Microstructure and current transport in Ti/Al/Ni/Au ohmic contacts to n-type AlGaN epilayers grown on Si(111)

The microstructure and the current transport in Ti/Al/Ni/Au ohmic contacts on AlGaN were investigated in this paper.Significant structural changes of the metal stack occurred upon annealing and ohmic contacts were obtained after thermal treatments above 700 C, with specific contact resistance values , which depend on the thickness of the Ti layer.Although the formation of a TiN interfacial layer is independent of the Ti thickness, different contact structures, i.e. the phases and grain location, were found as a function of the Ti layer, which were crucial for the nanoscale current transport through the contact stack. In particular, conductive atomic force microscopy combined with the resistivity measurement of the main phases formed upon annealing (AlNi, AlAu₄, Al₂Au) indicated that the low resistivity Al₂Au phase provides preferential conductive paths for the nanoscopic current flow through the contact.     

Reaction of evaporated Ti films with large-grained Al substrates

We have studied the reaction kinetics of titanium films on large-grained aluminium substrates during furnace annealing in vacuum for temperatures between 450–550°C. Oxygen was profiled by elastic resonance¹⁶O(, )¹⁶O backscattering. A TiAl₃ aluminide layer always forms at the Ti/Al interface. In addition, a second TiAl₃ layer grows at the free Ti surface when the contamination of the annealing ambient by oxygen-carrying species is reduced during annealing. Otherwise, the nucleation of the second compound layer is inhibited by an oxygen-rich surface layer of the Ti.     

Ion mixing in Al,Si, and their oxides

The redistribution of thin metallic markers due to ion irradiation was studied by backscattering spectrometry in Al, Al₂O₃, Si, and SiO₂. Marker species were selected for their similar masses and different chemical reactivities with the host media and included Ti, Fe, W, Pt, and Au. It was found that the marker signals are Gaussian and that the variance ² of the marker atom distributions increases linearly with the dose of the irradiation, is insensitive to the temperature of irradiation in the range of 80–300 K, and depends linearly on the nuclear stopping power of the incident ions. The absolute values of ² for Ti, Fe, W, Pt, and Au markers in Al and Al₂O₃, W, and Pt in SiO₂ and W in Si is, within±50 %, of 6.5×10³Å² for 300 keV, 8×10¹⁵ Xe ions/cm². These observations suggest that collisional cascade mixing is a dominant mechanism in this type of impurity-matrix combinations. Only Au and Pt in Si mix at a larger rate: ² for Pt is about 3 and for Au about 5 times larger than ² for all other markers. Lower threshold displacement energies and/or the contribution of processes other than cascade mixing are possible considered reasons. In polycrystalline Al, a rapid migration of Au and Pt atoms throughout the Al layer, similar to grain boundary diffusion, is observed.     

High-Temperature Characteristics of Ti/Al/Ni/Au Ohmic Contacts to n-GaN

We present the high-temperature characteristics of Ti/Al/Ni/Au（15 nm/220 nm/40 nm/50 nm） multiplayer contacts to n-type GaN （Nd = 3.7 × 10^17 cm^-3, Nd = 3.0 × 10^18 cm^-3）. The contact resistivity increases with the measurement temperature. Furthermore, the increasing tendency is related to doping concentration. The higher the doped, the slower the contact resistivity with decreasing measurement temperature. Ti/Al/Ni/Au ohmic contact to heavy doping n-GaN takes on better high temperature reliability. According to the analyses of XRD and AES for the n-GaN/Ti/Al/Ni/Au, the Au atoms permeate through the Ni layer which is not thick enough into the AI layer even the Ti layer.     

Phase transformations in Cu-Sn alloys containing Ni,Al, Ge,and In

After quenching from 700C and aging, Cu-Sn alloys containing Ni and Al were found to have a precipitation of-solid solution, with a DO₃ type of ordering, of metastable ,, and phases. It was established that the phase has an 4 type of ordering while the phase has the Cu₃Ti type. Observations revealed that Cu-Sn-Al alloys contained two phases, and, with an identical structure but with different ratios of electron concentration per atom.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 4, pp. 34–37, April, 1981.     

Wetting transition on grain boundaries in Al contacting with a Sn-rich melt

The contact angle at the intersection of a grain boundary in Al bicrystals with the solid Al/liquid Al–Sn interphase boundary has been measured for two symmetric tilt <011> {001} grain boundaries with tilt angles of 32° and 38.5°. The temperature dependencies (T) present the evidence of the grain boundary wetting phase transition at T_w. The observed hysteresis is consistent with the assumption that the wetting transition is of first order. The determined discontinuity in the temperature derivative of the grain boundary energy is–5.6 J/m²K (T w1=617°C) for the boundary with a low energy (=38.5°) and –17 J/m²K (T w2=604°C) for the grain boundary with a high energy (=32°).     

Streuung spinpolarisierter Elektronen an Au(110)

Using the the spin modulated polarized electron gun based on photoemission from positive affinity GaAs the intensityI(E, , ) and asymmetry (E, , ) are measured in LEED from Au(110). The asymmetry is compared with the polarizationS(E, , ) which N. Müller obtained with a Mott detector after scattering an unpolarized electron beam from the same crystal. There is excellent agreement for the (00) beams, if the scattering plane is a mirror symmetry plane of the crystal (=0°, =90°). From the differences for the (00) and (11) beams at =35° and the (01/2) beam at =90° conditions for possible models for the reconstructed Au(110)–(1×2) surface may be derived.

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Die vorliegende Arbeit ist ein Auszug aus [1]

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Neue Addresse ab 1. Oktober 1980: B. Reihl, IBM Thomas J. Watson Research Center, Yorktown Heights, NY 10598, USA     

Beta-decay studies of neutron-rich Sc- Cr nuclei

The neutron-rich nuclei ₂₁^{57, 58}Sc, ₂₂^58-60Ti, ₂₃^60-63V, ₂₄^62-66Cr have been produced at Ganil via interactions of a 61.8A MeV ⁷⁶Ge beam with a ⁵⁸Ni target. Beta-decay studies have been performed using combined - and -ray spectroscopy. Half-lives have been determined and -decay schemes are proposed for ⁵⁸Ti, ⁶¹V and ⁶²Cr. From these studies, new hints for the existence of -decaying isomers in ⁶⁰V and in ⁶²Mn are provided. These results are compared to shell model calculations. The role of the f_7/2- f_5/2 proton-neutron interaction is examined through its influence on the lifetime values.     

Electrical characterization of Al/AlOx/molecule/Ti/Al devices

We report experimental electrical characterization of Al/AlO_x/molecule/Ti/Al planar crossbar devices incorporating Langmuir–Blodgett organic monolayers of eicosanoic acid, fast blue, or chlorophyll-B. Current–voltage and capacitance–voltage measurements on all three molecular device structures exhibited controllable switching hysteresis. Control devices containing no molecules showed no evidence of switching. A model of interface trapped charge mediating electronic transport appears consistent with all of the data. This data illustrates the importance of considering the complete device system (consisting of the molecules, the electrodes, and the interfaces) when analyzing its electrical behavior. PACS 85.65.+h; 73.40.Rw; 73.50.Gr     

НИЗКОЧАСТОТНЫЕ КОЛЕ БАНИЯ ПРЯМОУГОЛЬНЫХ ПЛАСТИНОК ADP

- — . , - NH₄H₂PO₄,- ADP. ; - .     

тРЕхлУЧЕВыЕ ВжАИМОД ЕИстВИь π−-МЕжОНОВ с ИМпУльсОМ 4 GeV/c В пРОпАНОВОИ пУжыРь кОВОИ кАМЕРЕ

Altogether 1648 cases of three-prong interaction of ^–-mesons with a 4 GeV/c impulse were found on 90 000 pictures from a propane bubble chamber 55 × 28 × 14 cm³ in size; all three secondary particles were pions, two having a negative and one a positive charge. Analysis of these cases showed that at an impulse of 4 GeV/c of primary ^–-mesons the process of the coherent production of pions was not observed. On the other hand, this analysis led to an interesting result: (19 ± 9) % of the total number of (⁺, ^–) pairs in A interactions is due to the decay of the meson ^{0 +} + ^–. A value of = (764 ± 36) MeV was obtained for the mass of mesons and = (166 ± 55) MeV fort he width of its resonance curve. Investigation of the distribution of masses in the case in question gave no answer due to the insufficiently determined course of the background curve.

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On leave from:Institute of Physics, Czechosl. Acad. Sci., Lumumbova 1, Praha 8, Czechoslovakia.

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Joint Institute of Nuclear Research, Dubna, USSR.

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Institute of Physics, Czechosl. Acad. Sci., Lumumbova 1, Praha 8, Czechoslovakia.

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Faculty of Mathematics and Physics, Charles University, Brehová 7, Praha 1, Czechoslovakia.

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. , . , . , . . , , . . . .     

Four-wave mixing in CO via the C 1Σ+ (υ′=0) state

Coherent vacuum ultraviolet (VUV) radiation was generated by four-wave difference frequency mixing (_VUV=2₁–₂) of pulsed dye laser radiation in carbon monoxide (CO). The frequency ₁ was tuned to the C ¹⁺(=0)X ¹⁺(=0) two-photon transition, while the dye laser frequency ₂ was scaned around 17650 cm^–1 which corresponds to the A ¹(=7)«C ¹⁺(=0) transition energy. The VUV intensity was found to be strongly wavelength dependent. The analysis of the spectrum revealed (i) that the VUV intensity was enhanced by the rotational levels of the A ¹(=7) state and (ii) that the off-resonance excitation in the C ¹⁺(=0)X ¹⁺(=0) two-photon transition greatly contributed to the present four-wave mixing process. The effects of pumping laser detuning, saturation and foreign gases are briefly discussed.     

Effects of annealing temperature on the alloying behavior of the AuGe-GaAs〈100〉 interface

UV(He I) and X-ray photoelectron spectroscopies (UPS and XPS) were used to examine the alloying behavior of AuGe ohmic contacts to silicon-doped 100 oriented n-type GaAs substrates. The reacted interface was then revealed by Ar ion sputter depth profiling at room temperature and after annealing in ultra high vacuum at 300°, 500°, or 700°C. The indiffusion of Au and the outdiffusion of Ga and As are evident. Instead of obtaining a maximum peak of the Ge profile on annealing in forming gas, we observed an increase of Ge indiffusion with temperature. The Au indiffusion results in a decrease in the Au 5d splitting and a shift of both levels to higher binding energy. Au-Ga alloy formation is indicated by the Au 4f levels, and is further supported by the observation of the metallic Ga peak. It has been concluded that the sample annealed at 500°C forms the Au-Ga alloy and the compound of As containing Ge more easily than the samples annealed at 300° or 700°C. This result is consistent with the observations of low contact resistance at the annealing temperature of 500°C for AuNiGe ohmic contacts to n-type GaAs.     

Gamma-radiation of193Au

The gamma-radiation of¹⁹³Au has been studied by means of a Ge(Li) semiconductor detector. In addition to the transitions observed by Svahn et. al. (Z. Physik210 (1968), 466), 21 new transitions have been found. With the use of the relative conversion line intensities from the above reference and the -ray intensities of this work, the number of internal conversion coefficients _K has been determined. The multipolarities of the transitions have been deduced from a comparison of the experimental and theoretical _K -values. Some additions to the¹⁹³Au decay scheme were made on the basis of new experimental results.     

The thickness dependence of the domain structure of magnetoplumbite

The changes in domain structure as a function of the thickness of the crystal are studied on artificial magnetoplumbite crystals. The thickness dependence of the width of the domains is also studied; up to thicknesses of about 10 it follows the theoretical halfpower law. Above 10 the exponent is 0·633. The energy density of the Bloch walls=4·82 erg cm^–2 and the exchange constantA=0·66×10^–6 erg cm^–1 are calculated on the basis of the above measurements.

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. , 10 . 0,633. = =4,82 erg m^–2 =0,66.10^–6 erg cm^–2.

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We thank Z. Málek and V. Janovec for discussions and some remarks.     

Influence of temperature on integrated intensity of (200) reflection of pure Al

The temperature dependence of the intensity and reflecting range of the (200) reflection of X-rays on an aluminium crystal exhibiting strong primary extinction was studied. It was found that the observed temperature dependence cannot be even approximately expressed by the Debye-Waller factor. The reversible change in the system of imperfections in the crystal is suggested and discussed as a mechanism qualitatively explaining the observed phenomena.

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(200) A1

(200) , . , , , -. , .

     

Bemerkung über die Reziprozität beim Durchgang des Lichtes Durch Leitfähige Schichten

Zusammenfassung Im vorliegenden Artikel wird die Durchlässigkeit eines beliebigen Systems homogener oder inhomogener Schichten mit beliebiger Leitfähigkeit bei senkrechtem Einfall einer elektromagnetischen Welle untersucht. Es wird bewiesen, da\ das Verhältnis der Durch-lässigkeiten beim Auftreffen der Welle von der einen und von der anderen Seite lediglich von den Leitfähigkeiten der Medien auf beiden Seiten des Systems abhängt. Falls die Leitfähigkeiten beider Medien gleich sind, sind auch die Durchlässigkeiten in beiden Richtungen gleich.

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. , . , .

     

Stochastic Schrödinger operators and Jacobi matrices on the strip

We discuss stochastic Schrödinger operators and Jacobi matrices with wave functions, taking values in ^l so there are 2l Lyaponov exponents ₁..._l0 _l+1..._2l =–₁. Our results include the fact that if ₁=0 on a set positive measure, thenV is deterministic and one that says that {E|exactly 2j 's are zero} is the essential support of the a.c. spectrum of multiplicity 2j.Research partially supported by USNSF under grant DMS-8416049     

Comparison between static and adiabatic coupling mechanisms for nonradiative multiphonon transitions in semiclassical approximation

Semiclassical versions of the static (diabatic) and adiabatic coupling schemes are applied to a two-level-one-mode system at total energies above the cross-over level. The corresponding rates of nonradiative multiphonon transitions reduce to alternativemonotonous dependences on the usual Landau-Zener parameter. Static coupling gives an increasing transition probability (per oscillation) of the familiar formP ^st() = 4. Adiabatic coupling associated with a sufficiently low mechanism-specific potential barrier of Born's type produces a decreasing transition probability of the formP ^ad() exp (–2). The underlying Beyond-Non-Condon calculation procedure shows that (1) the weak dependence of the pre-exponential factorP ^ad is a consequence of the-independent normalization of the electronic matrix element governing the non-adiabaticity operator and (2) the occurrence of the mechanism-specific tunnelling factor exp(–2) is due to the avoided crossing of adiabatic oscillator potentials. Ranges of applicability of both alternative coupling schemes are limited by comparison with earlier non-perturbational results.     

High-temperature resistivity of Ti1-X Al X alloys

We have measured the high-temperature resistivities of dilute Ti_1-x Al _x alloys withx0.135 up to 1100 K (2.6 _D , where _D is the Debye temperature). We observe that possesses a strong downward deviation from a linear temperature-dependence at high temperatures (several hundred degrees Kelvin). Eventually, saturates to a constant. This non-Bloch-Grüneisen-like behavior is compared with the predictions of current theories.