TiO2–silicon nanowire arrays for heterojunction diode applications

• SiNWs presents large scale and high porosity, aligned vertically on the Si wafer surface.
• HRTEM image and SAED pattern of TiO2 layer shows polycrystalline nature and anatase structure.
• Optoelectronic performances of n-TiO2/p-SiNWs heterojunction have been investigated.
• The length of SiNWs arrays is shorter, the resistance is lower, has the best cell performance.

Vertically aligned silicon nanowire (SiNW) arrays are synthesized using low-cost Ag-assisted electro-less etching on p (100) Si wafer substrates. The SiNW arrays exhibit large scale and high porosity, as shown by the SEM image of SiNWs aligned vertically on the surface of a Si wafer. The n-TiO2/p-SiNWs heterojunction diode is fabricated using radio frequency magnetron sputtering of a TiO2 thin film (about 150 nm) onto vertically aligned p-Si nanowire arrays. The TiO2 modification increases the surface energy of the SiNW arrays. The high-resolution transmission electron microscopy (HRTEM) image and the corresponding selected area electron diffraction (SAED) pattern for the TiO2 layer show polycrystalline characteristics and the crystal structure of TiO2 layer is anatase. The optoelectronic performance of n-TiO2/p-SiNWs heterojunction is determined using current-voltage (I-V) measurements. There is a well-defined rectifying behavior with a low turn-on voltage of about 0.8 V in forward bias. The experimental results show that the SiNW arrays are shorter and the resistance is lower, which gives better cell performance.