A comparative study of non-destructive techniques for estimating dislocation densities in heteroepitaxial AlN layers

The threading dislocation density is an important quality metric for semiconductor layers. This work presents a comparative study of three non-destructive analytical techniques employed to analyze 200 nm thick aluminum nitride layers with high threading dislocation densities (∼10¹⁰ cm⁻²) deposited via metalorganic vapor phase epitaxy on Si-polar 4° off-cut N-doped 4H-SiC. X-ray diffraction (XRD), atomic force microscopy (AFM), and electron channeling contrast imaging (ECCI) are utilized to determine the threading dislocation densities of three samples grown under different V/III ratios. The XRD-based analysis using only 0002 and 101̅ 2 rocking curves significantly underestimates dislocation densities relative to AFM and ECCI, while the approach based on a series of skew-symmetrical rocking curves proves to be more accurate but still yields lower values. The underestimation is consistent with known XRD artifacts, such as correlation effects that lead to narrower XRD rocking curves. Techniques capable of local characterization (AFM and ECCI) reveal similar threading dislocation densities, with ECCI yielding slightly lower values, likely due to reduced contrast of some edge dislocations. A correlative AFM–ECCI measurement from the same location underscores the agreement between local characterization techniques. Additionally, the results demonstrate ECCI's effectiveness for real-world characterization of thin layers with high dislocation densities grown on foreign substrates.