Polytypism in GaAs/GaNAs core–shell nanowires

Abstract

We report the crystal structures of GaAs and GaAs/GaNAs/GaAs core–multishell nanowires (NWs). From statistical investigations by x-ray diffraction (XRD) and electron backscattered diffraction (EBSD) pattern analysis, we statistically and microscopically resolve the zinc-blende (ZB) and wurtzite (WZ) polytypism within the NWs. The XRD analysis shows a smaller fraction of WZ segments in the NWs with a larger concentration of nitrogen. With increasing nitrogen content in the GaNAs shell, the ZB peak position shifts toward higher angles and the WZ peak intensity decreases. The EBSD measurements also confirm the coexistence of ZB and WZ polytypes in all of the NWs. Their polytype switches along the length. Twin defects are observed in the ZB segments in all of the NWs. The unique grain map and grain size distribution show a decrease of the WZ segments in the GaAs/GaNAs/GaAs NW, in agreement with the XRD results. Microscopically, the local area where the polytype switches from WZ in the inner-core side to ZB toward the outer-shell surface is observed. Overall, we propose that the WZ polytype in the GaAs NWs decreases because of the strain induced by the growth of the GaNAs shell with a smaller lattice constant.

Wafer-scale integration of GaAs/AlGaAs core–shell nanowires on silicon by the single process of self-catalyzed molecular beam epitaxy

“…47 The NWs are hence predominantly zinc blende structures. 48 The results indicate the presence of a larger volume AlGaAs shell compared to the inner GaAs core, as designed for the structure. 7(a) shows good agreement with the EDS images of O, Al, and As shown in Fig.…”

Growth, Crystal Structure, and Photoluminescent Properties of Dilute Nitride InAsN Nanowires on Silicon for Infrared Optoelectronics

“…Narrow-band-gap InAs-based semiconductor nanowires (NWs) have emerged as promising materials for a wide range of applications in the field of infrared optoelectronics and photonics, including photodetectors, sensors, transistors, and light-emitting diodes. − The high surface-to-volume ratio of NWs allows for elastic relaxation of a lattice mismatch-induced strain at the surface, enabling the formation of axial and radial NW heterostructures using semiconductor materials with a high lattice mismatch . This also allows for the NW growth on the lattice-mismatched Si substrates, epitaxial stabilization of metastable phases, , and suppression of the composition miscibility gap . It was shown that the formation of the ordered NW arrays with a given morphology and a predetermined NW pattern can substantially improve light trapping and optical absorption. , Thus, the performance of NW-based infrared (IR) photodetectors can be improved by reducing the volume of the active detector’s region, resulting in the decrease of dark current. , …”

“…1−3 The high surface-to-volume ratio of NWs allows for elastic relaxation of a lattice mismatchinduced strain at the surface, enabling the formation of axial and radial NW heterostructures using semiconductor materials with a high lattice mismatch. 4 This also allows for the NW growth on the lattice-mismatched Si substrates, 5 epitaxial stabilization of metastable phases, 6,7 and suppression of the composition miscibility gap. 8 It was shown that the formation of the ordered NW arrays with a given morphology and a predetermined NW pattern can substantially improve light trapping and optical absorption.…”