Shanshan Chen

Honeycomb-like NiO/ZnO heterostructured nanorods: photochemical synthesis, characterization, and enhanced UV detection performance

Honeycomb-like NiO/ZnO heterostructured nanorods (NRs) were fabricated by a simple photochemical deposition method. The morphology of the NiO nanostructures can be rationally tailored by changing the concentration of the solution, reaction time and annealing temperature. A reasonable formation mechanism of the honeycomb-like NiO/ZnO NRs is proposed, which is closely related to the production of OH− in the vicinity of ZnO NRs during the photochemical deposition process. The fabricated NiO/ZnO p–n heterojunction shows a well-defined rectifying characteristic with a turn-on voltage of 0.66 V and a negligible leakage current. Moreover, the UV detection performance increases considerably compared to that of bare ZnO NRs, which is attributed to the change of nanostructure and the extended carrier depletion region near p-NiO/n-ZnO junctions.

ZnO homojunction UV photodetector based on solution-grown Sb-doped p-type ZnO nanorods and pure n-type ZnO nanorods

A ZnO homojunction UV photodetector based on Sb-doped p-type ZnO nanorods (NRs) and n-type ZnO NRs was fabricated by a low temperature solution method. The fabricated homojunction shows well-defined rectifying characteristics, confirming the p-type conductivity of the Sb-doped ZnO NRs. Moreover, a high UV sensitivity of 3300% and a fast reset time to UV illumination are also achieved.

Enhanced UV detection performance using a Cu-doped ZnO nanorod array film

A compact Cu-doped ZnO nanorod (NR) array film was synthesized by a facile hydrothermal method and post-annealing process. The obtained ZnO NR array film-based UV photodetectors exhibit not only enhanced UV sensitivity but also faster reset time compared to undoped ZnO NR samples, which are attributed to the trapping and de-trapping of electrons by Cu-related defects.

Enhanced photoluminescence of nonpolar p-type ZnO film by surface plasmon resonance and electron transfer

Nonpolar oriented Na-doped ZnO films were grown on m-plane sapphire substrates by plasma-assisted molecular beam epitaxy. The films show repeatable p-type conductivity with a hole concentration of about 3.0×10(16) cm(-3) as identified by the Hall-effect measurements. 10-fold enhancement in the near-band-edge (NBE) emission of the nonpolar p-type ZnO by employing Pt nanoparticle surface plasmons has been observed. In addition, the deep level emission has been entirely suppressed. The underlying mechanism behind the enhancement of NBE emission and the quenching of defect emission is a combination of the electron transfer and the resonant coupling between NBE emission and Pt nanoparticle surface plasmons.

Enhanced internal quantum efficiency in non-polar ZnO/Zn0.81Mg0.19O multiple quantum wells by Pt surface plasmons coupling.

Non-polar-oriented ZnO/Zn0.81Mg0.19O multiple quantum wells (MQWs) were grown on r-plane sapphire substrates by plasma-assisted molecular beam epitaxy. The internal quantum efficiency (η(int)) of the non-polar MQWs was only 1.8%. The degraded quality of non-polar MQWs is the main factor for the low η(int). Besides improving the quality of non-polar MQWs, an effective way to enhance the UV emission of the non-polar MQWs by sputtering Pt nanoparticles has been used. Employing the resonant coupling between UV emission from the MQWs and Pt nanoparticle surface plasmons (SPs), a 20-fold enhancement of the UV emission has been achieved under the optimized sputtering time. Moreover, the η(int) value of the non-polar MQWs has been strongly improved with the help of Pt. 6.7-fold enhancement of η(int) has been achieved due to SPs coupling. It paves a new way in designing highly efficient non-polar LEDs.

60-fold photoluminescence enhancement in Pt nanoparticle-coated ZnO films: role of surface plasmon coupling and conversion of non-radiative recombination.

Giant 60-fold enhanced ultraviolet (UV) emission is obtained in Pt nanoparticle-assembled ZnO film. Besides surface plasmons coupling, the conversion of non-radiative recombination into UV emission makes great contributions to the enhancement. It paves a new way in designing high-efficiency UV optoelectronic devices without defect-related energy loss.

Large degree of polarization of photoluminescence caused by anisotropic strain in nonpolar a-plane Mg_xZn_1−xO layers grown by plasma-assisted molecular beam epitaxy

A large degree of polarization (ρ) of photoluminescence (PL) approximate to 1 is obtained in each nonpolar a-plane MgxZn1-xO layer grown by plasma-assisted molecular beam epitaxy (MBE) with x=0.01, 0.03, and 0.10, respectively. Anisotropic in-plane strains are selectively introduced by using foreign substrates and doping with different Mg contents, which strongly modify the valence band structures, leading to anisotropic optical properties. A polarized Raman measurement shows that anisotropic in-plane strains along the y and z axes increase with the increasing Mg contents. Polarized PL spectra show that ρ gradually increases to 0.97 with decreasing in-plane strains, resulting from an increasing difference in transition energy (ΔE) between E⊥c and E‖c caused by a lift of the degeneracy of valence band structures. The obtained highly polarized emission is close to linear polarized light, which is desirable in the backlighting of liquid crystal displays.

Electric-field driven insulator-metal transition and tunable magnetoresistance in ZnO thin film

Electrical control of the multistate phase in semiconductors offers the promise of nonvolatile functionality in the future semiconductor spintronics. Here, by applying an external electric field, we have observed a gate-induced insulator-metal transition (MIT) with the temperature dependence of resistivity in ZnO thin films. Due to a high-density carrier accumulation, we have shown the ability to inverse change magnetoresistance in ZnO by ionic liquid gating from 10% to –2.5%. The evolution of photoluminescence under gate voltage was also consistent with the MIT, which is due to the reduction of dislocation. Our in-situ gate-controlled photoluminescence, insulator-metal transition, and the conversion of magnetoresistance open up opportunities in searching for quantum materials and ZnO based photoelectric devices.Electrical control of the multistate phase in semiconductors offers the promise of nonvolatile functionality in the future semiconductor spintronics. Here, by applying an external electric field, we have observed a gate-induced insulator-metal transition (MIT) with the temperature dependence of resistivity in ZnO thin films. Due to a high-density carrier accumulation, we have shown the ability to inverse change magnetoresistance in ZnO by ionic liquid gating from 10% to –2.5%. The evolution of photoluminescence under gate voltage was also consistent with the MIT, which is due to the reduction of dislocation. Our in-situ gate-controlled photoluminescence, insulator-metal transition, and the conversion of magnetoresistance open up opportunities in searching for quantum materials and ZnO based photoelectric devices.