Structural and Optical Properties of Boron Doped Cadmium Oxide

Thin films of transparent and conductive CdO and B1,3)w% doped cadmium oxide (CdO: B) (1 and 3) wt %, have been deposited using chemical spray pyrolysis (CSP)) technique on glass substrate temperature of 300°C. Microstructural analysis indicates that X-ray diffraction study shows that the obtained films were polycrystalline. The preferred orientation was along the direction (200) and that the average crystallite size increases with the increasing B content. Morphological properties were studied, by scanning electron microscope (SEM) and atomic force microscopy (AFM) which reveals that the grains have a similar column shape. UV-visible transmission spectroscopy reveal that the prepared thin films are transparent in the visible range, The value of the optical band gap obtained shows a slight increase in its values from 2.43 eV to 2.45 eV as B concentration increasing.


Introduction
Cadmium Oxide CdO is one of the most important materials in the semiconductor industry, according to the development of solid state devices [1]. Cadmium oxide is a transparent in the visible, ultraviolet and near infrared regions of the electromagnetic spectrum [2]. Cadmium oxide is considered to be a semiconductor of n type charge carriers and a direct energy band gap near 2.22 eV. It has ,which can be increased by doping [3]. In general, the undoped and nonstoichiometry cadmium oxide is considered to have little resistance because it contains a small amount of oxygen vacancies and interstitial defects [4]. It transitions from transparent materials in the region of 450 nm of the electromagnetic spectrum [5]. Synthesis of CdO films with different types of doping elements such as Cu [6], Ga [7], F [8], Li-Ni [9], Bi [10], Fe [11], In [12] confirms the possibility of tuning their material properties to be developed in new applications in optoelectronic devices and sensors, by approving electrical conductivity in pure cadmium oxides to the existence of oxygen vacancies [13]. It is possible to control electrical conductivity by producing thin films of cadmium Oxide is doped with metallic ions [14]. And cadmium oxide can be doped with many materials such as phosphorus tin and boron, which can shift the optical energy gap to the visible region [15]. Cadmium Oxide doping in the tin and prepared by sputtering can be used in pressure monitoring applications in the atmosphere [16].
Cadmium oxide can be prepared in the form of chemical evaporation. The optical, electrical, and structural properties can be affected by partial pressure and the substrate temperature, the thickness and the annealing can be obtained with a resistance of 14-17 Ω/ square unit and for pure cadmium oxides of thickness 120-150 nm [17]. Explained that there is a direct and indirect electronic transmission of the type of package to its package and associated with three and two and a half electron volts [18]. The aim of this work is to prepare B doped CdO by the simple and low cost spray pyrolysis technique in order to study their structural and optical properties.

Materials and Methods
The CdO thin films were prepared from O.1 M of CdCl 2 (provide by Sigma-Aldrich -German) that dissolved in 1:1 deionized water and ethanol. The doping agent was Boron trichloride (BCl 3 ) (provide by PubChem India) dissolved in deionized water, few drops of HCl were added to the solution in order to get clear solution. Chemical spray pyrolysis was used to prepare B-doped CdO film deposited on glass slide substrate. The preparation conditions are: Substrate temperature 300 O C, distance between the nozzle and the substrate was 27 cm, 3 spraying period 7 s lasted by 60s to avoid cooling, spray rate was 4ml/min, and Nitrogen gas was used as a carrier gas.
The film thickness was measured using the gravimetric method to be 300 ± 30 nm. The XRD (SHIMADZU XRD-6000), SEM (Jeol JSM 6335F), and AFM (AA3000 SPM) were used to determine the structure and the morphology of the films. UV-Visible spectrophotometer (UV SPECTROPHOTOMETER SHIMADZU MODEL UV-1800) that used to record the absorbance spectra in the wavelength range 300-900 nm.

Results and discussion:
Figure (1) (1) and is shown in Figure (1-a).  (2) [21] and the dislocation density (δ) by equation (3) [21] .The relationship between microstrain and the dislocation density was represented as a function of the deflection concentration as in Fig (1-b and c).   Table 1.With the increase of doping concentration up to 3 weight % as in fig. (4), we notice that the number of columns is decreasing and the height is about 2.66 nm and the average particle size (20-40) nm (Table 1). These results were in good agreement with the results obtained by XRD Here, "t" represents the thickness of the films. The direct transition was estimated through the following relation [23]: Where ℎߴ is the photon energy, n is an index related to the density of state (n= 1/2 for direct transition and n=2 for indirect transition) and E g is the optical band gap of the semiconductor films. Figure

Conclusions
CdO and B doped CdO was successfully prepared utilizing the most cheap and inexpensive chemical spray pyrolysis technique . The most important results were the decrease in crystallite size with the increase of doping concentration, the effect of doping was noticed clearly in the increase in the optical energy gap.