetic growth model calibrated by more than 600 individually investigated as-grown NWs to quantify the time evolution of NW length and contact angle. This growth model was applied to dynamically modify the Ga flux during growth in order to control and stabilize the contact angle in a range favoring the growth of phase-pure WZ GaAs NWs. Transmission electron microscopy analysis of the as-grown samples verified the growth of self-catalyzed GaAs NWs with 99−100% phase-pure WZ crystal structures on pre-patterned substrates for the first time. The developed model and the related growth strategy featuring phase-pure NWs are not only limited to self-catalyzed GaAs NWs but can be applied to the synthesis of phase-pure NWs from various III/V material systems. The results represent 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.

TEM CrystalFigure 2. TEM image (in [112 ̅0] zone axis) of an exemplary NW with a 99.9% phase-pure WZ crystal structure and [112 ̅0] side facets. The insets show the HR-TEM overviews of the three main sections of the NW with the respective Fast Fourier Formation (FFT) of the section.

Original publication: “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

ACS Applied Nano Materials, 2020 (ASAP),