Wurtzite phase control for self-assisted GaAs nanowires grown by molecular beam epitaxy

TL;DR

This paper introduces a method to precisely control the crystal phase of self-assisted GaAs nanowires during molecular beam epitaxy, enabling the growth of extended pure wurtzite segments by adjusting the V/III flux ratio.

Contribution

The study demonstrates a self-regulated growth regime where the V/III flux ratio controls the crystal phase, achieving extended pure WZ GaAs nanowires.

Findings

Successful control of WZ phase in GaAs NWs confirmed by multiple microscopy techniques.

Extended pure WZ segments of several micrometers achieved.

V/III flux ratio of 4.0 is optimal for WZ phase growth.

Abstract

The accurate control of the crystal phase in III-V semiconductor nanowires (NWs) is an important milestone for device applications. In this work, we present a method to select and maintain the wurtzite (WZ) crystal phase in self-assisted NWs. By choosing a specific regime where the NW growth process is a self-regulated system, the main experimental parameter to select the zinc-blende (ZB) or WZ phase is the V/III flux ratio. The latter can be monitored by changing the As flux, and drives the system toward a stationary regime when the wetting angle of the Ga droplet falls in a target interval, typically in the 90{\deg} - 125{\deg} range for the WZ phase growth. The analysis of the in situ RHEED evolution, high-resolution scanning transmission electron microscopy (HRSTEM), dark field transmission electron microscopy (DF-TEM), and photoluminescence (PL) data all confirm the control of an extended few micrometers long pure WZ segment obtained by MBE growth of self-assisted GaAs NWs with a V/III flux ratio of 4.0.