Jieming Qin

Performance enhancement of ZnO UV photodetectors by surface plasmons.

Surface plasmons, a unique property of metal nanoparticles, have been widely applied to enhance the performance of optical and electrical devices. In this study, a high quality zinc oxide (ZnO) thin film was grown on a quartz substrate by a radio frequency magnetron sputtering technique, and a metal-semiconductor-metal structured ultraviolet detector was prepared on the ZnO film. The responsivity of the photodetector was enhanced from 0.836 to 1.306 A/W by sputtering metal (Pt) nanoparticles on the surface of the device. In addition, the absorption of the ZnO thin film was enhanced partly in the ultraviolet band. It is revealed that Pt nanoparticles play a key role in enhancing the performance of the photodetectors, where surface plasma resonance occurs.

Experimental and first-principles study of ferromagnetism in Mn-doped zinc stannate nanowires

Room temperature ferromagnetism was observed in Mn-doped zinc stannate (ZTO:Mn) nanowires, which were prepared by chemical vapor transport. Structural and magnetic properties and Mn chemical states of ZTO:Mn nanowires were investigated by X-ray diffraction, superconducting quantum interference device (SQUID) magnetometry and X-ray photoelectron spectroscopy. Manganese predominantly existed as Mn2+ and substituted for Zn (Mn Zn) in ZTO:Mn. This conclusion was supported by first-principles calculations. MnZn in ZTO:Mn had a lower formation energy than that of Mn substituted for Sn (MnSn). The nearest neighbor MnZn in ZTO stabilized ferromagnetic coupling. This observation supported the experimental results. 2013 AIP Publishing LLC.

Electrically pumped random lasers with p-diamond as a hole source

Electrically pumped lasing has been one of the most challenging issues for random lasers. Since holes are rare in most semiconductors, hole injection is necessary for electrically pumped lasers. Here in this article, by employing p-type diamond synthesized via a temperature gradient method under high-pressure and high-temperature conditions as a hole source, electrically pumped random lasing has been observed from p-Mg0.35Zn0.65O/n-ZnO core–shell nanowire structures. The mechanism for the lasing can be attributed to the recombination of the electrons in the nanowires with the holes injected from the p-type diamond.

High-performance ultraviolet photodetectors based on ZnO/Au/ZnO sandwich structure

We developed sandwich ultraviolet photodetectors by a radio frequency magnetron sputtering method. As expected, the performances of the optimized ZnO/Au/ZnO sandwich photodetectors are much better than that of a metal-semiconductor-metal structure through combing high responsivity (enlarged ~60 times) and low dark current (reduced by more than two orders of magnitudes). To investigate the above phenomena, simulations of electric-field intensity distribution in the two structured photodetectors were performed using the ANSYS software. A proposed physical mechanism is used to explain the above results, which agree well with the simulations.

Responsivity enhancement of ZnO/Pt/MgZnO/SiO2 and MgZnO/Pt/ZnO/SiO2 structured ultraviolet detectors by surface plasmons in Pt nanoparticles

The structured (ZnO/Pt/MgZnO/SiO2) ultraviolet detector was fabricated and demonstrated to investigate how metallic nanoparticles localized surface plasmons contribute when the two different dielectrics surrounded simultaneously. After sandwiching the Pt nanoparticles between the double layers of MgZnO and ZnO, the extinction was increased largely. Meanwhile, by examining the dependence of MgZnO and ZnO peak responsivity enhancement ratio, we found that MgZnO was significantly larger than ZnO. The interpretation by considering is that the localized surface plasmons of energy match with MgZnO which is superior to ZnO. In order to validate this conclusion and make it more accurate, we also fabricated the MgZnO/Pt/ZnO/SiO2 structure. Our work suggests that rational integration of double-layer and metal nanoparticles is a viable approach to perceive localized surface plasmons with double-layer ultraviolet detectors, which may help to advance optoelectronic devices.

Electric-field-induced nonlinear optical switches of all-metal spherical aromatic molecules with infrared transparency: a theoretical study

Two new all-metal molecules Be6Li8 and Be6Li14 have been designed theoretically. They possess Oh symmetric geometries and centrosymmetric electric structures. The number of their valence electrons satisfying Hirschs rule and the highly negative nucleus independent chemical shifts at their centers reveal that they are spherical aromatic, which leads to their good chemical stabilities. When an external electric field is applied to Be6Li8 and Be6Li14, the centrosymmetry of their electric structures is broken, which brings high first hyperpolarizability (β0) contrasts. We find that β0 of Be6Li14 is larger than that of Be6Li8 under an electric field. The reason for this is that the electron density is altered more easily in Be6Li14 than in Be6Li8, which is clearly shown in the evolutions of their HOMOs with increasing electric field strength. The calculated electron spectra show that Be6Li8 and Be6Li14 have infrared transparent wavebands from 2.5 to 8.0 μm. Thus, our calculated results demonstrate that they can act as electric-field-induced infrared nonlinear optical switches.

Pressure-induced electrical transport properties, texture, and microstructure of the (Bi,Sb)2Te3 alloys

High pressure as an effective strategy was employed to synthesize and modulate the electrical transport properties of (Bi,Sb)2Te3 alloys. Intrinsic point defects could be significantly regulated via high pressure, inducing a suitable donor-like effect to optimize the carrier concentration. The texture and microstructure were improved with high pressure, and a nanograin with (00l) orientation was observed in the (Bi,Sb)2Te3 matrix, suggesting that high pressure could facilitate the recrystallization of lattice defects along the (00l) orientation. Based on the synergistic effect of high pressure on intrinsic point defects, texture, and microstructure, the carrier concentration and mobility are regularly modulated, resulting in the room-temperature power factor of the (Bi,Sb)2Te3 alloys exhibiting a strong correlation with pressure. Hence, these important results here provide a prospective strategy in the improvement in the electrical transport properties of the Bi2Te3-based alloys according to the rational design of intrinsic point defects, texture, and microstructure with high pressure.

Controlled response wavelength shifting in ultraviolet photodetectors based on double-layer films

By integrating ZnO and MgZnO films onto a quartz substrate (both films with the same growth time), the ultraviolet photodetectors (Au/ZnO/MgZnO/SiO2 and Au/MgZnO/ZnO/SiO2 structured photodetectors) have been fabricated. The responsivity peaks blue-shift from 380 to 370 nm (380 to 375 nm) by increasing the bias voltage in 1.0 h (1.5 h) photodetectors, which is denoted by the growth time of one layer of the films. More interestingly, the Au/MgZnO/ZnO/SiO2 photodetectors shift the same response wavelength range at smaller bias voltages than the Au/ZnO/MgZnO/SiO2 photodetectors. The results are well-rationalized in term of the role played by the double-layer structure.