DISLOCATION NUCLEATION MECHANISM IN NITROGEN-DOPED ZNSE GAAS

A new source for heterogeneous nucleation of 60-degrees-type misfit dislocations in ZnSe has been observed for the first time. This is identified as Frank-type partial dislocations bounding stacking faults induced by N doping at the initial stages of growth. Some of the Frank partials also act as pinning centres to produce threading dislocations on the relaxed N-doped ZnSe/GaAs heterostructures. In situ electron-beam-induced heating studies were carried out to observe the strain relaxation mechanism in the epitaxial layers. These studies show that by dissociation of a (a/3) [111BAR] Frank partial dislocation on the (111BAR) plane, a (a/2) [101] 60-degrees mixed dislocation and a (a/6) [121BAR] Shockley partial dislocation are produced. The Shockley partial dislocation expands along the faulted plane and interacts with the (a/3) [111BAR] Frank partial dislocation in the fault. This interaction produces a second segment of (a/2) [101BAR] 60-degrees mixed dislocation. The two 60-degrees mixed dislocation segments glide on a (111BAR)-type plane until they reach the interface and form 60-degrees interfacial misfit dislocations with two threading segments. Thus, after strain relaxation is fully achieved, a regular array of 60-degrees misfit dislocations, attached to some non-dissociated Frank partial dislocations, is produced on the N-doped ZnSe-GaAs interface for samples with film thicknesses larger than the critical thickness.