Andrzej Taube

Temperature-Dependent Thermal Properties of Supported MoS2 Monolayers

Thermal properties can substantially affect the operation of various electronics and optoelectronics devices based on two-dimensional materials. In this work, we describe our investigation of temperature-dependent thermal conductivity and interfacial thermal conductance of molybdenum disulfide monolayers supported on SiO2/Si substrates, using Raman spectroscopy. We observed that the calculated thermal conductivity (κ) and interfacial thermal conductance (g) decreased with increasing temperature from 62.2 W m(-1) K(-1) and 1.94 MW m(-2) K(-1) at 300 K to 7.45 W m(-1) K(-1) and 1.25 MW m(-2) K(-1) at 450 K, respectively.

Temperature-dependent nonlinear phonon shifts in a supported MoS2 monolayer.

We report Raman spectra measurements on a MoS(2) monolayer supported on SiO(2) as a function of temperature. Unlike in previous studies, the positions of the two main Raman modes, E(2g)(1) and A(1g) exhibited nonlinear temperature dependence. Temperature dependence of phonon shifts and widths is explained by optical phonon decay process into two acoustic phonons. On the basis of Raman measurements, local temperature change under laser heating power at different global temperatures is derived. Obtained results contribute to our understanding of the thermal properties of two-dimensional atomic crystals and can help to solve the problem of heat dissipation, which is crucial for use in the next generation of nanoelectronic devices.

Temperature dependence of Raman shifts in layered ReSe2 and SnSe2 semiconductor nanosheets

Transition metal dichalcogenides (TMDCs) are attractive for variety of nanoscale electronics and optoelectronics devices due to their unique properties. Despite growing progress in the research field of TMDCs, many of their properties are still unknown. In this letter, we report measurements of Raman spectra of rhenium diselenide (ReSe2) and tin diselenide (SnSe2) layered semiconductor nanosheets as a function of temperature (70–400 K). We analyze the temperature dependence of the positions of eight ReSe2 modes and SnSe2 A1g mode. All observed Raman mode shifts exhibit nonlinear temperature dependence at low temperatures which is explained by optical phonon decay process into two or three acoustics phonons. The first order temperature coefficients (χ), determined for high temperatures, of rhenium diselenide Raman modes are in the range between −0.0033 and −0.0118 cm−1/K, whereas χ of tin diselenide A1g mode was −0.0129 cm−1/K. Our findings are useful for further analysis of phonon and thermal properties o...

Temperature-dependent thermal properties of single-walled carbon nanotube thin films

We herein report the determination of the intrinsic thermal conductivity (κ) and interfacial thermal conductance (g) of single-walled carbon nanotube thin films (50 nm) on top of a SiO2 substrate. The study was performed as a function of temperature (300–450 K) using the opto-thermal technique. The value of κ decreases nonlinearly by approximately 60% from a value of 26 Wm−1 K−1 at 300 K to a value of 9 Wm−1 K−1 at 450 K. This effect stems from the increase of multi-phonon scattering at higher temperatures. The g increases with temperature, reaching a saturation plateau at 410 K. These findings may contribute to a better understanding of the thermal properties of the supported carbon nanotube thin films, which are crucial for any heat dissipation applications.

Raman Spectra of High-κ Dielectric Layers Investigated with Micro-Raman Spectroscopy Comparison with Silicon Dioxide

Three samples with dielectric layers from high-κ dielectrics, hafnium oxide, gadolinium-silicon oxide, and lanthanum-lutetium oxide on silicon substrate were studied by Raman spectroscopy. The results obtained for high-κ dielectrics were compared with spectra recorded for silicon dioxide. Raman spectra suggest the similarity of gadolinium-silicon oxide and lanthanum-lutetium oxide to the bulk nondensified silicon dioxide. The temperature treatment of hafnium oxide shows the evolution of the structure of this material. Raman spectra recorded for as-deposited hafnium oxide are similar to the results obtained for silicon dioxide layer. After thermal treatment especially at higher temperatures (600°C and above), the structure of hafnium oxide becomes similar to the bulk non-densified silicon dioxide.

Transparent Amorphous Ru–Si–O Schottky Contacts to In–Ga–Zn–O

Transparent amorphous oxide semiconductors (TAOSs), such as In-Ga-Zn-O (a-IGZO), are the subject of intensive experimental and theoretical research aimed at applications in transparent electronics. With the development of novel device applications came an increased demand for the understanding and control of a-IGZO Schottky contact properties. Rectifying contacts are suitable for the development of Schottky diodes and metal-semiconductor field-effect transistors (MESFETs) for fast and low power consumption integrated circuits and active-matrix displays. We propose fabrication of Schottky barrier to a-IGZO based on transparent conductive oxide (TCO), namely Ru-Si-O. We have found that atomic composition and microstructure of this TCO are effective in preventing interfacial reactions in the contact region which allows to avoid pre-treatment of the semiconductor surface. Ru-Si-O Schottky contacts to a-IGZO have been fabricated by means of reactive sputter-deposition. We provide comprehensive results on effects of Ru-Si-O chemical composition on properties of rectifying contacts to a-IGZO. Depending on oxygen content in Ru-Si-O sputtering atmosphere, for a specific process window (from 10% to 20% of O2 in sputtering atmosphere), highly rectifying transparent Schottky barriers are obtained without additional a-IGZO surface treatment.

In-Ga-Zn-O amorphous thin films for transparent electronics

In-Ga-Zn-O thin films fabricated by reactive RF magnetron sputtering have been investigated for their compositional, structural, morphological, electrical and optical properties. All resulting films present the amorphous microstructure, and root mean square roughness below 0.6 nm. The variation of the oxygen content in the deposition atmosphere from 0% to 0.9% results in the formation of a-IGZO thin films consisting of 15-29% indium, 16-28% gallium, 10-13% zinc and 30-60% oxygen, which significantly differs from the InGaZnO4 target composition. IGZO thin films present the transmittance in range of 75% to 90% for VIS-NIR wavelengths. Mechanism of free electrons generation via oxygen vacancies formation is proposed to determine the relation between oxygen content in the deposition atmosphere and the transport properties of the IGZO of the thin films.

High-temperature ultraviolet detection based on surface photovoltage effect in SiN passivated n-GaN films

We investigated the surface photovoltage (SPV) effect in n-GaN layers passivated with various insulators, i.e., Al2O3, SiO2, and SiN for ultraviolet (UV) light detection. We revealed that SPV in SiN/GaN shows markedly different behaviour than in oxide/GaN, i.e., the photo-signal exhibited very fast response (1 s) and recovery (2 s) times, contrary to oxide/GaN, and it was thermally stable up to 523 K. Furthermore, SPV spectra for SiN/GaN showed a sharp cut-off edge directly corresponding to the GaN band gap. We explained these results in terms of the different band structure of SiN/GaN and oxide/GaN junctions. All the observed properties of SPV response from SiN/GaN indicate that this relatively simple system can be applied to sensitive high temperature visible-blind UV detection.

Enhancement of Ru–Si–O/In–Ga–Zn–O MESFET Performance by Reducing Depletion Region Trap Density

In this letter, we investigated the effect of magnetron cathode current (I_c) during reactive sputtering of In-Ga-Zn-O (a-IGZO) channel layer on properties of metal-semiconductor field-effect transistors with Ru-Si-O Schottky gate electrode. One can observe that as I_c increased from 90 to 150 mA channel mobility (μ_ch) and subthreshold swing (S) improved from μch = 7.5 cm²/V·s and S = 580 V/dec to μch = 8.8 cm²/V ·s and S = 420 V/dec, respectively. This enhancement in transistors performance was attributed to the reduction of charge density in the depletion region of Ru-Si-O/In-Ga-Zn-O Schottky contacts, which we assigned to the densification of a-IGZO films fabricated at higher I_c.

AlGaN/GaN High Electron Mobility Transistors on Semi-Insulating Ammono-GaN Substrates with Regrown Ohmic Contacts

AlGaN/GaN high electron mobility transistors on semi-insulating bulk ammonothermal GaN have been investigated. By application of regrown ohmic contacts, the problem with obtaining low resistance ohmic contacts to low-dislocation high electron mobility transistor (HEMT) structures was solved. The maximum output current was about 1 A/mm and contact resistances was in the range of 0.3–0.6 Ω·mm. Good microwave performance was obtained due to the absence of parasitic elements such as high access resistance.