Approach for Al2O3 rear surface passivation of industrial p‐type Si PERC above 19%

Atomic layer deposition (ALD) of thin Al₂O₃ (≤10 nm) films is used to improve the rear surface passivation of large‐area screen‐printed p‐type Si passivated emitter and rear cells (PERC). A blister‐free stack of Al₂O₃/SiO_x/SiN_x is developed, leading to an improved back reflection and a rear recombination current (J_0,rear) of 92 ± 6 fA/cm². The Al₂O₃/SiO_x/SiN_x stack is blister‐free if a 700°C anneal in N₂ is performed after the Al₂O₃ deposition and prior to the SiO_x/SiN_x capping. A clear relationship between blistering density and lower open‐circuit voltage (V_OC) due to increased rear contacting area is shown. In case of the blister‐free Al₂O₃/SiO_x/SiN_x rear surface passivation stack, an average cell efficiency of 19.0% is reached and independently confirmed by FhG‐ISE CalLab. Compared with SiO_x/SiN_x‐passivated PERC, there is an obvious gain in V_OC and short‐circuit current (J_SC) of 5 mV and 0.2 mA/cm², respectively, thanks to improved rear surface passivation and rear internal reflection. Copyright © 2012 John Wiley & Sons, Ltd.     

Flat band voltage modulation of AlGaN/GaN MOS capacitor with stacked Al2O3/La2O3 high dielectric structures

AlGaN/GaN metal-oxide-semiconductor (MOS) capacitor structures using atomic layer deposited high-dielectric-constant (High-k) Al₂O₃/La₂O₃ bilayer films as dielectric have been investigated using high-frequency capacitance-voltage measurement. The stable thickness and uniform surface morphology of the bilayer films with different La/Al deposition cycle ratio (La/Al ratio) were observed after rapid thermal annealing by spectroscopic ellipsometry and atomic force microscopy, respectively. We have found that with a decrease of the La/Al ratio, the dipole layer observed by X-ray photoelectron spectroscopy at Al₂O₃/La₂O₃ interfaces is close to the surface of semiconductor and the flat band voltage shifts to the negative direction. Furthermore, the dramatic drop in dielectric constant of the films as La/Al ratio decrease was caused by the formation of La(OH)₃ in La₂O₃. Finally, the reason for the flat band voltage shifts, which is based on the dielectric constant of Al₂O₃ and La₂O₃ comprising the position of dipole layer in the dielectric films, is proposed.     

Alternative precursor systems for the MOCVD of aluminium nitride and gallium nitride

Two alternative precursor systems have been investigated for the growth of AlN and GaN by MOCVD. The first involved the reaction between Me₃M (M(DOUBLE BOND)Al, Ga) and tert-butylamine (^tBuNH₂), whilst the second route involved the pyrolysis of single-source precursors such as Me₃M(NH₃) (M(DOUBLE BOND)Al, Ga) and [Me₂Ga(NH₂)]₃. Both routes proved suitable for the deposition of AlN thin films, and epitaxial AlN layers have been deposited on sapphire (0001) from Me₃Al(NH₃) without any added NH₃. Attempts to grow GaN from Me₃Ga/^tBuNH₂ mixtures or Me₃Ga(NH₃) were unsuccessful, leading to the deposition of Ga droplets, although GaN films containing a large excess of Ga were deposited by low-pressure MOCVD from the single-source precursor [Me₂Ga(NH₂)]₃.     

Study of charge storage behavior in metal-alumina-silicon dioxide-silicon(MAOS) field effect transistor

The basic characteristics and charge storage behavior of metal-alumina-silicon dioxide-silicon(MAOS) field effect transistors have been investigated as a function of the oxide thickness. The typical charge storage behaviors have also been measured on devices with SiO₂ films of 50 Å and Al₂O₃ films of 700 Å and the results are interpreted in terms of electron and hole transport processes across thin SiO₂ layer and electron injection from Al electrode by tunneling mechanism. In the MAOS structure, the shift of threshold voltage from initial state is within about 23 V and can be reversibly controlled, more than 10⁶-times at least, by alternate electric fields under suitable stressing condition. It is considered that the charge storage time is practically infinite at room temperature and of the order of 10⁶ hr at 150°C. The failure behaviors of device parameters under the repeated field stressing and cycles can be also accounted for in terms of electron accumulation within Al₂O₃ films and at interfaces between Al₂O₃ and SiO₂ films.     

Stack engineering of low-temperature-processing Al2O3 dielectrics prepared by nitric acid oxidation for MOS structure

The electrical characteristics of low-temperature-processing Al₂O₃ films were studied. With an anodization SiO₂ film as a buffer layer, Al₂O₃ dielectric was grown on it by oxidizing an ultra-thin aluminum film in nitric acid, followed by a surface DAC-ANO compensation. The significant development is, when the Al₂O₃ film fabrication of this experiment was repeated, which means one more same Al₂O₃ layer deposition, the sample demonstrated satisfactory electrical properties.     

Optical Properties and Durability of Al2O3-NiP/Al Solar Absorbers Prepared by Electroless Nickel Composite Plating

A simple and low-cost method, electroless nickel composite plating, was used to deposit an Al₂O₃-NiP composite coating on an Al substrate to form an Al₂O₃-NiP/Al solar absorber. The effects of the Al₂O₃ content in the Al₂O₃-NiP composite coating, the thickness of the coating, and the use of a double-layer Al₂O₃-NiP composite coating and a TiO₂ antireflection (AR) layer on the optical characteristics of the Al₂O₃-NiP/Al absorbers were studied. The absorptance (α) and thermal emittance (ε) of the Al₂O₃-NiP/Al absorbers increased with the Al₂O₃ content in the Al₂O₃-NiP composite coating and decreased as the thickness of the coating increased. A double-layer Al₂O₃-NiP/Al absorber with 2:1 thickness ratio of the top layer (Al₂O₃-NiP with 25 vol.% Al₂O₃) to the inner layer (Al₂O₃-NiP with 7 vol.% Al₂O₃) had the best optical properties (α/ε = 0.746/0.103). The optimal double-layer Al₂O₃-NiP/Al absorber with a 106-nm-thick TiO₂ AR layer achieved absorptance of 0.893 and thermal emittance of 0.111. The results of a thermal stability test and a condensation test revealed that the TiO₂-coated double-layer Al₂O₃-NiP/Al absorbers had excellent thermal stability, and their failure time in the condensation test exceeded 100 h.     

Metalorganic chemical vapor deposition of silver thin films for future interconnects by direct liquid injection system

Deposition of Ag films by direct liquid injection-metal organic chemical vapor deposition (DLI-MOCVD) was chosen because this preparation method allows precise control of precursor flow and prevents early decomposition of the precursor as compared to the bubbler-delivery. Silver(I)-2,2-dimethyl-6,6,7,7,8,8,8-heptafluoro-3,5-octanedionato-triethylphosphine [Ag(fod)(PEt₃)] as the precursor for Ag CVD was studied, which is liquid at 30 °C. Ag films were grown on different substrates of SiO₂/Si and TiN/Si. Argon and nitrogen/hydrogen carrier gas was used in a cold wall reactor at a pressure of 50–500 Pa with deposition temperature ranging between 220 °C and 350 °C. Ag films deposited on a TiN/Si diffusion barrier layer have favorable properties over films deposited on SiO₂/Si substrate. At lower temperature (220 °C), film growth is essentially reaction-limited on SiO₂ substrate. Significant dependence of the surface morphology on the deposition conditions exists in our experiments. According to XPS analysis pure Ag films are deposited by DLI-MOCVD at 250 °C by using argon as carrier gas.     

Structural and Electrical Properties of Atomic Layer Deposited Al‐Doped ZnO Films

Structural and electrical properties of Al‐doped ZnO (AZO) films deposited by atomic layer deposition (ALD) are investigated to study the extrinsic doping mechanism of a transparent conducting oxide. ALD‐AZO films exhibit a unique layer‐by‐layer structure consisting of a ZnO matrix and Al₂O₃ dopant layers, as determined by transmission electron microscopy analysis. In these layered AZO films, a single Al₂O₃ dopant layer deposited during one ALD cycle could provide ≈4.5 × 10¹³ cm^?2 free electrons to the ZnO. The effective field model for doping is suggested to explain the decrease in the carrier concentration of ALD‐AZO films when the interval between the Al₂O₃ layers is reduced to less than ≈2.6 nm (>3.4 at% Al). By correlating the electrical and structural properties, an extrinsic doping mechanism of ALD‐AZO films is proposed in which the incorporated Al atoms take oxygen from the ZnO matrix and form doubly charged donors, such as oxygen vacancies or zinc interstitials.     

Sn掺杂对(In0.95-xSnxFe0.05)2O3薄膜的结构、电学及磁特性的影响

我们利用脉冲激光沉积的方法制备了一系列(In0.95-xSnxFe0.05)2O3 (x=0~0.09)薄膜,并在其中发现了室温铁磁性。X射线衍射结果表明锡与铁离子已掺入氧化铟晶格。随着锡的掺入,样品内的载流子浓度得到了很大的提高,但相应的铁磁性却几乎没有变化。我们认为氧空位相关的束缚磁极化子模型能够跟好的解释我们的铁掺杂氧化铟薄膜中的铁磁耦合的机制,而载流子传导的RKKY相互作用则不适用于这一系统。     

Rear‐Passivated Ultrathin Cu(In,Ga)Se2 Films by Al2O3 Nanostructures Using Glancing Angle Deposition Toward Photovoltaic Devices with Enhanced Efficiency

In this work, for the first time, the addition of aluminum oxide nanostructures (Al₂O₃ NSs) grown by glancing angle deposition (GLAD) is investigated on an ultrathin Cu(In,Ga)Se₂ device (400 nm) fabricated using a sequential process, i.e., post‐selenization of the metallic precursor layer. The most striking observation to emerge from this study is the alleviation of phase separation after adding the Al₂O₃ NSs with improved Se diffusion into the non‐uniformed metallic precursor due to the surface roughness resulting from the Al₂O₃ NSs. In addition, the raised Na concentration at the rear surface can be attributed to the increased diffusion of Na ion facilitated by Al₂O₃ NSs. The coverage and thickness of the Al₂O₃ NSs significantly affects the cell performance because of an increase in shunt resistance associated with the formation of Na₂Se_X and phase separation. The passivation effect attributed to the Al₂O₃ NSs is well studied using the bias‐EQE measurement and J–V characteristics under dark and illuminated conditions. With the optimization of the Al₂O₃ NSs, the remarkable enhancement in the cell performance occurs, exhibiting a power conversion efficiency increase from 2.83% to 5.33%, demonstrating a promising method for improving ultrathin Cu(In,Ga)Se₂ devices, and providing significant opportunities for further applications.     

Metal–Organic chemical vapour deposition (mocvd) growth utilising cu(acac)2 (acac  pentane-3, 5-dionato) as a source for copper-containing materials: Influence of carrier gas on surface morphology

The unsubstituted bis-β-diketonato complex of copper, Cu(acac)₂ (acac ? pentane-3, 5-dionato), has been used to deposit both elemental copper and copper oxide thin films by metal–organic chemical vapour deposition (MOCVD). For all Cu(II) bis-β-diketonates, growth of oxygen-free layers requires the breakage of four copper–oxygen bonds present in the precursor. The influence of carrier gas composition on deposit morphology has been examined for six parameter sets: both hydrous and anhydrous streams, each for reducing (H₂), inert (Ar) and oxidising (O₂) environments.     

Molecular Beam Epitaxy Deposition of In Situ O-Doped CdS Films for Highly Efficient Sb2(S,Se)3 Solar Cells

Antimony selenosulfide (Sb₂(S,Se)₃) is considered as a promising light-harvesting material and has been widely used in solar cells. For high-efficiency Sb₂(S,Se)₃ solar cells, the most commonly used electron-transporting layer of cadmium sulfide (CdS) is generally prepared by chemical bath deposition (CBD) approach. However, the hazardous waste liquid from the chemical bath and the sensitivity of the deposition process to the environment are challenges to practical applications. Herein, a molecular beam epitaxy deposition is reported to prepare CdS films, overcoming the drawbacks of CBD process. Furthermore, through introducing oxygen during the deposition of CdS, the sulfur vacancy defects generated in the vacuum deposition process are suppressed. The performance of Sb₂(S,Se)₃ solar cells is accordingly improved significantly. This improvement is attributed to the following aspects: i) the improved optical transmittance of CdS films. ii) The enhanced [hk1] orientation of Sb₂(S,Se)₃ absorber layer. iii) The improved heterojunction quality and suppressed carrier recombination. As a result, a power conversion efficiency of 8.59% for Sb₂(S,Se)₃ solar cells is achieved. This study provides a novel strategy for preparing electron-transporting layers for efficient chalcogenide thin-film solar cells and sheds new light on large-area solar cell applications.     

Chemical vapor deposition of AlxOyNz films

A chemical vapor deposition process for depositing dielectric films of aluminum oxynitride is described. AlCl₃, CO₂ and NH₃ were employed as the reactive gases in a nitrogen carrier. Films were grown from the mixed gases at 770 and 900°C in a resistively heated fused silica enclosure. The composition of the films could be varied over the entire range of the pseudobinary AlN-Al₂O₃ system by controlling the NH₃/CO₂ gas ratio with an appropriate flow of gaseous AlCl₃. Growth rate and index of refraction for the films were obtained using ellipsometric techniques. The film compositions reported were determined by electron microprobe analysis. Film structure, evaluated using transmission electron microscopy, and the electrical properties of the dielectric films have been correlated and are discussed separately in a companion paper entitled, “Some Properties of CVD Films of Al_xO_yN_z on Silicon”.     

Improved Interface and Electrical Properties by Inserting an Ultrathin SiO2 Buffer Layer in the Al2O3/Si Heterojunction

An ultrathin SiO₂ interfacial buffer layer is formed using the nitric acid oxidation of Si (NAOS) method to improve the interface and electrical properties of Al₂O₃/Si, and its effect on the leakage current and interfacial states is analyzed. The leakage current density of the Al₂O₃/Si sample (8.1 × 10^?9 A cm^?2) due to the formation of low‐density SiO_x layer during the atomic layer deposition (ALD) process, decreases by approximately two orders of magnitude when SiO₂ buffer layer is inserted using the NAOS method (1.1 × 10^?11 A cm^?2), and further decreases after post‐metallization annealing (PMA) (1.4 × 10^?12 A cm^?2). Based on these results, the influence of interfacial defect states is analyzed. The equilibrium density of defect sites (N_d) and fixed charge density (N_f) are both reduced after NAOS and then further decreased by PMA treatment. The interface state density (D_it) at 0.11 eV decreases about one order of magnitude from 2.5 × 10¹² to 7.3 × 10¹¹ atoms eV^?1 cm^?2 after NAOS, and to 3.0 × 10¹⁰ atoms eV^?1 cm^?2 after PMA. Consequently, it is demonstrated that the high defect density of the Al₂O₃/Si interface is drastically reduced by fabricating ultrathin high density SiO₂ buffer layer, and the insulating properties are improved.     

Composition,structure and electrical properties of DC reactive magnetron sputtered Al2O3 thin films

Thin films of alumina (Al₂O₃) were deposited over Si 〈1 0 0〉 substrates at room temperature at an oxygen gas pressure of 0.03 Pa and sputtering power of 60 W using DC reactive magnetron sputtering. The composition of the as-deposited film was analyzed by X-ray photoelectron spectroscopy and the O/Al atomic ratio was found to be 1.72. The films were then annealed in vacuum to 350, 550 and 750 °C and X-ray diffraction results revealed that both as-deposited and post deposition annealed films were amorphous. The surface morphology and topography of the films was studied using scanning electron microscopy and atomic force microscopy, respectively. A progressive decrease in the root mean square (RMS) roughness of the films from 1.53 nm to 0.7 nm was observed with increase in the annealing temperature. Al–Al₂O₃–Al thin film capacitors were then fabricated on p-type Si 〈1 0 0〉 substrate to study the effect of temperature and frequency on the dielectric property of the films and the results are discussed.     

In Situ Fabrication of Highly Luminescent Bifunctional Amino Acid Crosslinked 2D/3D NH3C4H9COO(CH3NH3PbBr3)n Perovskite Films

The perovskite quantum dots are usually synthesized by solution chemistry and then fabricated into film for device application with some extra process. Here it is reported for the first time to in situ formation of a crosslinked 2D/3D NH₃C₄H₉COO(CH₃NH₃) _n Pb_n Br_3n perovskite planar films with controllable quantum confine via bifunctional amino acid crosslinkage, which is comparable to the solution chemistry synthesized CH₃NH₃PbBr₃ quantum dots. These atomic layer controllable perovskite films are facilely fabricated and tuned by addition of bi‐functional 5‐aminovaleric acid (Ava) of NH₂C₄H₉COOH into regular (CH₃NH₃)PbBr₃ (MAPbBr₃) perovskite precursor solutions. Both the NH₃⁺ and the COO^? groups of the zwitterionic amino acid are proposed to crosslink the atomic layer MAPbBr₃ units via Pb? COO bond and ion bond between NH₃⁺ and [PbX₆] unit. The characterizations by atomic force microscopy, scanning electron microscopy, Raman, and photoluminescence spectroscopy confirm a successful fabrication of ultrasmooth and stable film with tunable optical properties. The bifunctional crosslinked 2D/3D Ava(MAPbBr₃)_n perovskite films with controllable quantum confine would serve as distinct and promising materials for optical and optoelectronic applications.     

Spatially separated atomic layer deposition of Al2O3, a new option for high‐throughput Si solar cell passivation

A next generation material for surface passivation of crystalline Si is Al₂O₃. It has been shown that both thermal and plasma‐assisted (PA) atomic layer deposition (ALD) Al₂O₃ provide an adequate level of surface passivation for both p‐ and n‐type Si substrates. However, conventional time‐resolved ALD is limited by its low deposition rate. Therefore, an experimental high‐deposition‐rate prototype ALD reactor based on the spatially separated ALD principle has been developed and Al₂O₃ deposition rates up to 1.2 nm/s have been demonstrated. In this work, the passivation quality and uniformity of the experimental spatially separated ALD Al₂O₃ films are evaluated and compared to conventional temporal ALD Al₂O₃, by use of quasi‐steady‐state photo‐conductance (QSSPC) and carrier density imaging (CDI). It is shown that spatially separated Al₂O₃ films of increasing thickness provide an increasing surface passivation level. Moreover, on p‐type CZ Si, 10 and 30 nm spatial ALD Al₂O₃ layers can achieve the same level of surface passivation as equivalent temporal ALD Al₂O₃ layers. In contrast, on n‐type FZ Si, spatially separated ALD Al₂O₃ samples generally do not reach the same optimal passivation quality as equivalent conventional temporal ALD Al₂O₃ samples. Nevertheless, after “firing”, 30 nm of spatially separated ALD Al₂O₃ on 250 µm thick n‐type (2.4 Ω cm) FZ Si wafers can lead to effective surface recombination velocities as low as 2.9 cm/s, compared to 1.9 cm/s in the case of 30 nm of temporal ALD Al₂O₃. Copyright © 2011 John Wiley & Sons, Ltd.     

Semiconductor nanowires surrounded by cylindrical Al2O3 shells

The GaN, GaP, InP, Si₃N₄, SiO₂/Si, SiC, and ZnO semiconductor nanowires were synthesized by a variety of growth methods, and they were wrapped cylindrically with amorphous aluminum oxide (Al₂O₃) shells. The Al₂O₃ was deposited on these seven different semiconductor nanowires by atomic layer deposition (ALD) at a substrate temperature of 200°C using trimethylaluminum (TMA) and distilled water (H₂O). Transmission electron microscopy (TEM) images taken for the nanowires revealed that Al₂O₃ cylindrical shells surround uniformly all these semiconductor nanowires. Our TEM study illustrates that the ALD of Al₂O₃ has an excellent capability to coat any semiconductor nanowires conformally; its coating capability is independent of the chemical component, lattice structure, and growth direction of the nanowires. This study suggests that the ALD of Al₂O₃ on nanowires is one of the promising methods to prepare cylindrical dielectric shells in coaxially gated, nanowire field-effect transistors (FETs).     

Fabrication and characterization of Zr-rich Zr-aluminate films for high-κ gate dielectric applications

Two kinds of Zr-rich Zr-aluminate films for high-κ gate dielectric applications with the nominal composition of (ZrO₂)_0.8(Al₂O₃)_0.2 and (ZrO₂)_0.9(Al₂O₃)_0.1, were deposited on n-type silicon wafer by pulsed laser deposition (PLD) technique at different deposition conditions. X-ray diffraction (XRD) reveals that the (ZrO₂)_0.8(Al₂O₃)_0.2 film could remain amorphous after being rapid thermal annealed (RTA) at the temperature above 800 °C, while the other one displays some crystalline peaks at 700 °C. The energy gap calculated from optical transmittance spectrum of (ZrO₂)_0.8(Al₂O₃)_0.2 film on quartz is about 6.0 eV. Sputtering depth profile of X-ray photoelectron spectroscopy and Auger electron spectroscopy indicate that a Zr-Si-O interfacial layer was formed at the near surface of the silicon substrate. The dielectric constant of the (ZrO₂)_0.8(Al₂ O₃)_0.2 film has been determined to be 22.1 by measuring a Pt/(ZrO₂)_0.8(Al₂ O₃)_0.2/Pt MIM structure. An EOT of 1.76 nm with a leakage current density of 51.5 mA/cm² at 1 V gate voltage for the film deposited in N₂ were obtained. Two different pre-treatments of Si substrates prior to depositions were also carried out and compared. The results indicate that a surface-nitrided Si substrate can lead to a lower leakage current density. The amorphous Zr-rich Zr-aluminate films fabricated by PLD have promising structure and dielectric properties required for a candidate material for high-κ gate dielectric applications.     

A Novel Pd Precursor Loaded γ-Al2O3 with Excellent Adsorbent Performance for Ultra-Deep Adsorptive Desulfurization of Benzene

Fabricating highly water-soluble and chlorine-free precursors from Pd complexes remains challenging. Here, a novel Pd precursor (ammonium dinitrooxalato palladium(II) ((NH₄)₂[Pd(NO₂)₂(C₂O₄)]·2H₂O)) is synthesized to address this challenge. Additionally, a Pd/Al₂O₃ adsorbent is prepared using γ-Al₂O₃ as a base material to host Pd. The ligand action of the Pd complex forms single Pd atoms and Pd sub-nano clusters on the surface of γ-Al₂O₃. Pd/Al₂O₃-4 as an adsorbent is evaluated using the benzene ultra-deep desulfurization procedure, wherein thiophene is used as a probe molecule. The sulfur adsorption capacity of Pd/Al₂O₃-4 is 1.76 mg g⁻¹ for the ultra-deep adsorptive desulfurization of benzene at a sulfur concentration of 50 ppm. The sulfur adsorption capacity of the new Pd/Al₂O₃-4 adsorbent is 21.8% higher than that of a commercial Pd/Al₂O₃ adsorbent. In addition, the stability and durability of Pd/Al₂O₃-4 are investigated at a sulfur concentration of 1 ppm. The Pd/Al₂O₃-4 adsorbent achieves ≈100% thiophene removal after 434 h, which is 62 h more than the time required by the commercial Pd/Al₂O₃ adsorbent. The novel Pd precursor shows excellent potential for industrial applications, and the Pd/Al₂O₃-4 adsorbent can be produced on a mass scale of 500 kg per batch.