To enable graphene-integrated interconnects in modern VLSI circuits, a major roadblock is developing an efficient Back End of Line (BEOL) compatible doping technique. In this paper, we demonstrate metal-induced doping of graphene in graphene-ruthenium hybrid structures. We study doping by systematically performing different material characterization techniques - Internal Photoemission Spectroscopy (IPE), Raman Spectroscopy and Kelvin Probe Force Microscopy (KPFM) to gain a deeper understanding on the charge transfer at the graphene-Ru interface. In IPE, we measure the relative band alignment of graphene and Ru, the interface potential barrier and effective work function of 4.9eV. With Raman spectral mapping, we report p-type doping in single layer graphene on Ru film with carrier density 1.9E13cm(-2). And with KPFM, Fermi-level shift of similar to 420 meV (wrt intrinsic graphene) is observed implying downward shift of Fermi level in the graphene valence band. Electrically, graphene capping results in similar to 19 % drop in sheet resistance of Ru accompanied by significant decrease in contact resistance. Moreover, the temperature coefficient of resistance reduces after graphene capping indicating better response to thermal fluctuations. By performing an extensive study using different material and electrical techniques, our results provide a viable and practical basis for integrating graphene as a conductor in advanced interconnects. (C) 2021 Elsevier Ltd. All rights reserved.

The article overviews experimental results obtained by applying internal photoemission (IPE) spectroscopy methods to characterize electron states in single- or few-monolayer thick two-dimensional materials and at their interfaces. Several conducting (graphene) and semiconducting (transitional metal dichalcogenides MoS2, WS2, MoSe2, and WSe2) films on top of thermal SiO(2)have been analyzed by IPE, which reveals significant sensitivity of interface band offsets and barriers to the details of the material and interface fabrication, indicating violation of the Schottky-Mott rule. This variability is associated with charges and dipoles formed at the interfaces with van der Waals bonding as opposed to the chemically bonded interfaces of three-dimensional semiconductors and metals. Chemical modification of the underlying SiO(2)surface is shown to be a significant factor, affecting interface barriers due to violation of the interface electroneutrality.

To further understand the interaction of graphene-integrated interconnects, we focus on the interface characterization of graphene-ruthenium hybrid systems. A systematic characterization is performed to quantify the charge transfer between graphene and Ru. By studying the relative band alignment, we measure interface potential barrier height and report an effective work function of 4.9 eV. Carrier concentration of 1.9E13cm −2 is obtained. Surface potential mapping suggests a downward shift of Fermi level in graphene valence band implying hole-doping on Ru substrate. Concurrent physical characterizations complement each other and fully support the conductivity gain demonstrated earlier.

Internal photoemission of electrons from uncapped monolayer graphene to insulating SiO2 has been observed in samples prepared by water-intercalation based graphene transfer. The barrier height between the graphene Fermi level and the oxide conduction band bottom was reproducibly found to be 4.1-4.2 eV. Moreover, this value was weakly sensitive to the contacting metal work function (Al, Cu, Au). This barrier height corresponds to an effective work function of graphene close to 5.0 eV, which is nearly 0.5 eV higher than the usually reported vacuum value.

Spectral measurements of illumination-induced displacement currents related to trapping of charge carriers optically excited in semiconductor electrodes are shown to deliver information regarding energy onsets of electron transitions at the interface. Presented examples include determination of the conduction band offset at the GaN/Al2O3 interface and determination of charge carrier excitation spectra of two-dimensional (2D) semiconductors MoS2 and WS2 at the interface with insulating SiO2.

It has been shown that the precursors (long-chain amines and alkanethiols) used in liquid-phase colloidal synthesis of InP@ZnS quantum dots exert a significant influence on their spectral and luminescent properties. It has been found that dodecylamine and 1-dodecanethiol facilitate obtaining the particles with a narrow luminescence band and a low quantum yield, whereas oleylamine, 1-octanethiol, and 1,6-hexanedithiol stimulate the formation of the quantum dots with broad and intense luminescence. Conditions have been found under which the narrowing of the emission band to 46.3 nm becomes possible.

Using colloidal solutions of ZnS-shell indium phosphide quantum dots with two average sizes of 2.1 and 3.0 nm and a size distribution variance of 10%, it has been shown that the luminescence and the luminescence excitation spectra of the colloidal quantum dots substantially depend on the wavelength of exciting light and the detection wavelength, respectively, with both the relationships being nonlinear in character, which may indicate the bimodal type of the size distribution function. Similar measurements for CdSe colloidal quantum dots with an average particle size of d av = 2.5 nm and a variance of 6% have shown that the effect of dependence of the luminescence peak position on the excitation wavelength is manifested to a much lesser extent.