The AlON film with homogeneous nitrogen-doping profile was grown by plasma-enhanced atomic layer deposition (PEALD) at low temperature. In this work, the precursors of the NH3 and the O2 were simultaneously introduced into the chamber during the PEALD growth at a relatively low temperature of 185 °C. It is found that the composition of the obtained film quickly changes from AlN to Al2O3 when a small amount of O2 is added. Thus, the NH3:O2 ratio should be maintained at a relatively high level (>85%) for realizing the AlON growth. Benefited from the growth method, the nitrogen can be doped evenly in the entire film. Moreover, the AlON films exhibit a lower surface roughness than the AlN as well as the Al2O3 ones. The Al 2p and N 1s X-ray photoelectron spectra show that the AlON film is composed of Al–N, Al–O, and N–Al–O bonds. Moreover, a three-layer construction of the AlON film is proposed through the Si 2p spectra analysis and reconfirmed by the transmission electron microscopy characterization. At last, the electrical and optical tests indicate that the AlON films prepared in this work can be employed as the gate dielectric in transistor application as well as the antireflection layer in photovoltaic application.Keywords: aluminum oxynitride (AlON); doping profile; interface; plasma-enhanced atomic layer deposition (PEALD); X-ray photoelectron spectroscopy;

The thermal stability of Ge/Al2O3 and Ge/AlN/Al2O3 stacks has been systematically studied upon post deposition annealing (PDA) at 400, 500 and 600 °C with nitrogen gas flow. X-ray photoelectron spectroscopy (XPS) with the incident photon energy of 1486.7 eV and synchrotron radiation photoemission spectroscopy (SRPES) with the incident photon energy of 720, 500 and 200 eV have been used to characterize the interface chemistry and the diffusion of Ge-oxides. More aggressive “clean-up” effect takes place with a higher substrate temperature during the atomic layer deposition (ALD) process for the growth of Al2O3 and AlN thin films. A competitive process among the Ge-oxides growth at the Ge/high-k dielectrics interface, the Ge-oxides diffusion, and GeO desorption has been suggested upon PDA treatments. The effective suppression for formation of Ge-oxides by an ultrathin AlN layer has been observed for the samples before PDA and after PDA at 400 °C. Ge-oxide diffusion in proximity to the gate oxide surface has been characterized from the Ge2p3/2 spectra by XPS after PDA at 400 °C for Ge/Al2O3 and Ge/AlN/Al2O3 stacks. The diffusion mechanism is hypothesized by diffusion of oxygen vacancy. Moreover, a significant desorption of GeO occurs after PDA at 600 °C for the AlN passivated sample.

•A large-scale array of 3D heterostructured hierarchical WO3@ZnWO4@ZnO-ZnO nanoacatus was formed.•The nanocactus array shows an improvement of light absorption and the transfer of charge carriers.•The proposed photoanode has an efficent PEC performance.Hierarchical heterostructures with large surface areas and multiple interfaces as photoanode materials, are holding great promise for photoelectrochemical (PEC) water splitting toward efficient solar energy utilization. In this work, the cactus-like WO3@ZnWO4@ZnO-ZnO (i.e. W@WZ@Z-Z) arrays compromising the first-order W@WZ@Z core-shell nanosheets and the second-order ZnO nanosheets, have been fabricated by combining atomic layer deposition (ALD) technique and hydrothermal process. The modification of ZnO nanosheets on the surface of WO3 and the simultaneous formation of ZnWO4 in-between buffer layer have endowed the photoanode a drastic enhancement in both ultraviolet light absorption and charge separation via the favorable band alignment at the WO3-ZnWO4-ZnO interfaces. Particularly, the W@WZ@Z-Z nanocactus (NC) array photoanode with a 30 nm ZnO layer on WO3 precisely controlled by ALD, exhibited around 3.8 times higher photocurrent density (~ 1.57 mA/cm2) at 1.23 V vs. RHE than pristine WO3 photoanode (~ 0.41 mA/cm2), with little loss after long-term continuous illumination as well. Overall, the novel combination of WO3 with ZnO and the ZnWO4 buffer layer, and construction of hierarchical heterostructures, along with the resulted improvement in light absorption and charge separation which have been confirmed by spectroscopic characterizations and finite-difference time-domain simulation, suggest many exciting opportunities for further development of high-performance PEC devices for solar energy conversion.Download high-res image (281KB)Download full-size image

Preparation of highly active, stable and earth-abundant photoanodes for water oxidation is an important strategy to meet the demand of developing clean-energy technologies. In this paper, efficient and stable photoanodes based on oxygen-deficient black WO3−x@TiO2−x core–shell nanosheets with precisely controlled shell thickness have been fabricated for photoelectrochemical (PEC) conversion from neutral water solutions. The black WO3−x@TiO2−x core–shell nanosheet photoanode with the shell thickness of ∼15 nm achieved around 8 times higher photocurrent density (∼3.20 mA cm−2) than the pure WO3 photoanode at 1.23 V vs. the RHE. An improved onset potential with long-term PEC durability was also realized with the obtained black WO3−x@TiO2−x core–shell nanosheet photoanodes. The promoted PEC water oxidation performance was likely to be originated from enhanced light absorption, interfacial charge transfer and charge separation in these WO3−x@TiO2−x nanosheets which were revealed by finite-difference time-domain simulations and specific band alignment, along with optical and electrochemical spectroscopic evidence. In a word, such black WO3−x@TiO2−x nanosheet photoanodes suggest many exciting opportunities for PEC water splitting toward highly efficient solar fuel generation and many other PEC sensing applications.

The effects of shell thickness and rapid thermal annealing on photoluminescence properties of one-dimensional ZnO/ZrO2 core/shell nanowires (NWs) are studied in this work. The ZnO/ZrO2 core/shell structures were synthesized by coating thin ZrO2 layers on the surface of ZnO NWs using atomic layer deposition. The morphological and structural characterization studies reveal that the ZrO2 shells have a polycrystalline structure, which are uniformly and conformally coated on the high quality single-crystal ZnO NWs. As compared with bare ZnO NWs, the ZnO/ZrO2 core/shell structures show a remarkable and continuous enhancement of ultraviolet (UV) emission in intensity with increasing ZrO2 shell thickness up to 10 nm. The great improvement mechanism of the UV emission arises from the surface passivation and the efficient carrier confinement effect of the type-I core/shell system. Moreover, it is observed that the UV emission of ZnO/ZrO2 core/shell structures after thermal annealing increases with increasing annealing temperature. The dominant surface exciton (SX) emission in the bare ZnO NWs and the ZnO/ZrO2 core/shell nanostructures has been detected in the low temperature photoluminescence spectra. A blue shift of the NBE emission peak as well as the varied decay rate of the SX emission intensity are also found in the ZnO NWs after the growth of ZrO2 shells and further thermal treatment. Our results suggest that the ZnO/ZrO2 core/shell nanostructures could be widely implemented in the optical and electronic devices in the future.

•Thin HfO2/Al2O3 film is grown on silicon substrate by atomic layer deposition.•XPS is used to investigate the interface of HfO2/Al2O3/Si after NH3 annealing.•The nitrogen can be doped into HfO2/Al2O3 film after NH3 annealing treatment.The effect of NH3 annealing on the chemical properties and thermal stability of ultrathin HfO2/Al2O3 film grown on silicon substrate by atomic layer deposition are investigated as a function of post deposition annealing temperature. X-ray photoelectron spectroscopy shows that nitrogen incorporation can be approached by a NH3 annealing treatment and its composition evidently increases after annealing at 700 °C. Nitrogen atoms are found to bond to hafnium, aluminum and silicon atoms with annealing temperature above 800 °C, respectively. In addition, ultrathin Al2O3 layer is demonstrated as a robust barrier layer for preventing silicon diffusion.

Inverted pyramid-based nanostructured black-silicon (BS) solar cells with an Al2O3 passivation layer grown by atomic layer deposition (ALD) have been demonstrated. A multi-scale textured BS surface combining silicon nanowires (SiNWs) and inverted pyramids was obtained for the first time by lithography and metal catalyzed wet etching. The reflectance of the as-prepared BS surface was about 2% lower than that of the more commonly reported upright pyramid-based SiNW BS surface over the whole of the visible light spectrum, which led to a 1.7 mA cm−2 increase in short circuit current density. Moreover, the as-prepared solar cells were further passivated by an ALD-Al2O3 layer. The effect of annealing temperature on the photovoltaic performance of the solar cells was investigated. It was found that the values of all solar cell parameters including short circuit current, open circuit voltage, and fill factor exhibit a further increase under an optimized annealing temperature. Minority carrier lifetime measurements indicate that the enhanced cell performance is due to the improved passivation quality of the Al2O3 layer after thermal annealing treatments. By combining these two refinements, the optimized SiNW BS solar cells achieved a maximum conversion efficiency enhancement of 7.6% compared to the cells with an upright pyramid-based SiNWs surface and conventional SiNx passivation.

The morphological, structural and photoluminescence properties of one-dimensional ZnO/HfO2 core–shell nanowires (NWs) with various thicknesses of HfO2 shell layers are studied in detail in this work. The ZnO NWs have been fabricated by a simple hydrothermal method, which are then coated by thin HfO2 shell layers using atomic layer deposition (ALD). The morphological and structural characterization demonstrates that the HfO2 shells with polycrystalline structures grow on the single-crystalline ZnO NWs conformally. Moreover, the ZnO/HfO2 core/shell NWs show remarkable enhanced ultraviolet (UV) emission with increasing thickness of the HfO2 shell layer compared with bare ZnO NWs. The UV emission intensity for the sample with HfO2 shell thickness of ∼16 nm is about 9 times higher than that of bare ZnO NWs. It mainly results from the decreased surface states by surface passivation of the HfO2 shell layer as well as a typical type-I band alignment in the ZnO/HfO2 core/shell structure. A model is also proposed to explain the evolution of the wide visible emission band with the relatively low intensity of the core/shell structures. Our results suggest that the ZnO/HfO2 core/shell structures have potential applications for high-efficiency optoelectronic devices such as UV light-emitting diodes and lasers.

•p-Type ZnO:Cu films were grown by atomic layer deposition.•The optical bandgap of ZnO:Cu films was narrowing after RTA treatments in N2.•The observed electrical conductivity degradation stems from an increase in hole-killer defects.The p-type Cu-doped ZnO (ZnO:Cu) films were grown by atomic layer deposition and subsequently rapid thermal annealed (RTA) in N2. X-ray diffraction patterns demonstrated that the position of (0 0 2) peaks shift to a slightly higher angle with increasing RTA temperature. The optical bandgap was detected to decrease from 3.36 eV for as-grown sample to 3.27 eV for 600 °C-annealed ZnO:Cu film. Moreover, the observed degradation of conductivity with the narrowing of the bandgap for the ZnO:Cu films was correlated to the change of hole-killer defects including oxygen vacancy (VO) and zinc interstitial (Zni) under RTA treatment.

•Hafnium-doped zinc oxide films were deposited by atomic layer deposition.•The incorporated Hf atoms would take oxygen from ZnO and form oxygen vacancies and Zn interstitials.•A minimum resistivity of 1.6 × 10− 3 Ωcm was obtained for the HZO film with 4.6 at.% Hf.Hafnium-doped zinc oxide (HZO) films were deposited by atomic layer deposition at 220 °C. The influences of Hf content on the structure, optical and electrical properties of HZO films were investigated systematically. The X-ray diffraction spectra revealed that the grown HZO films have a hexagonal structure with the preferential orientation changing from a-axis to c-axis with increasing Hf-doping concentrations. The X-ray photoelectron spectra showed the HZO films contain oxygen vacancies and Zn interstitials. Based on photoluminescence measurements, the dominating ultraviolet emission peak exhibited a blue-shift and its intensity was found to decrease with the increasing of Hf-doping content. In addition, a minimum resistivity of 1.6 × 10− 3 Ωcm was obtained for the HZO film with 4.6 at.% Hf.

HfO2/Al2O3 stacks are grown on Si (100) substrate by atomic layer deposition and then nitridized using ammonia (NH3) annealing in the temperature range of 600–900 °C. The effects of NH3 annealing temperature on the structural and physical properties are investigated. HfO2 phase changes from monoclinic to orthorhombic with the annealing treatment. Moreover, the increasing of the grain size and decreasing of the valence band maximum with increasing annealing temperature are demonstrated. In addition, the film annealed at 900 °C clearly shows that there exists an amorphous Al2O3 layer between partially crystalline HfO2 layer and the Si substrate.Highlights► Nitriding of HfO2/Al2O3 stacks is done by NH3 annealing. ► Upon annealing the HfO2 phase changes from monoclinic to orthorhombic. ► The valence band maximum decreases with increasing annealing temperature.

Niobium–aluminate (NbAlO) thin films have been prepared on silicon (100) with different Nb2O5:Al2O3 growth cycle ratio by atomic layer deposition (ALD) technology. The structural, chemical and optical properties of NbAlO thin films are investigated using X-ray diffraction (XRD), X-ray photoelectron spectroscopy (XPS), and spectroscopic ellipsometry (SE). The results show that all the obtained NbAlO films are amorphous and fully oxidized. It is also found that the proportion of components in the NbAlO film can be well-controlled by varying the ALD growth cycles of the independent oxides. Furthermore, the refraction index of the prepared films is observed to increase with an increase of the concentration of Nb in the mixtures.

Aluminum-doped zinc oxide (AZO) films were grown by atomic layer deposition at 200 °C. The influence of Al content on the structure, optical, and electrical properties of AZO films was investigated. The X-ray diffraction spectra revealed that the grown ZnAlO films have a hexagonal structure with a preferential c-axis orientation perpendicular to the substrate surface. Furthermore, a 0.1° peak shift at a diffraction angle of 34.5° from the wurtzite structure to higher values was observed after Al doping. The X-ray photoelectron spectra of AZO film showed that Zn exists only in the oxide states with an oxygen-deficient ZnO1-x matrix. In photoluminescence studies, the intensity of the dominant peak at ∼380 nm was found to decrease with increasing Al doping concentration. In addition, a minimum resistivity of 9.36 × 10–4 Ωcm was obtained for the AZO film with 2.7 at.% Al.

The effects of shell thickness and rapid thermal annealing on photoluminescence properties of one-dimensional ZnO/ZrO2 core/shell nanowires (NWs) are studied in this work. The ZnO/ZrO2 core/shell structures were synthesized by coating thin ZrO2 layers on the surface of ZnO NWs using atomic layer deposition. The morphological and structural characterization studies reveal that the ZrO2 shells have a polycrystalline structure, which are uniformly and conformally coated on the high quality single-crystal ZnO NWs. As compared with bare ZnO NWs, the ZnO/ZrO2 core/shell structures show a remarkable and continuous enhancement of ultraviolet (UV) emission in intensity with increasing ZrO2 shell thickness up to 10 nm. The great improvement mechanism of the UV emission arises from the surface passivation and the efficient carrier confinement effect of the type-I core/shell system. Moreover, it is observed that the UV emission of ZnO/ZrO2 core/shell structures after thermal annealing increases with increasing annealing temperature. The dominant surface exciton (SX) emission in the bare ZnO NWs and the ZnO/ZrO2 core/shell nanostructures has been detected in the low temperature photoluminescence spectra. A blue shift of the NBE emission peak as well as the varied decay rate of the SX emission intensity are also found in the ZnO NWs after the growth of ZrO2 shells and further thermal treatment. Our results suggest that the ZnO/ZrO2 core/shell nanostructures could be widely implemented in the optical and electronic devices in the future.

Preparation of highly active, stable and earth-abundant photoanodes for water oxidation is an important strategy to meet the demand of developing clean-energy technologies. In this paper, efficient and stable photoanodes based on oxygen-deficient black WO3−x@TiO2−x core–shell nanosheets with precisely controlled shell thickness have been fabricated for photoelectrochemical (PEC) conversion from neutral water solutions. The black WO3−x@TiO2−x core–shell nanosheet photoanode with the shell thickness of ∼15 nm achieved around 8 times higher photocurrent density (∼3.20 mA cm−2) than the pure WO3 photoanode at 1.23 V vs. the RHE. An improved onset potential with long-term PEC durability was also realized with the obtained black WO3−x@TiO2−x core–shell nanosheet photoanodes. The promoted PEC water oxidation performance was likely to be originated from enhanced light absorption, interfacial charge transfer and charge separation in these WO3−x@TiO2−x nanosheets which were revealed by finite-difference time-domain simulations and specific band alignment, along with optical and electrochemical spectroscopic evidence. In a word, such black WO3−x@TiO2−x nanosheet photoanodes suggest many exciting opportunities for PEC water splitting toward highly efficient solar fuel generation and many other PEC sensing applications.