Structural, Electrical and Optical Characterization of Crystal ErAs Layers Grown on GaAs by MBE Single-

A detailed study is presented of the structural, electrical, and optical prope~ies of ErAs films grown on GaAs by molecular beam epitaxy (MBE). ErAs layers 1500A thick were grown successfully over a relatively wide range of substrate temperatures (420-580 ~ C), although overgrowth of GaAs on ErAs was found to be difficult. In-situ reflection highenergy electron diffraction (RHEED), x-ray diffraction, and Rutherford backscattering (RBS) measurements all indicate single crystal growth. Analysis of X-ray rocking curves reveals that, over the range of substrate temperatures studied, strain due to the lattice mismatch between ErAs and GaAs is completely inelastically relieved in the 1500/k thick ErAs layers. Variable-temperature Hall measurements reveal metallic behaviour in all samples, with no pronounced dependence on substrate temperature. Spectrally narrow (0.6 meV) intra 4f-shell transitions of Er 3§ (4f1~), at 1.54 ~m, have been observed in ErAs epitaxial layers both in absorption (by Fourier transform infra-red spectroscopy, FTIR) and in emission (by cathodoluminescence). The crystal-field splittings observed in the FTIR spectra are consistent with the cubic (Oh) symmetry expected for the Er lattice site in unstrained ErAs, in good agreement with the x-ray analyses.