OPTICALLY ACTIVE SI SURFACES

The optoelectronics and photonics properties of silicon are fundamentally influenced by the density of carriers present near the sample surface. One way of generating very large densities of such carriers is to confine them in a Si nanolayer made by implantation followed by a suitable thermal treatment. In that way, one can photo-generate a two dimensional (2D) plasma which modifies the complex refractive index of the nanolayer. Our work describes the modification of the reflection and absorption induced by incident light in the same devices when varying their electronic passivation. The different studied samples contain a buried amorphous substructure and are distinguishable exclusively by the thickness of the SiO2 covering layer. The measurements of the different samples show large differences in their absorption coefficients. The absorption coefficient a measured at 450 nm for a Si sample with a thin passivation layer is alpha similar to 4.0x10(4) cm(-1) that is nearly 5 times lower than a sample which is processed with a complementary passivation alpha similar to 1.8x10(5) cm(-1). In both cases average flux of photons (10(15) s(-1) cm(-2)) is the same. This result confirms the role of the free-carrier population, induced by the incident light, which is confined near the surface. In the conventional modeling of the absorption only the surface recombination rate governed by the thickness of the SiO2 covering layers has to be taken into account [1]. In the present work, we show that the carrier confinement also plays an important role. Such results are very interesting in the context of optoelectronics and photonics silicon nanostructured devices.