Correlation between Morphological Structure and Optoelectronic Properties of Al 2 O 3 thin layer coated silicon nanowires

This study reports on correlation between morphological structure and optoelectronic properties of Al 2 O 3 /silicon nanowires (SiNWs). The SiNWs were prepared from etching a silicon substrate via a silver supported chemical etching (Ag-SCE), then layered by an Al 2 O 3 ultrathin film (about 80 nm) by means of the pulsed laser deposition (PLD) process. Scanning electron microscopy (SEM) observations shows a non-linear dependence of the length of the SiNWs on etching time (10 to 40 min), while individual SiNWs have relatively rough sidewalls with a diameter in the range of ~10–15 nm. The total reflectivity of the SiNWs was found to depend on their length and diameter; it decreases from ~35% to about ~10% (in the 600–1100 nm range) as etching time varies from 10 to 40 min. The reflectivity of the Al 2 O 3 /SiNWs nanostructures was found to stabilize around 10% - 15% for all etching times (10–40 min). A Raman redshift was observed as etching time decreases and was attributed to a spatial confinement in thinner SiNWs. The photoluminescence (PL) emission of the Al 2 O 3 /SiNWs nanocomposite shows two bands, red and blue, attributed to quantum confinement of photogenerated carriers in thin SiNWs and to defects related to SiOx formed on the sidewalls of SiNWs via the oxidizing capability of the Al 2 O 3 material, respectively.