**3.3.2 Surface morphology**

390 Solar Cells – Thin-Film Technologies

**a**

01234 **N, deposition q-ty**

Fig. 2. The CdS thin film thickness dependence on time and quantity of deposition from aqueus solution: CdCl2 (a); CdSO4 (b); CdJ2 (c). The mean deposition rate of CdS thin films

0

20

40

60

**d, нм**

0 3 6 9 12 15 **time, min.**

80

100

120

**deposition rate ,**

**nm/min.**

structures that consist of pores and channels. Further film growth is, in fact, filling the pores and channels. It slows the increase of film thickness, but does not alter the film weight gain. At later stages of the growth occurs reflection of the particles stream from the surface that leads to film growth rate decrease, and in the future - to its almost complete stop. Maximum growth rate of CSD at 343 K had films deposited from CdI2 solution. Big deposition rates cause to the significant film defections, which confirm the results of their structural studies.

0 3 6 9 12 15

**deposition rate** 

**nm/min.**

**,**

0 10 20

0

20

40

60

**d, n**

**m**

80

100

120

01234

**N, deposition q-ty**

**c**

0 3 6 9 12 15 **time, min.**

**deposition rate** 

**nm/min.**

**,**

0 10 20 **b**

01234

**deposition q-ty**

**time, min.**

on figure inset.

0

30

60

**d, n**

**m**

90

120

The results of the CdS films investigation by scanning electron microscopy, deposited from diferent aqueous salt solutions are shown in Fig. 3-7, in the reflected and secondary electrons mode.

Fig. 3. Surface morphology of CdS film deposited from CdSO4 aqueus solution, A modification (a) and C modification (b). REMMA-102-02, accelerating voltage 20 kV, scale 1:2000

Fig. 4. Surface morphology of CdS film deposited from CdSO4 aqueus solution on ITO coated glass in the secondary-electron mode (a) and reflected-electron mode (b). REMMA-102-02, accelerating voltage 30 kV, scale 1:8000

Chemical Surface Deposition of CdS Ultra Thin Films from Aqueous Solutions 393

In reflected electron mode the photo qualitatively displays the surface composition (the lighter point, the heavier elements), and in secondary electron mode - the surface morfology. As seen all CdS film fabricated by C modification completely covers the substrate across the sample area, are homogeneous and solid. In reflected electrons mode are observed white dots indicating the localization heavier compared to the film phase. Comparison of CdS film images, obtained in both reflected and secondary electrons (Fig. 4-6), indicates that the

So, these heavier phase inclusions are particles on the surface (surface macrodefects) and most likely were formed in the final phase of deposition. The concentration of macrodefects on the surface in the investigated CdS films deposited from varus cadmium salts are presented in table 3. Regardles of applied salt surface macrodefects concentration is almost the same and is 100 times smaler than for CBD films (Romeo at al., 2003). Using EDS and WDS measurements, the stoichiometry of all films were studied. The generalized results of the surface morphology and X-ray microanalysis investigation of thin CdS films, deposited from various cadmium salts are given in Table 3. We determined that the particles on the CdS films surface (macrodefects) are CdS particles with a different stoichiometry than the film. The stoichiometry deviation towards sulfur is quite unexpected because in most

Fig. 7. Surface morphology of CdS film deposited from CdI2 aqueus solution before (a) and

The CdI2-based films had composition close to stoichiometric while the CdSO4-based films showed the biggest deviation from stoichiometric composition that agre with results of CBD (Ortega-Borges & Lincot, 1993) (Table 3). Sulfur excess in CSD CdS films gives us the opportunity to perform annealing in the normal (air), not sulfur medium because they do

after annealing (b). JSM-6490LV, accelerating voltage 20 kV, scale 1:15000

heavier phase inclusions are on the film surface.

nonvacuum deposition methods the lack of sulfur is observed.

Fig. 5. Surface morphology of CdS film deposited from CdCl2 aqueus solution in the secondary-electron mode (a) and reflected-electron mode (b). REMMA-102-02, accelerating voltage 30 kV, scale 1:600

Fig. 6. Surface morphology of CdS film deposited from CdI2 aqueus solution in the secondary-electron mode (a) and reflected-electron mode (b). REMMA-102-02, accelerating voltage 30 kV, scale 1:1200

Fig. 5. Surface morphology of CdS film deposited from CdCl2 aqueus solution in the secondary-electron mode (a) and reflected-electron mode (b). REMMA-102-02, accelerating

Fig. 6. Surface morphology of CdS film deposited from CdI2 aqueus solution in the

secondary-electron mode (a) and reflected-electron mode (b). REMMA-102-02, accelerating

voltage 30 kV, scale 1:600

voltage 30 kV, scale 1:1200

In reflected electron mode the photo qualitatively displays the surface composition (the lighter point, the heavier elements), and in secondary electron mode - the surface morfology. As seen all CdS film fabricated by C modification completely covers the substrate across the sample area, are homogeneous and solid. In reflected electrons mode are observed white dots indicating the localization heavier compared to the film phase. Comparison of CdS film images, obtained in both reflected and secondary electrons (Fig. 4-6), indicates that the heavier phase inclusions are on the film surface.

So, these heavier phase inclusions are particles on the surface (surface macrodefects) and most likely were formed in the final phase of deposition. The concentration of macrodefects on the surface in the investigated CdS films deposited from varus cadmium salts are presented in table 3. Regardles of applied salt surface macrodefects concentration is almost the same and is 100 times smaler than for CBD films (Romeo at al., 2003). Using EDS and WDS measurements, the stoichiometry of all films were studied. The generalized results of the surface morphology and X-ray microanalysis investigation of thin CdS films, deposited from various cadmium salts are given in Table 3. We determined that the particles on the CdS films surface (macrodefects) are CdS particles with a different stoichiometry than the film. The stoichiometry deviation towards sulfur is quite unexpected because in most nonvacuum deposition methods the lack of sulfur is observed.

Fig. 7. Surface morphology of CdS film deposited from CdI2 aqueus solution before (a) and after annealing (b). JSM-6490LV, accelerating voltage 20 kV, scale 1:15000

The CdI2-based films had composition close to stoichiometric while the CdSO4-based films showed the biggest deviation from stoichiometric composition that agre with results of CBD (Ortega-Borges & Lincot, 1993) (Table 3). Sulfur excess in CSD CdS films gives us the opportunity to perform annealing in the normal (air), not sulfur medium because they do

a

b

c

d

CdJ2, C modification (d)

Chemical Surface Deposition of CdS Ultra Thin Films from Aqueous Solutions 395

Fig. 8. AFM images and mean roughness distribution of CdS thin films grown from aqueus solution: CdSO4, B modification (a); CdSO4, C modification (b); CdCl2, C modification (c);

not need to enter in film extra amount of sulfur to ensure stoichiometry. Analysis of CdS films surface morphology, obtained by AFM (Fig. 8) shows that the method of deposition and the nature of the initial cadmium-containing salt have significant affect on the CdS film surface structures. Using the deposition B modification ensure much more evenly cover over the sample area than A modification. The best results were obtained by C modification. The CdS films deposited from CdSO4 aqueous solution by B and C (Fig. 8, a and b, respectively) have different surface morphology. The surface of all films obtained in the C modifications, is completely packed with crystalline grains. The exception is the film obtained from cadmium iodide aqueous solution. Along with the films surface morphology the results of surface roughness analysis are presented.


Table 3. Summarized results of surface morphology and X-ray microanalysis investigation of CdS thin films, deposited from various cadmium salts

#### **3.3.3 Crystal structure**

Experimental diffraction intensities of CdS films, obtained by B and C modification of (curves 2 and 3), respectively, are shown in Fig. 9. In all tested samples polycrystallinity of CdS films is expressed with the noticeable presence of cubic phase. The curves 2 and 4 on fig. 9. indicates that the samples are almost completely polycrystalline.

The first 26,450 peak of cubic phase (curves 2 and 4) is slightly expressed and shifted compered to the corresponding XRD peak from single CdS crystal (curve 1), which can be explained by the small size of grains as the probability of mechanical stress in films is very small because of low speed growth (Table 2).

In addition to the 26,450 peak on curve 3 (Fig. 9) are present two more – 43,900 and 52,000, corresponding to the cubic phase. Implemented sample heat treatment does not result in a significant increase in the intensity of any of the three peaks, and even the intensity of first one decreases (curve 4). The shift of the first (26,450) peak (curves 3 and 4) related with a decrease after annealing of mechanical tensions in the film, and intensity decrease of this peak indicates a simultaneous transition in polycrystalline cubic phase. Size grains expected increase by recrystallization has not occurred. Thus, annealing conditions to improve crystallinity of films need correction. Based on the data diffraction pattern most of the cubic phase is contained in the films deposited by C modification C(CdSO4) = 0,001 mol/l. The transition to the hexagonal phase after annealing is not observed, unlike CBD CdS film (Archbold at al., 2005, Romeo at al., 2000).

Fig. 10 shows the experimental diffraction intensities obtained from CdS films, deposited from aqueous solutions of CdSO4, CdCl2, CdI2 salts on glass substrates before and after annealing. In all tested samples polycrystallinity of CdS films is expressed with the noticeable presence of cubic phase. From the curves 2 (Fig. 10, a, b, c) can be seen that as deposited samples are almost entirely polycrystalline. The first peak of 26,45 ° for the cubic

not need to enter in film extra amount of sulfur to ensure stoichiometry. Analysis of CdS films surface morphology, obtained by AFM (Fig. 8) shows that the method of deposition and the nature of the initial cadmium-containing salt have significant affect on the CdS film surface structures. Using the deposition B modification ensure much more evenly cover over the sample area than A modification. The best results were obtained by C modification. The CdS films deposited from CdSO4 aqueous solution by B and C (Fig. 8, a and b, respectively) have different surface morphology. The surface of all films obtained in the C modifications, is completely packed with crystalline grains. The exception is the film obtained from cadmium iodide aqueous solution. Along with the films surface morphology

> Cd/S rate on film surface

> > 0,911 1,061

Cd/S rate of surface macrodefects

the results of surface roughness analysis are presented.

cm-2

106–107, the pineholes are observed, for films deposited from two other salts the pinholes are almost absent

fig. 9. indicates that the samples are almost completely polycrystalline.

of CdS thin films, deposited from various cadmium salts

small because of low speed growth (Table 2).

(Archbold at al., 2005, Romeo at al., 2000).

CdSO4 106–107 0,880 0,800 CdCl2 107 0,898 0,908

Table 3. Summarized results of surface morphology and X-ray microanalysis investigation

Experimental diffraction intensities of CdS films, obtained by B and C modification of (curves 2 and 3), respectively, are shown in Fig. 9. In all tested samples polycrystallinity of CdS films is expressed with the noticeable presence of cubic phase. The curves 2 and 4 on

The first 26,450 peak of cubic phase (curves 2 and 4) is slightly expressed and shifted compered to the corresponding XRD peak from single CdS crystal (curve 1), which can be explained by the small size of grains as the probability of mechanical stress in films is very

In addition to the 26,450 peak on curve 3 (Fig. 9) are present two more – 43,900 and 52,000, corresponding to the cubic phase. Implemented sample heat treatment does not result in a significant increase in the intensity of any of the three peaks, and even the intensity of first one decreases (curve 4). The shift of the first (26,450) peak (curves 3 and 4) related with a decrease after annealing of mechanical tensions in the film, and intensity decrease of this peak indicates a simultaneous transition in polycrystalline cubic phase. Size grains expected increase by recrystallization has not occurred. Thus, annealing conditions to improve crystallinity of films need correction. Based on the data diffraction pattern most of the cubic phase is contained in the films deposited by C modification C(CdSO4) = 0,001 mol/l. The transition to the hexagonal phase after annealing is not observed, unlike CBD CdS film

Fig. 10 shows the experimental diffraction intensities obtained from CdS films, deposited from aqueous solutions of CdSO4, CdCl2, CdI2 salts on glass substrates before and after annealing. In all tested samples polycrystallinity of CdS films is expressed with the noticeable presence of cubic phase. From the curves 2 (Fig. 10, a, b, c) can be seen that as deposited samples are almost entirely polycrystalline. The first peak of 26,45 ° for the cubic

salt surface macrodefects concentration,

CdI2

**3.3.3 Crystal structure** 

Fig. 8. AFM images and mean roughness distribution of CdS thin films grown from aqueus solution: CdSO4, B modification (a); CdSO4, C modification (b); CdCl2, C modification (c); CdJ2, C modification (d)

Chemical Surface Deposition of CdS Ultra Thin Films from Aqueous Solutions 397

Fig. 10. XRD pattern of CdS film deposited on glass substrate from aqueus solution: CdSO4

Absorption coefficient in the fundamental absorption area for all CdS samples was 105 cm-1.The absorption spectra of samples (Fig. 12.) clearly shows the existence of the CdS compounds in all films deposited from aqueous solutions of cadmium-containing salts. Spectral dependence of CdS films absorption in the coordinates (\*h)2 vs h demonstrate the presence of fundamental absorption edge (Fig. 12), localized in the region 2,5 eV. The calculated band gaps of the films are in good agreement with the reported values (Landolt-Börnstein, 1999, Aven & Prener, 1967) and correspond to the direct allowed band transition. We do not observe a straight-line behaviour on graphs of (αhν)2/3 vs hν (direct forbidden), (αhν)1/2 vs hν (indirect allowed) (αhν)1/3 vs hν (indirect forbidden). These plots (not shown) reveal that the type of transition is neither direct forbidden nor indirect. For films deposited in the same technological modes on glass and ITO coated glass substrates, the location of fundamental absorption edge are olmost the same. A small (0,01 eV) difference between the fundamental absorption edge values for films on glass and ITO/glass are caused by the

(a); CdCl2 (b); CdJ2 (c); as deposited (2); after annealing (1).

**3.3.4 Optical properties** 

difference of substrates surface roughness.

Fig. 9. XRD pattern of CdS film deposited on glass substrate from CdSO4 aqueous solution with С(CdSO4)=0,001 mol/l by B and C modification (curves 2 and 3); С(CdSO4)=0,001 mol/l by C modification, after annealing (curve 4); with С(CdSO4)=0,0001 mol/l C modification (curve 5); CdS cubic monocrystal reference pattern (curve 1).

phase have low intensitivity and is slightly shifted against the corresponding peak of CdS single crystal. This can be explained by the small size of grains as the probability of mechanical tensions in films deposited from CdSO4, CdCl2 salts solutions is neglectible due too low growth speed. Besides peak 26,45°, on curve 2 (Fig. 10 b) are present two more - 43,90° and 52,00° corresponding to the cubic phase. The heat treatment of samples leads to a significant increase in the intensity of the first two peaks for films deposited from CdSO4, CdI2. For films deposited from CdCl2 aqueous solutions, the nature of XRD curve practically unchanges due to annealing. For CdS films, deposited from CdI2 aqueous solution (fig. 10c curve 1) after annealing were observed intensity increases of 26,45°, 52,00° peaks and the appearance of third peak 43,90°. This indicates a reduction of disordered polycrystalline phase which transforms into crystalline phase and a rather significant restructure of CSD film, that cinsides with the results of the surface morphology investigations (Fig. 7).

Experimental diffraction intensities of CdS films deposited on Si and CdTe substrates are presented in Fig. 11. As seen, the results for various substrates were different, but both express polycrystallinity of CdS films. Besides the peaks of Si (Fig. 11 a, № 3) and CdTe (Fig. 11 b, № 5, 8) substrates are present a significant number of peaks corresponding to different phases of CdS compound. These results indicate the existence of a mixture of two structural phases (cubic and hexagonal) that is often observed for CdS films fabricated by nonvacuum methods (Calixto & Sebastian, 1999). The X-ray diffraction peaks N 1, 2, 7, 4, 9 (Fig. 11a) on silicon corespond to hexagonal structure, cubic may respond only the peak number 1. For films on CdTe substrate peaks intensity of hexagonal and cubic phases is much higher.

Fig. 10. XRD pattern of CdS film deposited on glass substrate from aqueus solution: CdSO4 (a); CdCl2 (b); CdJ2 (c); as deposited (2); after annealing (1).

#### **3.3.4 Optical properties**

396 Solar Cells – Thin-Film Technologies

0

1

2

3

4

1000

I, arb. unit

2000

20 40 60 80

2

with С(CdSO4)=0,001 mol/l by B and C modification (curves 2 and 3); С(CdSO4)=0,001 mol/l by C modification, after annealing (curve 4); with

(curve 1).

morphology investigations (Fig. 7).

hexagonal and cubic phases is much higher.

Fig. 9. XRD pattern of CdS film deposited on glass substrate from CdSO4 aqueous solution

С(CdSO4)=0,0001 mol/l C modification (curve 5); CdS cubic monocrystal reference pattern

phase have low intensitivity and is slightly shifted against the corresponding peak of CdS single crystal. This can be explained by the small size of grains as the probability of mechanical tensions in films deposited from CdSO4, CdCl2 salts solutions is neglectible due too low growth speed. Besides peak 26,45°, on curve 2 (Fig. 10 b) are present two more - 43,90° and 52,00° corresponding to the cubic phase. The heat treatment of samples leads to a significant increase in the intensity of the first two peaks for films deposited from CdSO4, CdI2. For films deposited from CdCl2 aqueous solutions, the nature of XRD curve practically unchanges due to annealing. For CdS films, deposited from CdI2 aqueous solution (fig. 10c curve 1) after annealing were observed intensity increases of 26,45°, 52,00° peaks and the appearance of third peak 43,90°. This indicates a reduction of disordered polycrystalline phase which transforms into crystalline phase and a rather significant restructure of CSD film, that cinsides with the results of the surface

Experimental diffraction intensities of CdS films deposited on Si and CdTe substrates are presented in Fig. 11. As seen, the results for various substrates were different, but both express polycrystallinity of CdS films. Besides the peaks of Si (Fig. 11 a, № 3) and CdTe (Fig. 11 b, № 5, 8) substrates are present a significant number of peaks corresponding to different phases of CdS compound. These results indicate the existence of a mixture of two structural phases (cubic and hexagonal) that is often observed for CdS films fabricated by nonvacuum methods (Calixto & Sebastian, 1999). The X-ray diffraction peaks N 1, 2, 7, 4, 9 (Fig. 11a) on silicon corespond to hexagonal structure, cubic may respond only the peak number 1. For films on CdTe substrate peaks intensity of Absorption coefficient in the fundamental absorption area for all CdS samples was 105 cm-1.The absorption spectra of samples (Fig. 12.) clearly shows the existence of the CdS compounds in all films deposited from aqueous solutions of cadmium-containing salts. Spectral dependence of CdS films absorption in the coordinates (\*h)2 vs h demonstrate the presence of fundamental absorption edge (Fig. 12), localized in the region 2,5 eV. The calculated band gaps of the films are in good agreement with the reported values (Landolt-Börnstein, 1999, Aven & Prener, 1967) and correspond to the direct allowed band transition. We do not observe a straight-line behaviour on graphs of (αhν)2/3 vs hν (direct forbidden), (αhν)1/2 vs hν (indirect allowed) (αhν)1/3 vs hν (indirect forbidden). These plots (not shown) reveal that the type of transition is neither direct forbidden nor indirect. For films deposited in the same technological modes on glass and ITO coated glass substrates, the location of fundamental absorption edge are olmost the same. A small (0,01 eV) difference between the fundamental absorption edge values for films on glass and ITO/glass are caused by the difference of substrates surface roughness.

Chemical Surface Deposition of CdS Ultra Thin Films from Aqueous Solutions 399

This allows to expand CdS/CdTe solar cells phototransformation area and increase their efficiency. Reducing energy fundamental absorption edge of CdS films after annealing (Fig. 12, curves 2) can be coused by grain growth (Nair at al., 2001). Sharpest edge of fundamental absorption have CdS films, deposited on glass substrate. This indicates a smaller number of macro defects in these films compared with annealed. Energy levels of this defects are lying near the edge zones. The increase long-wave "tail" of the absorption curve for annealed film (Fig. 12, a, b, curve 2) is caused by increase of absorption near the CdS film surface, where in

All films have high transmission, with the transmission in the CdI2 case being better than that of the other three films. This was expected, since the SEM micrographs, showed the pinholes on CdI2-based film. The lowered transmission of our films is caused by their surface roughness, due to coverage by surface macrodefects which are overgrowth crystallite, causes light scattering. Spectral dependence of optical transmission in the visible region of CSD CdS films before and after annealing are shown in Fig. 13. The main feature of the annealed CdS films spectra is small (0.033 eV) shift of fundamental absorption edge in the longwave region and reducing the optical transmission more than 20%. Reducing the transmission is determined not only by absorption and reflection from the film surface, but olso by quite significant changes in the film structure after annealing. From the SEM holes were observed (Fig. 7) after annealing they completely disappeared. X-ray pattern (Fig. 10, c, curve 1) also confirm a significant increase in the film's crystallinity structure as a result of

0

Wavelenght , nm

Fig. 13. Optical transmittance spectra of CSD CdS films deposited from aqueus solution:

The n-CdS/p-CdTe HJ was fabricated and their electrical and photoelectric properties were investigated. The CdS thin films with 100 nm thickness were deposited by CSD using CdCl2

20

40

**a b**

 1 2 3

60

80

the process of annealing in air CdO can be formed.

annealing, despite indifferent directing effect of the glass substrate.

400 500 600 700 800 900

CdCl2 (1); CdSO4 (2), CdJ2 (3) as deposited (a) and after annealing (b).

400 500 600 700 800 900

0

**4. Solar cell performance** 

20

40

60

80

 1 2 3

T, %

Fig. 11. XRD pattern of CdS films deposited from CdCl2 aqueus solution on Si (a) and CdTe (b) substrates

The fundamental absorption edge localization feature in CdS films, in comparison with CdS monocrystal, is that in films it is shifted to higher energy region (2,537 eV and 2,547 eV for films on glass and ITO/glass, respectively).

Fig. 12. Optical absorbance spectra of CdS film deposited on glass substrate from aqueus solution: CdSO4 (a); CdCl2 (b); CdJ2 (c); as deposited (1); after annealing (2).

7

2

3

4

4

8

7

Fig. 11. XRD pattern of CdS films deposited from CdCl2 aqueus solution on Si (a) and CdTe

The fundamental absorption edge localization feature in CdS films, in comparison with CdS monocrystal, is that in films it is shifted to higher energy region (2,537 eV and 2,547 eV for

> *h*eV

Fig. 12. Optical absorbance spectra of CdS film deposited on glass substrate from aqueus

solution: CdSO4 (a); CdCl2 (b); CdJ2 (c); as deposited (1); after annealing (2).

2,474 eV

9

**a** - CdS/Si **b** - CdS/CdTe

3. Si.

c

2,516 eV

2,549 eV

1. c-CdS (111); h-CdS (002). 2. h-CdS (61,7).

4. h-CdS (75,5). 5. CdTe (111). 6. h-CdS (48,75) 7. h-CdS (68,00) 8. CdTe (333 or 511) 9. h-CdS (83,46).

9

2,2 2,4 2,6 2,8 2,2 2,4 2,6 2,8

2,537 eV

0 20 40 60 80 100

a b

2 <sup>0</sup>

6

**b**

(b) substrates

0

20

40

(*h*

)

2, arb.unit

60

80

100

120

140

5

**a**

I, arb.unit

1

films on glass and ITO/glass, respectively).

 1 2

2,2 2,4 2,6 2,8

2,531 eV

2,564 eV

1

This allows to expand CdS/CdTe solar cells phototransformation area and increase their efficiency. Reducing energy fundamental absorption edge of CdS films after annealing (Fig. 12, curves 2) can be coused by grain growth (Nair at al., 2001). Sharpest edge of fundamental absorption have CdS films, deposited on glass substrate. This indicates a smaller number of macro defects in these films compared with annealed. Energy levels of this defects are lying near the edge zones. The increase long-wave "tail" of the absorption curve for annealed film (Fig. 12, a, b, curve 2) is caused by increase of absorption near the CdS film surface, where in the process of annealing in air CdO can be formed.

All films have high transmission, with the transmission in the CdI2 case being better than that of the other three films. This was expected, since the SEM micrographs, showed the pinholes on CdI2-based film. The lowered transmission of our films is caused by their surface roughness, due to coverage by surface macrodefects which are overgrowth crystallite, causes light scattering. Spectral dependence of optical transmission in the visible region of CSD CdS films before and after annealing are shown in Fig. 13. The main feature of the annealed CdS films spectra is small (0.033 eV) shift of fundamental absorption edge in the longwave region and reducing the optical transmission more than 20%. Reducing the transmission is determined not only by absorption and reflection from the film surface, but olso by quite significant changes in the film structure after annealing. From the SEM holes were observed (Fig. 7) after annealing they completely disappeared. X-ray pattern (Fig. 10, c, curve 1) also confirm a significant increase in the film's crystallinity structure as a result of annealing, despite indifferent directing effect of the glass substrate.

Fig. 13. Optical transmittance spectra of CSD CdS films deposited from aqueus solution: CdCl2 (1); CdSO4 (2), CdJ2 (3) as deposited (a) and after annealing (b).
