摘要:

This article reports on the properties of hydrogenated carbon films deposited using a cathodic arc decomposition process with a graphite cathode used in a plasma assisted chemical vapor deposition mode. In this application of the cathodic arc, acetylene is broken down into radicals to form hydrogenated amorphous carbon films. Some results are also reported using hydrogen gas. The density in terms of plasmon energy orsp3fraction of the films has been found to decrease with increasing acetylene or hydrogen flow rate, approaching the value for glow discharge deposited polymer‐like hydrogenated amorphous carbon. When substrate bias is used, the hydrogen content is reduced and graphite microcrystals appear, together with cauliflower‐like growths. In the range between 100 and 500 V, negative substrate bias increases the density of the films. Overall, the hydrogen content decreases with the density of the films. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.362649

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The deposition temperature of hydrogenated amorphous silicon films deposited by dc glow discharge was found to affect the crystallinity, hydrogen content, and silicon–hydrogen bonding after laser crystallization of the film. This in turn affected the electrical properties of the crystallized film. The crystallinity of the film after laser annealing was always higher than that of the corresponding furnace‐crystallized films, for the same deposition temperature, and it increased with decreasing deposition temperature, similar to that observed in furnace crystallized films (650 °C, 30 h). However, the dark and photoconductivity, photoresponse (defined as the ratio of photo to dark conductivity), and the carrier diffusion length increased with increasing deposition temperature (150–350 °C). This was due to both an increase in hydrogen content and the SiH and SiH2bonding, as shown by evolved gas analysis and infrared spectroscopy. Carrier transport measurements indicated that the dominant transport mechanism changed from localized hopping to extended state transport with increasing deposition temperature for the laser‐crystallized films. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361000

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

A semiconductor with a high resistivity due to a deep trap is called a semi‐insulator. A semi‐insulator does not always behave like a normal insulator because of so‐called bias voltage propagation, which arises from space charge in the deep trap. This effect is a factor in the operation of various devices based on semi‐insulators. We investigate by numerical simulation its role in the transient photoresponse of a planar metal–semiconductor–metal photodetector. We simulate a realistic case where the active layer is InGaAs made semi‐insulating by addition of Fe. The simulation uses a two‐dimensional, drift/diffusion calculation with realistic conditions where the semi‐insulating material is represented by a two‐level compensation model with Fe as a deep acceptor that compensates shallown‐type impurities. The results give a microscopic picture on a picosecond time scale of factors that affect the transient response: trapping, space charge, propagation of the bias field, and the spatial distribution of the carriers.

ISSN:0021-8979    

DOI:10.1063/1.361001

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We have combined thermally stimulated‐current (TSC) and capacitance–voltage (C–V) measurements to estimate oxide, interface, and effective border trap densities in 6–23 nm thermal, N2O, and N2O‐nitrided oxides exposed to ionizing radiation or high‐field electron injection. Defect densities depend strongly on oxide processing, but radiation exposure and moderate high‐field stress lead to similar trapped hole peak thermal energy distributions (between ∼1.7 and ∼2.0 eV) for all processes. This suggests that similar defects dominate the oxide charge trapping properties in these devices. Radiation‐induced hole and interface trap generation efficiencies (0.1%–1%) in the best N2O and N2O‐nitrided oxides are comparable to the best radiation hardened oxides in the literature. After ∼10 Mrad(SiO2) x‐ray irradiation or ∼10 mC/cm2constant current Fowler–Nordheim injection, effective border trap densities as high as ∼5×1011cm−2are inferred fromC–Vhysteresis. These measurements suggest irradiation and high‐field stress cause similar border trap energy distributions. In each case, even higher densities of compensating trapped electrons in the oxides (up to 2×1012cm−2) are inferred from combined TSC andC–Vmeasurements. These trapped electrons prevent conventionalC–Vmethods from providing accurate estimates of the total oxide trap charge density in many irradiation or high‐field stress studies. Fewer compensating electrons per trapped hole (∼26%±5%) are found for irradiation of N2O and N2O‐nitrided oxides than for thermal oxides (∼46%±7%). More compensating electrons are also found for high‐field electron injection than radiation exposure, emphasizing the significance of border traps to metal‐oxide‐semiconductor long term reliability. The primary effect of nitrogen on charge trapping in these oxides appears to be improvement of the near interfacial oxide in which border traps are found.

ISSN:0021-8979    

DOI:10.1063/1.361002

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The dynamic microwave magnetization (DMM) amplitude of magnetostatic waves in yttrium iron garnet films at 5–6 GHz has been measured as a function of input power. The measurement is based on the characteristic frequency shift in the power transmission spectrum. This shift is related to the reduction of the effective static magnetization and, therefore, the increase of the DMM amplitude at high power. The measurements were made on 7.2‐&mgr;m‐thick, single‐crystal yttrium iron garnet films. A pulsed frequency‐swept microwave signal at 5–6 GHz was used to launch the magnetostatic waves. The signals were excited and detected by planar microstrip transducers. Measurements were made for magnetostatic forward volume waves (MSFVW) and magnetostatic surface waves (MSSW). The duty cycle of the pulsed microwave signal was kept at 0.1% in order to avoid sample heating effects. The shifts for small features in the transmission vs frequency profiles were used to determine the DMM amplitudes. At low power, the DMM amplitude increased with power. Saturation occurred at high power. The results indicate a saturation DMM response at about 10% of the saturation magnetization for input power in the 3–4 W range for MSFVW signals and above 0.5 W for MSSW signals. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361003

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

We studied an antiferromagnetic (AF) NiO film for an exchange‐biased layer, focusing especially on the relationships between the exchange coupling properties of the Ni81Fe19(top)/NiO(bottom) films and the character of its NiO film. Among the variable sputtering conditions, our experimental data showed that the dominant factor determining the exchange coupling properties was the Ar pressure during the NiO film preparation. Better exchange coupling properties resulted when the NiO film was deposited at low Ar pressure which was attributed to: (i) the smooth surface of the NiO film and (ii) the presence of relatively large particle sizes within it. The former was thought to bring about not only an increase in the number of unidirectional exchange coupled Ni81Fe19/NiO spins, but also the appearance of exchange paths having large local exchange anisotropies. The latter was thought to produce an increase in the AF clusters with a particle volume larger thanKeiA/KAFi, whereKei,A, andKAFiare local unidirectional anisotropy, interfacial area of the NiO cluster in contact with the Ni81Fe19film, and local magnetocrystalline anisotropy of the NiO cluster, respectively. Moreover, the NiO film was thermally stable up to 250 °C, although the AF anisotropy of the NiO film was weakened on increasing the annealing temperature above 250 °C. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361004

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

To elucidate unique Faraday spectra observed in porous magnetic films, we theoretically analyzed the magneto‐optical Faraday effect of discontinuous media with an ideal one‐dimensional array structure. The media are constituted by magnetic materials (widthDM) and air gaps (widthDG) which are aligned interchangingly. Propagation properties of optical waves in the media, such as the dispersion characteristics and the polarization states, were explored circumstantially, and apparent Faraday rotation and ellipticity spectra of the discontinuous media were obtained. The analysis reveals that the apparent Faraday spectra of the media vary to a large extent from those of a continuous medium depending strongly on the media structures. The key factors which govern the magneto‐optical effect of the discontinuous media are structural elements ofDMand 2(DM+DG): The Faraday spectra are subject to change only whenDM<&lgr; (&lgr;: the wavelength of optical wave in a vacuum). Then, the magneto‐optical effect of the magnetic materials is related to mode conversion from TE to TM when 2(DM+DG)<&lgr;. IfDM<&lgr;<2(DM+DG), the mode conversions of both directions from TM to TE and TE to TM are possible. The mode conversion dominates the apparent Faraday spectra of the media, causing the enhancement in the Faraday rotation and systematic shift of the spectra toward shorter and/or longer wavelength of the optical waves. These results explain very well the unique Faraday spectra of the porous films. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361005

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The dynamic behavior of the magnetization for (111)‐oriented films with cubic crystalline structures has been studied theoretically, and the permeability for such textured films has been confirmed to be isotropic. Meanwhile, Co‐rich CoFeAlCu films with high saturation magnetization (4&pgr;Ms=15.8 kG) and low magnetostriction (&lgr;s=1.3×10−6), prepared by the dc sputtering method, are found to exhibit perfect fcc (111) orientation with grain size of about 400 A˚. A fairly good isotropic magnetic softness has been attained for CoFeAlCu films with Zr underlayers even in the as‐sputtered state withHcof about 1.5 Oe in every measuring direction. After annealing in a rotating magnetic field at 380 °C for 2 h, the magnetic softness is further improved withHcas low as 0.85 Oe, and the permeability is isotropic in the film plane and as high as 500–600. The perfect (111) orientation of the CoFeAlCu films leads to the isotropic softness, which is consistent with the theoretical prediction. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361006

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

The magnetic properties and field‐dependent specific heat of melt‐spun amorphous RE70TM30(RE=Gd, Tb, Dy, Ho and Er; TM=Fe and Ni) and Gd65Co35alloys were investigated as potential magnetic refrigerants. Essentially zero magnetic hysteresis was observed in all the Gd–TM alloys at temperatures from 5 K up to the ordering temperatures. The coercive force of the RE70TM30alloys depended mainly on the RE species and increased according to the order of RE=Gd<Ho<Er<Dy<Tb. The magnetic susceptibility of most of the alloys showed apparently normal Curie–Weiss behavior above the ordering temperatures. The heat capacity measurements in zero field and applied fields of 4 and 8 T indicated that the magnetic transition in these alloys are significantly broadened. The maximum adiabatic temperature changes for Er70Fe30, Gd70Ni30and Gd65Co35amorphous alloys in a field change of 8 T are 4.0, 3.4, and 3.0 K, respectively. Mo¨ssbauer spectroscopy revealed that Fe atoms in the amorphous RE70Fe30alloys carry a small magnetic moment that may complicate the magnetic ordering in the alloys. A simple model assuming a Gaussian distribution of ordering temperatures around the apparent Curie temperature was constructed to attempt to reconcile the differences in the observed magnetic properties of these amorphous alloys. The broad magnetic transition is attributed to the fluctuation of the exchange integral caused by the structural disorder in amorphous alloys. The calculated susceptibility, magnetization, and heat capacity agreed reasonably well with the experimental data and show that the magnetic susceptibility and magnetization are only weakly affected by the distribution of ordering temperatures, but the heat capacity is much more sensitive to such a distribution. To effectively screen out magnetic refrigerants with sharp magnetic transitions and correspondingly large adiabatic temperature changes from those with broadened transitions and small adiabatic temperature changes, the field‐dependent heat capacity measurement technique is a powerful tool to use. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361007

出版商:AIP    

年代:1996

数据来源: AIP

摘要:

Iron particles of diameters in the range 5.5–8.5 nm have been synthesized within a suitably chosen oxide glass by subjecting the latter to a 3Na+&rlarr2;Fe3+exchange reaction followed by reduction treatment in hydrogen. Magnetic measurements have been carried out over the temperature range 20–300 K. The coercive force increases as the iron particle size is decreased. The maximum value of coercive force corresponding to 0 K (Hc0)∼548 Oe is obtained for a specimen having diameter of 6.5 nm. The magnetocrystalline anisotropy constant in the case of nanosized iron particles is estimated to be one order of magnitude higher than that of bulk iron. ©1996 American Institute of Physics.

ISSN:0021-8979    

DOI:10.1063/1.361008

出版商:AIP    

年代:1996

数据来源: AIP