Improved GaN-on-Si epitaxial quality by incorporating various Si _xN_y interlayer structures

In this study, 1.61-μm-thick GaN/graded AlGaN/AlN epilayers were prepared on Si substrates by using metalorganic chemical vapor deposition. To determine whether the insertion of a Si_xN_y interlayer enhances the epitaxial quality of the GaN layer, various numbers of Si _xN_y interlayers were inserted at different locations, and the effects were investigated. In addition to analyzing crystal quality, epilayer stress was investigated in detail by performing Raman, photoluminescence, and curvature measurements. Inserting Si_xN _y into the AlGaN layer resulted in a deterioration in epitaxial quality and the appearance of serious surface cracks because of the concentration of Al atoms near pits, which enabled new and bigger centers of defects to form. A crack-free surface and relatively high crystal quality were achieved by inserting a Si_xN_y interlayer into a GaN epilayer; the resultant improvement in crystal quality was attributed to the bending and annihilation of dislocations. For a sample in which Si _xN_y was not inserted, Raman and photoluminescence measurements revealed that the stresses were 0.535 and 0.741 GPa, respectively. The addition of a single Si_xN_y interlayer into the GaN epilayer significantly reduced these stresses to 0.279 and 0.556 GPa, respectively.