Growth Kinetics and Polymorphism of Chemically Deposited CdS Films

Abstract

The kinetics of growth for chemical deposition of normalCdS films from alkaline solutions of cadmium salts has been studied with respect to temperature of deposition and the relative concentrations of the various reactants in the solution. It has been established that the growth of the film takes place either by ion‐by‐ion condensation of Cd+2 and S−2 ions or by adsorption of colloidal particles of normalCdS formed in the solution, depending on the various deposition parameters and the method of preparation. The former process of growth results in thin, hard, adherent and specularly reflecting films, whereas the latter results in thick, powdery and diffusely reflecting films. Occurrence of different polymorphic phases of normalCdS (hexagonal and cubic) has been observed under different growth conditions. A model for growth mechanism has also been proposed.

Detailed Analysis of Five Aspects Addressed to Minimize Costs and Waste in the Chemical Bath Deposition of CdS Films Using the Cd<i>B</i>–<i>A</i>C<sub>6</sub>H<sub>5</sub>O<sub>7</sub>–<i>A</i>OH–(NH<sub>2</sub>)<sub>2</sub>CS System

“…However, several authors have reported explicitly or implicitly that the lower the reaction temperature the lower the thin film growth rate [12,15,20,21,23,28,34,35,54,[77][78][79][80][81]84,87,90,[103][104][105][106][107][108][109][110][111][112][113][114][115][116][117][118][119][120][121]. Thus, without delving into the cases in which homogeneous precipitation is favored, which limits the maximum d-a limit which was directly reported [12,15,21] or simply evident in the results reported [115,118,120] by some authors-the use of low temperatures lengthens the time required to achieve a thin film with determined d compared to the time required at higher temperatures. For example, Figure 5 shows the log(T -1 ) value at 400 nm of the CdS thin films synthesized by using the economical formulation at different temperatures and different immersion times, and it confirms the increase in thin film growth rate with increasing temperature.…”

“…Mainly for the economical reason, from this point on we will refer to it as economical formulation-although this can be further enhanced-whose specifications are depicted in Table 3. These specifications can be changed-usually a variation in the Cd 2+ concentration is done-but it is necessary to take into account that the deposition conditions, like the pH of the On the other hand, although different authors have included in their reports studies in which the reaction temperature is varied [12,15,[20][21][22][23][24]27,28,34,35,54,73,[77][78][79][80][81]84,85,87,89,90,, there is no report about the energy consumption of the equipment that keeps constant the temperature of the water bath at a selected value. For this purpose, we measured the energy consumption during the first minutes when a temperature of 30˚C, 50˚C, and 70˚C is achieved, starting from a water bath at 25˚C.…”

“…Anyway, with the work of Mokrushin and Tkachev [6] a standard aqueous reaction system consisting of three components was established: a cadmium-salt (CdB) as Cd 2+ ions source, thiourea ((NH 2 ) 2 CS) as S 2-ions source, and ammonium-hydroxide (NH 4 OH) as OH -ions source, which, in the ammonia (NH 3 ) form, also acts as a Cd 2+ ions ligand. -OH --(NH 2 ) 2 CS aqueous system, which may contain an ammonium-salt (NH 4 B) to buffer the solution, remained basically unchanged in the studies reported by several authors during the following two decades [8][9][10][11][12][13]. The first modifications to this standard system were made by Call et al in 1980 [14], who used cyanide (CN -) as ligand instead of NH 3 , and by Mondal et al in 1983 [15] and Bhardwaj et al in 1984 [16], who introduced triethanolamine (N(CH 2 CH 2 OH) 3 ) as ligand besides NH 3 .…”

Mid-IR Range Photosensitive Device Based on Chemically Deposited Nanocrystalline Chalcogenide Thin Films with Tunable Opto-electrical properties

“…In the cases with high ammonia and high stir rates,the wurtzite structure of CdS was observed. In the same cases with no stir the more common zinc blende cubic CdS was observed [62]. It is assumed that the stirring prevented formation of clusters hence limited the sticking of the colloidal particles from the solution and limiting the formation of the zinc blende.…”

“…In general the most noticeable effect of non-stirring is the loose adherence of the film to the substrate [62]. This can be explained by the non-dissolution of the clusters in the solution.…”