Formation and properties of Al/Mg₂Si/Si/Au–Sb photodiode structures

Under ultra-high vacuum conditions, thick polycrystalline Mg₂Si films with thicknesses of 496 and 692 nm were grown on Si (111) substrates by the layer-by-layer co-deposition of pairs of Mg and Si layers at a temperature of 250 °C on a pre-formed amorphous buffer Si layer. The formation of the crystalline Mg₂Si was confirmed by Raman spectroscopy data. The absorption coefficient spectrum was calculated from the transmission and reflection spectra obtained by optical spectroscopy, which made it possible to determine the width of the indirect band gap in Mg₂Si films (0.80-0.86 eV) and determine the first direct interband transition with an energy of 1.09-1.10 eV, consistent with the literature data. Based on the grown films, photodiode structures were fabricated, for which dark current-voltage characteristics (CVC) and photoresponse spectra were measured under various biases on an Al/Mg₂Si/Si/Au-Sb heterostructure. The analysis of the CVC and photoresponse spectra showed that the characteristics are very different from those for a standard silicon p-n junction. The dependence of the photoresponse spectra on the sign and magnitude of the bias has been established. The main feature is the narrow spectral characteristic of the photoresponse at 1050 nm, which is absent in the silicon photodiode. Analysis of the data showed that during high-temperature annealing of silicon, a double p-n junction with a barrier layer is formed in it, which, together with the Mg₂Si/Si- p heterojunction, determines the unique properties of the created heterostructure.

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