XRD Evaluation of Wurtzite Phase in MBE Grown Self-Catalyzed GaP Nanowires

Abstract

Control and analysis of the crystal phase in semiconductor nanowires are of high importance due to the new possibilities for strain and band gap engineering for advanced nanoelectronic and nanophotonic devices. In this letter, we report the growth of the self-catalyzed GaP nanowires with a high concentration of wurtzite phase by molecular beam epitaxy on Si (111) and investigate their crystallinity. Varying the growth temperature and V/III flux ratio, we obtained wurtzite polytype segments with thicknesses in the range from several tens to 500 nm, which demonstrates the high potential of the phase bandgap engineering with highly crystalline self-catalyzed phosphide nanowires. The formation of rotational twins and wurtzite polymorph in vertical nanowires was observed through complex approach based on transmission electron microscopy, powder X-ray diffraction, and reciprocal space mapping. The phase composition, volume fraction of the crystalline phases, and wurtzite GaP lattice parameters were analyzed for the nanowires detached from the substrate. It is shown that the wurtzite phase formation occurs only in the vertically-oriented nanowires during vapor-liquid-solid growth, while the wurtzite phase is absent in GaP islands parasitically grown via the vapor-solid mechanism. The proposed approach can be used for the quantitative evaluation of the mean volume fraction of polytypic phase segments in heterostructured nanowires that are highly desirable for the optimization of growth technologies.

Formation of wurtzite sections in self-catalyzed GaP nanowires by droplet consumption

“…This is twice the stoichiometric value for planar GaP layers [29,30] corresponding to the atomic V/III flux ratio (V/III for brevity) of 2. These conditions yield stable ZB GaP NWs as previously reported [26][27][28]. The measured contact angles of Ga droplets on tops of these NWs are 120±5°(not shown), which is close to the previously reported value of 123° [22].…”

“…The Ga beam equivalent pressure (BEP) was kept constant at 7×10 −8 Torr throughout the growth, which corresponds to 3.17 nm min −1 Ga-limited planar growth rate of GaP. The P 2 flux was different in the two growth steps [28]. In the first step (1 h duration), the P 2 BEP was set at 8.4×10 −7 Torr, yielding a V/III BEP ratio of 12.…”

Red GaPAs/GaP Nanowire-Based Flexible Light-Emitting Diodes

“…Finally, NW growth was interrupted by closing both Ga and P 2 shutters and subsequent sample cooling. An in situ analysis of the NW crystal structure performed with reflection high energy electron diffraction (RHEED) patterns demonstrated that the described growth conditions yielded stable formation of GaP NWs with a zinc-blende structure as it was previously reported in [36][37][38].…”

Tailoring Morphology and Vertical Yield of Self-Catalyzed GaP Nanowires on Template-Free Si Substrates

“…The details on TEM studies of NW crystal structure are provided in Supplementary Materials . A more detailed investigation of GaP NW crystal structure and its dependence on the growth conditions was performed using X-ray diffraction technique with an in-house X-ray source [ 50 ].…”