On the density of misfit dislocations in double-and triple-layer heterojunction devices

Abstract

The energy of a double layer heterojunction device consisting of a substrate and two epilayers is calculated. The expression for the total energy of the system includes the coherency strain energy and the strain energy of the dislocations. The densities of misfit dislocations at the two interfaces are given as functions of the thickness of the second epilayer. The theory is extended to a similar system consisting of a substrate and three epilayers. The general theory is applied to the special case of GaAs-Ga0.95Al0.05As compound heterojunction structures. It is shown that a double-layer system attains coherency for small values of the first epilayer thickness. In the case of three-layer systems it is shown that for certain values of first and second epilayer thicknesses coherency can be attained at the second interface by increasing the thickness of the third epilayer.