Lattice location of Co implanted in silicon

Thermal treatment of CaF₂ has a significant influence on the number and intensity of the peaks seen by thermo-luminescence. A combination of ion implants and anneal cycles leads to the conclusion that the 90°C glow peak is derived from a defect of a substitutional trivalent impurity (e.g. Ce⁺³) linked to an interstitial fluorine ion. Perturbations of this centre by other defects modify the centre and the glow peak temperature is raised to 110°C.

The peaks at 180, 220 and 350°C all involve intrinsic defect clusters.

The building of models for the different glow peaks was helped by a comparison of impurity and self ion implantations.     

Lattice location of light implanted ions in Si and Ge after laser annealing

Abstract

Radiation damage produced by short ranged (ranges 20–30 μm) charged particles (alpha particles and fission fragments) in thick plastic track detectors (thickness ≈ 150 μm) has been enlarged to produce “through” holes by using a combination of electrochemical and chemical etching processes. A series of experiments were conducted with a view to optimize the operating conditions required to produce through holes with most suitable profiles for a particular application at hand. This novel technique has been employed in producing thick nuclear track filters using fission fragments from U-235 fission and alpha particles from radon and its daughters.     

Lattice location of implanted As in ZnO

Radioactive ⁷³As ions were implanted into a ZnO single crystal at room temperature with 60 keV up to a fluence of 2×10¹³ cm⁻². Subsequently, the angular emission channeling patterns of emitted conversion electrons were recorded by means of a position-sensitive detector in the as-implanted state and following annealing up to 900 C, and were compared to simulated emission yields for a variety of different lattice sites. We find that As does not occupy substitutional O sites, but mainly occupies the substitutional Zn sites. The fraction of As on O sites was at most a few per cent. Arsenic in ZnO is thus an interesting example of an impurity in a semiconductor where the major impurity lattice site is determined by atomic size and electronegativity rather than its position in the periodic system. Possible consequences with respect to the role of arsenic as a p-type dopant in ZnO are being discussed.     

Lattice location and trapping of hydrogen implanted in FCC metals

Hydrogen implantation in fcc metals is studied by ion-beam analysis methods. The lattice location and long-range migration are carried out after low-temperature implantation defects is found.     

Lattice location and stability of ion implanted Cu in Si

We report on the lattice location of ion implanted Cu in Si using the emission channeling technique. The angular distribution of beta(-) particles emitted by the radioactive isotope 67Cu was monitored following room temperature implantation into Si single crystals and annealing up to 600 degrees C. The majority of Cu was found close to substitutional sites, however, with a significant displacement, most likely 0.50(8) A along the <111> directions towards the bond center position. The activation energy for the dissociation of near-substitutional Cu is estimated to be 1.8-2.2 eV.     

Stiffness properties of porous silicon nanowires fabricated by electrochemical and laser-induced etching

Nanowires with dimensions of few nanometers were formed on the whole etched surface. The optical analysis of silicon nanostructures was studied. Blue shift luminescence was observed at 660 nm for PS produced by electrochemical etching, and at 629 nm for laser-induced etching. PS produced a blue shift at 622 nm using both etching procedures simultaneously. X-ray diffraction (XRD) was used to investigate the crystallites size of PS as well as to provide an estimate of the degree of crystallinty of the etched sample. Refractive index, optical dielectric constant, bulk modulus and elasticity are calculated to investigate the optical and stiffness properties of PS nanowires, respectively. The elastic constants and the short-range force constants of PS are investigated.     

Hg ION implantation in silicon: Lattice disorder created and hg atom lattice location

Abstract

The lattice disorder produced by 42-keV and 75-keV Hg ions implanted in Silicon at room temperature and the lattice location of the Hg atoms were studied by means of the channeling technique with a 2.0 MeV ⁴He⁺ beam. The damage produced was found to increase linearly with ion dose until a saturation value, connected to the ion range, is reached. The number of Si atoms displaced for Hg ion implanted was evaluated and compared with the theoretical expectation. The substitutional Hg fraction is connected to the disorder produced: the replacement mechanism is discussed.     

Blue photo- and electroluminescence of silicon dioxide layers ion-implanted with group IV elements

The microstructural, optical and electrical properties of Si-, Ge- and Sn-implanted silicon dioxide layers were investigated. It was found, that these layers exhibit strong photoluminescence (PL) around 2.7 eV (Si) and between 3 and 3.2 eV (Ge, Sn) at room temperature (RT), which is accompanied by an UV emission around 4.3 eV. This PL is compared with that of Ar-implanted silicon dioxide and that of Si- and Ge-rich oxide made by rf magnetron sputtering. Based on PL and PL excitation (PLE) spectra we tentatively interpret the blue–violet PL as due to a T₁→S₀ transition of the neutral oxygen vacancy typical for Si-rich SiO₂ and similar Ge- or Sn-related defects in Ge- and Sn-implanted silicon dioxide. The differences between Si, Ge and Sn will be explained by means of the heavy atom effect. For Ge-implanted silicon dioxide layers a strong electroluminescence (EL) well visible with the naked eye and with a power efficiency up to 5×10^-4 was achieved. The EL spectrum correlates very well with the PL one. Whereas the EL intensity shows a linear dependence on the injection current over three orders of magnitude, the shape of the EL spectrum remains unchanged. The I-V dependence exhibiting the typical behavior of Fowler–Nordheim tunneling shows an increase of the breakdown voltage and the tunnel current in comparison to the unimplanted material. Finally, the suitability of Ge-implanted silicon dioxide layers for optoelectronic applications is briefly discussed. Received: 9 March 2000 / Published online: 30 June 2000     

Preparation of a nanopatterned surface of bonded silicon wafers using electrochemical thinning and chemical etching: A scanning tunnel microscopy investigation

Sacrificial anodic oxidation is used to thin silicon wafer bonding substrates. Chemical solutions, sensitive to the periodic strain field present in the upper ultra-thin silicon layer, are employed for selective etching. Subsequent scanning tunnel microscopy observations reveal a square array of trenches corresponding to the buried screw dislocation network initially formed at the bonding interface. The influence of the initial thickness and the annealing of the ultra-thin film on roughness and trench depth of the nanopatterned substrates are examined. Germanium growth experiments are performed in order to show the self-organization character of resulting structured surfaces.     

Regularities of the photoluminescence of porous silicon after chemical etching in HF

The effect of chemical treatment of porous silicon samples by HF on its photoluminescence and its evolution with time in sample aging in air is investigated. It is shown that the effect of HF on the luminescence parameters depends on the duration of the treatment and the initial photoluminescence intensity of the sample. It is found that chemical etching in HF accelerates the growth of the total luminescence intensity in aging of the sample in air. The evolution of the photoluminescence spectrum in aging of the sample in air after chemical etching can be explained within the framework of the quantum-size model of the luminescence of porous silicon. Presented at the Fall Meeting of the Material Research Society, December 1–5, 1997, Boston, USA Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 66, No. 3, pp. 423–427, May–June, 1999.     

Rapid thermal annealing of electrically-active defects in virgin and implanted silicon

Chemical etching of single-crystalline (100)Si induced by pulsed laser irradiation at 308, 423, and 583 nm has been investigated as a function of the laser fluence and C1₂ pressure. Without laser-induced surface melting, etching requires Cl radicals which are produced only at laser wavelengths below 500 nm. With low laser fluences ((308 nm)<100 mJ/cm²) etching is non-thermal and based on direct interactions between photocarriers and Cl radicals. For fluences which induce surface melting ((308 nm)>440 mJ/cm²) etching is thermally activated. In the intermediate region both thermal and non-thermal mechanisms contribute to the etch rate.     

Depth dependence of photoluminescence and chemical bonding in porous silicon

Porous silicon (PS) is studied by stepwise peeling of the surface layer to clarify the non-uniformity in the photoluminescence (PL) and correlate it with the in-depth chemical bonding and structure of the 30 μm thick layer. The PL intensity grows by an order of magnitude after the peeling off of the first 10 μm and decreases five times in the next 5 μm while the peak maximum position shifts from 730 to 800 nm. X-ray photoelectron spectroscopy (XPS) measurements show that Si–Si and Si–O bonds are present both on the surface and below, and the preferential oxidation state of silicon changes from 3+ and 4+ on the surface to 1+ and 2+ below 10 μm. Using Raman spectroscopy silicon nanocrystals are shown to exist. Their mean size can be estimated at about 3 nm. These results show that the strongest PL comes from a region in the PS layer where silicon nanocrystallites are surrounded by oxides with a low level of oxidation and not from the strongly oxidized surface layer.     

铒离子注入碳化硅的射程和退火行为研究

用300—500 keV能量的铒(Er)离子注入碳化硅(6H-SiC)晶体中,利用卢瑟福背散射技术研究了剂量为5×10¹⁵ cm^-2 的Er离子注入6H-SiC晶体的平均投影射程R_p和射程离散ΔR_p,将测出的实验值和TRIM软件得到的理论模拟值进行了比较,发现R_p的实验值与理论值符合较好,ΔR_p的实验值和理论值差别大一些 关键词： 离子注入 投影射程和射程离散 退火行为 卢瑟福背散射技术     

A comparative study of indoor radon level measurements in the dwellings of Punjab and Himachal Pradesh, India

The LR-115 type-II plastic track detector has been used for measuring the indoor radon levels in the dwellings of some villages of Punjab and Himachal Pradesh. In Punjab, the villages surveyed are Rampura Phul, Lehra Mahabat and Pitho (villages in Bathinda district), and Amritsar city. The average indoor radon levels in these areas are found to vary from 64 to 152 Bq/m³, which are quite within the safe limits recommended by International Commission on Radiological Protection (Ann. ICRP 23(2)). The indoor radon levels have also been measured in the dwellings of Hamirpur district of Himachal Pradesh. The villages surveyed in this area are Nukhel, Badarn, Galore-Khas, Har-Upper, Tikker Brahamana and Awah-Lower where radon concentration has been found to vary from 261 to 724 Bq/m³. These values are higher than the recommended limit.     

硅尖阵列的制备及其在真空微电子加速度计中的应用

针对微电子器件,提出了一种简单、低成本、便于批量加工的硅尖阵列制备方法。分析了各向异性和各向同性湿法腐蚀的特点,研究了不同腐蚀液中硅尖的形成机理和腐蚀速率,采用扫描电子显微镜（SEM）观测硅尖形貌。结果表明：在质量分数40%KOH 腐蚀液中添加I2和 KI,显著减小了削角速率,得到了呈火箭尖的硅尖阵列。各向同性腐蚀采用HNA腐蚀液,腐蚀的硅尖呈埃菲尔铁塔形。通过调整腐蚀液配比,氧化锐化后,硅尖尖端曲率半径小于15 nm。该硅尖阵列已成功应用于真空微电子加速度计之中。     

On the nature of point defects and the effect of oxidation on substitutional dopant diffusion in silicon

An extensive analysis of the substitutional dopant diffusion phenomena in silicon during oxidation is presented. The analysis covers qualitative as well as quantitative aspects of the oxidation-enhanced and -retarded diffusion (OED and ORD) phenomena, and examines three different possible assumptions that can be made on the nature of the silicon thermal equilibrium point defect species: silicon self-interstitials (I) only, vacancies (V) only, coexistence of I and V. The only consistent way to interpret all properly documented OED/ORD data is to assume that I and V coexist under oxidation as well as under thermal equilibrium conditions at high temperatures.     

Coupled chemical reactions in dynamic nanometric confinement: IV. Ion transmission spectrometric analysis of nanofluidic behavior and membrane formation during track etching in polymers

In recent papers, it was shown that coupled chemical-topological reactions (CCRs) with both NaOH etchant and silver salts, performed in thin swift-heavy ion-irradiated polymers under the application of a test voltage across the polymer foils, eventually gave rise to characteristic current/voltage features and Bode plots that were tentatively attributed to the formation of Ag₂O membranes within the etched tracks. The same was also found when replacing the silver ions by lithium ions, and adding fluoride ions to the NaOH etchant, to promote LiF membrane formation. Ion Transmission Spectrometry (ITS) enabled us to reconfirm the existence of these membranes beyond doubt. The membrane thickness was determined to be ～0.2–0.4?µm in the best cases.

ITS also revealed that hitherto membrane formation occurs only in ～1% of all tracks, or even less. The reason for this poor abundance seems to be that the decisive factor for membrane formation, which is the firm anchoring of the emerging solid Ag₂O or LiF reaction products on the etched track walls, was hitherto rarely fulfilled. We attribute this tentatively to the too high test voltage applied for controlling the CCR process that might hinder the product anchoring on the walls by promoting nanofluidic electromigration. Indeed, voltage reduction seems to improve the situation.     

A comparative study of donor formation in dysprosium, holmium, and erbium implanted silicon

Formation of donor centers in Czochralski grown silicon doped with dysprosium, holmium, and erbium is discussed. Donor states of three kinds are introduced in the implanted layers after annealing at T=700°C. Shallow donor states with ionization energies between 20 and 40 meV are attributed to oxygen -related thermal donors. Other donor centers in the energy range of E_C−(60…70) meV and E_C−(100…120) meV appear to be dependent on dopants. After a 900°C anneal strong changes in the donor formation are observed only in silicon doped with erbium. Instead of donors at E_C−(118±5) meV, new donor centres at E_C−(145±5) meV are formed. Reportedly, the latter ones are involved in the excitation process of the Er³⁺ ions with a characteristic luminescence line at ≈1.54 μm.     

Mechanism and enhancement of photoluminescence from silicon nanocrystals implanted in SiO2 matrix

Photoluminescence (PL) spectra of Si nanocrystals (NCs) prepared by 130 keV Si ions implantation onto SiO2 matrix were investigated as a function of annealing temperature and implanted ion dose. PL spectra consist of two PL peaks, originated from smaller Si NCs due to quantum confinement effect (QCE) and the interface states located at the surface of larger Si NCs. The evolution of number of dangling bonds (DBs) on Si NCs was also investigated. For hydrogen-passivated samples, a monotonic increase in PL peak intensity with the dose of implanted Si ions up to 3×1017 ions /cm2 is observed. The number of DBs on individual Si NC, the interaction between DBs at the surface of neighbouring Si NCs and their effects on the efficiency of PL are discussed.