Atomic Layer Epitaxy Research Articles

Electrical properties of GaAsN/GaAs-superlattice films with different N distributions fabricated by atomic layer epitaxy

The effects of nitrogen (N) distribution on the electrical properties of GaAsN films were evaluated by intentionally changing the N distribution using atomic layer epitaxy (ALE) and post-annealing. The N distribution was controlled in the growth direction by growing superlattice (SL) thin films repeatedly growing 1 GaAsN layer and 0, 3, and 5 layers of GaAs by ALE. These films were referred to as (1:0), (1:3), and (1:5), respectively. To change the N distribution in the same thin film, N atoms were diffused by post-annealing. Changes in N distribution were evaluated by X-ray diffraction as changes in GaAsN superstructure. N atoms diffused from GaAsN layers to the adjacent layers in (1:3) films annealed above 750 °C, while they remained stable in those of (1:5) films annealed at temperatures up to 850 °C. The carrier mobility of both films increased monotonically with the annealing temperature. The concentration of ionized scattering centers decreased significantly in films annealed at 650 °C (independent of their N distributions) owing to the elimination of donor-type defects by annealing. Contrarily, the concentrations of N-induced scattering centers in (1:5) films annealed below 900 °C were similar, while those in (1:3) films annealed above 750 °C decreased significantly, in agreement with the N-atom diffusion behavior of GaAsN layers. Thus, N-distribution homogenization can be related to the reduction of N-induced scattering centers.

Controllable synthesis of Ag2Se binary thin-film via electrochemical atomic layer epitaxy (ECALE) and its characterization

Herein, synthesis of Ag2Se nanofilms was attempted for the first time at room temperature using electrochemical atomic layer epitaxy (ECALE) in underpotential deposition (UPD) basis. Spectrochemical/electrochemical measurements verified a 2-D growth for the Ag–Se films when the deposition potentials were gradually adjusted to negative (−1 mV/cycle). Electrochemical impedance spectroscopy (EIS) measurements illustrated less interfacial charge transfer resistance at the nanofilm coated surface. Scanning electron microscope (SEM) indicated that the film was composed of crystallites with size of around 110 nm. Energy dispersive X-ray spectroscopy (EDS) analyzes verified the 2:1 stoichiometric ratio for the compound and X-ray diffraction (XRD) analysis confirmed an orthorhombic β-Ag2Se crystalline phase. Ultraviolet–visible (UV–Vis) absorption measurements were performed to estimate the band gap of Ag2Se thin-film. Contact angle (CA) measurements demonstrated a decreased surface wettability. The proposed ECALE approach offered a low-cost and a facile method for the synthesis of epitaxial Ag2Se nanofilms that could be controlled at the atomic level.

(Invited) Understanding Plasma-Assisted Atomic Layer Epitaxy of InN and Opportunities for Collaboration through the Office of Naval Research Global

The family of III-V nitride compound semiconductors has provided the foundation to a number of advanced electronic device technologies from light emitting diodes to radio frequency transistors to power switches. Of the family, binary indium nitride (InN) and ternaries/quaternaries containing InN have progressed at a slower pace due the material properties and related growth challenges. Having the weakest bonds in the family, the material has a lower melting point and more easily decomposes and phase separates (in ternaries and quaternaries). As such, a number of research efforts are looking for new growth approaches to overcome these challenges and realize the InN-based materials that will enable devices such has high speed switches and IR emitters and detectors.To this end, plasma-assisted atomic layer epitaxy (PA-ALE) of InN and InN-containing ternaries has been explored in recent years. Much like atomic layer deposition, ALE consists of a sequence of self-limiting surface half-reactions that promotes “layer-by-layer” growth of films. The cyclical growth process starts with exposure of the growth surface first to the group III precursor (trimethylindium, for example), then purging excess precursor and reaction byproducts leaving only the ad-/physi-/chemi-sorbed species on the surface. After this purge, these surfaces are then exposed to a collection of plasma species (ions, radicals, neutrals, etc.) which reacts with the “sorbed” layer. The growth cycle is finished with a purge of the surface reaction by-products and unreacted plasma species before repeating. The potential of the process is based on the premise that by providing energy from plasma species to the growth surface, one can lower the temperature of growth to improve the stability of the material. Further, the reactive neutral plasma species also play a role by lowering activation energies for chemical reactions compared to thermal ALD, without necessarily providing energy to the growth surface.A brief review of previous experimental demonstrations of epitaxial growth of InN and InN-containing ternaries will be presented showing the promise of the growth method to grow quality InN binary films and metastable ternaries containing InN not possible by conventional growth methods. For example, a metastable cubic phase of InN (NaCl) was realized as were ternary stoichiometries for both InAlN and InGaN that lie in the thermodynamic miscibility gap. Further, and in an effort to begin to understand this growth process and the role that plasma might play in growth mechanisms, synchrotron-based studies have been employed during growth of binary InN and digital InAlN and InGaN alloys. The results of these studies will be highlighted and key findings identified. Most recently, coherent x-ray scattering has been employed to provide additional insights including surface diffusion during each step of the cyclical growth process. The cumulative findings of these efforts will be presented, and future directions outlined.As the presenting author is now detailed as a Science Director for Power & Energy and Advanced Materials to the U.S. Office of Naval Research Global in London, the last portion of the talk will be dedicated to introducing ONRG and its mission to engage international researchers through research grants, travel grants and conference support. The hope is to increase awareness of collaborative opportunities to the global research community expected to be in attendance.

Overview of the process technology for the preparation of ultrahigh purity indium required for the fabrication of indium phosphide related epitaxial structures based devices needed for advanced electronic applications

Indium, a rare metal, is created incidentally during the zinc refining process. When a zinc metal is produced, valuable elements, such as indium, are recovered and reused. The sulfide minerals, sphalerite, galena, and chalcopyrite, are all common hosts for indium metals. Indium metals of varying purities (from 99% to 99.9%) are used in many different commercial, other exclusive, specialty, dentistry, and research and development settings. In the production of indium phosphide and related select bulk single crystals, such as InP, InAs, InSb, etc., and select multilayered epitaxial material-systems based device structures, such as InGaAs/InP, InGaAsP/InP, etc., an ultrahigh purity (99.99999%) indium metal is used as one of the initial and primary input materials. light-emitting diodes, infrared detectors, lasers, and other components cannot be made without these device topologies. Triple junction solar cells made of GaInP, GaAs, and Ge with 40% conversion efficiency are being developed for use in space. Metal-organic and molecular beam epitaxial methods utilize trimethyl/triethyl-indium-epi-precursors, the high purity indium derivatives, as starting materials to develop and manufacture multilayered structures of InGaAs/InP, InGaAsP/InP, InGaN/InP AlInN, etc. The purpose of this review is to quickly touch on indium mineral sources, important uses for different indium metal grades, and the processes needed to refine, purify, and ultrahigh purify indium to higher purity levels using a zone refining–melting–leveling process, as well as impurity segregation considerations. The use of vacuum, inert gas environments, and an external electromagnetic field to efficiently segregate, levitate, stir, homogenize, and mix the molten zone/melt interface area (region) as well as purity analyses at ppb levels, class clean room, and packaging concepts were also discussed. This review also touched briefly on the use of ultrahigh purity indium in the preparation of TMIn, TEIn, and InCl precursors necessary for the growth of device structures by molecular beam, metal-organic vapor phase, atomic layer epitaxial, and chemical vapor deposition processes. Purifying and preparing polycrystalline indium to a type 7 N purity level as well as standardization and criticality testing for fine-tuning system parameters are essential parts of developing the purification process technology. It also highlights various compound semiconductors and epitaxial systems, such as high purity indium compounds, such as indium phosphide, for cutting-edge electronic applications. Material yield enhancement, impurity management (including C, O, N, and others), consistent results, impurity reduction (down to the ppb level), and class clean packaging are all active topics of research and development. There has been a rise in demand for ultrapure metals (7–10 N) with stringent purity criteria in the aerospace and defense sectors, where they are used in cutting-edge nanoelectronic applications. This literature review delves into these and related topics regarding the production of ultrahigh purity indium. The major objective of this review is to provide a concise summary of the research and development progress made toward the ultrahigh purity (7N-99.99999%) indium preparation and its epitaxial electronics application considerations as of the time of this writing.

Influence of Pulse Atomic-Layer Epitaxy (PALE) AlN Buffer Layer on Quality of MOCVD Grown GaN on Si(111) Substrate.

A crack-free GaN-on-Si with a high capability to grow a thick GaN layer is important for the performance of optoelectronic devices. Regrettably, a large lattice and thermal mismatch degraded the quality of GaN-on-Si. Therefore, we introduce the pulse atomic-layer epitaxy (PALE) AlN buffer layer to overcome the surface crack issues and improve the quality of GaN epilayers. The effect of PALE AlN buffer layer with 0, 35, 70, and 140 cycle numbers towards the quality of grown GaN on Si(111) substrate is studied. All samples have been observed using AFM, FESEM, XRD and Raman spectroscopy. AFM imaging revealed a fully-coalesced and clear step flow GaN layer with the lowest RMS roughness of 0.606 nm. FESEM surface morphology shows a crack occurs on a sample without AlN PALE (0 pulse cycle) while crack-free GaN is obtained for samples with AlN PALE layer (35, 70 and 140 cycles). It was observed by XRD that the AlN PALE pulse cycle number greatly affects the structural properties of the top GaN layer where the lowest x-ray rocking curve for (002) and (102) achieved at 70 cycles, indicating the reduction of threading dislocations density in the growth structure. Further, the transition of the GaN E2 (high) from the Raman spectroscopy revealed a tensile strain in the GaN epilayers reduces with the increasing number of pulse cycles.

Hybrid of Bi/PbS submicron-plates NIR photodetector with localized surface plasmon resonance enhanced effect

Metal nanoparticle-enhanced lead sulfide as a sensing material for the near-infrared has attracted much attention because it can produce a remarkable photoelectric phenomenon. In this paper, we report a hybrid structure of nanoparticle Bi/PbS submicron plate photodetector was fabricated by electrochemical atomic layer epitaxy (ECALE). The PbS rods of as-synthesized hybrid structure is a high-quality single crystal and Bi is perfectly coated on the surface of PbS were verified by SEM, AFM, TEM, and so on. Meanwhile, the influence of Bi on the device performance was systematically studied, and the photodetector was fabricated based on the Bi/PbS hybrid structure exhibiting excellent properties with the responsivity (R) and detectivity (D*) of about 80.13 A/W and 4.89 × 109 Jones in 1550 nm, respectively. And its response speed has also been greatly improved compared to previous studies. Our work paves the way for the high-sensitivity photodetector based on metal nanoparticles (MNPs) and semiconductors for industrial and commercial applications.

Enhancement of gallium nitride on silicon (111) using pulse atomic-layer epitaxy (PALE) AlN with composition-graded AlGaN buffer

The ability to configure the optimal buffer layer for GaN growth depends on the knowledge of relaxation processes that occurs during the cooling step while countering the tensile stresses due to the contrast of thermal expansion coefficient between GaN and Si(111) substrate. Here, we inaugurate the pulse atomic-layer epitaxy (PALE) AlN layer to reinforce the buffer layer to achieve a thick GaN epilayer which is crucial for high performance power devices. The characteristics of grown GaN on Si substrate based on PALE AlN thickness of 0 ~ 100 nm are investigated along with microstructural evolution between AlN NL and composition-graded AlGaN buffer layer. PALE AlN layer deposited with an optimum thickness of 50 nm and above was observed to exhibit a highly uniform coalesced GaN epilayer surface with root-mean square (RMS) roughness of 0.512 nm. The thickness of the PALE AlN layer substantially affected the crystallinity of the top GaN epilayer where the lowest value for symmetric (0 0 0 2) and asymmetric (1 0 -1 2) x-ray rocking curve analysis were achieved, indicating the reduction of threading dislocation density in the growth structure. Transition of the E2 (high) peak from the Raman spectrum shows that the strain compression in GaN epilayer is directly proportional to the thickness of the PALE AlN layer.

Sulfide‐Inhibiting Growth of Lead Sulfide Rods Array Film from Micron to Nano for NIR Photodetector

In general, the growth rate of lead sulfide (PbS) crystals in the solution is fast, and it is difficult to obtain nanosized structure films without the presence of inhibitors. Herein, highly crystalline 1D single‐crystal PbS nanorods array on the graphene substrate is prepared in the solution containing a high‐concentration sulfur ion as the inhibitors by electrochemical atomic layer epitaxy (ECALE) method. Meanwhile, the diameter of the PbS array from micrometers to nanometers can be controlled by adjusting the ratio of lead and sulfur. Through polarization studies on graphene substrates, the critical role of Au–thiolate in the vertical growth of PbS nanorod is controlled. Finally, the PbS array–graphene heterostructure photodetector presents an extraordinary photoresponsivity in 1.55 μm at room temperature.

Growth and characterization of PALE Si-doped AlN on sapphire substrate by MOVPE

In this study, we report different SiH4 flow condition effects on crystal, surface, optical, and electrical characteristics of heteroepitaxial Metal-Organic Vapor Phase Epitaxy (MOVPE) grown AlN layers on sapphire substrates. Adjustment of growth kinetics is very important to control the doping. Therefore, pulsed atomic layer epitaxy (PALE) was used to control the growth kinetics and reduce parasitic reactions that inevitably caused adverse impact on the properties of the epitaxial AlN films. As a result of HRXRD (high resolution x-ray diffraction) analysis, the (002) ω FWHM decreased significantly with the PALE method, while the increase occurred due to the development of V defects for the (102) ω scan. Atomic force microscopy (AFM) analyzes showed that SiH4 led to a 3D-like growth mode. It was demonstrated that the increased SiH4 flow increased Si incorporation into the Si-doped AlN layer while increased the sheet resistance due to the self-compensating effect obtained from secondary ion mass spectroscopy (SIMS) and I–V measurement results.

Spectroscopic evidence of tunnel coupling between CdTe quantum wells in the CdTe/ZnTe heterostructures

The photoluminescence (PL) spectra of CdTe/ZnTe double quantum wells (QWs) are studied on a series of samples containing two CdTe layers with nominal thicknesses of 2 and 4 monolayers (ML) in the ZnTe matrix. The QWs were grown in atomic-layer epitaxy and separated by ZnTe spacers with the thicknesses dsp =40−160 ML. The dependences of the relative intensity of shallow QW1 and deep QW2 PL bands (I1 and I2 , respectively) on the pump intensity (J) when excited by the lasers with different radiation wavelengths are investigated. It is found that in the sample with dsp=40 ML, the ratio Y(J)=I1/I2 depends on J and the shape of the Y(J) dependency changes with the excitation wavelength. In the samples with dsp > 70 ML Y(J) also changes with the excitation intensity J, but the shape of this dependence is the same for various excitation wavelengths. It is concluded that the energy relaxation in these samples is influenced not only by the tunneling of charge carriers from QW1 to QW2, but also by carrier relaxation at the nonradiative centers, for which the recombination rate is different for shallow and deep QWs.

Correlation of early-stage growth process conditions with dislocation evolution in MOCVD-based GaP/Si heteroepitaxy

To identify the complex relationships between early-stage growth processes and the resultant defect microstructure in GaP/Si heteroepitaxy, a holistic study of several key metal–organic chemical vapor deposition (MOCVD) parameters was conducted, focusing on Si surface preparation and GaP atomic layer epitaxy (ALE) based nucleation processes. Crystalline defects related to the lattice mismatch and/or interfacial heterovalency, namely misfit dislocations (MD), threading dislocations (TD), and stacking fault pyramids (SFP), were quantitatively characterized via electron channeling contrast imaging (ECCI) and correlated against the different process variations. Choice of Si surface preparation method between the two examined (dilute SiH4 annealing versus Si2H6 based homoepitaxy) had little impact on resultant GaP film morphology and defect content, whereas differing GaP ALE nucleation conditions produced much more substantial changes. In particular, the initial precursor species (tert-butylphosphine versus triethygallium) and ALE cycle purge times both yielded significant influence over threading dislocation densities (TDD) in thin (100 nm), post-critical thickness GaP/Si films, with TDD spanning two orders of magnitude, from 6.7 × 107 cm−2 to 7.1 × 105 cm−2, depending on the specific process conditions employed. SFP densities were also found to follow a similar trend, ranging from 2.0 × 107 cm−2 to 1.8 × 105 cm−2, but with no apparent causal relationship between SFP density and TDD. To help explain the dramatic differences observed, detailed, large-area MD network characterization was used to provide statistically-relevant quantitative analyses of the critical dislocation dynamics (introduction rates and glide velocities) associated with the different process variants. These extracted values are then correlated against the ALE process variants to provide insight into the potential mechanistic roles of the different growth processes.

Surface Diffusion of Underpotential‐Deposited Lead Adatoms on Gold Nanoelectrodes

AbstractA simple and readily applicable voltammetric approach is described to characterize and measure the site‐hopping surface diffusion of underpotential‐deposited (UPD) metal adatoms at nanoelectrodes. UPD refers to the deposition of atoms on foreign metal supports at potentials lower than those predicted by Nernst law for a bulk deposition. Despite its importance in several fields of catalysis, advanced nanofabrication or even atomic nanoengineering by atomic layer epitaxy, diffusion of UPD adatoms is difficult to observe at micro‐ and macroelectrodes. In fact, at electrodes of usual dimensions, UPD adatoms surface diffusion is masked by other electrochemical phenomena of greater relative amplitudes. Conversely, at nanowires electrodes sealed in glass, only an extremely small fraction of the surface of the wires is exposed to the electrolyte solution and is rapidly loaded. This allows the spillage of UPD adatoms onto the much larger area of the nanowire rod which is immune to Faradaic reactions due to its isolation from the electrochemical solution by the glass casing. Therefore, surprisingly for a UPD process, voltammetric peaks currents and integral desorption charges primarily reflect these diffusional surface processes so that the integral charges vary linearly with the inverse of the square root of the scan rate. This is easily observable and measurable with usual bench‐level electrochemical instrumentation. In this work, by using nanoelectrodes with diameters between 90 and 260 nm, we were able to establish the major involvement of this site‐hopping surface diffusion of UPD Pb adatoms on polycrystalline gold (Au) and characterize it quantitatively. The equivalent surface diffusion coefficient of UPD Pb adatoms was determined to be ∼4.4×10−11 cm2 s−1 at room temperature, corresponding to a Gibbs free energy activation barrier of ca. 18.72 kJ mol−1 (i. e., 0.19 eV per Pb adatom) for the reaction of inter‐sites exchange of Pb adatoms on a polycrystalline Au surface.

Fabrication of Plasmonic Nano-Slit Pore Double Layer for Single Molecule Detection

We fabricated the plasmonic nano-slit pore platforms for single molecule detection and other various applications. The nano-apertures on the Au/insulator/Au/SiN flat membrane, in addition to the 200 nm thick Au film on ~ 20 nm thick SiN membrane were fabricated using a focused ion beam drilling technique. The insulating materials of SiO2 or Al2O3 were deposited using an atomic layer epitaxy technique. The nanopores with a few nanometer size were fabricated under the proper control of drilling depth and pore opening. Optical characteristics were carried out dependent upon the pore opening width and sample thickness. The broad emission spectra from the (7x 7) slit pore array are obtained via spp-mediated emission on the ~200 nm thick Au/~ 20 nm thick SiN flat samples. A sharp strong infrared emission peak is also obtained due to Au nanoparticle. The fabricated Au double layer platform will be investigated for a single molecule sensor device and a possible radiative thermal energy transfer device.

Microstructure and Interfaces of Ultra-Thin Epitaxial AlN Films Grown by Plasma-Enhanced Atomic Layer Deposition at Relatively Low Temperatures

We demonstrate the growth of ultra-thin AlN films on Si (111) and on a GaN/sapphire (0001) substrate using atomic layer epitaxy in the temperature range of 360 to 420 °C. Transmission electron microscopy and X-ray diffraction were used to characterize the interfaces, fine scale microstructure, and the crystalline quality of thin films. Films were deposited epitaxily on Si (111) with a hexagonal structure, while on the GaN/sapphire (0001) substrate, the AlN film is epitaxial and has been deposited in a metastable zinc-blende cubic phase. Transmission electron microscopy reveals that the interface is not sharp, containing an intermixing layer with cubic AlN. We show that the substrate, particularly the strain, plays a major role in dictating the crystal structure of AlN. The strain, estimated in the observed orientation relation, is significantly lower for cubic AlN on hexagonal GaN as compared to the hexagonal AlN on hexagonal GaN. On the Si (111) substrate, on the other hand, the strain in the observed orientation relation is 0.8% for hexagonal AlN, which is substantially lower than the strain estimated for the cubic AlN on Si(111).

Influence of the PALE growth temperature on quality of MOVPE grown AlN/Si (111)

In the present study, the PALE-AlN (pulsed atomic layer epitaxy) epilayers were grown on the Si (111) substrates at different growth temperatures by metal organic vapor phase epitaxy (MOVPE) technique. The oxygen (O) and silicon (Si) concentrations of grown PALE-AlN epilayers and interface between epilayer and substrate were investigated by secondary ion mass spectroscopy (SIMS). It was observed that O and Si concentration change with growth temperature of epilayers as well as the interface significantly. HRXRD (high-resolution x-ray diffraction) analyses showed that the highest growth temperature results with the lowest full width at half maximum (FWHM) value for both ɷ scans. Scanning electron microscope (SEM) and atomic force microscopy (AFM) analyses indicated that relatively low growth temperature grown samples gave rise to 2D-like growth mode with openings while increased growth temperature resulted in change the growth mode to a columnar mode with increasing V-shape pits because of the increasing diffusion coefficient of O impurities and Si atoms in AlN epilayers.

Diminishing the Induced Strain and Oxygen Incorporation on Aluminium Nitride Films Deposited Using Pulsed Atomic-Layer Epitaxy Techniques at Standard Pressure MOCVD

A pulsed atomic-layer epitaxy growth technique has been introduced to substantially diminish the induced strain and oxygen incorporation on aluminium nitride films grown at standard pressure by metal organic chemical vapour deposition. The qualities of the as-deposited aluminium nitride films were studied by varying the aluminium nitride nucleation layer growth temperature at 700°C, 800°C, 900°C, 1000°C and 1100°C, respectively. The compressive strain inside the as-deposited aluminium nitride films, induced by the hetero-epitaxial growth on sapphire, was investigated through Raman spectroscopy by focusing on the evolution of E2 (high) peak frequency, where almost stress-free aluminium nitride films were attained at nucleation layer growth temperature of 1100°C. Then, the correlation between luminescence defect and level of foreign impurities respective to the varied nucleation layer growth temperatures were also systematically analysed through photoluminescence spectroscopy and x-ray photoelectron spectroscopy, respectively.

Band offset determination for amorphous Al2O3 deposited on bulk AlN and atomic-layer epitaxial AlN on sapphire

Valence and conduction band offsets of atomic layer deposition (ALD) Al2O3 deposited on bulk AlN crystals were determined using x-ray photoelectron spectroscopy to be ΔEV = 0.75 eV and ΔEC = −1.45 eV, with a measured energy gap of the Al2O3 film of 6.9 eV. In addition, crystalline AlN deposited by atomic layer epitaxy on sapphire was evaluated, resulting in a valence band offset of ΔEV = −0.75 eV and a conduction band offset of ΔEC = 3.25 eV due to the wider bandgap of the crystalline Al2O3 substrate compared to amorphous ALD Al2O3. Both heterojunctions exhibited type-II behavior and similar valence band offsets.

Deposition of Sb2Se3 thin films on Pt substrate via electro-chemical atomic layer epitaxy (EC-ALE)

Abstract This work deals with the deposition of a Sb2Se3 thin film on a Pt substrate using Electro-Chemical Atomic Layer Epitaxy (EC-ALE). We first investigated the UPD of selenium on a Pt substrate. Two routes have been evidenced to get a UPD layer of Se, either the polarization of the Pt-substrate at around 0.35 V in the Se solution or the deposition of full UPD Se together with bulk deposition of Se and dissolution of the latter one at lower potentials. The following investigation on the electrochemical behavior of antimony on selenium-covered platinum electrode by cyclic voltammetry and anodic potentiodynamic studies led us to choose the two-steps procedure for the Se deposition. After an optimization of the deposition parameters, the alternate deposition of Sb and Se elements to form the Sb2Se3 compound by EC-ALE on platinum substrate has been performed. The stoichiometry of the deposited film has been evaluated by coulometry and it has been confirmed by atomic force microscopy (AFM).

Atomic Layer Epitaxy of III-Nitrides: A Microscopic Model of Homoepitaxial Growth.

We develop a microscopic theoretical model of AlN, GaN, and InN film growth by atomic layer epitaxy. To make the model realistic, we take into account the atomic hydrogen that is created by the hydrogen plasma commonly used in plasma-assisted atomic layer epitaxy. This growth technique relies on separate deposition steps for nitrogen and the group-III cation. Our model addresses the processes that occur after a complete monolayer of nitrogen has formed, that is, the deposition, adsorption, surface diffusion, island nucleation, and island growth of group-III cations. According to our model, the three nitrides grow in a standard and qualitatively similar manner: during a brief nucleation phase, a modest attractive interaction leads to stable island nuclei consisting of just a few atoms. These then grow in place at a nearly constant island density and with an island size distribution which obeys an expected universal scaling relationship that depends only on the critical island size.

Electrodeposition of copper (II) sulfide and zinc sulfide onto polycrystalline gold electrode

An electrodeposition-based process was developed in this work. Electrochemical atomic layer epitaxy (ECALE) and co-deposition methodologies were employed to grow copper (II) sulfide (CuS) and zinc sulfide (ZnS) thin films as photovoltaic semiconductors on polycrystalline gold electrode. The deposition potentials of copper (Cu), zinc (Zn) and sulfur (S) were defined separately by cyclic voltammetry. Thin films were created from an electrolyte containing copper (II) sulfate (CuSO4), sodium sulfur (Na2S) and zinc sulfate (ZnSO4) in ethylenediaminetetraacetic acid (EDTA) using both cyclic voltammetry and bulk electrolysis techniques. The influence of bath temperature at the deposition potential was studied to determine the crystallinity of deposits. From the chronoamperometry results including the transients obtained within the under potential region, the nucleation and growth process of deposits were estimated. In this way, an electrodeposition-based method for CuS and ZnS semiconductors in a comparable basis was improved on polycrystalline gold substrate.