Influence of substrate temperature on the electrical and optical properties of amorphous germanium films

The influence of substrate temperature on electrical and optical properties of the amorphous germanium films deposited under well-defined conditions has been investigated. DC electrical conductivity in the temperature range of 80–573°K has been measured. In the low temperature region Mott’sT ^−1/4 law of conductivity is obeyed. The estimated values ofT ₀ andN show significant decrease with change inT _s in steps of 50°K. Similar results are seen in annealed films. The values of activation energy and optical energy increase withT _s.     

Effect of laser irradiation on structural,electrical and optical properties of SnO2 films

Thin films of SnO₂ were prepared using a spray pyrolysis technique. Films were irradiated with Nd:YAG laser pulses of various energy densities (2–50 mJ cm^–2) with varying number of pulses from 1–50. X-ray diffraction studies were made to investigate the structural changes due to laser irradiation. An improvement in crystallinity and an increase in grain size were observed in laser-irradiated films. Hall coefficient and Hall mobility studies were made in the temperature range 77–300 K for the as-grown as well as laser-irradiated films. An increase in mobility and a decrease in carrier concentration were observed in the films after laser irradiation. Optical transmission studies revealed that the refractive index increased as a result of laser irradiation.     

Effect of gamma irradiation on the optical properties of amorphous GeSe films

We have studied the influence of gamma irradiation in a ⁶⁰Co source (1.25 MeV, gamma doses from 10² to 10⁶ Gy) and subsequent storage for a year on the structure, fundamental absorption edge, and refractive index of a-GeSe films prepared by flash evaporation in vacuum on silica substrates (T _s = 293 K). The high-energy irradiation has been shown to stimulate structural transformations and to produce changes in the electron-defect subsystem of the films.     

Influence of annealing on the optical properties of amorphous germanium films

The influence of annealing on the optical, electrical and structural properties of thin amorphous Ge films deposited under well-defined conditions has been investigated. The results below the onset of recrystallization are interpreted as due to a progressive elimination of defects and an evolution of the films towards an “ideal” amorphous state. Various mechanisms are discussed in relation with various structural models.     

Some electrical properties of mixed amorphous thin films of germanium and silicon monoxide before electroforming

The co-evaporated SiO _x -Ge system was studied. Thin-film MIM sandwich structures were deposited by vacuum evaporation at a pressure of 10^–4 Pa and were measured at a pressure of 10^–3 Pa. The conductivity at low temperature and under d.c. fields has been found to be governed by a combination of an electronic hopping process and free-band conduction. At fields greater than 2 × 10⁶ V m^–1, it is concluded that the conduction process is governed by the Poole-Frenkel effect. Comparison with earlier results on SiO _x -GeO₂ films showed small differences in activation energy for conduction for samples of broadly similar overall composition.     

Structural peculiarities of amorphous germanium films

The number of nuclei grown as a function of time, overpotential and eletrolyte concentration have been investigated experimentally during the electrodeposition of Hg from an aqueous solution of Hg₂(NO₃)₂ onto a plane structureless platinum electrode and a hemispherical single-crystal electrode. It has been established that: (i) at constant overpotential after an induction period the number of nuclei grows linearly with time and reaches a saturation value after a sufficient time has elapsed; (ii) the higher the overpotential the shorter the induction period and the higher both the steady state nucleation rate and the saturation nucleus density; (iii) the smaller the electrolyte concentration the lower the nucleation rate, the longer the induction period and the larger the saturation nucleus density. It is shown that the time dependence of the number of nuclei can be described by an equation derived by assuming that nuclei are formed on active energetically preferred sites on the electrode surface, and that the saturation nucleus density is determined by the deactivation of the active centres by overlapping nucleation exclusion zones. Experimental data confirming the idea of Mutaftschiew and Toschev that the active centres are defects in the oxide layer covering the platinum are presented.     

Electrical properties of epitaxial germanium films on germanium

Thin films of germanium have been formed by vacuum deposition on single-crystal germanium (111) surfaces over a range of temperatures from 700° to 920°C. The films were carefully transferred to plane parallel sapphire substrates for measurements of their Hall mobility and Hall constant between 78° and 400°K. It was found that the Hall mobility values approached bulk values for films deposited onto Ge substrates near their melting point.     

Structural and electrical properties of amorphous carbon-sulfur composite films

In this paper, we discuss the synthesis of carbon-sulfur composite (a-C:S) films by vapour phase pyrolysis of maleic anhydride and sulfur. Structural changes in the system are analysed by scanning electron microscopy and powder X-ray diffraction. Microhardness test depicts an increase in the value of hardness with an increase in sulfur concentration. Electrical conductivity of composite samples varies with sulfur concentration. Magnetoresistance (MR) measurements show a drastic increase in the value of MR for the samples prepared at < 900°C. Thermal stability of these samples is analysed by thermogravimetric analysis, which depends on the host structure and the amount of intercalated species.     

Electrical characterization of amorphous germanium dioxide films

Amorphous germanium dioxide (GeO₂) films have been deposited by electron beam evaporation onto different substrates including glass, SnO₂ conducting glass, evaporated gold and n-type silicon in order to examine the electrical behaviour of GeO₂ in metal/insulator/metal (MIM) and metal/insulator/semiconductor (MIS) structures. In MIM structures the as-deposited films are strongly influenced by electrode barriers but heat treatment at 600 K induced ohmic behaviour. The dielectric response of the films in the frequency range 0.1–100 kHz and the temperature range 180–350 K showed that the dielectric constant at 300 K was 9 and was virtually independent of frequency, while the a.c. conductivity follows the relation σ ∞ ω^s, where s is temperature dependent. Good agreement with a classical electronic hopping model is obtained. In MIS structures, GeO₂ on silicon gives rise to heterojunction behaviour at low voltages while, at higher voltages, the d.c. conduction is bulk dominated and exhibits space-charge-limited conduction. The dielectric response of MIS structures is strongly influenced by the depletion capacitance at the interface between GeO₂ and silicon.     

Recrystallization behaviour and electrical properties of germanium ion implanted polycrystalline silicon films

The recrystallization behaviour of undoped and phosphorus-doped polycrystalline silicon films amorphized by germanium ion implantation at doses ranging from 1 × 10¹⁵ to 1 × 10¹⁶cm^-2 are investigated, and the electrical properties of phosphorus-doped films after recrystallization are studied. The phosphorus doping concentration ranges from 3 × 10¹⁸ to 1 × 10²⁰cm^-3. It is found that the nucleation rate decreases for undoped films and increases for phosphorus-doped films with increasing germanium dose; the growth rates decrease for both doped and undoped films. The decrease in nucleation rate is caused by the increase in implantation damage. The decrease in growth rate is considered to be due to the increase in lattice strain. The grain size increases with germanium dose for undoped films, but decreases for phosphorus-doped films. The dependence of the electrical properties of the recrystallized films as a function of phosphorus doping concentration with different germanium doses can be explained in terms of the grain size, crystallinity and grain boundary barrier height.     

Annealing and crystallization of amorphous germanium thin films

The isochronal and isothermal annealing of the room temperature electrical resistivity of vacuum-deposited a-e thin films was studied for different annealing temperatures up to about 500°C. By analysing the annealing kinetics, it is possible to show that the crystallization process can be characterized by a single activation energy of 3.5 eV and the nucleation process by an activation energy of 3 eV for different coating conditions. It is proposed that the crystal growth takes place by diffusion of extended divacancies to the crystalline-amorphous interface and by subsequent rearrangement of the relaxed atoms fit the crystalline matrix.     

A study of the optical properties of amorphous thin films of germanium and silicon monoxide

Amorphous films of Ge-SiO have been co-evaporated and some of their optical properties are reported. The optical constants have been measured and estimated. At the high absorption end of the absorption edge, an equation due to non-direct transitions inK-space is found to match the optical absorption data. The variation of the optical band gapE _opt with film composition is reported. The infrared spectrum of a mixed layer is presented and a simple conclusion is drawn.     

The effect of electron irradiation on the electrical properties of ferroelectric BSTO films

We have experimentally studied the effect of a 200-eV electron beam on the capacitance, loss factor, and tunability factor of planar capacitor structures based on ferroelectric (Ba,Sr)TiO₃ films. A significant drop in the level of dielectric losses with a slight decrease in the capacity upon irradiation to a dose of 10¹⁴ and 10¹⁵ cm⁻² was observed in film structures for the first time. The mechanisms of the observed effects and the role of structural defects are discussed.     

准分子激光引起的非晶硅薄膜晶化行为的研究

利用KrF准分子激光对非晶硅薄膜的表层进行了晶化.研究了激光能量密度和照射脉冲数对薄膜结晶度的影响,并对晶化后薄膜的形貌和结构进行了表征.结果表明:该非晶硅薄膜晶化阈值约为110 mJ/cm2,且不受照射脉冲数的影响;激光能量密度是影响薄膜结晶度的首要因素,但在较低的能量密度时,增加照射脉冲数也会显著的提高薄膜结晶度;结构及形貌表征发现,薄膜晶化层厚度约为400～500 nm,平均晶粒尺寸为30～50 nm.     

Effect of nanocrystalline phase on the electrical conductivity of amorphous tantalum-containing silicon-carbon films

We have studied the effect of metal concentration on the electrical conductivity of tantalum-containing silicon-carbon nanocomposite films. The results demonstrate that carrier transport in the films follows different mechanisms at low and high metal concentrations. When the concentration of the conducting nanocrystalline tantalum carbide phase is under 28 at %, conduction is due to hopping. Conducting-phase concentrations from 28 to 34 at % correspond to a percolation threshold. At higher tantalum carbide concentrations, conduction is through the tantalum carbide nanocrystals. The effect of heat treatments on the electrical conductivity of the material is analyzed.     

The effect of ion irradiation on the adherence of germanium films

Germanium films deposited under simultaneous argon ion irradiation show substantially better adherence on glass and other substrate materials than conventionally produced films.The ion bombardment leads to a strengthening of the interfacial bonding, an effect believed to be associated with a thin layer of intermediate composition produced at the substrate surface by ion knock-on processes. In addition irradiation causes a significant reduction in film stress.     

氮气退火对氟化非晶碳膜结构和电学性能的影响

采用电子回旋共振等离子体化学气相淀积(ECR-CVD)方法以C4F8和CH4为源气体制备了氟化非晶碳(a-C:F)膜并在氮气气氛中对a-C:F膜进行了退火处理研究.X光电子能谱(XPS)化学结构分析表明,退火后a-C:F膜中CF3,CF2和CF含量减少,而C-CFx(x=1～3)交联结构增多.电学性能研究指出,退火后a-C:F薄膜的介电常数由于电子极化和薄膜密度的增大而上升,Al/a-C:F/Si结构的阻滞效应由于界面态密度下降而减弱,同时a-C:F膜的π-π*带隙和电荷陷阱能量减小并导致薄膜漏电流增大.