Physical Characteristics of CBD Synthesized CdZnS Thin Films: CdZnS Thin Film Preparation Techniques, Properties, and Characterization

Introduction

In modern age industrial application, semiconductor materials have received great interest due to their novel properties. Among different semiconductor materials, chalcogenides have received a great attention for their ability to easily form binary and ternary compound. The wide-band gap binary II–VI compounds and their alloys have been investigated most extensively for their potential application in different fields such as opto-electronic devices, solar cells, nonlinear optical and luminescence devices because of their quantum size effect and especially due to their tunable optical properties (Rajathi, 2012; Raviprakash, 2010; Baykul, 2010) Modern day’s material science needs advanced, low cost smart ternary material for its wide applications. The ternary materials have advantage over binary one as their physical and chemical properties hugely depend on their composition. So the importance of ternary chalcogenides is increasing day by day. Ternary material can be achieved either by alloying three different elements or by alloying two binary materials with same anion. The other way to create ternary material is doping one element on a binary material. Though doping is very popular technique, alloying of semiconductors is also one of the simplest techniques used for tailoring the energy band gap, lattice parameter, electronic and optical properties (Nagamani, 2012).

Those ternary chalcogenides can be fabricated in both particles and thin film form. The main reason for interest in thin films is that they can change both the physical and chemical properties of the surface of the underlying material as well as they can promote desired properties on it. A thin film could improve the hardness and roughness which is beneficial for use as a protective layer in different optoelectronic devices such as solar cells or flexible LED displays (Park, 2011). Many of the device applications requires material in thin film form as it possess specific thickness, well defined phase content, uniform distribution of material over the surface. A thin film also have special benefit of cost effectiveness: instead of manufacturing the total expensive desired material, it is enough to have a cheaper material as a backbone with a thin film with desired properties on top. So, the surface area can be increased using thin film form than particle-form. For example, to fabricate a solid car catalyst we need about 1 kg of platinum in the device. In reality there is only about 3-4 g on a ceramic backbone – lowering the cost by nearly 300 times.

Different chalcogenides such as cadmium sulfide, zinc sulphide, lead sulphide etc. has potential application in different optoelectronics devices. Cadmium sulfide is a II–VI compound semiconductor with a wide direct band gap of 2.42 eV (bulk value) and a small exciton Bohr radius of 2.5 nm. The properties of those semiconductors are greatly influenced by the effects of low dimensionality when the radius of the particle is comparable to the value of Bohr exciton radius in the consequent bulk material. CdS is used as window material for heterojunction solar cells as its wide bandgap helps to avoid the recombination of photogenerated carriers and further improves the solar cells efficiency (Sekhar, 2012). Therefore CdS continues to hold an important position in CdS/ CdTe and CdS/ CuInSe₂ solar cell with efficiency nearly 19.2%.