Nucleation mechanism of misfit dislocations in multi-quantum wells

Abstract

A series of plan-view and cross-section samples of multi-quantum wells (MQWs) consisting of 32nm GaAs and 10.5nm In0.15Ga0.85As grown by molecular beam epitaxy on GaAs substrates were examined by TEM. Tne number of periods (n) of the MQWs were 3, 6, 12, 24, and 48. The results showed that for n smaller than or equal to 12 periods, almost all misfit dislocations (MDs) were found near the epitaxial surface (see figure 1) which is far away from the interface between the MQWs and the substrate; but for n equal to or larger than 24 periods, most MDs were observed at the bottom interface between the MQWs and the substrate (shown in figure 2).To explain these observations, a new nucleation mechanism for the MDs has been derived from energy considerations, based on the theory of the critical thickness of the half circular dislocation loop (HCDL) in a single epitaxial layer and the strain contribution in the MQWs.