Mass-separated 56Fe+ ions were implanted into Si(100) at 350°C using three different energies and doses of 140 keV (1.32×1017 cm-2), 80 keV (6.20×1016 cm-2), and 50 keV (3.56×1016 cm-2). Their optical properties were investigated as a function of subsequent annealing temperature and its duration time. X-ray diffraction analysis revealed that polycrystalline semiconducting β-FeSi2 layers are formed in the as-implanted and annealed samples. From Rutherford backscattering spectrometry analysis, the formation of β-FeSi2 up to the surface was confirmed, and the average thickness and composition of the layers at peak concentration were estimated to be 70-75 nm and Fe:Si = 1:2.0-2.2, respectively. The types of optical transition and the inverse logarithmic slope (E0) of the Urbach tail were investigated using room temperature optical absorption measurements. All the synthesized β-FeSi2 layers exhibited a direct transition with direct band-gap energies (Edir g) of 0.802-0.869 eV and with high optical absorption coefficients extending to 105 cm-1 at photon energy above 1.0 eV. The E0 value characteristic of the Urbach tail was observed to decrease from 260 to 100 meV with elevating annealing temperature. Some of the materials having E0<160 meV showed two strong photoluminescence (PL) emissions peaked at 0.805-0.807 eV (No. 1) and 0.840-0.843 eV (No. 2) at 2 K, whereas those with E0>250 meV exhibited only weak emissions. From the results of the temperature- and excitation power-dependent PL measurements, emissions Nos. 1 and 2 were attributed to the trap-related recombinations related to β-FeSi2, with thermal activation (quenching) energies of 54.7 and 46.7 meV, respectively.
|ジャーナル||Journal of Applied Physics|
|出版ステータス||Published - 1996 11 15|
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