Formation of CuIn (1-x) Ga x Se 2 (CIGS) by Electrochemical Atomic Layer Deposition (ALD)

The chalcopyrite CuIn (1-x) Ga x Se 2 (CIGS) thin films were grown on Mo substrate by electrochemical atomic layer deposition (E-ALD) of superlattice sequencing 2InSe/2GaSe/1CuSe, recently developed on model Au surface by Stickney and coworkers (J. Electrochem. Soc. 161, D141 (2014)). The cyclic voltammetry studies were conducted on copper, selenium, indium and gallium on molybdenum substrate and CIGS films were grown by different numbers of superlattice sequencing. The deposited films were examined for phase and microstructure formations by X-ray diffraction (XRD), scanning electron microscopy (SEM), scanning tunneling microscopy (STM) and energy dispersive spectroscopy (EDS). The XRD pattern corresponded to those of chalcopyrite crystalline phase of CIGS and the crystallite size increased with the number of cycles or periods of whole superlattice sequencing increased. The SEM and STM results were in line with those of XRD by showing that the particle size increased as the number of E-ALD cycles increased. The EDS results revealed the CIGS with near stoichiometry. Finally, the deposited E-ALD films were shown to be photoelectrochemically active with p-type conductivity. We wish to describe the preparation of CuIn (1-x) Ga x Se 2 (CIGS) by means of electrochemical atomic layer deposition (E-ALD) on Mo substrate of each component element in aqueous solutions at ambient laboratory conditions and to show that the resulting films are photoelectrochemically active with p-type conductivity.Solar energy, the prominent energy source of the universe could be properly utilized for the current increasing trends for energy needs of our entire planet. Alternate energy production technologies like thin film solar cells have been successfully competing traditional energy production methods raised over recent years.1-3 The chalcopyrite Cu(In,Ga)(Se/S) 2 modules of thin films are the promising tool in commercially manufacturing thin film photovoltaic (PV) technologies available in PV market today. 4 The chalcopyrites CIGS are compound semiconductors which are largely known for high absorption coefficient (1 × 10 5 cm −1 ) at photons above the bandgap. 5 The Ga substitution can make the compound with highly adjustable bandgap (1.04 eV for CuInSe 2 (x = 0) to 1.68 eV for CuGaSe 2 (x = 1)) 6 with high stability under high energy irradiation. 7,8 The bandgap of the material is more closely found with the optimum conversion efficiency range (1.4 ∼ 1.5 eV) of solar radiation.9 Because of these properties, it attracted considerable interests by the researchers and industrialists to use CIGS as light-absorbing materials for thin film photovoltaic cells.7-10 Recent works on CIGS have achieved the power conversion efficiency up to 22.6% in laboratory scale. [20][21][22][23] These synthesis methods need larger investment in machinery and workspace which involve highly complicated instruments. The difficulties are with the problems in maintaining the laboratory conditions, complicated procedures and unusual release of heat and toxic byprod...

Section: Resultsmentioning

confidence: 99%

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confidence: 99%

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confidence: 99%

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Electrochemical Atomic Layer Deposition of CuIn_(1-x)Ga_xSe₂on Mo Substrate

Ramasamy¹,

Jung²,

Yeon³

et al. 2017

“…In the present work, an electrochemical technique * Electrochemical Society Member. [39][40][41] In the following introductory discussion, the process of e-ALD of Cu is described as a representative example. The conventional Cu e-ALD process begins with the deposition of a sacrificial lead (Pb) monolayer onto a foreign substrate via underpotential deposition (UPD) in a Pb +2 -containing electrolyte.…”

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Electrochemical Atomic Layer Deposition of Cobalt Enabled by the Surface-Limited Redox Replacement of Underpotentially Deposited Zinc

Venkatraman

Dordi

Akolkar

2017

Electrochemical atomic layer deposition (e-ALD) process for fabricating cobalt (Co) nano-films is reported. The e-ALD process employs a two-step approach in which underpotential deposition (UPD) is first used to form a sacrificial adlayer of zinc (Zn) on a ruthenium (Ru) substrate. The sacrificial Zn adlayer then undergoes spontaneous surface-limited redox replacement (SLRR) by nobler Co. This provides an atomic layer of Co on the substrate surface. The two-step process is repeated cyclically to build multilayers of Co. The unique feature of the e-ALD approach presented herein is that it utilizes Zn as the sacrificial adlayer instead of Pb or Cu used conventionally in the e-ALD sequence of noble metals. The use of sacrificial Zn uniquely renders its redox replacement by Co to be thermodynamically favorable, thereby enabling Co e-ALD. In the present report, we discuss the electrochemical characteristics of the UPD and SLRR process steps, the e-ALD deposition rate and the deposit surface roughness. The Co deposits formed via e-ALD do not exhibit roughness amplification during the first 10 cycles of e-ALD, which is indicative of atomic-scale layer-by-layer growth of Co on the underlying Ru substrate. High-performance integrated circuits utilize nano-scale, currentcarrying copper (Cu) interconnects. In accordance with the Moore's law, 1 miniaturized interconnects are required in modern devices to obtain superior device performance. The continued shrinkage in the size (cross-sectional area) of each interconnect leads to an increase in its electrical resistance. This detrimentally impacts the electrical performance of the integrated circuit.2 Furthermore, aggressive interconnect size scaling below the 10 nm node poses challenges to void-free interconnect fabrication. State-of-the-art interconnects are fabricated of Cu metal due to its low electrical resistivity and superior electromigration resistance.3 The interconnect signal delay (τ) is given by τ = RC, where R is the interconnect resistance and C is the capacitance of the surrounding inter-layer dielectric. The interconnect resistance R increases dramatically for Cu interconnect dimensions below 40 nm due to the substantial increase in the electrical resistivity of Cu at such narrow dimensions. The resistivity increase is typically attributed to electron scattering processes at grain boundaries and at interfaces within the Cu interconnect structure. Such scattering processes become dominant when the interconnect dimension approaches the electron mean free path (EMFP = 39 nm at room temperature) in Cu.4,5 As a consequence, the interconnect signal delay increases. To overcome this critical issue, an interconnect material which exhibits lower electrical resistivity at narrow (sub 10 nm) dimensions is required. Cobalt (Co) is considered as a promising alternative interconnect material to replace the conventionally used Cu.6,7 At narrow dimensions, i.e., below 10 nm, Co exhibits comparable or lower electrical resistivity compared to Cu, largely attributed to the lower ...

“…Recent reports demonstrated the potential of electrodeposited ternary and quaternary chalcopyrite absorber layers for various solar energy conversion devices. [23][24][25][26] In spite of a good number of investigations on the electrodeposition of Cu, Se, In and Ga and the various compositions on different electrodes, [1][2][3][4] several concepts and explanations on the origin of different voltammetric peaks are still under debates. Reported works that methodically investigated the development of voltammetric peaks in unary, binary, ternary and quaternary compositions on Mo electrode (consolidated and compared in one work) are rare.…”

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Electrodeposition of Copper, Selenium, Indium, and Gallium on Molybdenum/Surface Oxides: Unary, Binary, Ternary and Quaternary Compositions

Saji

Jung

Lee

2015

A systematic investigation was performed to study the variation of cyclic voltammetry (CV) peaks during cathodic electrodeposition of unary, binary, ternary and quaternary compositions of copper (Cu), selenium (Se), indium (In) and gallium (Ga) on molybdenum/glass electrode. The major objective of the work was to methodically understand the variation of different oxidation-reduction peaks from unary to quaternary composition so that a comprehensible idea on their appearance could be arrived. The electrodeposits were further characterized by anodic stripping voltammetry and frequency response analyzer-impedance spectroscopy. Phase and microstructure of the electrodeposits were examined by X-ray diffraction, scanning electron microscopy and energy dispersive spectroscopy. The results presented were helpful to arrive at new conclusions on the variation of different CV peaks such as Mo/surface oxide'scharacteristic redox peak and In-characteristic oxidation peak. The present work will be of significance in different application areas like surface coatings, electronics and chalcopyrite solar cells, where electrodeposited Cu-Se-In-Ga is of importance.Electrodeposition has been widely investigated as a simple and economic alternative to the vacuum deposition techniques in fabricating various industrially important materials in thin film and bulk dimensions. 1-4 Electrodeposition of unary, binary, ternary and quaternary compositions of copper (Cu), selenium (Se), indium (In) and gallium (Ga) has a wide range of applications. 1-8 Cu electrodeposition on foreign substrates plays a key role in electronic industry 1 and protective/decorative coatings. 2 Electrodeposition of trigonal Se and compound semiconductors of Se have a variety of interesting applications in solar cells, rectifiers, medical diagnostics and xerography. 4 In has been widely used in alloys, 5 electronics and catalytic organic synthesis. 6 Ga is important in semiconductor and electronics industries due to its unique electrical and thermal properties. Ga plays an important role in achieving high efficiency chalcopyrite solar cells. 3,7,8 One-step electrodeposition was widely investigated for growing large area polycrystalline CuInSe 2 /Cu(In x Ga (1-x) )Se 2 (CIS/CIGS) films on molybdenum (Mo) at potentials as high as −0.90 V (vs. Ag/AgCl). A number of studies have investigated the mechanism of deposition of ternary CIS 9-17 and quaternary CIGS. 13,18-22 Proper understanding of voltammetric behaviors of individual elements and their variation on moving from unary to quaternary composition is vital in optimizing the deposition parameters and elucidating the deposition mechanism. Recent reports demonstrated the potential of electrodeposited ternary and quaternary chalcopyrite absorber layers for various solar energy conversion devices. [23][24][25][26] In spite of a good number of investigations on the electrodeposition of Cu, Se, In and Ga and the various compositions on different electrodes, 1-4,7-46 several concepts and explanations on the origin of differ...