Measuring Three-Dimensional Strain and Structural Defects in a Single InGaAs Nanowire Using Coherent X-ray Multiangle Bragg Projection Ptychography

Abstract

III-As nanowires are candidates for near-infrared light emitters and detectors that can be directly integrated onto silicon. However, nanoscale to microscale variations in structure, composition, and strain within a given nanowire, as well as variations between nanowires, pose challenges to correlating microstructure with device performance. In this work, we utilize coherent nanofocused X-rays to characterize stacking defects and strain in a single InGaAs nanowire supported on Si. By reconstructing diffraction patterns from the 21̅1̅0 Bragg peak, we show that the lattice orientation varies along the length of the wire, while the strain field along the cross-section is largely unaffected, leaving the band structure unperturbed. Diffraction patterns from the 011̅0 Bragg peak are reproducibly reconstructed to create three-dimensional images of stacking defects and associated lattice strains, revealing sharp planar boundaries between different crystal phases of wurtzite (WZ) structure that contribute to charge carrier scattering. Phase retrieval is made possible by developing multiangle Bragg projection ptychography (maBPP) to accommodate coherent nanodiffraction patterns measured at arbitrary overlapping positions at multiple angles about a Bragg peak, eliminating the need for scan registration at different angles. The penetrating nature of X-ray radiation, together with the relaxed constraints of maBPP, will enable the in operando imaging of nanowire devices.

Correlated Nanoscale Analysis of the Emission from Wurtzite versus Zincblende (In,Ga)As/GaAs Nanowire Core–Shell Quantum Wells

“…In the transition region close to the ZB interface (cyan), the diffraction spreads to high q y due to the interference between stacking variations that are smaller than the size of the projected beam. [41][42][43] This structure was observed in all eight NWs measured by nanoXRD. Indeed, a high density of short, alternating segments of WZ and ZB stacking, including stacking faults (SFs) and twins, have been reported for the transition from the ZB to the WZ phase.…”

Using automatic differentiation as a general framework for ptychographic reconstruction

“…Multi-angle Bragg projection ptychography (maBPP) [63] is a ptychographic experiment that allows for two degrees of freedom in the scan parameters: 1) the choice of the planar scan positions for the usual two-dimensional ptychographic scan, and 2) the choice of angular scan positions corresponding to small object rotations of a crystalline object oriented to satisfy a Bragg diffraction condition. The maBPP experiment uses the far-field ptychography setup, but with the detector placed to measure a crystalline Bragg peak, typically displaced from the direct beam by tens of degrees.…”

“…The corresponding change in the object-probe interaction can be encoded in terms of a phase shift operator defined as Q j = exp (ir · Q j ). The 2D exit wave is then given by [63] ψ j = RQ j (P (S j O)) ,…”

Three-Dimensional Imaging of Phase Ordering in an Fe-Al Alloy by Bragg Ptychography

“…In this Letter, we present the visualization of APD structures in three dimensions together with the associated general lattice strain. This is achieved by Bragg ptychography [21][22][23][24][25], which has shown robustness in retrieving images of materials exhibiting strong phase shifts [26], allowing us to compare and combine 3D images obtained at two different reflections, a fundamental and a superlattice peak, but originating from the same crystal grain. The superlattice peak is sensitive to both antiphase domain boundaries and phase variations from lattice strain and tilts while the fundamental peak is only sensitive to strain and tilts.…”