Scalable printing of two-dimensional single crystals of organic semiconductors towards high-end device applications

The past several decades have witnessed a vast array of developments in printable organic semiconductors, where successes both in synthetic chemistry and in printing technology constituted a key step forward to realization of printed electronics. In this review, we highlight specifically on materials science, charge transport, and device engineering of —two-dimensional single crystals—. Defect-free organic single-crystalline wafers manufactured via a one-shot printing process allows remarkably reliable implementations of organic thin-film transistors with decently high carrier mobility up to 10 cm2 V-1 s-1, which has revolutionized the current printing electronics to be able to meet looming IoT challenges. This review focuses on the perspective of printing two-dimensional single crystals with reasonable areal coverage, showing their promising applications for practical devices and future human society, particularly based on our recent contributions.

Phonon Drag Thermopower in Silicene in Equipartition Regime at Room Temperature

Similar to graphene, zero band gap limits the application of Silicene in nanoelectronics despite of its high carrier mobility. In this article we calculate the contribution of electron-phonon interaction to thermoelectric effects in silicene. One considers the case of free standing silicene taking into account interaction with intrinsic acoustic phonons. The temperature considered here is at room temperature. We noticed that the contribution to thermoelectromotive force due to electron drag by phonons is determined by the Fermi energy. The explicit temperature dependence of the contribution to thermoelectromotive force deriving from by phonons is weak in contrast to that due to diffusion, which is directly proportional to temperature. Thus a theoretical limit has been established for a possible increase of the thermoelectromotive force through electron drag by the intrinsic phonons of silicene. Keywords: Phonon-drag thermopower, electron-diffusion thermopower, silicene, fermi energy, zero band gap

Investigation on electrical characteristics of TFTs fabricated with germanium films crystallized by atmospheric pressure micro-thermal-plasma-jet irradiation

Crystalline-germanium (c-Ge) is an attractive material for a thin-film transistor (TFT) channel because of its high carrier mobility and applicability to a low-temperature process. We present the electrical characteristics of c-Ge crystallized by atmospheric pressure micro-thermal-plasma-jet (µ-TPJ). The µ-TPJ crystalized c-Ge showed the maximum Hall mobility of 1070 cm2·V−1·s−1 with its hole concentration of ~ 1016 cm−3, enabling us to fabricate the TFT with field-effect mobility (μ FE) of 196 cm2·V−1·s−1 and ON/OFF ratio (R ON/OFF) of 1.4 × 104. On the other hand, RON/OFFs and μFEs were dependent on the scanning speed of the TPJ, inferring different types of defects were induced in the channel regions. These findings show not only a possibility of the TPJ irradiation as a promising method to make a c-Ge TFT on insulating substrates.

Combined experimental-theoretical study of electron mobility-limiting mechanisms in SrSnO3

The discovery and development of ultra-wide bandgap (UWBG) semiconductors is crucial to accelerate the adoption of renewable power sources. This necessitates an UWBG semiconductor that exhibits robust doping with high carrier mobility over a wide range of carrier concentrations. Here we demonstrate that epitaxial thin films of the perovskite oxide NdxSr1−xSnO3 (SSO) do exactly this. Nd is used as a donor to successfully modulate the carrier concentration over nearly two orders of magnitude, from 3.7 × 1018 cm−3 to 2.0 × 1020 cm−3. Despite being grown on lattice-mismatched substrates and thus having relatively high structural disorder, SSO films exhibited the highest room-temperature mobility, ~70 cm2 V−1 s−1, among all known UWBG semiconductors in the range of carrier concentrations studied. The phonon-limited mobility is calculated from first principles and supplemented with a model to treat ionized impurity and Kondo scattering. This produces excellent agreement with experiment over a wide range of temperatures and carrier concentrations, and predicts the room-temperature phonon-limited mobility to be 76–99 cm2 V−1 s−1 depending on carrier concentration. This work establishes a perovskite oxide as an emerging UWBG semiconductor candidate with potential for applications in power electronics.

High carrier mobility in single-crystal PtSe2 grown by molecular beam epitaxy on ZnO(0001)

PtSe2 is attracting considerable attention as a high mobility two-dimensional material with envisioned applications in microelectronics, photodetection and spintronics. The growth of high quality PtSe2 on insulating substrates with wafer-scale uniformity is a prerequisite for electronic transport investigations and practical use in devices. Here, we report the growth of highly oriented few-layers PtSe2 on ZnO(0001) by molecular beam epitaxy. The crystalline structure of the films is characterized with electron and X-ray diffraction, atomic force microscopy and transmission electron microscopy. The comparison with PtSe2 layers grown on graphene, sapphire, mica, SiO2 and Pt(111) shows that among insulating substrates, ZnO(0001) yields films of superior structural quality. Hall measurements performed on epitaxial ZnO/PtSe2 with 5 monolayers of PtSe2 show a clear semiconducting behaviour and a high mobility in excess of 200 cm2V-1s-1 at room temperature and up to 447 cm2V-1s-1 at low temperature.