Study of ErAs/GaAs strained-layer structures using optical absorption.

The crystal-field splittings recently observed in the Er-related optical absorption spectra of ErAs films grown on GaAs molecular-beam epitaxy are further in investigated with respect to their applicability in characterizing strain accommodation in ErAs/GaAs multilayer structures. Rutherford backscattering axial channeling measurements are used directly assess strain accommodation in the epitaxial films. The crystal-fields splittings observed in room-temperature absorption spectra of samples containing thick strain-relieved ErAs layers are consistent with the cubic (O h) symmetry expected for the Er lattice site in unstrained ErAs. In sharp contrast, a multilayer structure containing two-monolayer-thick, coherently strained ErAs layers shows pronounced changes in the energies, linewidths, and relative intensities of the crystal-field-spectral lines, as well as the appearance of additional weak absorption lines. This behavior is attributed to strain-induced distortion of the crystal fie ld in which the rare-earth ions reside. The relative influence of hydrostatic and uniaxial strain components on the optical spectra is discussed.