Excellent Si surface passivation by low temperature SiO2 using an ultrathin Al2O3 capping film

It is demonstrated that the application of an ultrathin aluminum oxide (Al₂O₃) capping film can improve the level of silicon surface passivation obtained by low‐temperature synthesized SiO₂ profoundly. For such stacks, a very high level of surface passivation was achieved after annealing, with S_eff < 2 cm/s for 3.5 Ω cm n‐type c‐Si. This can be attributed primarily to a low interface defect density (D_it < 10¹¹ eV^–1 cm^–2). Consequently, the Al₂O₃ capping layer induced a high level of chemical passivation at the Si/SiO₂ interface. Moreover, the stacks showed an exceptional stability during high‐temperature firing processes and therefore provide a low temperature (≤400 °C) alternative to thermally‐grown SiO₂. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

TiO2/SiO2 multilayer as an antireflective and protective coating deposited by microwave assisted magnetron sputtering

In this paper designing, preparation and characterization of multifunctional coatings based on TiO₂/SiO₂ has been described. TiO₂ was used as a high index material, whereas SiO₂ was used as a low index material. Multilayers were deposited on microscope slide substrates by microwave assisted reactive magnetron sputtering process. Multilayer design was optimized for residual reflection of about 3% in visible spectrum (450–800 nm). As a top layer, TiO₂ with a fixed thickness of 10 nm as a protective film was deposited. Based on transmittance and reflectance spectra, refractive indexes of TiO₂ and SiO₂ single layers were calculated. Ultra high vacuum atomic force microscope was used to characterize the surface properties of TiO₂/SiO₂ multilayer. Surface morphology revealed densely packed structure with grains of about 30 nm in size. Prepared samples were also investigated by nanoindentation to evaluate their protective performance against external hazards. Therefore, the hardness of the thin films was measured and it was equal to 9.34 GPa. Additionally, contact angle of prepared coatings has been measured to assess the wetting properties of the multilayer surface.     

Evaluation of the energy distribution of trap states in polymer films

This paper reports on the results of an investigation of polymer thin films by the methods of thermally stimulated currents and current-voltage characteristics. It has been found using these methods that, in the band gap of the poly(diphenylene phthalide) films, there are three groups of electron traps with maxima in the density of states at energies of 0.50, 1.06, and 2.40 eV with respect to the bottom of the conduction band. These results correlate well with the data obtained in our investigation of the fluorescence excitation spectra.     

在离子阱中应用Raman激发制备离子振动Fock态

基于囚禁离子与驻波激光场相互作用的Jaynes-Cummings模型,应用Raman激发,我们提出了一种制备离子振动Fock态的新方法.适当选择相互作用时间和Trapping条件,可把离子制备在所需的振动Fock态上.     

Effective silicon surface passivation by atomic layer deposited Al2O3/TiO2 stacks

In this work atomic layer deposition of Al₂O₃ and TiO₂ has been used to obtain dielectric stacks for passivation of silicon surfaces. Our experiments on n‐ and p‐type silicon wafers deposited by thin Al₂O₃/TiO₂ stacks show that a considerably improved passivation is obtained compared to the Al₂O₃ single layer. For Al₂O₃ films thinner than 20 nm the emitter saturation current density decreases with increasing TiO₂ thickness. Especially the passivation of ultrathin (～5 nm) Al₂O₃ is very effectively enhanced by TiO₂ due to a decreased interface defect density as well as an increased fixed negative charge in the stacks. Hence, the thin Al₂O₃/TiO₂ stacks developed in this work can be used as a passivation coating for Si‐based solar cells. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Enhanced quantum efficiency in polymer electroluminescence devices by inserting an ultrathin PMMA layer

We report an increase of electroluminescence (EL) efficiency by about two times for poly(2-methoxy-5-(2′-ethylhexyloxy)-1,4-phenylene vinylene) (MEH-PPV) based polymer light-emitting diodes (PLED) while employing an ultrathin layer of poly(methyl methacrylate) (PMMA) between a hole injection layer, polyethylenedioxythiophenne:polystyrenesulfonate (PEDOT:PSS) and an emitting layer, MEH-PPV. The peak power efficiency of the control device (ITO/MEH-PPV/LiF/Al) was 0.42 lm/W with a current efficiency of 0.66 cd/A. The device with the optimized thickness of PMMA interface layer shows the highest power efficiency of 1.15 lm/W at a current efficiency exceeding 1.83 cd/A. The significant improvement in the device performance is attributed to the decrease of holes injection and the promotion of electrons injection, which cause the balance of the carriers within the emitting layer.     

PEG200改性SiO_2溶胶制备光学增透膜的研究

采用ＴＥＭ、ＳＤＰ 等分析手段对ＰＥＧ２００ 改性的ＳｉＯ２ 溶胶制备参数与光学增透膜的性质进行了研究。结果表明：ＰＥＧ２００ 改性后的ＳｉＯ２ 溶胶簇团粒度分布与交联状况发生显著变化,形成不同的网络结构特征,由此影响膜层的光学增透性能。     

Acoustic spectroscopy and electrical characterization of SiO2/Si structures with ultrathin SiO2 layers formed by nitric acid oxidation

Ultrathin silicon dioxide (SiO₂) layers formed on Si substrate with nitric acid have been investigated using both acoustic deep-level transient spectroscopy (A-DLTS) and electrical methods to characterize the interface states. The set of SiO₂/Si structures formed in different conditions (reaction time, concentrations of nitric acid (HNO₃), and SiO₂ thickness [3–9 nm]) was prepared. The leakage current density was decreased by post-oxidation annealing (POA) treatment at 250°C in pure nitrogen for 1 h and/or post-metallization annealing (PMA) treatment at 250°C in a hydrogen atmosphere for 1 h. All structures of the set, except electrical investigation, current-voltage (I - V), and capacitance — voltage (C - V) measurements, were investigated using A-DLTS to find both the interface states distribution and the role of POA and/or PMA treatment on the interface-state occurrence and distribution. The evident decreases of interface states and shift of their activation energies in the structures with PMA treatment in comparison with POA treatment were observed in most of the investigated structures. The results are analyzed and discussed.      

Surface passivation of crystalline silicon by sputter deposited hydrogenated amorphous silicon

This letter shows that intrinsic hydrogenated amorphous silicon (a‐Si:H) films deposited by RF magnetron sputtering can provide outstanding passivation of crystalline silicon surfaces, similar to that achieved by plasma enhanced chemical vapour deposition (PECVD). By using a 2% hydrogen and 98% argon gas mixture as the plasma source, 1.5 Ω cm n‐type FZ silicon wafers coated with sputtered a‐Si:H films achieved an effective lifetime of 3.5 ms, comparable to the 3 ms achieved by PECVD (RF and microwave dual‐mode). This is despite the fact that Fourier transform infrared spectroscopy measurements show that sputtering and PECVD deposited films have very different chemical bonding configurations. We have found that film thickness and deposition temperature have a significant impact on the passivation results. Self‐annealing and hydrogen plasma treatment during deposition are likely driving forces for the observed changes in surface passivation. These experimental results open the way for the application of sputtered a‐Si:H to silicon heterojunction solar cells. (© 2014 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Investigation of amorphous states of SiO2 by Raman scattering spectroscopy

The vitreous SiO₂ samples irradiated with fast neutrons at a dose of 5×10¹⁷?2.2×10²⁰ per cm² are investigated by the Raman scattering technique. It is demonstrated that the maximum of the low-frequency Raman spectrum (boson peak) shifts with an increase in the irradiation dose, and the medium-range order size decreases from 25 Å for the initial glass to 19 Å for the sample subjected to irradiation at a maximum dose. It is revealed that the fast relaxation intensity obtained from analysis of the low-frequency Raman spectra linearly correlates with the specific volume of the studied samples.     

Tight-binding investigation of electron tunneling through ultrathin SiO2gate oxides

We investigate electron tunneling through ultrathin gate oxides using scattering theory within a tight-binding framework. We employ Si[100]/SiO₂/Si[100] model junctions with oxide thicknesses between 7 and 18 Å. This approach accounts for the three-dimensional microscopic structure of the model junctions and for the three-dimensional nature of the corresponding complex energy bands. The equilibrium positions of the atoms in the heterostructure are derived from first-principles density-functional calculations. We show that the present method yields qualitative and quantitative differences from conventional effective-mass theory.     

Nature of chemical states of sulfur embedded in atomic‐layer‐deposited HfO2 film on Ge substrate for interface passivation

Sulfur was embedded in atomic‐layer‐deposited (ALD) HfO₂ films grown on Ge substrate by annealing under H₂S gas before and after HfO₂ ALD. The chemical states of sulfur in the film were examined by S K‐edge X‐ray absorption spectroscopy. It was revealed that the valences of S‐ions were mostly –2 at Ge/HfO₂ interface (GeS_x or HfO_2–yS_y to passivate the interface), while they were mostly +6 in HfO₂ layers (sulfates; HfO_2–z(SO₄)_z). The leakage current density in post‐deposi‐tion‐treated film was lower than that in pre‐deposition‐treated one. This suggests that the passivation of defects in oxide layer by sulfate ions is more effective to lower the leakage current rather than the interface defect passivation by S^2– ions. (© 2015 WILEY‐VCH Verlag GmbH &Co. KGaA, Weinheim)     

Photoactivity passivation of TiO<Subscript>2</Subscript> nanoparticles using molecular layer deposited (MLD) polymer films

Pigment-grade anatase TiO₂ particles (160 nm) were passivated using ultra-thin insulating films deposited by molecular layer deposition (MLD). Trimethylaluminum (TMA) and ethylene glycol (E.G) were used as aluminum alkoxide (alucone) precursors in the temperature range of 100–160 °C. The growth rate varied from 0.5 nm/cycle at 100 °C to 0.35 nm/cycle at 160 °C. Methylene blue oxidation tests indicated that the photoactivity of pigment-grade TiO₂ particles was quenched after 20 cycles of alucone MLD film, which was comparable to 70 cycles of Al₂O₃ film deposited by atomic layer deposition (ALD). Alucone films would decompose in the presence of water at room temperature and would form a more stable composite containing aluminum, which decreased the passivation effect on the photoactivity of TiO₂ particles.     

Thermal instability of HfO2 on InP structure with ultrathin Al2O3 interface passivation layer

We studied the thermal stability of HfO₂ on an InP structure when an Al₂O₃ interface passivation layer (PL) was introduced. In contrast to the thick (～4 nm) Al₂O₃‐PL, an almost complete disappearance of the thin (～1 nm) Al₂O₃‐PL was observed after a post‐deposition anneal at 600 °C. Based on various chemical and electrical analyses, this was attributed to the intermixing of the thin Al₂O₃‐PL with HfO₂, which might have been accompanied by the out‐diffusion of a substantial amount of substrate elements. (© 2012 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

H2对Ar稀释SiH4等离子体CVD制备多晶硅薄膜的影响

以SiH4,Ar和H2为反应气体,采用射频等离子体化学气相沉积方法在300℃下制备了低温多晶Si薄膜.实验发现,反应气体中H2的比例是影响薄膜结晶质量的重要因素,在适量的H2比例下制备的多晶Si薄膜具有结晶相体积分数高,氢含量低,生长速率快、抗杂质污染等特性.     

Defect reduction and surface passivation of SiO2/Si by heat treatment with high-pressure H2O vapor

Heat treatment with high-pressure H₂O vapor was applied to improve interface properties of SiO₂/Si and passivate the silicon surface. Heat treatment at 180–420 °C with high-pressure H₂O vapor changed SiO_x films, 150 nm thick formed at room temperature by thermal evaporation in vacuum, into SiO₂ films with a Si-O-Si bonding network similar to that of thermally grown SiO₂ films. Heat treatment at 130 °C with 2.8×10⁵ Pa H₂O for 3 h reduced the recombination velocity for the electron minority carriers from 405 cm/s (as-fabricated 150-nm-thick SiO_x/Si) to 5 cm/s. Field-effect passivation was demonstrated by an additional deposition of defective SiO_x films on the SiO₂ films formed by heat treatment at 340 °C with high-pressure H₂O vapor. The SiO_x deposition reduced the recombination velocity from 100 cm/s to 48 cm/s. Received: 1 March 1999 / Accepted: 28 March 1999 / Published online: 24 June 1999     

Two fold coordinated silicon atom: a hole trap in SiO2

The capturing properties of a neutral diamagnetic two fold coordinated silicon atom with two paired electrons (silylene center =Si:) in SiO₂ are studied with ab initio density functional method. We prove that this defect is a hole trap in SiO₂. Hole capture results in creation of a paramagnetic two-fold coordinated silicon atom with unpaired electron =Si(+). According to this prediction silylene centers can be with silicon-silicon bonds responsible for the positive charge accumulation in MOS devices at ionising radiation.     

Optical properties of ultrathin PbI2 microcrystallite in polymer

We have prepared PbI₂ microcrystallites embedded in polymer, which have a layer structure and are ultrathin crystals consisting of two to nine monolayers.

A very large energy shift of the exciton absorption band has been observed in these microcrystallites and interpreted in terms of size confinement of the translational motion of excitons in the c-direction perpendicular to the crystal surface. The simple effective mass approximation is broken down in 2, 3, 4 layer crystallites, because the crystal thickness is smaller compared to the exciton Bohr radius.

Secondly, in the Raman spectrum where the excitation energy is resonant to the exciton energy, there appears a new line in the energy region below 20cm⁻¹ which is characteristic of a ultrathin crystal. The Raman shift increases with decreasing the crystal thickness. This line is assigned as due to a longitudinal mode of a rigid-layer phonon.

Thirdly, the confinement of the internal motion is studied by measuring a diamagnetic shift of the exciton energy in the magnetic field up to 150 T and a bound exciton luminescence in the ultrathin microcrystallites. Much larger binding energy of the exciton compared to the bulk value is estimated. This fact suggests that the envelope function of the exciton shrinks not only by a strong spacial restriction in the c-direction but also by the dielectric screening from the surrounding polymer.

Fourthly, the exciton-phonon interaction is studied by the hole-burning measurement. From the temperature dependence of the hole width, it is suggested that the exciton is scattered by impurities or defects below 40 K and by a LO phonon above 40 K.

Finally, the hydrostatic pressure dependence of the exciton energy and the resonant Raman scattering in the energy region of the optical phonons have been measured and the size effect on the atomic bonding between I and Pb is discussed. It is concluded that covalent bonding between Pb and I atoms changes to ionic bonding in the ultrathin crystallites.