Laser Annealing of Chemical Bath Deposited CdS Films

Chemical Bath Deposited (CBD) CdS films have been exposed to a cw Ar⁺ laser annealing. Measurementes on the dark electrical resistivity have shown a two decade decrement in the resistivity. A trend of improving this resistivity is shown upon atmospheric pressure increase. The annealing mechanisms of the samples show a threshold laser power density of 50 W/cm². This power threshold accounts for some heating mechanisms and Cd ion evaporation from the samples; thus a gaseous Cd atmosphere annealing process is suggested. This laser annealing mechanism parallels thermal annealing of polycrystalline CdS films. Assessment of this mechanisms is supported by the fact that the mobility ratio, b = μ_n/μ_p, (greatly influenced by crystallite size and intergranular potential barrier in thin film semiconductors) does not show major changes to account for a two decade decrement of CBD laser annealed samples.     

Influence of proton implantation on the properties of CuInSe2 single crystals (I). Ion channeling study of lattice damage

The lattice damage of p-type CuInSe₂ single crystals implanted with 10 keV protons in the fluence range from 2.5 · 10¹⁴ to 8 · 10¹⁵ cm⁻² was investigated using the Rutherford backscattering/channeling technique. At proton fluences up to about 2 · 10¹⁵ cm⁻² radiation annealing of the defects is observed which is ascribed to very high defect concentrations in the unimplanted samples. At higher fluences radiation damage occurs but the concentration of radiation induced defects ramains low. There are indications that selenium interstitials or defect complexes with selenium interstitials involved are stable defects at room temperature.     

Determination of the Effective Vacancy Concentrations and the Vacancy Losses after the Quench of Al–Zn–Mg Alloys

On the basis of

• 1 the experimental observation of dislocation loops by means of TEM,
• 2 the conclusion from this that the concentration of vacancies in the dislocation loops exists at the cost of the vacancy concentration primarily present at T_q, and
• 3 the inversion of the decomposition kinetics of Al–Zn–Mg alloys found out by means of resistivity and microhardness measurements, the effective vacancy concentration c_v.eff being at disposal for the GP-zone formation was found out by means of the relation t_R,max (t_R,max being the time required to reach the maximum of resistivity) and the Arrhenius plot In t_R,max = f(1/T_q) of the isothermal resistivity measurements. From the comparison of c_v.eff with the theoretical V concentration at T_q it is possible to derive statements about the loss of vacancies during and after the quench through loop formation, building-in of vacancies in GP-zones and annealing of vacancies at lattice defects. From this comparison follows:
  • The ideal ZnV concentration at T_q (calculated by means of the Lomer equation) is sufficiently great to account for the effective vacancy concentration.
  • The part of c_MgV in the loss concentration is rising with increasing c_Mg.
  Both these statements support the hypothesis that the initial process of the decomposition in Al–Zn–Mg alloys is caused by the ZnV diffusion.

     

Low temperature electron irradiation of amorphous and crystalline FeB alloys

Three amorphous FeB based alloys and crystalline Fe₃B alloy were irradiated at a temperature of 21 K with 2.5 MeV electrons. The irradiation induced increase of electrical resistivity (Δ?) was measured during irradiation. the damage produced was analysed with the conventional production curve $\text{Δ}\text{dot}\text{?}\text{=}\text{d}\text{(Δ?)/}\text{d}\text{(?t)}$ versus Δ? where ?t is the electron dose. After irradiation, isochronal annealings were performed up to room temperature. The behaviour of the four alloys was found to be similar both during irradiation and annealing.For all the alloys: the production curve is linear at high doses; and the induced increase of electrical resistivity Δ? anneals out at low temperature following different stages. These results are interpreted in terms of the creation of well defined defects.These defects have the same nature in amorphous and crystalline alloys; i.e. probably of vacancy type.     

Low temperature investigations of e−-irradiated GaAs

Positron lifetime measurements have been performed on electron irradiated chromium doped semi-insulating GaAs as a function of annealing between 139 and 908 K. Trapping at negatively charged Ga_As defects and by a vacancy mixture dominated by trivacancies took place in the as-irradiated state. Upon annealing around 210 K divacancies were formed from the trivacancies as caused by migrating arsenic interstitials. Complete trapping prevailed up to 530 K but decreased then rapidly at higher temperatures due to the migration of divacancies which also remove the Ga_As defects.     

Electrical resistivity evolution in the annealed amorphous Fe78Si9B13 ribbons

The electrical resistivity was measured at room temperature for the amorphous Fe₇₈Si₉B₁₃ ribbons annealed at various temperatures for different holding time. Although the annealed Fe₇₈Si₉B₁₃ ribbons are in full amorphous state, their electrical resistivity obviously varies with the annealing time. At every annealed temperature, the electrical resistivity evolution can be divided into regions I, II, and III, respectively. Using X-ray diffraction (XRD), scanning electron microscope (SEM), and differential scanning calorimetry (DSC), we investigated the ribbons overlapping regions I and II (called the focused ribbons, FRs). The results show that the change of electrical resistivity, fracture morphology, thermal effect in DSC analysis of the focused ribbons (FRs) can be ascribed to the evolution of the short range order (SRO) in the amorphous alloy.     

TEM Investigation of Dislocations in RNi2B2C (R = Y,Tb, Ho,Er, Y0.6Tb0.4, Er0.8Tb0.2)

To evaluate the influence of different rare earth metals on dislocation type and stacking fault occurrence in RNi2B2C compounds samples with R = Y, Tb, Ho, Er, Y_0.6Tb_0.4 and Er_0.8Tb_0.2 were investigated. As a result of the TEM analysis the parameter decisive for the lattice defects in these compounds is not the type of components but the annealing treatment of the samples. In well homogenized material the dominant Burgers vector of perfect dislocations was <100] and stacking faults are hardly found. In inhomogeneous samples the dominant Burgers vector was <110] and the perfect dislocations often lie in the planes of the numerous stacking faults. In both types of materials the experimental results hint at the existence of two different slip systems.     

Electrical properties of nitrogen implanted GaSe single crystal

N‐implantation to GaSe single crystals was carried out perpendicular to c‐axis with ion beam of 6 × 10¹⁵ ions/cm² dose having energy values 30 keV and 60 keV. Temperature dependent electrical conductivities and Hall mobilities of implanted samples were measured along the layer in the temperature range of 100‐320 K. It was observed that N‐implantation decreases the resistivity values down to 10³ Ω‐cm depending on the annealing temperature, from the room temperature resistivity values of as‐grown samples lying in the range 10⁶‐10⁷ Ω‐cm. The temperature dependent conductivities exhibits two regions (100‐190 and 200‐320 K) with the activation energies of 234‐267 meV and 26‐74 meV, for the annealing temperatures of 500 and 700 °C, respectively. The temperature dependence of Hall mobility for the sample annealed at 500 °C shows abrupt increase and decrease as the ambient temperature increases. The analysis of the mobility‐temperature dependence in the studied temperature range showed that impurity scattering and lattice scattering mechanisms are effective at different temperature regions with high temperature exponent. Annealing of the samples at 700 °C shifted impurity scattering mechanism toward higher temperature regions. In order to obtain the information about the defect produced by N‐implantation, the carrier density was analyzed by using single donor‐single acceptor model. We found acceptor ionization energy as E_a = 450 meV, and acceptor and donor concentration as 1.3 × 10¹³ and N_d = 3.5 × 10¹⁰ cm⁻³, respectively. (© 2003 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Microstructural study of He<Superscript>+</Superscript>-implanted and thermally annealed silicon-on-sapphire layers

The effect of He⁺ ion implantation and subsequent annealing on the silicon-on-sapphire microstructure is studied by transmission electron microscopy and X-ray diffraction analysis. It is established that He⁺ ion implantation leads to the formation of defects in the Si layer and α-Al₂O₃, while subsequent annealing causes dissociation of radiation defects in Si and formation of nanopores in α-Al₂O₃. The effect of implanted-ion dose and annealing temperature on the parameters of the porous α-Al₂O₃ layer and structural quality of the Si layer is investigated.     

Electrical Properties of CuInSe2 Single Crystals Implanted with Xenon

Both p-type and n-type CuInSe₂ single crystals were implanted with 40 keV ¹³⁰Xe⁺ ions up to doses of 5 · 10¹⁶ cm⁻². Implanted layers on p-type substrates showed an initial increase of the resistivity followed by a continuous decrease of the resistivity at higher doses. Implanted layers on n-type substrates gave also an increase of the resistivity at lower doses, but at higher doses a conductivity type conversion from n-type to p-type took place, followed by a decrease of the resistivity. To explain the experimental results it is supposed that the increase of the resistivity is mainly due to charge carrier scattering at extended defects while the decrease of the resistivity at high doses is due to the predominant creation of intrinsic acceptor states during implantation.     

Effects of annealing on the lattice parameter of polycrystalline CdS thin films

Cubic CdS (β‐CdS) polycrystalline thin films were prepared on glass substrates by chemical synthesis at 80 °C. Samples were subjected to thermal treatments (TT) in the range of temperatures (T) 180 – 500 °C during 30 hours in different ambients. Annealing in air and in H₂ produces in CdS larger lattice parameter enlargements (≤2.5 %) when T of TT increases up to T ≤ 500 °C. Whereas, annealing in Ar + S₂ and vacuum provokes intermediate (≤1.2 %) and smaller (≤0.9 %) maxima values of the lattice parameter increments, respectively. Energy band gap (E_g) as a function of T of TT and as a function of the lattice parameter has been also studied where it was observed that E_g behaves in very different manners depending on the ambient chosen for annealing. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Estimation of point defect parameters of solids on the basis of a defect formation model of melting (I)

It is proposed that the melting process is governed by the creation of lattice defects followed by a relaxation of the lattice in the vicinity of the defects. At the melting point T_m the mole fraction x_L of defects within the melt is given by x_L = L/h_o (L heat of fusion; h_o formation enthalpy of defects within the solid).     

Study of structural relaxation of Ni78Si8B14 metallic glass by electrical resistivity and thermal expansion measurements

Electrical resistivity and thermal expansion measurements were made to elucidate the structural relaxation of Ni₇₈Si₈B₁₄ metallic glass, especially, the topological short range ordering. The decrease of the resistivity and the increase of its temperature coefficient were observed, and these changes due to the structural relaxation were discussed on the basis of the extended Ziman theory for metallic glasses proposed by Nagel. The densification of about 0.25% and the decrease of 4% in the thermal expansion coefficient were observed in the considerably relaxed sample. The topological short range ordering in Ni₇₈Si₈B₁₄ metallic glass occurs rapidly at the annealing temperature above 200°C.     

A Mechanism of High-Tc Superconductivity Relating to Perovskite Crystal Structure

A mechanism of high-T_c superconductivity related to the perovskite crystal structure is proposed by a “phonon attenuation model”, which means that in the perovskite-like crystal structure, a number of “ordering” vacancies or holes occur due to the non-stoichiometric structure features. Such a reticular “spongly-like” structure facilitates lattice thermovibration attenuation perovskite (phonon attenuation) during temperature reduction. This leads to an abrupt drop of the resistivity, owing to the conduction electrons transmitted through the media without collision with irregularities in the lattice due to the lattice thermovibration. This probably is the main reason for high-T_c superconductivity of the perovskite cuprates.     

Photoacoustic Spectroscopy of Defect States in Etched and Air-annealed CuInSe2 Single Crystals

Photoacoustic spectra of cleaved, polished and etched, and air-annealed n-type CuInSe₂ single crystals are measured at different frequencies between 30 and 312 Hz. The spectra related to the bulk of the crystals exhibit five structures due to defects that are also present in p-type crystals. Polishing and etching as well as subsequent air annealing at 100, 200 and 300 °C reveal rather complex changes of the defect equilibrium in the near-surface region of the crystals which include both relative concentration changes of existing defects and creation of new defects. The results for polished and etched crystals correspond to trends expected from etching induced local modifications of the composition and structure as revealed by electron spectroscopies and ion channeling. Air annealing is found to affect all existing defects and to create up to five new defects which cannot be explained in terms of the related point defect model proposed by CAHEN and NOUFI.     

EBIC/TEM Studies on the Relation between Electrical Properties,Crystallographic Structure,and Interaction with Point Defects of Epitaxial Stacking Faults in Silicon

Only after annealing, EBIC investigations on epitaxial layer defects partly gave contrasts. More information on the crystallographic structure of these defects was obtained in subsequent HVEM investigations. Experimental results confirmed the supposition that only the decoration of the crystallographic defects with additional recombination centres (impurity atoms), and not existence of the defects themselves, results in a detectable EBIC contrast. The observed getter efficiency of the various defect types is discussed. This efficiency is growing with increasing lattice distortion.     

Characterization of (Ba, Sr)RuO3 films deposited by metal organic chemical vapor deposition

(Ba, Sr)RuO₃ oxide electrodes have been studied for high dielectric (Ba, Sr)TiO₃ film in DRAM capacitors. Metal organic chemical vapor deposition (MOCVD) is used for large-scale deposition and provides better step coverage properties. In this work, methoxyethoxytetramethylheptanedionate (METHD) precursor and solvent [n-butylacetate(C₆H₁₂O₂)] were mixed together into a single solution source. Post deposition annealing is carried out in oxygen atmosphere using rapid thermal annealing (RTA) to investigate the effect of organic impurities such as carbon during deposition. After annealing, resistivity of the BSR film decreased drastically compared to the as-deposited film. X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) analysis were used to describe this phenomenon accurately. The decrease in carbonate with increasing annealing time was confirmed by XRD analysis.     

Co掺杂氧化锌的电学和磁学性质的研究

采用水热合成法实现了Co掺杂氧化锌材料,并对所制备的材料以及在空气中退火材料的电学和磁学性质进行了研究.通过 X 射线衍射(XRD)、扫描电镜(SEM)等方法对制得样品的结构、形貌进行了表征,结果表明:Zn0.9Co0.1O为六方纤锌矿结构,钴元素的掺入并不改变氧化锌的物相结构.由于掺杂过程中钴元素替代晶格中锌离子的位置,晶格常数发生了改变,同时也影响了材料的性质;退火后样品的晶粒尺寸减小,结晶性变得更好.通过霍尔效应测试系统对样品的电输运性质和磁阻效应进行了分析,结果表明初始样品零场电阻大于退火后样品.磁场对样品内的载流子浓度和迁移率产生了影响,从而影响样品的电导率.两组样品均表现为正磁阻效应,这主要是由于电子局域化作用和能带劈裂效应共同作用的结果,初始样品受到内部晶格缺陷影响,磁阻效应没有持续增加,而经退火处理后的样品内部晶格缺陷减少,水分子导电作用减弱,致使正磁阻作用越来越明显.     

Luminescence and Photoconductivity Caused by Antisite Defects in CdIn2S4 Single Crystals

Results of a study of the influence of nonstoichiometry as well as of annealing and argon ion implantation on photoluminescence and photoconductivity spectra of cadmium thioindate single crystals are presented. The energy positions of levels of antisite In_cd and Cd_In defects are found. The role of antisite defects in the process of conductivity compensation is analysed.     

Growth of epitaxial TmFeCuO4 thin films by pulsed laser deposition

Epitaxial thin films of TmFeCuO₄ with a two-dimensional triangular lattice structure were successfully grown on yttria-stabilized-zirconia substrates by pulsed laser deposition and ex situ annealing in air. The films as-deposited below 500 °C showed no TmFeCuO₄ phase and the subsequent annealing resulted in the decomposition of film components. On the other hand, as-grown films deposited at 800 °C showed an amorphous nature. Thermal annealing converted the amorphous films into highly (0 0 1)-oriented epitaxial films. The results of scanning electron microscopic analysis suggest that the crystal growth process during thermal annealing is dominated by the regrowth of non-uniformly shaped islands to the distinct uniform islands of hexagonal base.