Electron Channeling Contrast Imaging for Rapid III-V Heteroepitaxial Characterization

Abstract

Misfit dislocations in heteroepitaxial layers of GaP grown on Si(001) substrates are characterized through use of electron channeling contrast imaging (ECCI) in a scanning electron microscope (SEM). ECCI allows for imaging of defects and crystallographic features under specific diffraction conditions, similar to that possible via plan-view transmission electron microscopy (PV-TEM). A particular advantage of the ECCI technique is that it requires little to no sample preparation, and indeed can use large area, as-produced samples, making it a considerably higher throughput characterization method than TEM. Similar to TEM, different diffraction conditions can be obtained with ECCI by tilting and rotating the sample in the SEM. This capability enables the selective imaging of specific defects, such as misfit dislocations at the GaP/Si interface, with high contrast levels, which are determined by the standard invisibility criteria. An example application of this technique is described wherein ECCI imaging is used to determine the critical thickness for dislocation nucleation for GaP-on-Si by imaging a range of samples with various GaP epilayer thicknesses. Examples of ECCI micrographs of additional defect types, including threading dislocations and a stacking fault, are provided as demonstration of its broad, TEM-like applicability. Ultimately, the combination of TEM-like capabilities - high spatial resolution and richness of microstructural data - with the convenience and speed of SEM, position ECCI as a powerful tool for the rapid characterization of crystalline materials.

Reduced Dislocation Introduction in III–V/Si Heterostructures with Glide-Enhancing Compressively Strained Superlattices

“…TDD was determined via direct counting from electron channeling contrast imaging (ECCI) micrographs collected with a Thermo Scientific Quattro SEM using conditions and methods described previously. 25,29,30 To ensure statistically relevant quantification, large total area (∼10 000 μm 2 ) ECCI montages were composed, ensuring a raw count of at least 500 TDs per sample. 31 Mean TDD and standard error across all micrographs are reported herein.…”

“…High-resolution X-ray diffraction (XRD) reciprocal space mapping (RSM) was conducted in a Bede D1 triple-axis system using (224) and (004) reflections along both orthogonal ⟨110⟩ directions to assess relaxation/strain state of the epilayers. TDD was determined via direct counting from electron channeling contrast imaging (ECCI) micrographs collected with a Thermo Scientific Quattro SEM using conditions and methods described previously. ,, To ensure statistically relevant quantification, large total area (∼10 000 μm 2 ) ECCI montages were composed, ensuring a raw count of at least 500 TDs per sample . Mean TDD and standard error across all micrographs are reported herein.…”

A Route to Obtaining Low-Defect III–V Epilayers on Si(100) Utilizing MOCVD

“…The density of crystalline defects in the GaP/Si(100) virtual substrates should be minimized as it can impact the lifetime of the minority charge carriers and thereby the charge carrier diffusion lengths in the entire device. 16 In recent years, significant research has been carried out to achieve low-defect densities in the GaP buffer layers directly grown on Si(100) substrates for solar cell applications. 17−19 Defects in the GaP epilayer related to the polar-on-nonpolar epitaxy, 20 the so called antiphase domains, can be avoided by preparing the Si(100) substrates with a double-layer stepped surface.…”

Quantitative misfit dislocation characterization with electron channeling contrast imaging

“…Electron channeling contrast imaging (ECCI), a diffraction-based technique in the scanning electron microscope (SEM), has become an increasingly popular tool for characterization of defects in epitaxial heterostructures, especially in cases of lattice-mismatched growth. As an SEM-based measurement, ECCI is an attractive option compared to defect imaging in the transmission electron microscope: it is inherently non-destructive for plan-view measurements (no specimen thinning needed) and is able to probe large areas of material in a very short time [1]. Although this technique is regularly employed for qualitative characterization, its potential for accurate and statistically relevant quantitative characterization (beyond simple enumeration of threading dislocation density, TDD) is highly enticing.…”

“…In lattice-mismatched heterostructures, if the epilayer is sufficiently thin (< 200 nm), the strain-induced misfit dislocations (MDs) can be readily observed via ECCI [1]- [3]. Appearing in ECCI micrographs as straight lines with bright or dark contrast related to their specific Burgers vectors, MDs are easily segmented from the background using image processing software like MIPAR [4].…”