Correlating Dislocation Structure with Local Optical Response in β-Ga2O3 Using Hyperspectral STEM Cathodoluminescence

Ultra-wide-bandgap semiconductors such as β-Ga2O3 exhibit exceptionally high breakdown electric fields for next-generation power electronics, yet device performance is often limited by crystallographic defects that introduce localized electronic states and impede charge carriers [1]. Establishing quantitative relationships between defect structure and optoelectronic response at the nanometer scale remains a key challenge for materials-by-design approaches in emerging electronic and quantum technologies [2]. Hyperspectral imaging (HSI) in the scanning transmission electron microscopy (STEM) mode enables spectrum-imaging modalities such as electron energy-loss spectroscopy (EELS) and cathodoluminescence (CL), providing a pathway to correlate structural and functional properties with nanometer-scale spatial resolution. Here, we combine transmission electron microscopy (TEM) phase-contrast imaging with STEM-based CL hyperspectral imaging to directly link point defects associated with dislocation loops to spatially resolved optical emission in a Si-doped β-Ga2O3 epitaxial film. Bright-field TEM (BF-TEM, Fig. 1a) acquired under two-beam conditions using the (310) reflection (g) reveals threading dislocations (TDs) consisting of prismatic dislocation loops (PDLs), which produce strong scattering and dark contrast. Weak-beam dark-field (WBDF) TEM acquired along the [001] (Fig. 1b) and [108] zone axes resolves the dislocation configuration and confirms the Burgers vector (b = [010]) of the TDs and the dislocation line direction of the edge component (a) based on the visibility criterion g⋅b×a=0 at selective reflections [3]. Theoretically, these PDLs form through the accumulation of point defects, such as vacancies or impurities, during epitaxial growth. Nanoscale CL spectra acquired via a line-scan across individual TDs (Fig. 1c) exhibit pronounced attenuation of emission intensity relative to the surrounding crystal (Fig. 2 a and b). Spectral decomposition using multiple Gaussian components (Fig. 2c) yields energy centers consistent with ultraviolet (UV) emission (≈ 3.5 eV) associated with self-trapped holes (STH, Fig. 2d) and blue emission (≈ 3.0 eV) mediated by (VGa + VO)-1 divacancies. A third component reveals spatially varying blue emission, including a blue-shifted feature (≈ 3.1 eV) attributed to octahedral-site VGa-1 (Fig. 2e) and a redshifted feature (≈ 2.7 eV) associated with the tetrahedral site VGa-2 (Fig. 2f) near adjacent TDs [4,5]. These variations in CL emission energy may have correlated with local Si dopant concentrations that modify defect formation energetics. These results demonstrate how cathodoluminescence-enabled HSI in the TEM provides access to local defect-mediated electronic states that are inaccessible using conventional optical probes and establishes a multimodal framework for nanoscale defect classification in wide- and ultra-wide-bandgap materials for power electronic applications. Phase contrast imaging of TDs in a β-Ga2O3 epitaxial film. (a) BF-TEM at the two-beam condition with the (310) reflection showing the epilayer grown on the β-Ga2O3 substrate, separated by the green dashed line. The inset shows the transmission electron diffraction patterns at the [001] and [108] zone axes, respectively, along with the selective reflections. The green arrows point at the same TDs seen in b. (b) WBDF using the “weak” (310) reflection showing the edge component of the PDLs within individual TDs. (c) Bright-field STEM showing the TD, across which the STEM-CL line-scan is measured. STEM-CL hyperspectral imaging across a TD. (a) BF-STEM indicating the line-scan across the TD. (b) Corresponding CL intensity-energy contour map across the TD denoted by the yellow line. (c) CL spectrum at position = -45 nm fitted using three Gaussian profiles. (d) Peak 2 indicates the UV emission associated with self-trapped holes (STH). (e) Peak 1 showing the blue emission associated with the (VGa + VO)-1 divacancies and the blue-shifted emission at the side of the TD bounded by another TD. (f) Peak 3 showing the blue emission associated with the (VGa + VO)-1 divacancies and the redshifted emission at the side of the TD without any other TD.