Engineering of CdxZn1–xS Nanomaterials for Fabrication of Hybrid CdxZn1–xS/Si Heterojunction Broadband Photo Detectors

Effective engineering of nanostructured materials provides a scope to explore the underlying photoelectric phenomenon completely. A simple cost-effective chemical reduction route is taken to grow nanoparticles of Cd _x Zn_1-x S with varying x = 1, 0.7, 0.5, 0.3, and 0. X-ray diffraction confirms the formation of different phases of targeted Cd _x Zn_1-x S, while field emission scanning electron microscopy shows change of nanostructures. Energy-dispersive X-ray spectroscopy determines the composition of the grown nanostructures as CdS, Cd_0.7Zn_0.3S, Cd_0.5Zn_0.5S, Cd_0.3Zn_0.7S, and ZnS. The optical absorption study determines the band gap shift with change of composition as well as with quantum confinement. The fluorescence lifetime for each nanomaterial is determined by time-correlated single photon counting, and Raman analysis revealed that ZnS exhibits the highest blue shift. Thus, there is a possibility to apply such grown nanomaterials for fabrication of heterojunction-based photodetectors (PDs) in a broad wavelength region. Cd _x Zn_1-x S nanostructures on n-type bulk silicon (Si) were successfully fabricated by a simple cost-effective spin coating method and present hybrid heterojunction PDs. The fabricated p-n heterojunction exhibits good rectifying behavior at room temperature under a reverse bias condition. Also, it was observed that the heterojunction is extremely sensitive to the irradiation of visible light because of the significant optoelectric effect with a good I _light/I _dark ratio (here, I _light is the current in the presence of light and I _dark is the dark current), quick response time (40 to 1005 ms), and good reproducibility (three cycles of I _light/I _dark for each sample are observed). It was observed that the responsivity value gradually decreases for x = 1 to x = 0 in the Cd _x Zn_1-x S/n-Si heterojunction, i.e., it is maximum for CdS NRs (6.74 × 10^-3 mA/W), intermediate for Cd_0.5Zn_0.5S NPs (4.49 × 10^-3 mA/W), and minimum for ZnS NPs (2.72161 × 10^-4 mA/W). A similar nature has been observed in the case of detectivity, and hence it is a maximum (1.45 × 10⁶ Jones) for CdS NRs. The photocurrent generation at the heterojunction showed excellent "on" and "off" switching behavior in the presence and absence of light illumination. Response time and gain change significantly with change of composition. The responsivity and detectivity with good photoresponse originated from the realization of special microstructures, enhancing the photoelectric behavior of Cd _x Zn_1-x S materials for applications in low-dimensional PDs covering a large wavelength region.