Comparative Study of Residual Stress and Defects in Single‐Crystalline (0001) AlN Wafers by Scanning Infrared Depolarization and White‐Beam X‐ray Topography

The residual shear stress and the defect distribution in single‐crystalline c ‐plane AlN wafers prepared from crystals which were grown by physical vapor transport are visualized by scanning infrared depolarization (SIRD) and compared to synchrotron white‐beam X‐ray topography (WB‐XRT) measurements. Although at lower resolution, the SIRD images resemble the defect distribution seen in WB‐XRT, which provides an order of magnitude higher spatial resolution and, in this case, enables discerning individual dislocations. For a wafer prepared from a crystal grown at high lateral temperature gradients dT (5 K cm −1 ), the global maximum shear stress is determined to be about 6 MPa, and both SIRD and WB‐XRT reveal a global hexagram‐shaped pattern that is formed by prismatic glide of a‐type dislocations on m ‐planes while a wafer prepared from a crystal grown at low lateral dT (3 K cm −1 ) with a global maximum shear stress of 3 MPa does not show a similar pattern. The results are in good agreement with previous investigations that observed dislocation glide and additional cross glide in crystals with a two‐inch diameter grown at a dT of ≈5 K cm −1 .