Chong-Xin Shan

Low‐Threshold Electrically Pumped Random Lasers

Electrically pumped random lasers are realized in ZnO nanocrystallite films in a simple metal-oxide-semiconductor structure. By introducing an i-ZnO layer, a threshold current of 6.5 mA is obtained. The reported results provide a simple route to electrically pumped random lasing (see figure) with relatively low threshold, a significant step towards the future applications of this kind of laser.

Temperature dependent photoluminescence study on phosphorus doped ZnO nanowires

We report temperature dependent photoluminescence studies on phosphorus doped ZnO nanowires. The shape of the spectra is very similar to those of phosphorus doped ZnO films. The photoluminescence spectrum at 10K is dominated by neutral acceptor bound exciton (AX0) emissions. The acceptor binding energy determined also agrees with the corresponding value in phosphorus doped films. Studies on the AX0 intensity show two quenching channels, associated with the thermal dissociations of AX0 to a free exciton and of shallow residual donors. The residual donors revealed provide a clue for the difficulty in p doping of ZnO.

High responsivity ultraviolet photodetector realized via a carrier-trapping process

Metal-semiconductor-metal structured ultraviolet (UV) photodetector has been fabricated from zinc oxide films. The responsivity of the photodetector can reach 26u2009000 A/W at 8 V bias, which is the highest value ever reported for a semiconductor ultraviolet photodetector. The origin of the high responsivity has been attributed to the carrier-trapping process occurred in the metal-semiconductor interface, which has been confirmed by the asymmetric barrier height at the two sides of the metal-semiconductor interdigital electrodes. The results reported in this paper provide a way to high responsivity UV photodetectors, which thus may address a step toward future applications of UV photodetectors.

Dual-color ultraviolet photodetector based on mixed-phase-MgZnO/i-MgO/p-Si double heterojunction

We report a dual-color ultraviolet (UV) photodetector based on mixed-phase-MgZnO/i-MgO/p-Si double heterojunction. The device exhibits distinct dominant responses at solar blind (250u2009nm) and visible blind (around 330u2009nm) UV regions under different reverse biases. By using the energy band diagram of the structure, it is found that the bias-tunable two-color detection is originated from different valence band offset between cubic MgZnO/MgO and hexagonal MgZnO/MgO. Meanwhile, due to the large conduction band offset at the Si/MgO interface, the visible-light photoresponse from Si substrate is suppressed.

A reproducible route to p-ZnO films and their application in light-emitting devices

Although great efforts have been made, reproducible p-type doping is still one of the largest hurdles that hinders the optoelectronic applications of ZnO. In this Letter, a reproducible route to p-type ZnO films employing lithium-nitrogen as a dual-acceptor dopant has been demonstrated, and p-i-n structured light-emitting devices (LEDs) have been constructed. Obvious purple emissions have been observed from the LEDs, confirming the applicability of the p-type ZnO films in optoelectronic devices. The results reported in this Letter provide a reproducible route to p-type ZnO films, and thus may lay a solid ground for future optoelectronic applications of ZnO.

Metal-insulator-semiconductor-insulator-metal structured titanium dioxide ultraviolet photodetector

Titanium dioxide (TiO2) thin films were prepared by an atomic layer deposition technique and a metal–insulator–semiconductor–insulator–metal structured ultraviolet photodetector was fabricated from the TiO2 thin films. Meanwhile, a metal–semiconductor–metal structured photodetector was also fabricated under the same condition for comparison. By measuring their photoresponse properties, it was found that the existence of an insulation layer is effective in improving the photodetector’s responsivity. The mechanism for the improvement has been attributed to the carrier multiplication occurring in the insulation layer under a high electric field. (Some figures in this article are in colour only in the electronic version)

Localized surface plasmon enhanced light-emitting devices

In this paper, localized surface plasmon enhanced n-ZnO/i-ZnO/MgO/p-GaN structured light-emitting devices have been designed and constructed. It is found that the electroluminescence of the devices can be enhanced at selective wavelengths that match the localized surface plasmon extinction spectra of the metal nanoparticles.

Stable surface plasmon enhanced ZnO homojunction light-emitting devices

Ag nanoparticle surface plasmon enhanced ZnO homojunction light-emitting devices (LEDs) have been constructed. It is found that the Ag nanoparticles can increase the emission of the devices greatly, and the Ag nanoparticle decorated LEDs degrade little after placing in ambient air for three months, revealing their good stability.

A route to improved extraction efficiency of light-emitting diodes

The electroluminescence from an n-MgZnO/i-ZnO/MgO/p-GaN asymmetric double heterojunction has been demonstrated. With the injection of electrons from n-MgZnO and holes from p-GaN, an intense ultraviolet emission coming from the ZnO active layer was observed. It is revealed that the emission intensity of the diode recorded from the MgZnO side is significantly larger than that from the MgO side because of the asymmetric waveguide structure formed by the lower refractive index of MgO than that of MgZnO. The asymmetric waveguide structure reported in this letter may promise a simple and effective route to light-emitting diodes with improved light-extraction efficiency.

Deep-ultraviolet light-emitting device realized via a hole-multiplication process

By proper controlling the carrier generation and multiplication processes, an Au/MgO/Mg0.52Zn0.48O/MgxZn1−xO/n-ZnO structure has been designed and fabricated. In this structure, holes are multiplied via an impact ionization process in the MgO layer and injected into the Mg0.52Zn0.48O layer, and electrons are injected into the Mg0.52Zn0.48O layer from the n-ZnO layer through a composition-gradient MgxZn1−xO bridging layer. With the injection of electrons and holes, a deep ultraviolet emission at around 276 nm, coming from the Mg0.52Zn0.48O active layer, has been observed. The results reported in this letter may provide a promising route to high performance deep ultraviolet light-emitting devices.