OPTICAL-ABSORPTION AND PHOTOLUMINESCENCE STUDIES OF BETA-FESI2 PREPARED BY HEAVY IMPLANTATION OF FE+ IONS INTO SI

Mass-separated Fe-56(+) ions were implanted into Si(100) at 350 degree s C using three different energies and doses of 140 keV (1.32X10(17) c m(-2)), 80 keV (6.20X10(16) cm(-2)), and 50 keV (3.56X10(16) cm(-2)). Their optical properties were investigated as a function of subsequent annealing temperature and its duration time. X-ray diffraction analys is revealed that polycrystalline semiconducting beta-FeSi2 layers are formed in the as-implanted and annealed samples. From Rutherford backs cattering spectrometry analysis, the formation of beta-FeSi2 up to the surface was confirmed, and the average thickness and composition of t he layers at peak concentration were estimated to be 70-75 nm and Fe:S i=1:2.0-2.2, respectively. The types of optical transition and the inv erse logarithmic slope (E(0)) of the Urbach tail were investigated usi ng room temperature optical absorption measurements. All the synthesiz ed beta-FeSi2 layers exhibited a direct transition with direct band-ga p energies (E(g)(dir)) of 0.802-0.869 eV and with high optical absorpt ion coefficients extending to 10(5) cm(-1) at photon energy above 1.0 eV. The E(0) value characteristic of the Urbach tail was observed to d ecrease from 260 to 100 meV with elevating annealing temperature. Some of the materials having E(0)<160 meV showed two strong photoluminesce nce (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 emi ssions. From the results of the temperature- and excitation power-depe ndent PL measurements, emissions Nos. 1 and 2 were attributed to the t rap-related recombinations related to beta-FeSi2, with thermal activat ion (quenching) energies of 54.7 and 46.7 meV, respectively. (C) 1996 American Institute of Physics.