EXTENDED DEFECTS IN WURTZITE NITRIDE SEMICONDUCTORS

A synthesis of the latest results on extended defects in wurtzite nitr ide semiconductors is presented. The principle defect type is that of threading dislocations, the majority of which are edge in character wi th their lines parallel to the growth direction and Burgers vector a. The other important defects which may influence the device performance s 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 inve rsion domain boundaries which cross the active layers can be eliminate d. A large number of optical measurements has established that the cry stallographic defects (dislocations, stacking faults,...) have an infl uence on the optical properties of the epitaxial layer. It is noted th at better devices will be made in the near future using homoepitaxial GaN layers.