EFFICIENT VISIBLE-LIGHT EMISSION FROM SI/CAF2(111) HETEROSTRUCTURES GROWN BY MOLECULAR-BEAM EPITAXY

The elaboration by molecular beam epitaxy of a new luminescing Si-based material is presented, i.e. small grain polycrystalline Si/CaF2 multi-quantum wells. The static luminescence properties are studied as a function of Si layer thickness, and the time dependent luminescence features as a function of wavelength and temperature. There is a rather striking similarity with the photoluminescence of porous Si, both in spectral position as in decay dynamics. The disappearance of the luminescence when the Si layers become too thick, and the blue-shift of the spectra when the Si layer thickness decreases, favour the quantum confinement hypothesis for the origin of the light emission. The important role of oxygen as passivating agent after ageing in air, is also pointed out.