Impact of arsenic species (As_2/As_4) on the relaxation and morphology of step-graded InAs_xP_(1-x) on InP substrates

摘要

The influence of arsenic species (As_2 or As_4) on compositionally graded InAs_xP_(1-x) buffer layers (x=0.15 -0.8) grown by molecular beam epitaxy on InP is investigated. It was found that As_2 has a higher incorporation rate than As_4. Anisotropic strain relaxation occurs for samples grown with As_4, with higher relaxation along [110] and lower relaxation along [1—10]. Relatively high and isotropic strain relaxation occurs for buffers grown with As_2. The observed mosaic broadening is much greater when using As_2. Atomic force microscopy morphological features are consistent with the strain relaxation results. Strong corrugations along [1-10] dominate the surface of films grown with As_4, while grainy surfaces occur with As_2. The use of As_4 increased the overall surface roughness. The authors interpret these results with a simple model: the higher incorporation rate of As_2 enables In to incorporate more uniformly in the two perpendicular < 110 > directions, while the lower incorporation rate of As_4 decreases this uniformity. The different incorporation rates of In in the [110] and [1-10] directions may result in diverse morphologies and strain relaxation induced by arsenic spices.