Influence of annealing on the optoelectronic properties of the GLAD synthesized SiO x –ZnO heterostructure nanoclusters
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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.
The authors would like to express their thanks to Dr. Ardhendu Saha, NIT Agartala, Department of Electrical Engineering, Tripura, India, for availing the optical absorption measurement facility, SAIF, Indian Institute of Technology, Bombay for providing FEG-SEM facility, SAIF NEHU for performing TEM characterization, NIT Manipur for providing photoluminescence measurement and XRD characterization facilities and NIT Nagaland for financial support.
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