Metamorphic and non-conventional ‘buffer’ layers

The integration of large lattice mismatch materials through epitaxial growth requires the introduction of a controlled interface or transitional region, often referred to as a buffer layer. These, often relatively thick, transitional layers allow for a change in lattice parameter and a reduction in the threading dislocation density attributed to the required mismatch dislocations in the strain-relaxed materials. New designs for these transitional layers are emerging which allow for a reduction in buffer layer thickness, smoother morphology, and lower threading dislocation densities. These metamorphic buffer layers allowed the development of devices accessing new ranges of performance and, in the case of optical devices, wavelength regimes. The reduction of the buffer layer to a ‘single interface’ may be possible through the use of nano-patterning and advanced processing which provides control over the initial phases of nucleation and strain relaxation.