Influence of annealing on the optoelectronic properties of the GLAD synthesized SiO _x –ZnO heterostructure nanoclusters

Abstract

We utilized Glancing angle deposition (GLAD) technique to synthesize SiO _x –ZnO heterostructure nanoclusters. The as deposited heterostructure nanoclusters were annealed at 550 °C for 1 h in an open air using heating and cooling ramp of 5°C min⁻¹. The FEG-SEM image represents the uneven growth of SiO _x –ZnO heterostructure nanoclusters. Due to the agglomeration of smaller nanocluster, SiO _x –ZnO heterostructure nanoclusters become more prominent after annealing. EDX indicates the presence of O, Si and Zn. The increase in the concentration of oxygen in annealed SiO _x –ZnO heterostructure nanoclusters is attributed to the absorption of O₂ molecules during an open air annealing. The formation of heterostructure is shown by the TEM image. The nanoclusters consist of SiO _x and ZnO indicating the length of ~ 126 and ~ 97 nm, respectively. The SAED pattern depicts the crystalline nature of ZnO nanoclusters. The XRD pattern revealed that ZnO nanoclusters had wurtzite structure with (100), (002) and (101) orientations. The PL emission at 420 nm is ascribed to the radiative recombination of photoexcited electrons in the conduction band (CB) of ZnO and acceptor such as traps present in SiO _x . The band gap significantly increases to 3.45 eV after annealing and it corresponds to main band gap of ZnO. The FTIR result shows the bonding of SiO _x –ZnO heterostructure nanoclusters. In addition to the above measurement, we determined the I–V characteristics of the as deposited and annealed SiO _x –ZnO heterostructure nanoclusters. The as deposited sample shows schottky behavior which is applicable for nanoscale optoelectronic devices whereas the ohmic nature obtained after open air annealing is suitable for the application of solar cells.