Chirped Superlattices as Adjustable Strain Platforms for Metamorphic Semiconductor Devices

Abstract

Chirped superlattices are of interest as buffer layers in metamorphic semiconductor device structures, because they can combine the mismatch accommodating properties of compositionally-graded layers with the dislocation filtering properties of superlattices. Important practical aspects of the chirped superlattice as a buffer layer are the surface strain and surface in-plane lattice constant. In this work we studied two basic types of InGaAs/GaAs chirped superlattice buffers; type I is compositionally modulated while type II is thicknesses modulated. For both types, we have investigated the equilibrium surface strain and surface in-plane lattice constant, and have compared the behavior to linearly-graded buffers having the same top target composition of indium.