Eight In. Wafer-Scale Epitaxial Monolayer MoS2.

Large-scale, high-quality, and uniform monolayer molybdenum disulfide (MoS2) films are crucial for their applications in next-generation electronics and optoelectronics. Epitaxy is a mainstream technique for achieving high-quality MoS2 films and is demonstrated at a wafer scale up to 4-in. In this study, the epitaxial growth of 8-in. wafer-scale highly oriented monolayer MoS2 on sapphire is reported as with excellent spatial homogeneity, using a specially designed vertical chemical vapor deposition (VCVD) system. Field effect transistors (FETs) based on the as-grown 8-in. wafer-scale monolayer MoS2 film are fabricated and exhibit high performances, with an average mobility and an on/off ratio of 53.5 cm2 V-1 s-1 and 107, respectively. In addition, batch fabrication of logic devices and 11-stage ring oscillators are also demonstrated, showcasing excellent electrical functions. This work may pave the way of MoS2 in practical industry-scale applications.

Epitaxy of wafer-scale single-crystal MoS2 monolayer via buffer layer control.

Monolayer molybdenum disulfide (MoS2), an emergent two-dimensional (2D) semiconductor, holds great promise for transcending the fundamental limits of silicon electronics and continue the downscaling of field-effect transistors. To realize its full potential and high-end applications, controlled synthesis of wafer-scale monolayer MoS2 single crystals on general commercial substrates is highly desired yet challenging. Here, we demonstrate the successful epitaxial growth of 2-inch single-crystal MoS2 monolayers on industry-compatible substrates of c-plane sapphire by engineering the formation of a specific interfacial reconstructed layer through the S/MoO3 precursor ratio control. The unidirectional alignment and seamless stitching of MoS2 domains across the entire wafer are demonstrated through cross-dimensional characterizations ranging from atomic- to centimeter-scale. The epitaxial monolayer MoS2 single crystal shows good wafer-scale uniformity and state-of-the-art quality, as evidenced from the ~100% phonon circular dichroism, exciton valley polarization of ~70%, room-temperature mobility of ~140 cm2v-1s-1, and on/off ratio of ~109. Our work provides a simple strategy to produce wafer-scale single-crystal 2D semiconductors on commercial insulator substrates, paving the way towards the further extension of Moore's law and industrial applications of 2D electronic circuits.

Freestanding Crystalline ß-Ga2O3 Flexible Membrane Obtained via Lattice Epitaxy Engineering for High-Performance Optoelectronic Device.

Wearable and flexible ß-Ga2O3-based semiconductor devices have attracted considerable attention, due to their outstanding performance and potential application in real-time optoelectronic monitoring and sensing. However, the unavailability of high-quality crystalline and flexible ß-Ga2O3 membranes limits the fabrication of relevant devices. Here, through lattice epitaxy engineering together with the freestanding method, we demonstrate the preparation of a robust bending-resistant and crystalline ß-Ga2O3 (-201) membrane. Based on this, we fabricate a flexible ß-Ga2O3 photodetector device that shows comparable performance in photocurrent responsivity and spectral selectivity to conventional rigid ß-Ga2O3 film-based devices. Moreover, based on the transferred ß-Ga2O3 membrane on a silicon wafer, the PEDOT:PSS/ß-Ga2O3 p-n heterojunction device with self-powered characteristic was constructed, further demonstrating its superior heterogeneous integration ability with other functional materials. Our results not only demonstrate the feasibility of obtaining a high-quality crystalline and flexible ß-Ga2O3 membrane for an integrated device but also provide a pathway to realize flexible optical and electronic applications for other semiconducting materials.

Unveiling Strong Ion-Electron-Lattice Coupling and Electronic Antidoping in Hydrogenated Perovskite Nickelate.

Despite being highly promising for applications in emergent electronic devices, decoding both the ion-electron-lattice coupling in correlated materials at the atomic scale and the electronic band structure remains a big challenge due to the strong and complex correlation among these degrees of freedom. Here, taking an epitaxial thin film of perovskite nickelate NdNiO3 as a model system, hydrogen-ion-induced giant lattice distortion and enhanced NiO6 octahedra tilting/rotation are demonstrated, which leads to a new robust hydrogenated HNdNiO3 phase with lattice expansion larger than 10% on a series of substrates. Moreover, under the effect of ion-electron synergistic doping, it is found that the proposed electronic antidoping, i.e., the doped electrons mainly fill the ground-state oxygen 2p holes instead of changing the Ni oxidation state from Ni3+ to Ni2+ , dominates the metal-insulator transition. Meanwhile, lattice modification with enhanced Ni-O-Ni bond tilting or rotation mainly modifies the orbital density of states near the Fermi level. Last, by electric-field-controlled hydrogen-ion intercalation and its strong coupling to the lattice and electron charge, selective micrometer-scale patterns with distinct structural and electronic states are fabricated. The results provide direct evidence for a strong ion-electron-lattice coupling in correlated physics and exhibit its potential applications in designing novel materials and devices.

Tracing the ionic evolution during ILG induced phase transformation in strontium cobaltite thin films.

Ionic liquid gating (ILG) that drives the ions incorporate into or extract from the crystal lattice, has emerged as a new pathway to design materials. Although many intriguing emergent phenomena, novel physical properties and functionalities have been obtained, the gating mechanism governing the ion and charge transport remains unexplored. Here, by using the model system of brownmillerite SrCoO2.5 and the corresponding electric-field controlled tri-state phase transformation among the pristine SrCoO2.5, hydrogenated HSrCoO2.5 and oxidized perovskite SrCoO3-δ through the dual ion switch, the ionic diffusion and electronic transport processes were carefully investigated. Through controlling gating experiment by design, we find out that the collaborative interaction between charge transport and ion diffusion plays an essential role to prompt the hydrogen or oxygen ions incorporate into the crystal lattice of SrCoO2.5, and therefore leading to formation of new phases. At region closer to the electrode, the electron can shuttle more readily in (out) the material, correspondingly the incorporation of hydrogen (oxygen) ions and phase transformation is largely affiliated. With the compensated charge of electron as well as the reaction front gradually moving away from the electrode, the new phases would be developed successively across the entire thin film. This result unveils the underlying mechanism in the electric-field control of ionic incorporation and extraction, and therefore provides important strategy to achieve high efficient design of material functionalities in complex oxide materials.