Structure and Electronic Properties of Amorphous Ge–Pd Alloys Manifesting the Metal-Insulator Transition. II. Photoemission Spectroscopy and Electronic Structure Calculations

Suzuki, Atsuko; Endo, Atsushi; Tanaka, Kazuhide

doi:10.1143/jpsj.68.3623

Cited by 4 publications

(11 citation statements)

References 9 publications

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“…Since the MIT takes place at 11.5 < x c < 12.8 as shown in the previous section, electrons occupying the states in the vicinity of E F are still localized and the metallic conduction is prohibited in alloys with x m < x < x c . This picture is similar to those in amorphous Si-Ni 17) and Ge-Pd 19,20) alloys. It is worth noting here that the present energy resolution of UPS is not enough to detect a Coulomb gap Δ formed at E F as predicted by Efros and Shklovskii 21) for x < x c .…”

Section: Photoemission Spectroscopysupporting

confidence: 85%

“…25) The calculation has been performed by the DV-Xα molecular orbital method in a similar way as described elsewhere. 18,20) Figure 8 shows the model cluster of Si 35 used for the calculation, where thirty-five Si atoms are arranged in diamond structure together with thirty-six H atoms added to terminate the surface dangling bonds. This cluster is larger in size than the Ge 17 cluster employed in the previous calculations.…”

Section: Dv-xα Cluster Calculationsmentioning

confidence: 99%

“…This cluster is larger in size than the Ge 17 cluster employed in the previous calculations. 18,20) The alloy clusters, Si 34 Ti, Si 33 Ti 2 , Si 31 Ti 4 and Si 30 Ti 5 , are obtained by substituting the respective number of Ti atoms for the central, two 1st-neighbor, four 1st-neighbor, and the central plus four 1st-neighbor Si atoms, respectively. The interatomic distances, d Si-Si = 0.235 nm and d Si-H = 0.146 nm, are taken to be consistent with those of Si crystal and SiH 4 molecule, respectively.…”

Section: Dv-xα Cluster Calculationsmentioning

confidence: 99%

“…From the calculated MOs for the alloy clusters, we can derive information on the localization of electronic states, which is an important aspect of the electronic states in a disordered alloy manifesting the metal-insulator transition. Figure 12 shows the energy distribution of the localization index (LI) 20) for the MOs of the clusters. The LI gives a degree of spread of a MO with respect to the AOs constituting the MO.…”

Section: Dv-xα Cluster Calculationsmentioning

confidence: 99%

“…This transition, called Anderson transition, has long been investigated for a variety of alloy systems and its mechanisms have been theoretically explored. [12][13][14][15] We have investigated the MIT effects in amorphous Si-Pd, 16) Si-Ni, 17) Ge-Ag 18) and GePd 19,20) alloys, and related them with the bandstructure or bonding characteristics of the alloys as revealed by photoemission spectroscopy. The reason for choosing the Si-Ti system in this study is as follows.…”

Section: §1 Introductionmentioning

confidence: 99%

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Electronic Structure and Electrical Conductivity of Amorphous Si–Ti Alloys Manifesting the Metal-Insulator Transition

2000

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The electrical conductivity σ of amorphous Si 100−x Ti x alloys prepared by ion-beam sputtering has been measured over a temperature range between 4.2 and 290 K. The temperature dependence of σ is well expressed by a formula derived by the variable-range hopping theory with an exponent n ∼ 0.40 for x ≤ 11.5, whereas, for x ≥ 12.8, it is better expressed by a formula describing the conduction by electrons liberated from weakly localized states through inelastic electron-electron scattering. Thus, the metal-insulator transition takes place at 11.5 < x c < 12.8 in this system. The electronic structure of these alloys has been studied by measuring XPS and UPS spectra. Furthermore, DV-Xα calculation has been carried out for certain Si-Ti alloy clusters of diamond structure to simulate the electronic structure of the amorphous alloys. The calculated total and partial density of states well reproduces the features of the photoemission spectra. The calculation also provides information on the localization of electronic states in the amorphous alloys. §1. IntroductionThe structure, stability and electronic properties of semiconductor (Si, Ge)-transition-metal (TM) alloys have long been the subjects of a number of investigations. For understanding the characteristic properties of the alloys, many experimental and theoretical studies have been carried out, among which those revealing the nature of chemical bonding in TM silicides appear to be fundamentally most important. 1, 2) A stable crystalline silicide is readily formed in a stoichiometric composition at a contact interface between Si and a TM when the couple is annealed at an appropriate temperature, and it is known to provide a good ohmic contact between them. 3) In addition, the formation of a non-stoichiometric solid solution of Si and a TM is also important in the semiconductor technology. It is readily formed by coevaporation or cosputtering onto a substrate, although it usually takes a metastable amorphous structure. The atomic structure, 4) thermal stability 5) and electronic properties 6, 7) of amorphous Si-TM alloys have also been studied and their bonding characteristics have been revealed. Specifically, much attention has been payed to Ti-silicides in crystalline and amorphous forms in recent years [8][9][10][11] The objective of the present study is to make clear the electronic structure and electronic transport properties of amorphous Si-Ti alloys over a wide range of composition. Amorphous Si(or Ge)-TM alloys manifest the metal-insulator transition (MIT) at a critical concentration x c of the TM which usually falls between ∼10 and ∼15 at.%. This transition, called Anderson transition, has long been investigated for a variety of alloy systems and its mechanisms have been theoretically explored. 12-15) We have investigated the MIT effects in amorphous Si-Pd, 16) Si-Ni, 17) Ge-Ag 18) and GePd 19, 20) alloys, and related them with the bandstructure or bonding characteristics of the alloys as revealed by photoemission spectroscopy. The reason for choosing the...

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Section: Photoemission Spectroscopysupporting

confidence: 85%

Section: Dv-xα Cluster Calculationsmentioning

confidence: 99%

Section: Dv-xα Cluster Calculationsmentioning

confidence: 99%

Section: Dv-xα Cluster Calculationsmentioning

confidence: 99%

Section: §1 Introductionmentioning

confidence: 99%

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Electronic Structure and Electrical Conductivity of Amorphous Si–Ti Alloys Manifesting the Metal-Insulator Transition

2000

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In Situ Study of the Interface-Mediated Solid-State Reactions during Growth and Postgrowth Annealing of Pd/a-Ge Bilayers

Krause

Abadias

Babonneau

et al. 2023

ACS Appl. Mater. Interfaces

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Ohmic or Schottky contacts in micro- and nanoelectronic devices are formed by metal–semiconductor bilayer systems, based on elemental metals or thermally more stable metallic compounds (germanides, silicides). The control of their electronic properties remains challenging as their structure formation is not yet fully understood. We have studied the phase and microstructure evolution during sputter deposition and postgrowth annealing of Pd/a-Ge bilayer systems with different Pd/Ge ratios (Pd:Ge, 2Pd:Ge, and 4Pd:Ge). The room-temperature deposition of up to 30 nm Pd was monitored by simultaneous, in situ synchrotron X-ray diffraction, X-ray reflectivity, and optical stress measurements. With this portfolio of complementary real-time methods, we could identify the microstructural origins of the resistivity evolution during contact formation: Real-time X-ray diffraction measurements indicate a coherent, epitaxial growth of Pd(111) on the individual crystallites of the initially forming, polycrystalline Pd2Ge[111] layer. The crystallization of the Pd2Ge interfacial layer causes a characteristic change in the real-time wafer curvature (tensile peak), and a significant drop of the resistivity after 1.5 nm Pd deposition. In addition, we could confirm the isostructural interface formation of Pd/a-Ge and Pd/a-Si. Subtle differences between both interfaces originate from the lattice mismatch at the interface between compound and metal. The solid-state reaction during subsequent annealing was studied by real-time X-ray diffraction and complementary UHV surface analysis. We could establish the link between phase and microstructure formation during deposition and annealing-induced solid-state reaction: The thermally induced reaction between Pd and a-Ge proceeds via diffusion-controlled growth of the Pd2Ge seed crystallites. The second-phase (PdGe) formation is nucleation-controlled and takes place only when a sufficient Ge reservoir exists. The real-time access to structure and electronic properties on the nanoscale opens new paths for the knowledge-based formation of ultrathin metal/semiconductor contacts.

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Synthesis and Characterization of Crystalline and Amorphous Palladium Nanoparticles

Lü

Wang

et al. 2003

Langmuir

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Ligand-stabilized palladium amorphous nanoparticles with various monodispersed sizes ranging from 2 to 6 nm were synthesized and compared with palladium crystalline nanoparticles. The nanoparticles were characterized by high-resolution electron microscopy (HREM), X-ray photoelectron spectroscopy, and scanning tunneling microscopy/spectroscopy (STM/STS). Both HREM images and electron diffraction patterns show quite clear differences in structures between crystalline and amorphous palladium nanoparticles. STS spectra exhibit fine structures in addition to the Coulomb blockade and the Coulomb staircases in the current-voltage (I-V) curves for the crystalline Pd nanoparticles when the diameters are smaller than 4 nm but only pure effect of Coulomb blockade and Coulomb staircases for amorphous Pd nanoparticles, which further indicates the differences in electronic structures.

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Structure and Electronic Properties of Amorphous Ge–Pd Alloys Manifesting the Metal-Insulator Transition. II. Photoemission Spectroscopy and Electronic Structure Calculations

Cited by 4 publications

References 9 publications

Electronic Structure and Electrical Conductivity of Amorphous Si–Ti Alloys Manifesting the Metal-Insulator Transition

Electronic Structure and Electrical Conductivity of Amorphous Si–Ti Alloys Manifesting the Metal-Insulator Transition

In Situ Study of the Interface-Mediated Solid-State Reactions during Growth and Postgrowth Annealing of Pd/a-Ge Bilayers

Synthesis and Characterization of Crystalline and Amorphous Palladium Nanoparticles

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