Transmission electron microscope study of semiconductor heterostructures grown by molecular beam epitaxy

Chin Choi, Purdue University

Abstract

At present the growth of lattice mismatched heterostructures is attracting many interests because of the possibility of development of a variety of new semiconductor devices. Until recently, the control of growth of such systems has solely relied on theories which predict the accommodation of lattice mismatch based on the energetic factor. Recent studies, however, suggest the significance of kinetic factor involved in generation and migration of misfit dislocations. It is the object of the present study to understand how the formation of misfit dislocations is determined by the energetic and kinetic factors, in systems grown by molecular beam epitaxy. Three (100) heterostructure systems, ZnSe/GaAs, GaAs/Si and CdTe/GaAs, have been studied by transmission electron microscopy. This is the first study which has directly analyzed structures of misfit dislocations in various semiconductor interfaces with a wide range of lattice mismatch. Two different types of misfit dislocations are observed. The type I misfit dislocations have Burgers vectors parallel to the interface. They are energetically favorable for misfit accommodation but less favorable for the formation because of their sessile nature. The type II misfit dislocations have Burgers vectors inclined to the interface. They are energetically unfavorable but kinetically favorable because both Burgers vectors and dislocation lines lie on the slip plane. The present study has revealed a remarkably close correlation between the type of dominant misfit dislocations and the size of lattice mismatch. In ZnSe/GaAs with a 0.25% lattice mismatch, the majority of misfit dislocations are identified as type II. In CdTe/GaAs with a 14.6% lattice mismatch, all observed misfit dislocations are type I. In GaAs/Si with a 4% lattice mismatch, both types of misfit dislocations are observed, while the annealing leads to the dominance of type I misfit dislocations. These observations suggest that the formation of misfit dislocations is more kinetically controlled as the size of lattice mismatch becomes smaller while the energetic factor is still dominant in the systems with large lattice mismatch. The results of these observation are discussed, along with those of other semiconductor systems, based on the theories developed recently.

Degree

Ph.D.

Advisors

Otsuka, Purdue University.

Subject Area

Materials science

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