Spontaneous core–shell elemental distribution in In-rich In_xGa_1−xN nanowires grown by molecular beam epitaxy

Abstract

The elemental distribution of self-organized In-rich In(x)Ga1-xN nanowires grown by plasma-assisted molecular beam epitaxy has been investigated using three different techniques with spatial resolution on the nanoscale. Two-dimensional images and elemental profiles of single nanowires obtained by x-ray fluorescence and energy-dispersive x-ray spectroscopy, respectively, have revealed a radial gradient in the alloy composition of each individual nanowire. The spectral selectivity of resonant Raman scattering has been used to enhance the signal from very small volumes with different elemental composition within single nanowires. The combination of the three techniques has provided sufficient sensitivity and spatial resolution to prove the spontaneous formation of a core–shell nanowire and to quantify the thicknesses and alloy compositions of the core and shell regions. A theoretical model based on continuum elastic theory has been used to estimate the strain fields present in such inhomogeneous nanowires. These results suggest new strategies for achieving high quality nonpolar heterostructures.

Self-Assembled and Selective-Area Growth of Group III-Nitride Semiconductor Nanorods by Magnetron Sputter Epitaxy

“…[49] Another method consists of a single-step growth and refers to the spontaneous formation of core-shell nanorods consisting of two phases with different concentrations. [50,17] In a ternary III-nitride, a complete phase separation can occur, resulting in nanorods where the core and the shell are each composed of a binary compound. An incomplete phase separation results in compositional fluctuation, and both the shell and core of the nanorods are composed of ternary material, but with a different concentrations x.…”

“…Bottom-up methods require less effort and result in a better crystalline quality of nanorods and smoother side surfaces since no nanorod etching step is involved. [50] The growth process can be catalyst-assisted, also termed as vapor-liquid-solid (VLS) growth, or catalyst-free leading to the selfassembled nanorods.…”

Magnetron Sputter Epitaxy of Group III-Nitride Semiconductor Nanorods

“…[42] Another method consists of a single step growth and refers to the spontaneous formation of core-shell nanorods consisting of two phases with different concentrations. [43,17] In a ternary III-nitride, a complete phase separation can occur, resulting in nanorods where the core and the shell are each composed of a binary compound. An incomplete phase separation results in compositional fluctuation, and both the shell and core of the nanorods are composed of ternary material, but with a different concentrations x.…”

Impact of microscopic In fluctuations on the optical properties of InxGa1-xN blue light-emitting diodes assessed by low-energy X-ray fluorescence mapping using synchrotron radiation

“…However, surface coating with a conductive film is often necessary. In addition, due to the spread of irradiated electrons within the material, the spatial resolution of SEM-EDX is limited to a few hundreds of nm, which is one order worse than that of state-of-the-art SR-XRF 13–15 . Therefore, SR XRF enables more detailed analyses.…”

“…Here we briefly review previous studies on SR XRF applied to In x Ga 1- x N. In-rich In x Ga 1- x N nanowires have been investigated using the ID22NI beam line of the European Synchrotron Radiation Facility (ESRF) 13–15 . One characteristic of the In-rich In x Ga 1- x N nanowires is significant spatial In compositional distributions ranging from 0.30 to 0.95 induced by the nano-structure effect 13 .…”