Epitaxial nanowire formation in metamorphic GaAs/GaPAs short-period superlattices

Nan Zheng,S Phillip Ahrenkiel

doi:10.1063/1.4985550

Abstract

Metamorphic growth presents routes to novel nanomaterials with unique properties that may be suitable for a range of applications. We discuss self-assembled, epitaxial nanowires formed during metalorganic chemical vapor deposition of metamorphic GaAs/GaPAs short-period superlattices. The heterostructures incorporate strain-engineered GaPAs compositional grades on 6°-&lt;111&gt;B miscut GaAs substrates. Lateral diffusion within the SPS into vertically aligned, three-dimensional columns results in nanowires extending along &lt;110&gt;A directions with a lateral period of 70-90 nm. The microstructure is probed by transmission electron microscopy to confirm the presence of coherent GaAs nanowires within GaPAs barriers. The compositional profile is inferred from analysis of {200} dark-field image contrast and &lt;210&gt; lattice images.

Highlights

INTRODUCTIONSuperlattice (SPS) layers is desirable to enhance optical density and allow coupling to form electronic minibands.[18] These quantum-dot superlattices share clear commonalities with epitaxial, embedded nanowire-like structures formed in AlAs/InAs SPSs that are associated with lateral composition modulation.[19] A similar morphology of GaAs/AlGaAs quantum wires is obtained by growth on patterned substrates.[20] most reported semiconductor nanowires have been synthesized by either metal-assisted methods[21] or catalyst-free selective-area epitaxy.[22] These usually grow in the (111)
Metamorphic, epitaxial thin films offer a broad range of materials combinations and microstructures that are not available by pseudomorphic growth on an arbitrary, preferred substrate
Most epitaxial semiconductor nanostructures studied to date, such as self-assembled quantum dots and nanowires, are typically restricted to materials that are nominally lattice-matched to the substrate,[1,2] or to those grown with insufficient thickness for strain relaxation by misfit-dislocation formation.[3]

Summary

INTRODUCTION

Superlattice (SPS) layers is desirable to enhance optical density and allow coupling to form electronic minibands.[18] These quantum-dot superlattices share clear commonalities with epitaxial, embedded nanowire-like structures formed in AlAs/InAs SPSs that are associated with lateral composition modulation.[19] A similar morphology of GaAs/AlGaAs quantum wires is obtained by growth on patterned substrates.[20] most reported semiconductor nanowires have been synthesized by either metal-assisted methods[21] or catalyst-free selective-area epitaxy.[22] These usually grow in the (111). Orientation of the underlying cubic crystal structure, making conventional semiconductors susceptible to the formation of planar defects, progress has been made to reduce the defect densities.[23,24]. Numerous applications for semiconductor nanowires have been identified for nanoelectronics,[25] optoelectronics,[26] and photovoltaics.[27]

EXPERIMENT

RESULTS AND DISCUSSION

CONCLUSION