Enhancement of photo-sensing properties of CdS thin films by changing spray solution volume

Highlights

• CdS is a II–IV family semiconductor chalcogenide that that has been deposited on amorphous glass substrates.

• photo-sensitivity characteristics of the responsivity of 1.01 AW−1, detectivity of 2.21 × 1012 Jones, photo-sensitivity of ∼4.9 × 103, and external quantum efficiency (EQE) of 257 %.

• The obtained results show that the CdS films are good semiconductor material for photodetector applications.

Abstract

CdS is a IIIV family semiconductor chalcogenide that has been deposited on amorphous glass substrates as thin films form with various solution (precursor) volume (5, 10, and 15 mL) by employing a cost-effective spray technique using a nebulizer. The effect of the varying quantity of coating solution on the structural and optoelectronic properties has been studied. The X-ray diffraction (XRD) patterns reveal the polycrystalline nature of CdS with a hexagonal structure with preferential orientation along the c-axis. Atomic force microscope (AFM) demonstrated the film prepared with a 10 mL solution possesses uniform coating with spherical shaped nanograins. Energy dispersive X-ray analysis (EDX) reveals the coated film contains Cd and S elements. The direct bandgap values decreased with the increase in precursor volume and reached a minimum value for the film prepared with a 10 mL solution. Photoluminescence (PL) spectra revealed the two emission peaks in which a sharp dominant peak at 470 nm and a peak with a shoulder at 620 nm. The CdS film coated with a precursor spray volume of 10 mL resulted in better photo-sensitivity characteristics of the responsivity of 1.01 AW⁻¹, detectivity of 2.21 × 10¹² Jones, photo-sensitivity of ∼4.9 × 10³, and external quantum efficiency (EQE) of 257 %. The film-coated with a solution volume of 10 mL was found to have good optical characteristics which make them suitable for photo-detector applications.

Introduction

In the modern world, there is a huge demand for sophisticated optoelectronic devices for day-to-day life, industries, education field, and research organizations, etc. [[1], [2], [3]]. But with these demands, the utilization of power consumption is also rapidly increased. It is well known that the power issue is the biggest unsolved problem for the modern world. In the context of this, there is a huge need for reliable and rapid response semiconductor devices that could work with self-powered [1,[4], [5], [6]]. Group II–VI chalcogenide metal compounds have been attracting the modern world due to their wide variety of applications like solar cells, LEDs, photodetectors, optoelectronic devices, and so on [[7], [8], [9]]. Among different chalcogenide compounds, Cadmium sulfide (CdS) is a special class of material that possesses a wide direct bandgap for many photo-sensing and optoelectronics applications. It provided a direct bandgap of 2.4 eV with a low recombination rate for photogenerated carriers [10]. In addition to this, CdS is a wider studied material for the modification of different physical and photodetector properties with different dopants and different preparation conditions [[11], [12], [13]]. There are huge reports are available on the different growth methods of CdS viz., CBD [14], thermal [15], electro-deposition [16], electron beam evaporation [17], Sol-gel [18] and spray technique [19]. Nebulizer Spray Pyrolysis (NSP) is a kind of spray technique which function on the basis of the Bernoulli principle [20]. It has many noticeable advantages. They are (i) It is a very attractive, low cost, time-saving, and highly safe technique. (ii) This technique can be employed to deposit a high-quality film on a larger surface area with less chemical wastages. (iii) It is a more sought method because by using this route one can able to produce pinhole-free films. (iv) Good quality films can be grown to be even at a higher temperature of 650 °C [21]. (v) This spray pyrolysis is the most useful technique to control various parameters such as growth rate, thickness, temperature, uniformity, volume, etc. [[22], [23], [24]]. Gunavathy et al. studied the effect of precursor volume on the properties of Cu₂SnZnS₄ thin films [25]. Munde et al. have studied the response and decay time of the CdS thick films fabricated by using the spray pyrolysis technique [26]. Recently, Shkir et al. have studied Sm: CdS and Pr:CdS films coated using the spray pyrolysis procedure and reported photo-responsivities in the order of 0.213 and 2.71 AW⁻¹, respectively [27,19]. Although the spray technique produces a uniform and quality films there is a significant effect of precursor (solution) volume on the optical, electrical, and surface morphological characteristics of the deposited films [28]. Recently, Shinde et al. have studied the change in precursor solution volume will convert amorphous films into crystalline films [29]. There is a limited number of articles are available in the literature on the study of spray solution volume. Hence, in the present work, we prepared CdS thin films with different volumes of precursor solution by Nebulizer spray pyrolysis technique for photo-sensing properties. The structural, elemental composition, topographic, and optical properties the prepared films were studied. The photodetection ability of the films was also studied.