Extended defects in wurtzite nitride semiconductors

A synthesis of the latest results on extended defects in wurtzite nitride semiconductors is presented. The principle defect type is that of threading dislocations, the majority of which are edge in character with their lines parallel to the growth direction and Burgers vector a. The other important defects which may influence the device performances are open core screw dislocations which in these materials have been called "nanopipes". Recently, it has been possible to grow unipolar GaN layers by a tight control of the buffer layers, therefore the inversion domain boundaries which cross the active layers can be eliminated. A large number of optical measurements has established that the crystallographic defects (dislocations, stacking faults,...) have an influence on the optical properties of the epitaxial layer. It is noted that better devices will be made in the near future using homoepitaxial GaN layers.