Crystal phase engineering of self-catalyzed GaAs nanowires using RHEED diagram

TL;DR

This paper introduces a method to control the crystal structure of self-catalyzed GaAs nanowires during growth by analyzing in situ RHEED patterns, enabling precise engineering of their phase composition.

Contribution

It presents a novel in situ RHEED-based approach to selectively control the WZ or ZB phases in GaAs nanowires during molecular beam epitaxy.

Findings

Successful control of WZ and ZB phases in GaAs NWs.

Identification of the critical wetting angle for phase transition.

Realization of ZB NWs with WZ segments.

Abstract

It is well known that the crystalline structure of the III-V nanowires (NWs) is mainly controlled by the wetting contact angle of the catalyst droplet which can be tuned by the III and V flux. In this work we present a method to control the wurtzite (WZ) or zinc-blende (ZB) structure in self-catalyzed GaAs NWs grown by molecular beam epitaxy, using in situ reflection high energy electron diffraction (RHEED) diagram analysis. Since the diffraction patterns of the ZB and WZ structures differ according to the azimuth [1-10], it is possible to follow the evolution of the intensity of specific ZB and WZ diffraction spots during the NW growth as a function of the growth parameters such as the Ga flux. By analyzing the evolution of the WZ and ZB spot intensities during some NW growths with specific changes of Ga flux, it is then possible to control the crystal structure of the NWs. ZB GaAs NWs with a controlled WZ segment have thus been realized. Using a semi-empirical model for the NW growth and our in situ RHEED measurements, the critical wetting angle of the catalyst droplet for the structural transition is deduced.