The Enhanced Performance of Oxide Thin-Film Transistors Fabricated by a Two-Step Deposition Pressure Process

It is usually difficult to realize high mobility together with a low threshold voltage and good stability for amorphous oxide thin-film transistors (TFTs). In addition, a low fabrication temperature is preferred in terms of enhancing compatibility with the back end of line of the device. In this study, α-IGZO TFTs were prepared by high-power impulse magnetron sputtering (HiPIMS) at room temperature. The channel was prepared under a two-step deposition pressure process to modulate its electrical properties. X-ray photoelectron spectra revealed that the front-channel has a lower Ga content and a higher oxygen vacancy concentration than the back-channel. This process has the advantage of balancing high mobility and a low threshold voltage of the TFT when compared with a conventional homogeneous channel. It also has a simpler fabrication process than that of a dual active layer comprising heterogeneous materials. The HiPIMS process has the advantage of being a low temperature process for oxide TFTs.

Internal moisture barrier layer for improving high-humidity reliability of miniature light emitting diode die without encapsulation

Atomic layer deposited Al2O3 films are incorporated into miniature light emitting diodes (mini-LEDs) as an internal moisture barrier layer. The experimental results show that the water vapor transmission rate reaches ≤10-4 g/m2/day when the Al2O3 thickness is ≥40 nm. The mini-LED with a 40 nm-thick Al2O3 layer shows negligible degradation after 1000 h of 85°C/85% relative humidity testing, whereas the device without an Al2O3 layer fails after only 500 h due to delamination occurring at the GaN surface. Current-voltage characteristics of the device without an Al2O3 moisture barrier layer indicate an increase in series resistance and ideality factor. This study provides a simple, light-weighting method to have a satisfactory encapsulation function for miniature LEDs.

Improving Crystallization and Stability of Perovskite Solar Cells Using a Low-Temperature Treated A-Site Cation Solution in the Sequential Deposition

The two-step sequential deposition is a commonly used method by researchers for fabricating perovskite solar cells (PSCs) due to its reproducibility and tolerant preparation conditions. However, the less-than-favorable diffusive processes in the preparation process often result in subpar crystalline quality in the perovskite films. In this study, we employed a simple strategy to regulate the crystallization process by lowering the temperature of the organic-cation precursor solutions. By doing so, we minimized interdiffusion processes between the organic cations and pre-deposited lead iodide (PbI₂) film under poor crystallization conditions. This allowed for a homogenous perovskite film with improved crystalline orientation when transferred to appropriate environmental conditions for annealing. As a result, a boosted power conversion efficiency (PCE) was achieved in PSCs tested for 0.1 cm² and 1 cm², with the former exhibiting a PCE of 24.10% and the latter of 21.56%, compared to control PSCs, which showed a PCE of 22.65% and 20.69%, respectively. Additionally, the strategy increased device stability, with the cells holding 95.8% and 89.4% of the initial efficiency even after 7000 h of aging under nitrogen or 20-30% relative humidity and 25 °C. This study highlights a promising low-temperature-treated (LT-treated) strategy compatible with other PSCs fabrication techniques, adding a new possibility for temperature regulation during crystallization.

Growth of GaN Thin Films Using Plasma Enhanced Atomic Layer Deposition: Effect of Ammonia-Containing Plasma Power on Residual Oxygen Capture

In recent years, the application of (In, Al, Ga)N materials in photovoltaic devices has attracted much attention. Like InGaN, it is a direct band gap material with high absorption at the band edge, suitable for high efficiency photovoltaic devices. Nonetheless, it is important to deposit high-quality GaN material as a foundation. Plasma-enhanced atomic layer deposition (PEALD) combines the advantages of the ALD process with the use of plasma and is often used to deposit thin films with different needs. However, residual oxygen during growth has always been an unavoidable issue affecting the quality of the resulting film, especially in growing gallium nitride (GaN) films. In this study, the NH₃-containing plasma was used to capture the oxygen absorbed on the growing surface to improve the quality of GaN films. By diagnosing the plasma, NH₂, NH, and H radicals controlled by the plasma power has a strong influence not only on the oxygen content in growing GaN films but also on the growth rate, crystallinity, and surface roughness. The NH and NH₂ radicals contribute to the growth of GaN films while the H radicals selectively dissociate Ga-OH bonds on the film surface and etch the grown films. At high plasma power, the GaN film with the lowest Ga-O bond ratio has a saturated growth rate, a better crystallinity, a rougher surface, and a lower bandgap. In addition, the deposition mechanism of GaN thin films prepared with a trimethylgallium metal source and NH₃/Ar plasma PEALD involving oxygen participation or not is also discussed in the study.

Crystallinity Effect on Electrical Properties of PEALD-HfO2 Thin Films Prepared by Different Substrate Temperatures

Hafnium oxide (HfO₂) thin film has remarkable physical and chemical properties, which makes it useful for a variety of applications. In this work, HfO₂ films were prepared on silicon through plasma enhanced atomic layer deposition (PEALD) at various substrate temperatures. The growth per cycle, structural, morphology and crystalline properties of HfO₂ films were measured by spectroscopic ellipsometer, grazing-incidence X-ray diffraction (GIXRD), X-ray reflectivity (XRR), field-emission scanning electron microscopy, atomic force microscopy and x-ray photoelectron spectroscopy. The substrate temperature dependent electrical properties of PEALD-HfO₂ films were obtained by capacitance-voltage and current-voltage measurements. GIXRD patterns and XRR investigations show that increasing the substrate temperature improved the crystallinity and density of HfO₂ films. The crystallinity of HfO₂ films has a major effect on electrical properties of the films. HfO₂ thin film deposited at 300 °C possesses the highest dielectric constant and breakdown electric field.

Self-Powered Thermoelectric Hydrogen Sensors Based on Low-Cost Bismuth Sulfide Thin Films: Quick Response at Room Temperature

Thermoelectric (TE)-based gas sensors have attracted significant attention due to their high selectivity, low power consumption, and minimum maintenance requirements. However, it is challenging to find low-cost, environmentally friendly materials and simple device fabrication processes for large-scale applications. Herein, we report self-powered thermoelectric hydrogen (TEH) sensors based on bismuth sulfide (Bi₂S₃) fabricated from a low-cost Bi₂S₃ TE layer and platinum (Pt) catalyst. When working at room temperature, the monomorphic-type TEH sensor obtained an output response signal of 42.2 μV with a response time of 17 s at a 3% hydrogen atmosphere. To further improve device performance, we connected the patterned Bi₂S₃ films in series to increase the Seebeck coefficient to -897 μV K^-1. For comparison, the resulting N tandem-type TEH sensor yielded a distinguished output voltage of 101.4 μV, which was greater than the monomorphic type by a factor of 2.4. Significantly, the response and recovery time of the N-tandem-type TEH sensor to 3% hydrogen were shortened to 14 and 15 s, respectively. This work provides a simple, environmentally friendly, and low-cost strategy for fabricating high-performance TEH sensors by applying low-cost Bi₂S₃ TE materials.

Deposition Mechanism and Characterization of Plasma-Enhanced Atomic Layer-Deposited SnOx Films at Different Substrate Temperatures

The promising functional tin oxide (SnOx) has attracted tremendous attention due to its transparent and conductive properties. The stoichiometric composition of SnOx can be described as common n-type SnO2 and p-type Sn3O4. In this study, the functional SnOx films were prepared successfully by plasma-enhanced atomic layer deposition (PEALD) at different substrate temperatures from 100 to 400 °C. The experimental results involving optical, structural, chemical, and electrical properties and morphologies are discussed. The SnO2 and oxygen-deficient Sn3O4 phases coexisting in PEALD SnOx films were found. The PEALD SnOx films are composed of intrinsic oxygen vacancies with O-Sn4+ bonds and then transformed into a crystalline SnO2 phase with increased substrate temperature, revealing a direct 3.5−4.0 eV band gap and 1.9−2.1 refractive index. Lower (<150 °C) and higher (>300 °C) substrate temperatures can cause precursor condensation and desorption, respectively, resulting in reduced film qualities. The proper composition ratio of O to Sn in PEALD SnOx films near an estimated 1.74 suggests the highest mobility of 12.89 cm2 V−1 s−1 at 300 °C.

Thermal behavior of AlGaN-based deep-UV LEDs

This study utilized thin p-GaN, indium tin oxide (ITO), and a reflective passivation layer (RPL) to improve the performance of deep ultra-violet light-emitting diodes (DUV-LEDs). RPL reflectors, which comprise HfO₂/SiO₂ stacks of different thickness to maintain high reflectance, were deposited on the DUV-LEDs with 40 nm-thick p-GaN and 12 nm-thick ITO thin films. Although the thin p-GaN and ITO films affect the operation voltage of DUV-LEDs, the highly reflective RPL structure improved the WPE and light extraction efficiency (LEE) of the DUV-LEDs, yielding the best WPE and LEE of 2.59% and 7.57%, respectively. The junction temperature of DUV-LEDs with thick p-GaN increased linearly with the injection current, while that of DUV-LEDs with thin p-GaN, thin ITO, and RPL was lower than that of the Ref-LED under high injection currents (> 500 mA). This influenced the temperature sensitive coefficients (dV/dT, dLOP/dT, and dWLP/dT). The thermal behavior of DUV-LEDs with p-GaN and ITO layers of different thicknesses with/without the RPL was discussed in detail.

Compact Ga2O3 Thin Films Deposited by Plasma Enhanced Atomic Layer Deposition at Low Temperature

Amorphous Gallium oxide (Ga₂O₃) thin films were grown by plasma-enhanced atomic layer deposition using O₂ plasma as reactant and trimethylgallium as a gallium source. The growth rate of the Ga₂O₃ films was about 0.6 Å/cycle and was acquired at a temperature ranging from 80 to 250 °C. The investigation of transmittance and the adsorption edge of Ga₂O₃ films prepared on sapphire substrates showed that the band gap energy gradually decreases from 5.04 to 4.76 eV with the increasing temperature. X-ray photoelectron spectroscopy (XPS) analysis indicated that all the Ga₂O₃ thin films showed a good stoichiometric ratio, and the atomic ratio of Ga/O was close to 0.7. According to XPS analysis, the proportion of Ga³⁺ and lattice oxygen increases with the increase in temperature resulting in denser films. By analyzing the film density from X-ray reflectivity and by a refractive index curve, it was found that the higher temperature, the denser the film. Atomic force microscopic analysis showed that the surface roughness values increased from 0.091 to 0.187 nm with the increasing substrate temperature. X-ray diffraction and transmission electron microscopy investigation showed that Ga₂O₃ films grown at temperatures from 80 to 200 °C were amorphous, and the Ga₂O₃ film grown at 250 °C was slightly crystalline with some nanocrystalline structures.

Deciphering the Reduced Loss in High Fill Factor Inverted Perovskite Solar Cells with Methoxy-Substituted Poly(Triarylamine) as the Hole Selective Contact

A dopant-free polymeric hole selective contact (HSC) layer is ubiquitous for stable perovskite solar cells (PSCs). However, the intrinsic nonwetting nature of the polymeric HSC impedes the uniform spreading of the perovskite precursor solution, generating a terrible buried interface. Here, we dexterously tackle this dilemma from the perspective of dispersive and polar component surface energies of the HSC layer. A novel triarylamine-based HSC material, poly[bis(4-phenyl)(2,4-dimethoxyphenyl)amine] (2MeO-PTAA), was designed by introducing the polar methoxy groups to the para and ortho positions of the dangling benzene. These nonsymmetrically substituted electron-donating methoxy groups enhanced the polar components of surface energy, allowing more tight interfacial contact between the HSC layer and perovskite and facilitating hole extraction. When utilized as the dopant-free HSC layer in inverted PSCs, the 2MeO-PTAA-based device with CH₃NH₃PbI₃ as the absorber exhibited an encouraging power conversion efficiency of 20.23% and a high fill factor of 84.31% with negligible hysteresis. Finally, a revised detailed balance model was used to verify the drastically lessened surface defect-induced recombination loss and shunt resistance loss in 2MeO-PTAA-based devices. This work demonstrates a facile and efficient way to modulate the buried interface and shed light on the direction to further improve the photovoltaic performance of inverted PSCs with other types of perovskites.

Advanced Atomic Layer Deposition Technologies for Micro-LEDs and VCSELs

In recent years, the process requirements of nano-devices have led to the gradual reduction in the scale of semiconductor devices, and the consequent non-negligible sidewall defects caused by etching. Since plasma-enhanced chemical vapor deposition can no longer provide sufficient step coverage, the characteristics of atomic layer deposition ALD technology are used to solve this problem. ALD utilizes self-limiting interactions between the precursor gas and the substrate surface. When the reactive gas forms a single layer of chemical adsorbed on the substrate surface, no reaction occurs between them and the growth thickness can be controlled. At the Å level, it can provide good step coverage. In this study, recent research on the ALD passivation on micro-light-emitting diodes and vertical cavity surface emitting lasers was reviewed and compared. Several passivation methods were demonstrated to lead to enhanced light efficiency, reduced leakage, and improved reliability.

Enhanced external quantum efficiencies of AlGaN-based deep-UV LEDs using reflective passivation layer

In this study, deep ultraviolet light-emitting diodes (DUV-LEDs) with a reflective passivation layer (RPL) were investigated. The RPL consists of HfO₂/SiO₂ stacks as distributed Bragg reflectors, which are deposited on two DUV-LEDs with different p-GaN thicknesses. The RPL structure improved the external quantum efficiency droops of the DUV-LEDs with thick and thin p-GaN, thereby increasing their light output power by 18.4% and 39.4% under injection current of 500 mA and by 17.9% and 37.9% under injection current of 1000 mA, respectively. The efficiency droops of the DUV-LEDs with and without the RPL with thick p-GaN were 20.1% and 19.1% and with thin p-GaN were 18.0% and 15.6%, respectively. The DUV-LEDs with the RPL presented improved performance. The above results demonstrate the potential for development of the RPLs for DUV-LED applications.

The Influence of Oxygen Plasma on Methylammonium Lead Iodide (MAPbI3) Film Doped with Lead Cesium Triiodide (CsPbI3)

In recent years, the study of organic-inorganic halide perovskite as an optoelectronics material has been a significant line of research, and the power conversion efficiency of solar cells based on these materials has reached 25.5%. However, defects on the surface of the film are still a problem to be solved, and oxygen plasma is one of the ways to passivate surface defects. In order to avoid destroying the methylammonium lead iodide (MAPbI₃), the influence of plasma powers on film was investigated and the cesium triiodide (CsPbI₃) quantum dots (QDs) were doped into the film. In addition, it was found that oxygen plasma can enhance the mobility and carrier concentration of the MAPbI₃ film.

Deposition and Characterization of RP-ALD SiO2 Thin Films with Different Oxygen Plasma Powers

In this study, silicon oxide (SiO2) films were deposited by remote plasma atomic layer deposition with Bis(diethylamino)silane (BDEAS) and an oxygen/argon mixture as the precursors. Oxygen plasma powers play a key role in the quality of SiO2 films. Post-annealing was performed in the air at different temperatures for 1 h. The effects of oxygen plasma powers from 1000 W to 3000 W on the properties of the SiO2 thin films were investigated. The experimental results demonstrated that the SiO2 thin film growth per cycle was greatly affected by the O2 plasma power. Atomic force microscope (AFM) and conductive AFM tests show that the surface of the SiO2 thin films, with different O2 plasma powers, is relatively smooth and the films all present favorable insulation properties. The water contact angle (WCA) of the SiO2 thin film deposited at the power of 1500 W is higher than that of other WCAs of SiO2 films deposited at other plasma powers, indicating that it is less hydrophilic. This phenomenon is more likely to be associated with a smaller bonding energy, which is consistent with the result obtained by Fourier transformation infrared spectroscopy. In addition, the influence of post-annealing temperature on the quality of the SiO2 thin films was also investigated. As the annealing temperature increases, the SiO2 thin film becomes denser, leading to a higher refractive index and a lower etch rate.

Properties and Mechanism of PEALD-In2O3 Thin Films Prepared by Different Precursor Reaction Energy

Indium oxide (In₂O₃) film has excellent optical and electrical properties, which makes it useful for a multitude of applications. The preparation of In₂O₃ film via atomic layer deposition (ALD) method remains an issue as most of the available In-precursors are inactive and thermally unstable. In this work, In₂O₃ film was prepared by ALD using a remote O₂ plasma as oxidant, which provides highly reactive oxygen radicals, and hence significantly enhancing the film growth. The substrate temperature that determines the adsorption state on the substrate and reaction energy of the precursor was investigated. At low substrate temperature (100–150 °C), the ratio of chemically adsorbed precursors is low, leading to a low growth rate and amorphous structure of the films. An amorphous-to-crystalline transition was observed at 150–200 °C. An ALD window with self-limiting reaction and a reasonable film growth rate was observed in the intermediate temperature range of 225–275 °C. At high substrate temperature (300–350 °C), the film growth rate further increases due to the decomposition of the precursors. The resulting film exhibits a rough surface which consists of coarse grains and obvious grain boundaries. The growth mode and properties of the In₂O₃ films prepared by plasma-enhanced ALD can be efficiently tuned by varying the substrate temperature.

Chemical Reaction and Ion Bombardment Effects of Plasma Radicals on Optoelectrical Properties of SnO2 Thin Films via Atomic Layer Deposition

In this study, the effect of radical intensity on the deposition mechanism, optical, and electrical properties of tin oxide (SnO₂) thin films is investigated. The SnO₂ thin films are prepared by plasma-enhanced atomic layer deposition with different plasma power from 1000 to 3000 W. The experimental results show that plasma contains different amount of argon radicals (Ar*) and oxygen radicals (O*) with the increased power. The three deposition mechanisms are indicated by the variation of Ar* and O* intensities evidenced by optical emission spectroscopy. The adequate intensities of Ar* and O* are obtained by the power of 1500 W, inducing the highest oxygen vacancies (O_V) ratio, the narrowest band gap, and the densest film structure. The refractive index and optical loss increase with the plasma power, possibly owing to the increased film density. According to the Hall effect measurement results, the improved plasma power from 1000 to 1500 W enhances the carrier concentration due to the enlargement of O_V ratio, while the plasma powers higher than 1500 W further cause the removal of O_V and the significant bombardment from Ar*, leading to the increase of resistivity.

Suppression of Oxygen Vacancy Defects in sALD-ZnO Films Annealed in Different Conditions

Zinc oxide (ZnO) has drawn much attention due to its excellent optical and electrical properties. In this study, ZnO film was prepared by a high-deposition-rate spatial atomic layer deposition (ALD) and subjected to a post-annealing process to suppress the intrinsic defects and improve the crystallinity and film properties. The results show that the film thickness increases with annealing temperature owing to the increment of oxide layer caused by the suppression of oxygen vacancy defects as indicated by the X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) spectra. The film transmittance is seldom influenced by annealing. The refractive index increases with annealing temperature at 300–700 °C, possibly due to higher density and crystallinity of the film. The band gap decreases after annealing, which should be ascribed to the decrease in carrier concentration according to Burstein–Moss model. The carrier concentration decreases with increasing annealing temperature at 300–700 °C since the oxygen vacancy defects are suppressed, then it increases at 800 °C possibly due to the out-diffusion of oxygen atoms from the film. Meanwhile, the carrier mobility increases with temperature due to higher crystallinity and larger crystallite size. The film resistivity increases at 300–700 °C then decreases at 800 °C, which should be ascribed primarily to the variation of carrier concentration.

Effect of Annealing Temperature on Spatial Atomic Layer Deposited Titanium Oxide and Its Application in Perovskite Solar Cells

In this study, spatial atomic layer deposition (sALD) is employed to prepare titanium dioxide (TiO2) thin films by using titanium tetraisopropoxide and water as metal and water precursors, respectively. The post-annealing temperature is varied to investigate its effect on the properties of the TiO2 films. The experimental results show that the sALD TiO2 has a similar deposition rate per cycle to other ALD processes using oxygen plasma or ozone oxidant, implying that the growth is limited by titanium tetraisopropoxide steric hindrance. The structure of the as-deposited sALD TiO2 films is amorphous and changes to polycrystalline anatase at the annealing temperature of 450 °C. All the sALD TiO2 films have a low absorption coefficient at the level of 10-3 cm-1 at wavelengths greater than 500 nm. The annealing temperatures of 550 °C are expected to have a high compactness, evaluated by the refractive index and x-ray photoelectron spectrometer measurements. Finally, the 550 °C-annealed sALD TiO2 film with a thickness of ~8 nm is applied to perovskite solar cells as a compact electron transport layer. The significantly enhanced open-circuit voltage and conversion efficiency demonstrate the great potential of the sALD TiO2 compact layer in perovskite solar cell applications.

Low Reflection and Low Surface Recombination Rate Nano-Needle Texture Formed by Two-Step Etching for Solar Cells

In this study, needle-like and pyramidal hybrid black silicon structures were prepared by performing metal-assisted chemical etching (MACE) on alkaline-etched silicon wafers. Effects of the MACE time on properties of the black silicon wafers were investigated. The experimental results showed that a minimal reflectance of 4.6% can be achieved at the MACE time of 9 min. The height of the nanostructures is below 500 nm, unlike the height of micrometers needed to reach the same level of reflectance for the black silicon on planar wafers. A stacked layer of silicon nitride (SiN_x) grown by inductively-coupled plasma chemical vapor deposition (ICPCVD) and aluminum oxide (Al₂O₃) by spatial atomic layer deposition was deposited on the black silicon wafers for passivation and antireflection. The 3 min MACE etched black silicon wafer with a nanostructure height of less than 300 nm passivated by the SiN_x/Al₂O₃ layer showed a low surface recombination rate of 43.6 cm/s. Further optimizing the thickness of ICPCVD-SiN_x layer led to a reflectance of 1.4%. The hybrid black silicon with a small nanostructure size, low reflectance, and low surface recombination rate demonstrates great potential for applications in optoelectronic devices.

Deposition of Silicon-Based Stacked Layers for Flexible Encapsulation of Organic Light Emitting Diodes

In this study, inorganic silicon oxide (SiO_x)/organic silicon (SiC_xH_y) stacked layers were deposited by a radio frequency inductively coupled plasma chemical vapor deposition system as a gas diffusion barrier for organic light-emitting diodes (OLEDs). The effects of thicknesses of SiO_x and SiC_xH_y layers on the water vapor transmission rate (WVTR) and residual stress were investigated to evaluate the encapsulation capability. The experimental results showed that the lowest WVTR and residual stress were obtained when the thicknesses of SiO_x and SiC_xH_y were 300 and 30 nm, respectively. Finally, different numbers of stacked pairs of SiO_x/SiC_xH_y were applied to OLED encapsulation. The OLED encapsulated with the six-pair SiO_x/SiC_xH_y exhibited a low turn-on voltage and low series resistance, and device lifetime increased from 7 h to more than 2000 h.

Enhanced Si Passivation and PERC Solar Cell Efficiency by Atomic Layer Deposited Aluminum Oxide with Two-step Post Annealing

In this study, aluminum oxide (Al₂O₃) films were prepared by a spatial atomic layer deposition using deionized water and trimethylaluminum, followed by oxygen (O₂), forming gas (FG), or two-step annealing. Minority carrier lifetime of the samples was measured by Sinton WCT-120. Field-effect passivation and chemical passivation were evaluated by fixed oxide charge (Q_f) and interface defect density (D_it), respectively, using capacitance-voltage measurement. The results show that O₂ annealing gives a high Q_f of - 3.9 × 10¹² cm^-2, whereas FG annealing leads to excellent Si interface hydrogenation with a low D_it of 3.7 × 10¹¹ eV^-1 cm^-2. Based on the consideration of the best field-effect passivation brought by oxygen annealing and the best chemical passivation brought by forming gas, the two-step annealing process was optimized. It is verified that the Al₂O₃ film annealed sequentially in oxygen and then in forming gas exhibits a high Q_f (2.4 × 10¹² cm^-2) and a low D_it (3.1 × 10¹¹ eV^-1 cm^-2), yielding the best minority carrier lifetime of 1097 μs. The SiN_x/Al₂O₃ passivation stack with two-step annealing has a lifetime of 2072 μs, close to the intrinsic lifetime limit. Finally, the passivated emitter and rear cell conversion efficiency was improved from 21.61% by using an industry annealing process to 21.97% by using the two-step annealing process.

Temperature-Dependent HfO2/Si Interface Structural Evolution and its Mechanism

In this work, hafnium oxide (HfO₂) thin films are deposited on p-type Si substrates by remote plasma atomic layer deposition on p-type Si at 250 °C, followed by a rapid thermal annealing in nitrogen. Effect of post-annealing temperature on the crystallization of HfO₂ films and HfO₂/Si interfaces is investigated. The crystallization of the HfO₂ films and HfO₂/Si interface is studied by field emission transmission electron microscopy, X-ray photoelectron spectroscopy, X-ray diffraction, and atomic force microscopy. The experimental results show that during annealing, the oxygen diffuse from HfO₂ to Si interface. For annealing temperature below 400 °C, the HfO₂ film and interfacial layer are amorphous, and the latter consists of HfO₂ and silicon dioxide (SiO₂). At annealing temperature of 450-550 °C, the HfO₂ film become multiphase polycrystalline, and a crystalline SiO₂ is found at the interface. Finally, at annealing temperature beyond 550 °C, the HfO₂ film is dominated by single-phase polycrystalline, and the interfacial layer is completely transformed to crystalline SiO₂.

Surface Passivation of Silicon Using HfO2 Thin Films Deposited by Remote Plasma Atomic Layer Deposition System

Hafnium oxide (HfO₂) thin films have attracted much attention owing to their usefulness in equivalent oxide thickness scaling in microelectronics, which arises from their high dielectric constant and thermodynamic stability with silicon. However, the surface passivation properties of such films, particularly on crystalline silicon (c-Si), have rarely been reported upon. In this study, the HfO₂ thin films were deposited on c-Si substrates with and without oxygen plasma pretreatments, using a remote plasma atomic layer deposition system. Post-annealing was performed using a rapid thermal processing system at different temperatures in N₂ ambient for 10 min. The effects of oxygen plasma pretreatment and post-annealing on the properties of the HfO₂ thin films were investigated. They indicate that the in situ remote plasma pretreatment of Si substrate can result in the formation of better SiO₂, resulting in a better chemical passivation. The deposited HfO₂ thin films with oxygen plasma pretreatment and post-annealing at 500 °C for 10 min were effective in improving the lifetime of c-Si (original lifetime of 1 μs) to up to 67 μs.

Investigation on the passivated Si/Al2O3 interface fabricated by non-vacuum spatial atomic layer deposition system

Currently, aluminum oxide stacked with silicon nitride (Al2O3/SiNx:H) is a promising rear passivation material for high-efficiency P-type passivated emitter and rear cell (PERC). It has been indicated that atomic layer deposition system (ALD) is much more suitable to prepare high-quality Al2O3 films than plasma-enhanced chemical vapor deposition system and other process techniques. In this study, an ultrafast, non-vacuum spatial ALD with the deposition rate of around 10 nm/min, developed by our group, is hired to deposit Al2O3 films. Upon post-annealing for the Al2O3 films, the unwanted delamination, regarded as blisters, was found by an optical microscope. This may lead to a worse contact within the Si/Al2O3 interface, deteriorating the passivation quality. Thin stoichiometric silicon dioxide films prepared on the Si surface prior to Al2O3 fabrication effectively reduce a considerable amount of blisters. The residual blisters can be further out-gassed when the Al2O3 films are thinned to 8 nm and annealed above 650°C. Eventually, the entire PERC with the improved triple-layer SiO2/Al2O3/SiNx:H stacked passivation film has an obvious gain in open-circuit voltage (V oc) and short-circuit current (J sc) because of the increased minority carrier lifetime and internal rear-side reflectance, respectively. The electrical performance of the optimized PERC with the V oc of 0.647 V, J sc of 38.2 mA/cm(2), fill factor of 0.776, and the efficiency of 19.18% can be achieved.