Structural and luminescence imaging and characterisation of semiconductors in the scanning electron microscope

Christian Kühn ,Gergely Ferenczi ,J. Bai ,M. Weyers ,L. Jiu ,M. Nouf-Allehiani ,Frank Mehnke ,Y Zhang,Y. Gong ,Tim Wernicke ,Aimo Winkelmann ,C. Trager-Cowan ,Matthew D. Smith ,David Thomson ,R. Mcdermott ,A. Knauer ,Sebastian Walde ,T Wang,Elena Pascal ,B. Hourahine ,P. R. Edwards ,P. J. Parbrook ,G. Naresh-Kumar ,S. Kraeusel ,Sylvia Hagedorn ,R. M. Smith ,Gunnar Kusch ,Johannes Enslin ,Michael Kneissl ,S. Vespucci ,Albes Kotzai ,P. A. Shields ,Jochen Bruckbauer ,Pierre-Marie Coulon ,Robert Martin ,W. Avis ,A. Alasmari

doi:10.1088/1361-6641/ab75a5

Abstract

The scanning electron microscopy techniques of electron backscatter diffraction (EBSD), electron channelling contrast imaging (ECCI) and cathodoluminescence (CL) hyperspectral imaging provide complementary information on the structural and luminescence properties of materials rapidly and non-destructively, with a spatial resolution of tens of nanometres. EBSD provides crystal orientation, crystal phase and strain analysis, whilst ECCI is used to determine the planar distribution of extended defects over a large area of a given sample. CL reveals the influence of crystal structure, composition and strain on intrinsic luminescence and/or reveals defect-related luminescence. Dark features are also observed in CL images where carrier recombination at defects is non-radiative. The combination of these techniques is a powerful approach to clarifying the role of crystallography and extended defects on a material’s light emission properties. Here we describe the EBSD, ECCI and CL techniques and illustrate their use for investigating the structural and light emitting properties of UV-emitting nitride semiconductor structures. We discuss our investigations of the type, density and distribution of defects in GaN, AlN and AlGaN thin films and also discuss the determination of the polarity of GaN nanowires.

Highlights

The ‘spots’ in the image, most of which exhibit a black-white contrast (B-W), are threading dislocations (TDs) propagating to the surface of the sample and are revealed due to associated strain fields [48]
While the contrast in the electron channelling contrast imaging (ECCI) micrograph reveals the presence of sub-grains, it does not provide any quantitative information on their orientation
We have illustrated the capabilities of the scanning electron microscope (SEM) techniques of ECCI, electron backscatter diffraction (EBSD) and CL which can be used to provide complementary information on material properties encompassing topography, structure, composition and light emission down to the nanoscale

Summary

Introduction

Less well known are the techniques of electron channelling contrast imaging (ECCI) [5,6,7,8,9,10,11,12] and electron backscatter diffraction (EBSD) [5, 6, 13, 14] which exploit diffraction to provide information on crystal structure, crystal misorientation, grain boundaries, strain and extended defects such as dislocations and stacking faults. Note that in order to reveal all misorientations, and all the sub-grain boundaries, a number of ECCI micrographs need to be acquired under a range of diffraction conditions [49].

Results

Conclusion