Shun Han

Black Phosphorus Based Field Effect Transistors with Simultaneously Achieved Near Ideal Subthreshold Swing and High Hole Mobility at Room Temperature.

Black phosphorus (BP) has emerged as a promising two-dimensional (2D) material for next generation transistor applications due to its superior carrier transport properties. Among other issues, achieving reduced subthreshold swing and enhanced hole mobility simultaneously remains a challenge which requires careful optimization of the BP/gate oxide interface. Here, we report the realization of high performance BP transistors integrated with HfO2 high-k gate dielectric using a low temperature CMOS process. The fabricated devices were shown to demonstrate a near ideal subthreshold swing (SS) of ~69u2009mV/dec and a room temperature hole mobility of exceeding >400u2009cm2/Vs. These figure-of-merits are benchmarked to be the best-of-its-kind, which outperform previously reported BP transistors realized on traditional SiO2 gate dielectric. X-ray photoelectron spectroscopy (XPS) analysis further reveals the evidence of a more chemically stable BP when formed on HfO2 high-k as opposed to SiO2, which gives rise to a better interface quality that accounts for the SS and hole mobility improvement. These results unveil the potential of black phosphorus as an emerging channel material for future nanoelectronic device applications.

C-Axis oriented crystalline IGZO thin-film transistors by magnetron sputtering

We demonstrate the direct formation of c-axis oriented crystalline IGZO thin films at room temperature by magnetron sputtering. The influence of processing parameters such as oxygen partial pressure, post-annealing temperature and channel thickness on the electrical performance of IGZO films and thin-film transistors (TFTs) was intensively investigated. The as-deposited crystalline IGZO TFTs exhibited a mobility of 4.49 cm2 V−1 s−1 and an on/off ratio of 2.08 × 107. For the annealed device, a high mobility of 10.51 cm2 V−1 s−1, a subthreshold swing of 0.672 V decade−1, a threshold voltage of 0.38 V, as well as an on/off current ratio of ∼108 are achieved with an annealing temperature of 400 °C. These results present a significant step towards the development of high-performance TFTs using oriented crystalline IGZO.

Influence of lattice vibrations on luminescence and transfer of excitons in WS2 monolayer semiconductors

Monolayers of transition metal dichalcogenides (TMDs) have been recently demonstrated to be a new family of direct bandgap semiconductors exhibiting extraordinary excitonic effects and high-efficiency luminescence. Here we present a micro-photoluminescence (PL) study on temperature dependent luminescence of excitons from an exfoliated WS2 monolayer. It is found that lattice vibrations (i.e. phonons) have a profound influence on the excitonic luminescence of the WS2 monolayer in several aspects including the spectral peak shift, lineshape broadening, transfer, and even formation entropy of excitons. Our study not only leads to the determination of the fundamental excitonic bandgap: eV at , but also reveals that 120 K is a turning temperature for the competition and formation entropy of free excitons and defect-bound excitons in the studied 2D WS2 crystals.

Growth and Characteristics of High Quality (200) and (111) Orientations Cubic Structure MgZnO Thin Films by Pulse Laser Deposition (PLD) Method

High quality (200) and (111) orientations cubic MgZnO thin films were made on (200) and (111) orientations MgO substrates separately under different condition with higher and lower migration energy of reactive atoms separately. The crystal quality of (111) orientation MgZnO thin film is higher than (200) one because of the stronger horizontal migration of atoms on (111) surface under high temperature condition, the surface of (200) orientation MgZnO thin film is smoother than (111) orientation one because of lower vertical growth speed of (200) MgZnO grains. The band gap of (111) orientation MgZnO thin film is smaller than (200) one because of more Zn atoms in (111) orientation MgZnO lattice than that in (200) ones. This paper gives an effective method to improve crystal quality of different orientation MgZnO thin film under different condition, which is meaningful in application of cubic MgZnO in different areas.