Microstructural and Optical Characterization of Heterostructures of ZnS/CdS and CdS/ZnS Synthesized by Chemical Bath Deposition Method

Temesgen Geremew,Tizazu Abza,Miguel Navarro-Cia

doi:10.1155/2020/1401689

Temesgen Geremew, Tizazu Abza + Show 1 more

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https://doi.org/10.1155/2020/1401689

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Abstract

ZnS/glass and CdS/glass single layers and ZnS/CdS and CdS/ZnS heterojunction thin films were deposited by the chemical bath deposition method using zinc acetate and cadmium acetate as the metal ion sources and thioacetamide as a nonmetallic ion source in acidic medium. Na2EDTA was used as a complexing agent to control the free cation concentration. The single layer and heterojunction thin films were characterized with X-ray diffraction (XRD), a scanning electron microscope (SEM), energy dispersive X-ray (EDX), and a UV-VIS spectrometer. The XRD patterns of the CdS/glass thin film deposited on the soda lime glass substrate crystalized in the cubic structure with a single peak along the (111) plane. The ZnS/CdS heterojunction and ZnS/glass single layer thin films were crystalized in the hexagonal ZnS structure. The CdS/ZnS heterojunction thin film is nearly amorphous. The optical analysis results confirmed single band gap values of 2.75 eV and 2.5 eV for ZnS/CdS and CdS/ZnS heterojunction thin films, respectively. The CdS/glass and CdS/ZnS thin films have more imaginary dielectric components than the real part. The optical conductivity of the single layer and heterojunction films is in the order of 10 15 1/s. The optical study also confirmed refractive index values between 2 and 2.7 for ZnS/glass, ZnS/CdS, and CdS/ZnS thin films for incident photon energies between 1.2 eV and 3.8 eV. The surface morphology studies revealed compacted spherical grains covering the substrate surfaces with few cracks on ZnS/glass, ZnS/CdS, and CdS/glass and voids on CdS/ZnS thin films. The EDX result confirmed nearly 1 : 1 metallic to nonmetallic ion ratio in the single-layered thin films and the dominance of Zn ion over Cd ion in both ZnS/CdS and CdS/ZnS heterojunction thin films.

Highlights

Wide band gap II–VI compounds have received a lot of attention as optoelectronic materials
We report the study of structural, morphological, compositional, and optical properties of chemical bath-deposited zinc sulfide (ZnS)/Cadmium sulfide (CdS) and CdS/ZnS heterojunction thin films in acidic chemical baths
The CdS/ZnS heterojunction thin film has two very weak X-ray diffractometer (XRD) peaks along (0028) and (117) planes of the hexagonal ZnS structure. e absence of reflection from the CdS structure reveals the unsuitability of the ZnS substrate for the growth of the sufficient layer of CdS to diffract the X-ray. e broad hump in the 2θ range of 20° to 35° observed on the XRD patterns of all the samples is due to the glass substrate [34]

Summary

Introduction

Wide band gap II–VI compounds have received a lot of attention as optoelectronic materials. ZnS is an n-type semiconductor [8] with promising applications in solar control coating, optical and chemical sensors, and optoelectronic devices, such as electroluminescent devices, light-emitting diodes, lasers, and photovoltaic cells [9, 10]. Ey can be used as an n-type buffer layer to form thin film heterojunction solar cells [18, 19], quantum wells [20], and light-emitting devices [21] with a better performance than CdS and ZnS single layers. We report the study of structural, morphological, compositional, and optical properties of chemical bath-deposited ZnS/CdS and CdS/ZnS heterojunction thin films in acidic chemical baths

Experimental Techniques

Results and Discussion

Optical Analysis

Conclusion