Structural and optical properties of strain-relaxed InAsP/InP heterostructures grown by metalorganic vapor phase epitaxy on InP(001) using tertiarybutylarsine

Abstract

A combination of transmission electron microscopy and high-resolution x-ray diffraction analyses has been used to determine the exact strain in each layer of InAsP/InP multiple-quantum-well structures grown by metalorganic vapor phase epitaxy on InP(001) using trimethylindium, tertiarybutylarsine, and phosphine as precursors. The strain-relaxed structures are characterized by misfit dislocations located exclusively at (i) the interface between the buffer layer and the multilayer, and (ii) the interface between the multilayer and the cap layer. The low-temperature optical absorption spectra show well resolved excitonic transitions that are significantly shifted by strain relaxation. The spectra are analyzed with a solution to the Schrödinger equation in the envelope function formalism using the Bastard–Marzin model. The energies for the major transitions involving light- and heavy-holes are predicted accurately for all samples, allowing the determination of the heterojunction band offset. The heavy- and light-hole exciton binding energies deduced from that analysis range from 5 to 7 meV and 2 to 5 meV, respectively. The absolute values of the conduction band offset (expressed in meV) are consistent with the predictions of the quantum dipole model [J. Tersoff, Phys. Rev. B 30, 4874 (1984)] when calculating the midgap energy using a linear interpolation for the InAsP ternary composition between the values for the binaries InAs and InP. The absolute value of conduction band offset (in meV), which is dictated by the composition of the ternary layer, does not significantly depend on the degree of strain relaxation of the multilayer. However, the effect of this strain-relaxation on the InP and InAsP band gaps causes the conduction band offset to apparently increase from 72 to 82% of the partially-strained band gap difference when the strain-relaxation increases from 0 to 17%.