Structural and optical characterization of CdSe nanocrystals (NCs) embedded into a porous silicon nanostructure

The aim of this work is to study the effect of cadmium selenide nanocrystals (CdSe NCs) incorporation into porous silicon (PS) on its structural and opto-electronic properties using a simple method. We focused our investigation on the effect of thermal annealing after the deposition of CdSe into the (PS) layer. Obtained results prove the beneficial role of this treatment and its dependence with temperature. The CdSe NCs was incorporated into the PS layer by spin coating method and then annealed in ambient atmosphere for 30 min at different temperatures between 150 and 300 °C. The effect of thermal annealing on the structural and optical properties of the treated PS with CdSe NCs was investigated using Fourier transmission infrared spectroscopy (FTIR), X-ray diffraction (XRD), Scanning electron microscope (SEM), UV-vis-NIR spectrometer, WTC-120 lifetime tester and PL spectroscopy. The X-ray diffraction results clearly revealed the phase transformation of the deposited CdSe from metastable nanocrystalline cubic (zinc blende type) to a mixture of cubic and hexagonal (wurtzite type), and finally into stable hexagonal. A decrease in the reflectivity was obtained after incorporating the CdSe NCs onto the PS layers, before and after annealing. The samples PS treated with CdSe NCs show an important enhancement in the minority carrier lifetime (τeff) indicating an improved surface quality in comparison with the untreated sample (reference). The photoluminescence intensity shows an obvious dependence with the variation of the annealing temperature compared to the untreated porous silicon layer.