Poole-Frenkel conduction in Al/ZrO2 /SiO 2 /Si structures

Leakage currents through Al/ZrO₂/SiO₂/n-Si metal-insulator-semiconductor (MIS) capacitors were studied. Thin SiO₂ films were chemically grown on monocrystalline phosphorous doped silicon wafers. Zirconia films with thicknesses of 15 and 50 nm were deposited by radio frequency (rf) magnetron sputtering and, then, annealed in oxygen ambient at 850 ^○C, for 1 h. The dielectric constant of the sputtered and annealed ZrO₂ layer was of about 17.8. The equivalent oxide thickness (EOT) of the stack 15 nm and 50 nm-ZrO₂/SiO₂ structure was estimated to be 3.2 nm and 10.7 nm, respectively. The temperature dependence of the leakage currents was explained by Poole-Frenkel (PF) conduction mechanism. Shallow trap levels in the studied structure of about 0.2 eV and 0.46 eV were calculated. The existence of A and D-defects, due to the sputtering and high temperature annealing in oxygen, was suggested.     

First-principles calculations of the hole-induced depassivation of SiO2/Si interface defects

The holes induced by ionizing radiation or carrier injection can depassivate saturated interface defects. The depassivation of these defects suggests that the deep levels associated with the defects are reactivated, affecting the performance of devices. This work simulates the depassivation reactions between holes and passivated amorphous-SiO₂/Si interface defects (HP_b+h→ P_b+H⁺). The climbing image nudged elastic band method is used to calculate the reaction curves and the barriers. In addition, the atomic charges of the initial and final structures are analyzed by the Bader charge method. It is shown that more than one hole is trapped by the defects, which is implied by the reduction in the total number of valence electrons on the active atoms. The results indicate that the depassivation of the defects by the holes actually occurs in three steps. In the first step, a hole is captured by the passivated defect, resulting in the stretching of the Si-H bond. In the second step, the defect captures one more hole, which may contribute to the breaking of the Si-H bond. The H atom is released as a proton and the Si atom is three-coordinated and positively charged. In the third step, an electron is captured by the Si atom, and the Si atom becomes neutral. In this step, a P_b-type defect is reactivated.     

Photoconductivity of Si/Ge/Si structures with 1.5 and 2 ML of Ge layer

A photoconductivity (PC) of Si/Ge/Si structures with narrow Ge layer [thickness's 1.5 and 2 monolayers (ML)] on interband light intensity has been investigated for the different values of lateral voltage U, and temperature T. In contrast to the Si/Ge structure with 2 ML, where only monotonous PC growth was registered, for the 1.5 ML structure a stepped and a fluctuated PC were observed. These PC features are explained by a percolation of photoexcited carriers via the localized states induced by one monolayer scale Si/Ge interface roughnesses.     

Simulation of range profiles for boron implantation into SiO2/Si and Si3N4/SiO2/Si targets

The simple method of profile combination is shown to be applicable to the simulation of boron profiles in SiO₂/Si and Si₃N₄/Si layered targets. This is demonstrated by comparison with range distributions calculated by more sophisticated theoretical methods, i.e. TRIM Monte Carlo simulations and the algorithm of Christel et al., and with experimental data. The method of profile combination can also be applied to layered targets with a crystalline silicon substrate.     

Roles of interface and oxide trap density in the kinked current behavior of Al/SiO2/Si(p) structures with ultra-thin oxides

A clear current kinked phenomenon was observed in Al/SiO₂/Si(p) structures with nanoscale (<2.5 nm) SiO₂ in a forward biased region. It was found that the kinked points are dependent on oxide thickness and are not the same as flat-band voltages. A model regarding the oxide voltage dropping efficiency with the consideration of interface trap density ( $D_{\mathrm{it}}$ ) and effective charge number density ( $Q_{\mathrm{eff}}/q$ ) was proposed for the observation. It is noted that the kinked point is severely affected by the oxide quality and uniformity. However, Al/SiO₂/Si(n) structures in a forward biased region do not exhibit this current kinked phenomenon because the dropping behavior of oxide is absolutely different from Al/SiO₂/Si(p) structures.     

Specular X-ray reflectivity study of interfacial SiO2 layer in thermally annealed NiO/Si assembly

Present report details an analysis of X-ray reflectivity (XRR) for solution processed NiO thin films on Si (100) substrates. The films were annealed at 700–1,000 °C for 1 h in air. XRR data indicated growth of SiO₂ layer from ~8 nm at 700 °C to ~66 nm at 1,000 °C along with significant variation of electron density profile. X-ray photoelectron spectroscopy and X-ray diffraction studies were used as supporting studies for phase purity and oxidation states of the NiO thin films as well as interfacial SiO₂ layer.     

ESR of residual defects in silicon from recoil implantation of oxygen in Si/SiO2 systems

In ionic crystals or other insulators with partial ionic binding, the ion-target interaction differs from that of neutral atoms due to different electronic distributions and overall electrical charges Consequently, the nuclear stopping power and defect production by recoiling atoms will deviate from standard values, obtained from e g Moliere-potentials In the present paper, realistic potentials between projectile ion and target ion are determined by the free electron gas model of overlapping Hartree-Fock-Slater or Lenz-Jensen ions (and neutral atoms for comparison) With the new potentials, the transferred energies T and the range of interaction is determined for either damage production (T>E_d) and for nuclear stopping (T>hω> for bound ions) In addition the excitation of optical phonons is taken into account which are excited by the transient electrical field of the charged projectile     

非晶Si/SiO2超晶格结构的交流电致发光

设计并用磁控溅射方法制备了非晶Ｓｉ／ＳｉＯ２超晶格结构,以高纯多晶Ｓｉ为靶材,当以Ａｒ＋Ｏ２为溅射气氛时,得到ＳｉＯ２膜,仅以Ａｒ为气氛时,得到Ｓｉ膜。重复地开和关Ｏ２气,便交替地得到ＳｉＯ２和Ｓｉ膜。衬底在靶前往返平移,改变平移的速度或者改变溅射的功率,可以控制膜的厚度。通过透民镜的照片可以看出ＳｉＯ２和Ｓｉ膜具有均匀的周期结构,用低角Ｘ－射线反射谱表征了超晶格的周期结构和各层的厚度。透射光谱表     

On ultra-thin oxide/Si and very-thin oxide/Si structures prepared by wet chemical process

The properties of ultra-thin oxide/Si and very-thin oxide/Si structures prepared by wet chemical oxidation in nitric acid aqueous solutions (NAOS) and passivated in HCN aqueous solutions were investigated by electrical, optical and structural methods. n- and p-doped (1 0 0) crystalline Si substrates were used. There were identified more types of interface defect states in dependence on both post-oxidation treatment and passivation procedure. On samples prepared on n-type Si, continuous spectrum of defect states of 0.05-0.2 eV range and discrete defect traps, ∼E_CB − 0.26 eV and ∼E_CB − 0.39 eV, were found. All mentioned defects are related with various types of Si dangling bonds and/or with SiO_x precipitates. Post-metallization annealing of investigated MOS structures reduced the interface defect density and suppressed the leakage currents. It did not change spectral profile of interface defect states in the Si band gap. In addition, there are presented following two optical phenomena: relation between amplitude of photoluminescence signal of NAOS samples and parameters of chemical oxidation process and quantum confinement effect observed on samples containing Si grains of size less as ∼2 nm.     

Formation of Si nanowires by the electrochemical reduction of porous Ni/SiO2 blocks in molten CaCl2

Silicon nanowires (SiNWs) were prepared by the electrochemical reduction of solid Ni/SiO₂ blocks in molten CaCl₂ at 1173 K. The SiNWs have diameter distributions ranging from 80 to 350 nm, and the nickel–silicon droplets are found on the tips of the nanowires. The growth mechanism of SiNWs was investigated, which confirmed that the nano-sized nickel–silicon droplets formed at the Ni/SiO₂/CaCl₂ three-phase interline. The droplets lead to the oriented growth of SiNWs. Formation of nano-sized nickel–silicon droplets suggests that this method could be a potential way to produce nano-sized metal silicides.     

On the morphology of Si/SiO2/Ni nanostructures with swift heavy ion tracks in silicon oxide

Si/SiO₂/Ni nanostructures are fabricated by the irradiation of an oxidized Si surface with swift heavy ions, nanopore etching in the SiO₂ layer, and the electrochemical deposition of nickel in the nanopores with their partial (～50%) or complete filling. Studies of the morphology of the metal in the nanopores shows that the nickel-cluster structure is rather homogeneous and formed by crystallites ～30–50 nm in size. The effects of deposition modes and structure morphology on current transport are analyzed with the use of test temperature dependences of the magnetoresistance. The reproducibility and stability of the magnetoresistance values for the case of homogeneous structure and pore filling with nickel make the Si/SiO₂/Ni system promising for application as the base element for high-sensitivity low-temperature magnetic field sensors.     

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.      

Si／SiNx／SiO2多层膜的光致发光

采用射频磁控溅射法,制备了具有强光致可见发光的纳米Si/SiNx/SiO2多层膜,利用傅立叶红外吸收(FTIR)谱,光致发光(PL)谱对其进行了研究。用260nm光激发得到的PL谱中观察到高强度的392nm(3.2eV)和670nm(1.9eV)光致发光峰,分析认为它们分别来自于缺陷态≡Si-到价带顶和从导带底到缺陷态≡Si-的辐射跃迁而产生的光致激发辐射复合发光。PL谱中只有370nm(3.4eV)处发光峰的峰位会受退火温度的影响,结合FTIR谱认为370nm发光与低价氧化物—SiOx(x<2.0)结合体有密不可分的关系。当SiO2层的厚度增大时,发光强度有所增强,800℃退火后出现最强发光,认为具有较大SiO2层厚度的Si/SiNx/SiO2结构多层膜更有利于退火后形成Si—N网络,能够得到更高效的光致发光。用量子限制-发光中心(QCLC)模型解释了可能的发光机制,并建立了发光的能隙态(EGS)模型。     

Temperature and metal composition dependence of lateral photovoltaic effect in Al-Alq3/SiO2/Si structures

A series of Al=-（Alq3）l-x granular films is prepared on Si wafer with native oxide layer using co-evaporation technique. Large lateral photovoltaic effect （LPE） is observed, with an optimal LPV sensitivity of 75 mV/mm in x=0.35 sample. The dependence of LPE on temperature and A1 composition is investigated, and the possible mechanism is discussed.     

Vertical conduction in thin Si/CaF2/Si structures

Electrical characteristics of thin (∼100Å), single barrier Si/CaF₂/Si heterostructures have been measured for the first time for both A and B phase CaF₂. I(V,T) measurements for different thickness CaF₂ barriers show characteristics that are consistent with conduction through defect sites in the CaF₂ layer. The B-phase CaF₂ exhibits far more defects than the A -phase material. Measurements of different size mesas indicate a defect density on the order of one per 1000μm² in the 100Å barrier thickness A-phase material.     

Quantum confined luminescence in Si/SiO2 superlattices

Amorphous Si/SiO₂ superlattices with periodicities between 2 and 5 nm have now been grown on (1 00) Si wafers by several different techniques: molecular beam epitaxy, magnetron sputtering, and plasma enhanced chemical vapor deposition (PECVD). With the first two methods little or no hydrogen is incorporated during growth and visible photo-luminescence (PL) is obtained at wavelengths from 520 to 800 nm. The shift in the PL peak position with Si layer thickness is consistent with quantum confined band-to-band recombination. Annealing the sputtered superlattices at temperatures up to 1100°C results in a very bright red PL that is similar in intensity to that observed in porous Si samples. For large numbers of periods (e.g., 425) the PL is strongly modulated in intensity owing to optical interference within the superlattice. Similar quantum confined, but defect induced, PL is also observed in the PECVD grown superlattices, where the amorphous Si layers are heavily hydrogenated.