Strain relief and dislocation motion in III-nitride films grown on stepped and step-free 4H‐SiC mesas

The impetus for dislocation motion in thin films is generally understood in terms of Peach-Koehler forces. For the case of III-nitride films grown on step-free 4H-SiC mesas, however, it is the gradient of the strain energy from the mesa edge that is capable of driving misfit dislocations. Using the strain profile as a function of the distance from the mesa edge and the line tension of the c-plane threading arms, we have calculated the excess stress driving the half loop from the mesa edge into the mesa interior. We have also compared the half-loop excess stress with the excess stress driving the tilt of threading edge dislocations, which has been proposed as one of the principal strain relief mechanisms in III-nitride films. The excess stress driving c-plane half loops ranges from a few 1000MPa at the mesa edge to few 100MPa towards the mesa interior, while the excess stress driving the tilt of threading edge dislocations is in excess of 20000MPa. The greater excess stress driving dislocation tilt, however, does not dominate strain relief for III-nitride films on step-free SiC mesas due to the difficulty in nucleating threading dislocations in the absence of interfacial steps.