The low temperature annealing of p-cadmium telluride in gallium-bath

2017

Journal of Elec Materi

Ga-doped CdTe polycrystalline thin films were successfully electrodeposited on glass/fluorine doped tin oxide substrates from aqueous electrolytes containing cadmium nitrate (Cd(NO 3 ) 2 AE4H 2 O) and tellurium oxide (TeO 2 ). The effects of different Ga-doping concentrations on the CdTe:Ga coupled with different post-growth treatments were studied by analysing the structural, optical, morphological and electronic properties of the deposited layers using x-ray diffraction (XRD), ultraviolet-visible spectrophotometry, scanning electron microscopy, photoelectrochemical cell measurement and direct-current conductivity test respectively. XRD results show diminishing (111)C CdTe peak above 20 ppm Ga-doping and the appearance of (301)M GaTe diffraction above 50 ppm Ga-doping indicating the formation of two phases; CdTe and GaTe. Although, reductions in the absorption edge slopes were observed above 20 ppm Ga-doping for the as-deposited CdTe:Ga layer, no obvious influence on the energy gap of CdTe films with Ga-doping were detected. Morphologically, reductions in grain size were observed at 50 ppm Ga-doping and above with high pinhole density within the layer. For the as-deposited CdTe:Ga layers, conduction type change from n-to p-were observed at 50 ppm, while the n-type conductivity were retained after post-growth treatment. Highest conductivity was observed at 20 ppm Ga-doping of CdTe. These results are systematically reported in this paper.

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Section: Conductivity Properties Analysismentioning

confidence: 96%

Section: Structural Analysismentioning

confidence: 99%

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Effect of Gallium Doping on the Characteristic Properties of Polycrystalline Cadmium Telluride Thin Film

2017

Journal of Elec Materi

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“…This observations might be as a result of the recrystallization of the polycrystalline CdTe thin-films during treatment which results to the improvement in the Cd/Te stoichiometry by the sublimation of surplus elements or the formation of CdTe by the reaction between surplus elemental Te and Cd from CdCl 2 treatment [4,21]. It should be noted that no matter the deposition technique, Te -precipitation is one of the main challenges in the deposition of CdTe [22,23] Improvement in the crystallinity of CdTe after post-growth treatment in the presence of chlorine due to factors such as grain growth, recrystallization amongst others is generally accepted by the scientific community [24,25]. The stagnation observed in the crystallite size at 65.8 nm might be as a result of the limitation of the XRD machine utilized and/or that of the Scherrer's formula utilized in the measurement and analysis of CdTe thin-films respectively [26,27].…”

Section: X-ray Diffraction (Xrd) Analysismentioning

confidence: 99%

Factors Affecting Electroplated Semiconductor Material Properties: The Case Study of Deposition Temperature on Cadmium Telluride

2019

Coatings

Electrodeposition of cadmium telluride (CdTe) on fluorine doped tin oxide (FTO) using two electrode configurations was successfully achieved with the main focus on the growth temperature. The electroplating temperatures explored ranged between 55 and 85 • C for aqueous electrolytes containing 1.5 M cadmium nitrate tetrahydrate (Cd(NO 3 ) 2 ·4H 2 O) and 0.002 M tellurium oxide (TeO 2 ). The ensuing CdTe thin-films were characterized using X-ray diffraction (XRD), UV-Vis spectrophotometry, scanning electron microscopy (SEM), energy dispersive X-ray (EDX), and photoelectrochemical (PEC) cell measurements. The electroplated CdTe thin-films exhibit a dominant (111) CdTe cubic structure, while the crystallite size increases with the increase in the electroplating temperature. The dislocation density and the number of crystallites per unit area decrease with increasing growth temperature. The optical characterization depicts that the CdTe samples show comparable absorbance and a resulting bandgap of 1.51 ± 0.03 eV for as-deposited CdTe layers. A marginal increase in the bandgap and reduction in the absorption edge slope towards lower deposition temperatures were also revealed. The annealed CdTe thin-films showed improvement in the energy bandgap as it tends towards 1.45 eV while retaining the aforementioned absorption edge slope trend. Scanning electron microscopy shows that the underlying FTO layers are well covered with increasing grain size observable relative to the increase in the deposition temperature. The energy dispersive X-ray analyses show an alteration in the Te/Cd relative to the deposition temperature. Higher Te ratio with respect to Cd was revealed at deposition temperature lower than 85 • C. The photoelectrochemical cell study shows that both pand n-type CdTe can be electroplated and that deposition temperatures below 85 • C at 1400 mV results in p-type CdTe layers.Coatings 2019, 9, 370 2 of 15 cadmium telluride (CdTe) thin-films can be grown and incorporated for different applications. CdTe is one of the II-VI semiconductor materials that has been grown using several techniques including electroplating [4,5] and has been extensively researched owing to its properties [6]. Due to the direct bandgap of CdTe at room temperature (~1.45 eV), it is capable of absorbing a substantial fraction of the electromagnetic spectrum under AM1.5 conditions. This characteristic has been explored in the photovoltaic (PV) community in achieving high-efficiency CdTe-based solar cells [7]. The recent hike in the conversion efficiency from 16.5% in 2004 [8] to 22.1% in 2016 [9] as reported in the literature is mainly due to the eradication of defects within the crystal lattice or traps within the bandgap in addition to improved crystallinity, passivation of the grain boundaries which is due to better understanding of both material and device issues. Therefore, it is fundamental to strive towards process optimization amongst others. Under both two and three-electrode electrodeposition configurations, different deposition temp...

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“…This is justified by recrystallisation and grain growth, optimisation of electrical conductivity and doping concentration, passivation of grain boundaries, optimisation of the CdS/CdTe interface morphology, improvement in Cd:Te stoichiometric composition, reduction of Te precipitation amongst other advantages observed after PGT in the presence of some halogen based salts and gases [5]- [9]. As documented in the literature, it is challenging to completely avoid the presence of Te precipitates in CdTe by modifying the growth technique, growth process or postgrowth treatment [10]- [12]. Fernandez, 2003, discussed that the presence of Te precipitates is attributed to peculiarities of the CdTe phase diagram [13] with Te-rich composition in the vicinity of melting point and a strong retrograde character of solidus on Te-rich side of homogeneity region [14].…”

Section: Introductionmentioning

confidence: 99%

Effect of the inclusion of galium in normal cadmium chloride treatment on electrical properties OF CdS/CdTe solar cell

Olusola

Materials Chemistry and Physics

2017