Cracking of III-nitride multiple heterostructures grown by MOVPE on 6H-SiC and α.-Al2O3

In this chapter, the authors focus on their studies carried out in order to throw more light on cracking mechanisms in device relevant Ill-nitride heterostructures. They investigate laser diode structures with regard to layer thickness as a critical parameter for onset of fracture, while afterwards detailed cracking behaviour was analysed by transmission electron microscope (TEM). Fracture behaviour of III-nitride laser diode heterostructures grown on 6H-SiC and α- Al₂O₃ is studied by TEM. TEM cross sectional and plan-view specimens were prepared by standard techniques and investigated in a Philips CM200 microscope at 200 kV. By growing a set of laser diode structures on 6H-SiC with increasing waveguide layer thickness the authors firstly intended to check if this tendency also holds for more complex heterostructures. Typical cracking patterns for both types of substrate consist of a hexagonal crack network corresponding to the GaN directions.