Background: It is well-known that multi-layer films with nanostructure can give novel
properties by interfacial phenomenon and quantum confinement effects. Nanostructured multi-layer
thin films are presently being analyzed for their vast applications in the area of optoelectronics technology
particularly photovoltaics. Hereof, two dimensional thin films with nanostructure are of prime
importance due to their structure dependent optical, electrical, and opto-electronic properties. It has been revealed that
these films exhibit quantum confinement effects with band gap engineering. The main focus of the research is to evaluate
the effect on structural and optical properties with number of layers.
Methods: Nanostructured SnO2-Ge multi-layer thin films were fabricated using electron beam evaporation and resistive
heating techniques. Alternate layers of SnO2 and Ge were deposited on glass substrate at a substrate temperature of 300 °C
in order to obtain uniform and homogeneous deposition. The substrate temperature of 300 °C has been determined to be
effective for the deposition of these multi-layer films from our previous studies. The films were characterized by investigating
their structural and optical properties. The structural properties of the as-deposited films were characterized by Rutherford
Backscattering Spectroscopy (RBS) and Raman spectroscopy and optical properties by Ultra-Violet-Near infrared
Results: RBS studies confirmed that the layer structure has been effectively formed. Raman spectroscopy results show
that the peaks of both Ge and SnO2 shifts towards lower wavenumbers (in comparison with bulk Ge and SnO2, suggesting
that the films consist of nanostructures and demonstrate quantum confinement effects. UV-VIS-NIR spectroscopy
showed an increase in the band gap energy of Ge and SnO2 and shifting of transmittance curves toward higher wavelength
by increasing the number of layers. The band gap lies in the range of 0.9 to 1.2 eV for Ge, while for SnO2, it lies between
1.7 to 2.1 eV.
Conclusion: Analysis of results suggests that the nanostructured SnO2-Ge multi-layer thin film can work as heterojunction
materials with quantum confinement effects. Accordingly, the present SnO2-Ge multi-layer films may be employed for
photovoltaic applications. Few relevant patents to the topic have been reviewed and cited.