STUDY OF ERAS/GAAS STRAINED-LAYER STRUCTURES USING OPTICAL-ABSORPTION AND ION CHANNELING

The crystal-field splittings recently observed in the Er-related optical absorption spectra of ErAs films grown on GaAs by molecular-beam epitaxy are further investigated with respect to their applicability in characterizing strain accommodation in ErAs/GaAs multilayer structures. Rutherford backscattering axial channeling measurements are used to directly assess strain accommodation in the epitaxial films. The crystal-field splittings observed in room-temperature absorption spectra of samples containing thick strain-relieved ErAs layers are consistent with the cubic (Oh) 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-split spectral lines, as well as the appearance of additional weak absorption lines. This behavior is attributed to strain-induced distortion of the crystal field in which the rare-earth ions reside. The relative influence of hydrostatic and uniaxial strain components on the optical spectra is discussed.