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Dear Label_Name,

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I am writing on behalf of an international publishing house, Science and Education Publishing, USA (http://www.sciepub.com).

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Welcome to the April, 2013 edition of SciEP newsletter, providing monthly summaries of articles on science & education related topics of interest to scientist and professionals. The mission of our journals is to provide an open access forum for publishing new findings on issues pertinent to scientific and academic field. We also invite you to submit original research papers, review articles, short reports, or case studies are considered for publication in our Multidisciplinary Journals.

American Journal of Public Health Research
DOI: 10.12691/ajphr-1-1-3

The Implementation of a Tele-Homecare System with Service Oriented Architecture and HL7 Message Transmission Standard
Ching-Sung Wang

American Journal of Medical and Biological Research
DOI: 10.12691/ajmbr-1-1-2

The Influence of Ethanol on Pyruvate Kinases Activity in Vivo, in Vitro, in Silico
Lelevich Sergey Vladimirovich, Khrustalev Vladislav Victorovich, Barkovsky Eugene Victorovich, Shedogubova Tatyana Aleksandrovna

American Journal of Medical Sciences and Medicine
DOI: 10.12691/ajmsm-1-1-1

Clinical and Histological Features in Wegener Granulomatosis
Li Cavoli Gioacchino, Passantino Rita, Bono Luisa, Tortorici Calogera, Ferrantelli Angelo, Giammarresi Carlo, Rotolo Ugo

American Journal of Infectious Diseases and Microbiology
DOI: 10.12691/ajidm-1-1-2

The Curse of Lymphatic Filariasis: Would the Continual Use of Diethylcarbamazine Eliminate this Scourge in Papua New Guinea?
Anne Lanham, Lillian Mwanri

We have released issues of some journals on February 2013.
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American Journal of Medical Sciences and Medicine
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American Journal of Cancer Prevention
American Journal of Medicine Studies
American Journal of Infectious Diseases and Microbiology
American Journal of Cardiovascular Disease Research
American Journal of Biomedical Research
American Journal of Mechanical Engineering
American Journal of Microbiological Research
Journal of Preventive Medicine
American Journal of Food and Nutrition
American Journal of Hypertension Research
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Structural Characterization of P-type SnO₂: Ga and Sb-co-doped SnO2:Ga Thin Films Prepared by Sol-Gel Dip-Coating Method for Potential Optoelectronic Applications

Sally Kemuma Gichana*, David M. Mulati, Timonah N. Soitah

Department of Physics: Jomo Kenyatta University of Agriculture and Technology (JKUAT). P.O BOX 62000-00200, NAIROBI-KENYA

Abstract: This paper delves into the synthesis and characterization of p-type Transparent Conducting Oxides (TCOs), with a specific focus on Gallium-doped tin oxide (SnO2:Ga)and Antimony co-doped Gallium-tin oxide thin films. The films are deposited on blue microscope glass substrates utilizing the sol-gel dip-coating method. The study tackles the challenges related to the application of p-type TCOs, highlighting advancements in electrical performance compared to their n-type counterparts. Structural characterization through X-ray diffraction indicates both crystalline and amorphous nature of the films. Sharp and narrow diffraction peaks confirm the well-defined doped phases of Ga and Sb at atomic substitutional sites of SnO2. Different phases are identified for pure SnO2and Ga-doped SnO2 films. The preferential orientation shifts with doping concentrations. Sb-co-doped SnO2 films show the highest peak intensities. The average crystallite sizes of the thin films increase with doping concentrations, ranging from 19.83 nm to 32.24 nm for Ga-doped films and 33.91 nm to 40.88 nm for Sb-co-doped films. The structural analyses suggest that SnO2:Ga and Sb-co-doped SnO2:Ga thin films are suitable p-type TCO materials for optoelectronic applications. Overall, this research contributes valuable insights into improving the performance of p-type TCOs and addresses the limitations associated with their characterization.

Keywords: P-type, Thin Films, Sol-Gel, Structural properties

Received July 29, 2024; Revised August 30, 2024; Accepted September 05, 2024

Citation: Sally Kemuma Gichana, David M. Mulati, Timonah N. Soitah, Structural Characterization of P-type SnO₂: Ga and Sb-co-doped SnO2:Ga Thin Films Prepared by Sol-Gel Dip-Coating Method for Potential Optoelectronic Applications. Journal of Materials Physics and Chemistry, 12 (2). 37-41. January 2024. doi:10.12691/jmpc-12-2-3

1. Introduction

Transparent Conductive Oxides (TCOs) constitute a unique class of materials characterized by appreciable electrical conductivity, high optical transparency in the visible range, and significant infrared reflectivity [1]. Their distinctive properties underpin advancements in technology such as touch screen displays, solid-state sensors, organic light emitting diodes (OLEDs), liquid crystal displays, and photovoltaic cells [2,3]. However, unlike their n-type counterparts, the establishment of suitable p-type TCOs remains a challenge [4,5,6]. The complexity arises from the electronic configuration of oxide materials, where the Valence Band Maximum (VBM), the transport path for holes in p-type TCOs, is localized and anisotropic, leading to high hole effective mass and low hole mobility [7,8].

This difficulty impedes the formation of p-n junctions critical for various optoelectronic applications [9]. Despite these challenges, efforts guided by chemical design principles have led to the discovery of several p-type TCOs, including copper-bearing oxides (CuMO₂, M=Al, Ga, In), binary copper oxides (CuO and Cu₂O), and zinc spinel oxides [10,11]. Notably, Copper Aluminium oxide (CuAlO₂) has shown promise as a highly transparent p-type TCO, although its resistivity remains higher compared to n-type indium tin oxide [10,11] Zinc, when doped or deposited under specific conditions, also exhibits p-type TCO characteristics, albeit with challenges related to rapid decay due to the self-compensation effect [12].

The inadequacy of current p-type TCOs has repercussions, particularly in transparent electronic devices like solar cells, where stability and efficiency are compromised. Substituting p-type TCOs with semi-crystalline metallic organic materials has resulted in reduced device stability and efficiency [13,14,15]. Addressing this gap in suitable p-type TCOs could enable the fabrication of transparent p-n junctions for diverse applications in the transparent electronic industry [13,14,15].

Tin (IV) oxide stands out among TCOs due to its unique performance and versatility in optoelectronic industry and green energy devices [3,9,16]. SnO₂, an n-type semiconductor with a direct band gap of 3.6 eV to 4.0 eV, finds applications in gas sensors, solar cells, LEDs, transistors, and photo detectors [17,18,19]. Various studies have explored the fabrication of p-type tin-based films, particularly using group (III) elements such as Al and Ga, owing to their unique structures and sizes [20,21]. For instance, the smaller radius of Ga compared to Sn enhances the solubility of Ga ions into the tin site, facilitating p-type conductivity [21,22,23,24,25,26,27].

However, high resistivity due to low intrinsic carrier density and mobility poses a challenge for SnO₂ thin films in achieving p-type conductivity. Co-doping with Sb is proposed to produce thermally and chemically stable materials, as Sb acts as an acceptor at certain doping levels [28,29,30].

Various deposition techniques have been employed for tin-based thin films, including DC and RF magnetron sputtering, spray pyrolysis, chemical vapor deposition sputtering, thermal evaporation, pulsed laser deposition, and the sol-gel method [22,31,32,33,34,35]. Among these, the sol-gel method offers advantages such as cost-effectiveness, environmental friendliness, ease of controlling underlying materials and doping concentrations, low temperature requirements for film densification, and the formation of homogeneous structures [35,36,37].

In this study, transparent p-type conductive thin films of tin doped with Gallium and co-doped with Sb are prepared using the sol-gel dip-coating method, grown on Blue-plus microscope glass slides. Their structural properties are characterized for potential applications in transparent electronics.

2. Experimental

2.1. Materials

Tin (IV) chloride of trace metal basis (99.95 % purity) Sigma Aldrich, Gallium (III) chloride, ultra dry, 99.999 % purity (metal basis) Sigma Aldrich, Ethanol and acetone (solvents) Antimony (III) ethoxide, co-dopant, (99.999 % purity) Sigma Aldrich were used for sol preparations. The Blue plus microscope glass slides were used as the substrates for sol coatings.

2.2. Methods

2.2.1. Preparation of SnO₂:Ga sol

GaCl₃-ultra dry, was dissolved in Acetyl acetone at room temperature. Table 1 illustrates the concentration composition values of SnO₂:Ga and Sb-co-doped SnO₂:Ga with the obtained thin films. At various concentration weights; 0.25 g, 0.5 g, 0.75 g and 1.0 g of Ga, the solution was refluxed at 70o C using a reflux set-up for 2 hours to ensure effective homogenization. Hydrated SnCl4 was then dissolved in ethanol in another beaker with the help of a magnetic stirrer at room temperature, cooled down and the solution added drop wise to the Ga dissolved solution. The sol was then aged in the dark room for 7 days [36] as in the flow chart in Figure 1 which illustrates the dissolving, refluxing and aging of the sol.

Table 1. The concentration composition values of SnO₂:Ga and Sb-co-doped SnO₂:Ga

Figure 1. Flow chart of Preparation of SnO₂: Ga sol

2.2.2. Preparation of Sb-co-doped SnO₂: Ga sol

After preparation of the gallium oxide sol, Antimony (III) Ethoxide was added in various concentrations of 0.5 ml, 1.0 ml, 1.5 ml and 2.0 ml (Table 1). The solution was then aged for 7 days to obtain the Sb-co-doped SnO₂:Ga coating sols as shown in flow chart in Figure 2 which illustrates the dissolving, refluxing, co-doping and aging of the sol.

Figure 2. Flow chart of Preparation of Sb-co-doped SnO₂: Ga sol

2.3. Preparation of Glass Substrates

The Blue-Plus microscope glass substrates were used for sol coatings. The substrates were treated ultrasonically in ethanol and acetone and kept in a desiccator, ready for film deposition [38].

2.4. Film Deposition and Subsequent Treatment

Film deposition was carried out in air at room temperature by the dip-coating method (Figure 3) using the cleaned glass substrate. The substrates were left to dry horizontally at 50oC in the oven to remove any organic residuals. The coating-drying procedure was repeated 3-times with an approximated withdrawal speed of 4 cm/min to obtain the desired film thickness [39] The films were then annealed at 150oC (optimal temperature) for 5 minutes and then cooled down at room temperature for crystal formation.

Figure 3. Schematic of the dip-coating and withdrawal of substrate

3. Results and Discussions

3.1. Structural Properties

XRD analysis technique was utilized to determine the crystal structure and crystallinity of the thin films using a Bruker D8 SSS X-Ray diffractometer. X-rays were generated using a Cu source with CuKα radiation (λ=1.5418) at 20kV and 15mA. The grazing incident beam angle was kept at 0.8°. Angular ranges of the patterns collected were between 10 and 70 degrees at a rate of 1 minute per step with a scanning step size of 0.05. XRD spectra were indexed using the originPro85 software. The patterns were analyzed for crystallinity and preferred orientations as shown in Figure 4 and Figure 5.

The presence of fairly sharp and narrow significant diffraction peaks of the prepared thin films indicates the crystalline nature of the films. The doped phases of Ga and Sb were well defined and successfully replaced at atomic substitutional sites of SnO₂.

For pure (undoped) SnO2 thin film, 4 diffraction peaks were identified as (126), (151), (285) and (407) reflections of the orthorhombic structure. For the Ga doped SnO2 thin films, the samples related to the monoclinic structure with SnO2 phases identified due to the mixing of both Ga and SnO₂. The results indicate that the preferential orientation for pure SnO2 (407) is shifted to (408), (407) and (409) for the Ga-doped SnO2 and (404), (302), (115) and (408) for the Sb-co-doped SnO₂:Ga. Change of preferred orientation is attributed to the occupancy of additional tin vacancy sites by Ga and Sb sites which were initially unoccupied. The increase in preferred orientation is associated with increase of crystallite growth along that particular plane.

Figure 4. XRD spectra for the undoped (pure) and Ga-doped thin films

Figure 5. XRD spectra for the undoped (pure) and Sb-co-doped SnO₂:Ga thin films

Increase in peak intensity with film concentration is also observed for all the prepared thin films. All the films indicate one strong peak with the Sb-co-doped thin films registering the highest intensities as compared to the Ga-doped thin films. Thus, the spectra of the films show a well-defined orientation. This can be attributed to an improvement of the films with doping and enhancement in grain sizes. A similar result of increase in peak intensities with doping concentrations and change of preferred orientations is reported by [40] with morphological evaluation of co-precipitated ZnO nanoparticles.

3.2. Structural Parameters of the Prepared Thin Films for Different Ga and Sb Concentrations

The effective grain sizes of the thin films were calculated from the Full Width at Half Wavelength

(FWHW) of x-ray peak lines of plane orientation using the Debye-Scherrer formula;

[picture] | (1)

where; D = mean crystallite size

λ = wavelength of radiation (incident x-ray) used=0.15418

β = peak (line) broadening at half the maximum intensity

θ = Bragg angle (diffracted angle) in radians

Figure 6. Crystallite size and FWHM Variation with dopant concentration

An observed improvement in average crystallite sizes is noted as the doping concentrations increase for both the Ga-doped and Sb-co-doped SnO₂ thin films. Specifically, the grain sizes of the thin films exhibit an increase from 19.83 nm to 32.24 nm for the Ga-doped tin oxide thin films and from 33.91 nm to 40.88 nm for the Sb-co-doped SnO₂ films with increasing concentrations of Ga and Sb. Additionally, the Full Width at Half Maximum (FWHM) of all the films decreases with an increase in precursor concentration, indicating enhanced crystallinity of the thin films.

This observed increase in crystallite sizes and decrease in FWHM is attributed to the reduced strain on the surface of the films. This reduction in strain occurs because the dopants act as nucleation sites in nanoparticle synthesis, thereby lowering the energy required for particles to initiate formation. Similar results of increased crystallite sizes with doping have been reported in studies by Rahul et al. [41] with doped ZnO and Ian E. et al. [42] regarding the effect of doping-induced aggregation on film morphology, as well as by Peddavarapu et al. [43] with SnO₂ thin films.

4. Conclusions

In conclusion, the observed increase in crystallite sizes upon doping of SnO₂ and Sb-co-Doped SnO₂;Ga thin films signifies enhanced crystallinity, which is essential for their optimal performance.. The presence of sharp and narrow diffractions in XRD spectra indicates a combination of crystalline and amorphous nature in the prepared thin films. Moreover, the increase in preferred orientations of the thin films corresponds to enhanced crystallite growth along specific planes. The intensification of film peaks with doping concentrations is attributed to the creation of sub-energy levels within the film lattice. Notably, a strong peak observed in all XRD spectra signifies a well-defined orientation of the thin films. The homogeneous grain sizes observed in SnO₂ and Sb-co-Doped SnO₂;Ga films contribute to their optimal electrical properties. Overall, doping concentrations significantly influence the structural properties of the prepared p-type TCO thin films of SnO₂and Sb-co-Doped SnO₂, confirming their suitability for high-quality device applications, particularly in solar cell technology which still records low efficiency.

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