Hui Zhang

An easy-peeling growth method for hBN flakes with high crystalline quality was developed using a controlled reprecipitated BN powder layer. A high-performance vacuum ultraviolet photodetector was fabricated using the peeled and transferred hBN film.

A high-performance planar structure metal-semiconductor-metal-type solar-blind photodetector (SBPD) was fabricated on the basis of (010)-plane β-Ga₂O₃ thermally oxidized from nonpolar (110)-plane GaN. A full width at half maximum of 0.486° was achieved for the X-ray rocking curve associated with (020)-plane β-Ga₂O₃, which is better than most reported results for the heteroepitaxially grown (-201)-plane β-Ga₂O₃. As a result of the relatively high crystalline quality, a dark current as low as 6.30 × 10^-12 A was achieved at 5 V, while the photocurrent reached 1.86 × 10^-5 A under 254 nm illumination at 600 μW/cm². As a result, the photo-to-dark current ratio, specific detectivity, responsivity, and external quantum efficiency were calculated to be 2.95 × 10⁶, 2.39 × 10¹² Jones, 3.72 A/W, and 1815%, respectively. Moreover, the SBPD showed excellent repeatability and stability in the time-dependent photoresponse characteristics with fast relaxation time constants for the rise and decay processes of only 0.238 and 0.062 s, respectively. This study provides a promising approach to fabricate the device-level (010)-plane β-Ga₂O₃ film and a new way for the epitaxial growth of (010)-plane β-Ga₂O₃ and (110)-plane GaN as mutual substrates.

A 24 mm ² exfoliated hBN film is achieved within a total growth time of 49.17 hours. A signal-to-noise ratio of 2 orders of magnitude is reported for a metal–semiconductor–metal type photodetector based on hBN.

Understanding the mechanism of metal oxidation processes is critical for maintaining the desired properties of metals and catalysts, as well as for designing advanced materials. In this work, we investigate the electron beam induced oxidation of silver using in situ transmission electron microscopy. The additions of Ag-O columns on {111} and {110} planes were captured with atomic resolution. Interestingly, oscillatory growth on {110} planes was observed, which resulted from the double effect of electron beam irradiation. It was found that not only thermodynamic factors but also kinetic factors played significant roles in morphology evolutions. These results can facilitate the fundamental understanding of the oxidation process of Ag and provide a promising approach for the fabrication of desired nanostructures.

Using optical pump-terahertz (THz) time-domain spectroscopy measurements along with ab initio density functional theory (DFT) calculations, we studied the effect of 3,9-bis(2-methylene-(3-(1, 1-dicyanomethylene)-5-methylindanone)-5,5,11,11-tetrakis(4-hexylphenyl)-dithieno[2,3-d:2′,3′-d′]-s-indaceno [1,2-b:5,6-b′]-dithiophene (IT-M) molecules on the ultrafast dynamics and photoconductivity of the active layers of ternary organic solar cells (OSCs), which are composed by the conjugated polymer donor and fullerene derivative acceptor. The THz photoconductivity measurements show that the introduction of IT-M molecule increases the photoconductivity of the ternary OSC and the maximum value of photoconductivity is obtained in the sample with IT-M weight ratio of 15%. To reveal the mechanism of IT-M doping on the photoconductivity of OSC material, ab initio DFT calculations were performed to identify the band structures of the ternary OSC heterostructures. Resonant charge transfers induced by the band alignment of IT-M with the conjugated polymer donor and fullerene derivative acceptor, which lead to an increase of photoconductivity with a reduction of electron–hole recombination rate, were obtained from DFT calculations. In addition to the resonant charge transfer process, defect scattering induced by the doping of IT-M molecules leads to a reduction of photoconductivity. By competing these two effects, maximum photoconductivity of ternary OSC materials is obtained with IT-M weight ratio of 15%. Moreover, the charge carrier densities and scattering times of ternary OSC materials were derived from the measured THz photoconductivity via the classical Drude–Smith model. With these material properties, we identified that the maximum value of photoconductivity in OSC material with IT-M weight ratio of 15% is induced by its long scattering time instead of high carrier density.

CuInS₂ nanorod array structures are synthesized via a template-free and non-vacuum route for the first time. The obtained CuInS₂ thin films show promising conversion efficiency in a two-electrode photoelectrochemical cell.