The determination of Raman modes in the range between 280 and 500 cm−1 for a BaSi2(100) epitaxial film on a Si(001) substrate has been accomplished by polarized Raman measurements using a crystal rotation method. The six Raman lines from Si clusters in BaSi2 were observed in the range. In the analysis of their intensity changes as a function of crystal rotation angle based on the Raman tensors of the Si cluster, the six Raman internal modes of A1 (1), E (2), and F2 (3) were completely assigned to the observed Raman lines.

This article describes the development of an Si-based light-emitting diode with β-FeSi2 nanocrystals embedded in the active layer. Favorable epitaxial conditions allow us to obtain a direct band gap type-I band alignment Si/β-FeSi2 nanocrystals/Si heterostructure with optical transition at a wavelength range of 1500–1550 nm at room temperature. Transmission electron microscopy data reveal strained, defect-free β-FeSi2 nanocrystals of diameter 6 and 25 nm embedded in the Si matrix. Intense electroluminescence was observed at a pumping current density as low as 0.7 A/cm2. The device reached an optical emission power of up to 25 μW at 9 A/cm2 with an external quantum efficiency of 0.009%. Watt–Ampere characteristic linearity suggests that the optical power margin of the light-emitting diode has not been exhausted. Band structure calculations explain the luminescence as being mainly due to radiative recombination in the large β-FeSi2 nanocrystals resulting from the realization of an indirect-to-direct band gap electronic configuration transformation arising from a favorable deformation of nanocrystals. The direct band gap structure and the measured short decay time of the luminescence of several tens of ns give rise to a fast operation speed for the device. Thus a method for developing a silicon-based photonic integrated circuit, combining complementary metal-oxide-semiconductor technology functionality and near-infrared light emission, is reported here.

Direct transition energy (Eg) of β-FeSi2/Si(111) epitaxial films grown at different growth temperatures (Ts) was investigated by photoreflectance (PR) measurements. In Raman spectra, the wavenumber of Ag-mode in Fe-Fe and Si-Si vibrations shifted to higher wavenumber with decrease of Ts. The estimated Si/Fe composition ratio of the epitaxial layer became small (Si-poor) in the films grown at lower Ts. In PR spectra, Eg shifted to higher energy with decrease of Ts. These results show that the modification of electronic structure by a strain induced at β-FeSi2/Si hetero-interface is suppressed by an increase of Si vacancies in β-FeSi2.

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