Physical properties of amorphous Si: The role of annealing

The influence of annealing (up to 900 °C) on the absorption edge and the temperature dependence of the electrical conductivity of amorphous silicon (a-Si) thin layers prepared by cathode sputtering is reported. Up to 400 °C the changes by annealing on the above mentioned properties are explained by the decrease of the density of states within the mobility gap. At higher temperatures, two processes start to play role: the crystalization of the layer and the probable contamination, especially by oxygen.We thank Dr. M.Rozsíval for testing our samples by the electron diffraction.     

ESR studies on sputtered amorphous SiC,SiGe and GeC films

We have investigated how the ESR signals change with compositions of the binary alloys. Two signals originating from two components are interacting rather strongly with each other and narrowed somewhat by exchange interaction. The origin of the ESR signals has been made clear by comparing those at X-band and Q-band.     

Properties of amorphous silicon films: Dependence on deposition rate

We have measured the d.c. conductivity at 300 K, the spin density and the optical absorption in amorphous silicon films deposited at rates between 0.4 and 10 Å/sec. It is found that all these quantities reduce sharply as the deposition rate is decreased. The data are compared to the heat treatment behavior reported recently. The possibility of oxygen contamination is discussed.     

Influence of Se atoms on the properties of amorphous Ge

Electron spin resonance (ESR), electrical and optical measurements have been made for Ge_1?xSe_x (0?x?0.35) films in order to elucidate relations between tetrahedrally bonded amorphous semiconductors and chalcogenide amorphous semiconductors. The ESR signal due to dangling bonds in amorphous Ge decreases by increasing Se content. For more than about 20 at. % Se, the electrical conductivity is the activation type and the optical gap increases with the increase of Se content. The model of charged dangling bonds by Street and Mott seems to explain the experimental results.     

Magnetic properties of dc magnetron sputtered and evaporated amorphous films

Compositions of Fe₈₁B_13.5Si_3.5C₂, Fe₆₇Co₁₈Si₁B₁₄ and Fe_5.85Co_72.15Mo₂B₁₅Si₅ were deposited on to rigid and flexible substrates for the first time using a dc sputtering source as part of a novel Rotating Cryostat (RC). The films sputtered on silicon and glass show only isotropic magnetisation, whereas those sputtered on a polyimide (Kapton^TM) substrate exhibited either isotropic or anisotropic magnetisation depending upon composition. Similar findings were obtained for equivalent evaporated films. Received 23 October 2001 and Received in final form 29 January 2002     

Magnetic properties of amorphous Ge–Fe thin films

Thin films of Ge_100−xFe_x (x in at%) alloys, fabricated by thermal co-evaporation, have an amorphous structure at compositions x<∼40, although an unidentified crystalline phase with an FCC symmetry also exists at low Fe content. Magnetization versus temperature curves show that saturation magnetization is non-zero (1 to 2.5 emu/cm³) and remains nearly unchanged up to the highest measured temperature of 350 K. Magnetic hysteresis loops at room temperature show a typical ferromagnetic shape, complete saturation occurring by 1–2 kOe. These results may indicate ferromagnetic ordering at room temperature. No definite tendency is observed in the compositional dependence of saturation magnetization.     

New insight into the optical properties of amorphous Ge and Si

A short range disorder model, unlike present long range disorder theories, has been able to account well for both the density of states and the optical properties of amorphous Ge and Si. Our results indicate that the imaginary part of the dielectric function for amorphous Ge and Si has the same form as an averaged gradient matrix element as a function of energy. This conclusion should be valid for all tetrahedrally bonded amorphous solids.     

Physical properties of hydrogenated amorphous gallium arsenide

Summary The elemental composition and the optical properties of hydrogenated amorphous GaAs prepared by r.f. reactive sputtering at different hydrogen and argon pressure and substrate temperature have been determined. From the dependence of the absorption coefficient on photon energy the optical gap has been deduced according to the Tauc law. The data obtained for stoichiometric samples are compared with similar data obtained by different authors. The influence of various deposition parameters on stoichiometry and on the optical properties is briefly discussed.     

Magnetic and electrical transport properties of delta-doped amorphous Ge:Mn magnetic semiconductors

We report on the growth and characterization of delta-doped amorphous Ge:Mn diluted magnetic semiconductor thin films on GaAs (0 0 1) substrates. The fabricated samples exhibit different magnetic behaviors, depending on the Mn doping concentration. The Curie temperature was found to be dependent on both the Mn doping concentration and spacing between the doping layers. A sharp drop in magnetization and rise in resistivity are observed at low temperature in samples with high Mn doping concentrations, which is also accompanied by a negative thermal remanent magnetization (TRM) in the higher temperature range. The temperature at which the magnetization starts to drop and the negative TRM appears show a correlation with the Mn doping concentration. The experimental results are discussed based on the formation of ferromagnetic regions at high temperature and antiferromagnetic coupling between these regions at low temperature.     

Bi nanocrystals embedded in an amorphous Ge matrix grown by pulsed laser deposition

Received: 1 September 1997/Accepted 8 September 1997     

Physical characterization of Ge films on polyethylene obtained by pulsed laser deposition

A Nd:YAg laser, operating in fundamental wavelength at 1064 nm, is focused at an intensity of the order of 10¹⁰ W/cm² to ablate a solid Ge target. A Laser Ion Source (LIS) system is employed to produce ion emission at high directionality, high current, high rate of production and high charge states.     

Superconducting properties of amorphous sputtered Zr70Mo30

Specific heat, resistivity and critical superconducting fields (H_c and H_c2) measurements show that amorphous Zr₇₀Mo₃₀ is an intermediate superconductor (T_c = 4.3 K; λ = 0.77). The coupling strength is mainly governed by the electronic properties. Like in the Zr?3d alloys previously investigated, a discrepancy between the measured and calculated upper critical field slope is reported. The effect of two-level systems (TLS) needs to be clarified.     

Magnetic properties of amorphous sputtered CoxSi1−x films

Magnetic properties have been measured by transverse magneto-optic Kerr effect (MOKE) in amorphous sputtered Co_xSi_1?x films which are ferromagnetic and amorphous at room temperature with 0.55<x<0.80. These as-sputtered films show an in-plane easy axis with the ratio of coercitive force in the hard axis H_c (HA) to easy axis H_c (EA) and the value of the blocking field H_B almost constant with 0.60<x<0.80. Transverse magnetic susceptibilities with bias magnetic field parallel (χ_t0) and perpendicular $\text{(χ}{}_{\mathrm{<mtext>t\pi </mtext><mtext>2</mtext>}}\text{)}$ to the easy axis has been measured. These measurements show a deviation of Hoffmann's micromagnetic law for the susceptibilities.     

Velocity of propagation in the shock-crystallization of sputtered amorphous germanium

Shock-crystallization in sputtered amorphous germanium thin films has been studied by a high speed movie technique. One hundred cm/sec has been obtained as the velocity of propagation of the crystallization wave. This value is much smaller than that of the sound velocity and rules out the contribution of the acoustic shock-wave to this phenomenon.     

Magnetic and electrical properties in amorphous GeSeFe films

Amorphous GeSeFe films prepared by r.f. sputtering have shown paramagnetic, and ferromagnetic properties for the films with low and high Fe content, respectively. The temperature dependence of the electrical conductivity has indicated the variable range hopping conduction for the paramagnetic films and the metallic conduction for the ferromagnetic films. The films with intermediate Fe content have behaved intermediate between semiconductive and metallic conduction. These films are likely to be antiferromagnetic.     

Structure of amorphous Ge alloy films

Structural details of amorphous alloy films of Ge with Al, Cu and Fe up to 30 at.% metal concentrations have been studied. As determined by the electron diffraction studies, the short range order in these alloy films is essentially similar to that of amorphous (a-)Ge films. Electron microscopy and electrical resistivity measurements show that the concentration of voids and associated dangling bonds in a-Ge is reduced considerably on alloying. It is concluded from these studies that the metal atoms are accommodated in the tetrahedral network of a-Ge.     

Heat-radiation from shock-crystallization of sputtered amorphous germanium films

Temperature dependence of the shock-crystallization, effect of heat treatment, and heat radiation from the specimen during the process of the event have been investigated. Local temperature rise as high as 500°C accompanied with the propagation of crystallization wave has been observed.     

Influence of the calcium phosphate content of the target on the phase composition and deposition rate of sputtered films

Calcium phosphate was coated from tetracalcium phosphate (TTCP), hydroxyapatite (HA), β-tricalcium phosphate (TCP), β-calcium pyrophosphate (CPP), and β-calcium metaphosphate (CMP) powder targets using radio frequency magnetron sputtering. The composition of the crystal phase of the coated films was changed, depending on the target materials, and the Ca/P molar ratios of the films varied from 0.74 to 2.54, increasing with the Ca/P molar ratio of the target. The solubility of the target, determined using a microwave-induced plasma-mass spectrometer was: TTCP ≈ β-CMP > β-TCP > β-CPP > HA, and the deposition rate from each target showed a similar order to the solubility: TTCP ≈ β-CMP > β-TCP > β-CPP ≈ HA.