Carrier and heat transport properties of poly-crystalline GeSn films for thin-film transistor applications

Abstract

Thin-film transistors (TFTs) on insulator substrates are widely used in applications from liquid crystal displays to sensor devices. However, insulator substrates with low heat conductivity lead to unfavorable self-heating effects in the channel regions. Herein, the carrier and heat transport properties of polycrystalline GeSn films on SiO 2 /Si substrates were improved by suppressing Sn segregation in the films to fabricate GeSn channel TFTs. Alloying with 5.5% Sn enabled the formation of larger grains than those in poly-Ge films after low-temperature annealing (below 520 °C) without Sn segregation. In addition, the films had a hole mobility of 40 cm 2 V −1 s −1 at a hole density of 1.1 × 10 18 cm −3 and a thermal conductivity of 12.1 Wm −1 K −1 at room temperature. The temperature dependences of the carrier and heat transport properties of the poly-GeSn films were investigated to accurately simulate a device with a poly-GeSn channel TFT. This was achieved by using the carrier transport measurements and numerical simulations of the heat transport in the Debye model. The simulated device allowed an accurate assessment of the self-heating effects of the TFT and thus provides a design guide for TFTs.

Thermoelectric Efficiency of Epitaxial GeSn Alloys for Integrated Si-Based Applications: Assessing the Lattice Thermal Conductivity by Raman Thermometry

“…The lack of TE data for GeSn crystalline materials makes it difficult to benchmark our findings against the literature. However, if we consider large-grain polycrystalline Ge 0.95 Sn 0.05 layers, 18 a value of κ = 18.6 W/(m•K) extracted by thermoreflectance method was reported, very similar to the value obtained here for heteroepitaxial alloy of the same composition. For higher Sn composition, polycrystalline Ge 0.864 Sn 0.136 alloy, the reported value κ = 1 W/(m•K) 29 is lower than the value κ = 4.0 W/(m•K) obtained for crystalline Ge 0.86 Sn 0.14 .…”

“…Still, the thermal properties of GeSn alloys have not been explored yet, and their potential as CMOS-integrable TE materials remains unknown. The few existing experimental reports deal with amorphous or polycrystalline films, , while, ideally, good thermoelectric materials should be crystalline, where phonon scattering occurs without disrupting the electrical conductivity …”

“…15 These successes were enabled by the progress made in the GeSn epitaxy on Ge/Si substrates 16,17 as CMOS-integrable TE materials remains unknown. The few existing experimental reports deal with amorphous or polycrystalline films, 18,19 while, ideally, good thermoelectric materials should be crystalline, where phonon scattering occurs without disrupting the electrical conductivity. 20 In this work, the TE properties of high-quality GeSn epitaxial layers on Si are investigated.…”

Interfacial Nucleation Control in Amorphous GeSn Thin Films Using Bilayer Structure

“…Techniques for synthesizing thin films of high-mobility materials on insulating substrates have been extensively studied. Ge has been a preferred TFT channel material owing to its high carrier mobility and relatively low crystallization temperature. , The performance of metal-oxide semiconductor field-effect transistors (MOSFETs) based on single-crystal Ge (sc-Ge) has surpassed that of Si MOSFETs because of the gate stack technologies − and thin-film structure. − To date, polycrystalline Ge (poly-Ge) thin films have been synthesized at low temperatures using various techniques, such as solid-phase crystallization (SPC), − laser annealing, − chemical vapor deposition, − lamp annealing, − plasma irradiation, seed layer technique, and metal-induced crystallization. − However, owing to the poor quality of poly-Ge, particularly in thin films (<100 nm), which are required for reducing the off-current of TFTs, the practical use of poly-Ge-based TFTs on glass has yet to be achieved.…”

An efficient direct band-gap transition in germanium by three-dimensional strain

“…In light of these new 3D material deformation strategies, we explore here the properties of 3D isotropically strained Ge. It has been shown recently that GeSn alloys grown on Si can also exhibit a direct band gap -depending on the amount of Sn doping -which is investigated in the context of both laser [16][17][18][19][20] and electronic applications [21][22][23]. On the other hand, a direct band gap has already been observed in 111 uniaxial and (001) biaxial tensile strained Ge at values ∼ 4% (E g = 0.40 eV) and ∼ 2% (E g = 0.39 eV), respectively [5,24,25].…”