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

Abstract

The properties of InAs [subscript x]P1[subscript −x] compositionally graded buffers grown by metal organic chemical vapor deposition are investigated. We report the effects of strain gradient (ε/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 (>10[superscript 6]/cm[superscript 2]) 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 × 10[superscript 5] cm[superscript −2] for films graded from the InP lattice constant to InAs [subscript 0.15]P[subscript 0.85]. A model for a two-energy level dislocation nucleation system is proposed based on our results.