Zuxin Chen

Wafer-Size and Single-Crystal MoSe2 Atomically Thin Films Grown on GaN Substrate for Light Emission and Harvesting.

Two-dimensional (2D) atomic-layered semiconductors are important for next-generation electronics and optoelectronics. Here, we designed the growth of an MoSe2 atomic layer on a lattice-matched GaN semiconductor substrate. The results demonstrated that the MoSe2 films were less than three atomic layers thick and were single crystalline of MoSe2 over the entire GaN substrate. The ultrathin MoSe2/GaN heterojunction diode demonstrated ∼850 nm light emission and could also be used in photovoltaic applications.

Terahertz photodetector arrays based on a large scale MoSe2 monolayer

Large domains of monolayered transition-metal dichalcogenides (TMDCs) have emerged as exciting materials because of their potential to provide a platform for ultrathin circuits and optoelectronics systems. Herein, we report ambient pressure chemical vapor deposition (CVD) growth of large scale MoSe2 film for terahertz (THz) applications. Arrays of 100 × 60 μm MoSe2 rectangle layers were etched out and field effect transistors (FETs) were fabricated on these arrays. The device exhibits current on/off ratio of ∼104. The THz photoresponse of the devices was studied and a THz responsivity of ∼38 mV W−1 was demonstrated, suggesting that TMDCs can be promising materials for long wavelength optoelectronic applications.

Synthesis, microstructure, growth mechanism and photoluminescence of high quality [0001]-oriented InN nanowires and nanonecklaces

Novel indium nitride (InN) based nanomaterials are important for high speed electronics and infrared optoelectronics. In this paper, high quality indium nitride (InN) nanostructures, including nanowires and nanonecklaces, have been grown on one substrate by chemical vapor deposition. The morphologies and microstructures of the InN nanowires and nanonecklaces were characterized, which confirmed their chemical composition as well as single crystallinity. The InN nanonecklaces consist of multiple beads composed of two equilateral truncated hexagonal cones faceted with {10} and {101} planes. The growth mechanism of the InN nanonecklace was studied and a three-step process was suggested for the growth. Finally, the room temperature photoluminescence spectra of the two nanostructures showed near band edge emissions of around 0.73 eV, where the emission from the nanonecklace was found to be stronger, indicating promise for near-infrared optoelectronics applications.

Self-Organized Growth of Two-Dimensional GaTe Nanosheet on ZnO Nanowires for Heterojunctional Water Splitting Applications

Epitaxial two-dimensional GaTe nanosheets on ZnO nanowires were routinely prepared via a two-step chemical vapor deposition procedure. The epitaxial relationship and growth mechanism of the GaTe/ZnO core/shell structures were explored and attributed to a layer-overlayer model. The hybrid structures increased the surface area and the favorable p-n heterojunction enhanced the charge separation for photoelectrochemical performance in water splitting. The above synergistic effects boosted the photocurrent density from -0.3 mA cm-2 for the pristine ZnO nanowires to -2.5 mA cm-2 for the core/shell GaTe/ZnO nanowires at -0.39 V vs RHE under the visible light irradiation. This highlights the promise for utilization of GaTe nanosheet/ZnO nanowires as efficient photoelectrocatalyst for water splitting.

Bandgap-engineered CdxZn1 − xO nanowires as active regions for green-light-emitting diodes

A green-light-emitting diode device was fabricated based on a p-type Sb-doped ZnO segments/Cd-alloyed ZnO/n-type ZnO film/heteronanowires array structure. The structures and chemical components of the heteronanowire sample were studied by energy dispersive spectrometer, x-ray photoelectron spectrometer, etc, from which the statuses of Cd and Sb in the sample were confirmed. Spatially resolved photoluminescence measurement on a single heteronanowire revealed a large bandgap shift in the Cd(x)Zn(1 - x)O active region. In electroluminescence characterizations, the device showed that the green emission was centered at 550 nm, suggesting the successful formation and functioning of the double heterojunction nanowire light-emitting diodes.

Controllable Synthesis of [11−2−2] Faceted InN Nanopyramids on ZnO for Photoelectrochemical Water Splitting

Indium nitride (InN) is one of the promising narrow band gap semiconductors for utilizing solar energy in photoelectrochemical (PEC) water splitting. However, its widespread application is still hindered by the difficulties in growing high-quality InN samples. Here, high-quality InN nanopyramid arrays are synthesized via epitaxial growth on ZnO single-crystals. The as-prepared InN nanopyramids have well-defined exposed facets of [0001], [11-2-2], [1-212], and [-2112], which provide a possible routine for understanding water oxidation processes on the different facets of nanostructures in nanoscale. First-principles density functional calculations reveal that the nonpolar [11-2-2] face has the highest catalytic activity for water oxidation. PEC investigations demonstrate that the band positions of the InN nanopyramids are strongly altered by the ZnO substrate and a heterogeneous n-n junction is naturally formed at the InN/ZnO interface. The formation of the n-n junction and the built-in electric field is ascribed to the efficient separation of the photogenerated electron-hole pairs and the good PEC performance of the InN/ZnO. The InN/ZnO shows good photostability and the hydrogen evolution is about 0.56 µmol cm-2 h-1 , which is about 30 times higher than that of the ZnO substrate. This study demonstrates the potential application of the InN/ZnO photoanodes for PEC water splitting.