Stress relaxation mechanisms in mismatched epitaxial growth of HgCdTe

Stress relieving dislocations at heterojunctions are thought to introduce excess noise in Hg_(1-x)Cd_(x)Te infrared detectors. An understanding of dislocation formation in this material is useful in optimising device architectures, particularly on non-lattice matched substrates. A [211] Hg_(1-x)Cd_(x)Te/CdTe/Si epitaxial layer was grown by molecular beam epitaxy (MBE) and is investigated by asymmetric double crystal X-ray diffraction (DCXRD). Rocking curves are interpreted to give the lattice plane spacing and tilt of the epitaxial layer, both perpendicular to and in the plane of the interface. A quantitative model for strain relaxation is applied to the [211] HgCdTe system, so that the critical thickness at which edge dislocations form may be calculated. Interpretation of X-ray rocking curves show the strained layer to be partially relaxed, as would be expected from the critical thickness model.