Materials properties and dislocation dynamics in InAsP compositionally graded buffers on InP substrates

The properties of InAsxP1−x compositionally graded buffers grown by metal organic chemical vapor deposition are investigated. We report the effects of strain gradient (e/thickness), growth temperature, and strain initiation sequence (gradual or abrupt strain introduction) on threading dislocation density, surface roughness, epi-layer relaxation, and tilt. We find that gradual introduction of strain causes increased dislocation densities (>106/cm2) and tilt of the epi-layer (>0.1°). A method of abrupt strain initiation is proposed which can result in dislocation densities as low as 1.01 × 105 cm−2 for films graded from the InP lattice constant to InAs0.15P0.85. A model for a two-energy level dislocation nucleation system is proposed based on our results.