Shuangpeng Wang

Self-powered spectrum-selective photodetectors fabricated from n-ZnO/p-NiO core–shell nanowire arrays

Self-powered, highly spectrum-selective photodetectors have been fabricated from n-ZnO/p-NiO core–shell nanowire arrays. In the structure, the outer-layer of the p-NiO acts as a “filter” which can filter out the photons with short wavelength. In this way, highly spectrum-selective photodetectors that only respond to a narrow spectrum range have been obtained.

Photoconductive gain in solar-blind ultraviolet photodetector based on Mg0.52Zn0.48O thin film

An ultraviolet photodetector was fabricated on MgZnO thin film grown by metal-organic chemical vapor deposition. The peak response of the device centers at 238 nm and cutoff wavelength is 253 nm. The peak responsivity is 129 mA/W at 15 V bias, and the UV/visible reject ratio is 4 orders of magnitude. Internal gain is due to the hole trapping at interface that brings low response speed. Native defects at the Au/MgZnO interface degrade the barrier effect, which caused large dark current and high visible response.

Pure ultraviolet emission from ZnO nanowire-based p-n heterostructures

Well-aligned ZnO nanowires have been prepared on sapphire substrate, and structural and optical characterizations indicate that the nanowires are of single crystalline and have relatively high luminescent quality. By employing the ZnO nanowires as an active layer, p-Zn0.68Mg0.32O:N/n-ZnO nanowire heterostructure light-emitting devices (LEDs) have been fabricated. The LEDs show pure ultraviolet emission when a forward bias is applied, while the deep-level emission frequently observed in ZnO p-n junctions is almost totally invisible. The devices can work continuously for over 27 h under the injection of a current density of 500 mA/cm2, indicating their good stability.

Effect of compressive stress on stability of N-doped p-type ZnO

Nitrogen-doped p-type zinc oxide (p-ZnO:N) thin films were fabricated on a-/c-plane sapphire (a-/c-Al2O3) by plasma-assisted molecular beam epitaxy. Hall-effect measurements show that the p-type ZnO:N on c-Al2O3 degenerated into n-type after a preservation time; however, the one grown on a-Al2O3 showed good stability. The conversion of conductivity in the one grown on c-Al2O3 ascribed to the faster disappearance of NO and the growing N2(O), which is demonstrated by x-ray photoelectron spectroscopy (XPS). Compressive stress, caused by lattice misfit, was revealed by Raman spectra and optical absorption spectra, and it was regarded as the root of the instability in ZnO:N.

Intense emission from ZnO nanocolumn Schottky diodes

Zinc oxide (ZnO) nanocolumns have been prepared by a metal-organic chemical vapor deposition technique, and structural and optical characterization reveal that the nanocolumns have high crystalline and luminescent qualities. Au/MgO/ZnO/In structured Schottky diodes have been fabricated from the nanocolumns. An intense emission can be detected from the diodes under the drive of bias voltage, and the output power can reach 3.7 μW. The intense emission comes from both the high crystalline and luminescent qualities of the ZnO nanocolumns, and the ideal Schottky contact formed in the Au/MgO/ZnO/In structures.

Mott-type MgxZn1-xO-based visible-blind ultraviolet photodetectors with active anti-reflection layer

We report on a vertical geometry Mott-type visible (VIS)-blind Ultraviolet (UV) photodetector which was fabricated based on wurzite MgZnO (W-MgZnO) with a cubic MgZnO (C-MgZnO) anti-reflection layer. The C-MgZnO layer plays two roles in the detector, not only the conventional optical part but also electrical part. Photon-generated holes were restricted due to valence band offset. More “hot” electrons injected over a reduced Mott potential barrier at the metal-semiconductor interface, resulting in additional current contributing to photoresponse. This dual-function structure is a highly compact and wavelength-resonant UV detector, with a spectral response high-gain and fast.

Enhanced solar-blind responsivity of photodetectors based on cubic MgZnO films via gallium doping

We report on gallium (Ga) doped cubic MgZnO films, which have been grown by metal organic chemical vapor deposition. It was demonstrated that Ga doping improves the n-type conduction of the cubic MgZnO films. A two-orders of magnitude enhancement in lateral n-type conduction have been achieved for the cubic MgZnO films. The responsivity of the cubic MgZnO-based photodetector has been also enhanced. Depletion region electric field intensity enhanced model was adopted to explain the improvement of quantum efficiency in Ga doped MgZnO-based detectors.

Enhanced Responsivity of Photodetectors Realized via Impact Ionization

To increase the responsivity is one of the vital issues for a photodetector. By employing ZnO as a representative material of ultraviolet photodetectors and Si as a representative material of visible photodetectors, an impact ionization process, in which additional carriers can be generated in an insulating layer at a relatively large electric field, has been employed to increase the responsivity of a semiconductor photodetector. It is found that the responsivity of the photodetectors can be enhanced by tens of times via this impact ionization process. The results reported in this paper provide a general route to enhance the responsivity of a photodetector, thus may represent a step towards high-performance photodetectors.

Piezophototronic‐Effect‐Enhanced Electrically Pumped Lasing

This study demonstrates significant improvements of ZnO nanowire lasers by the piezophototronic effect. The laser output power can be enhanced by a factor of 4.96, and the threshold voltage can be decreased from 48 to 20 V by applying pressure. The mechanism of the improved performance can be attributed to the enhanced carrier injection and recombination due to the piezophototronic effect.

Intense electroluminescence from ZnO nanowires

Vertically aligned ZnO nanowires have been prepared, and intense electroluminescence (EL) has been observed with holes injected into the nanowires from p-type ZnO prepared via a high pressure high temperature route. The emission can be attributed to the radiative recombination between the electrons in the nanowires and the injected holes, and the power of the EL can reach about 10 μW when the injection current is 20 mA. The intense emission is believed to be resulted from both the relatively high quality of the nanowires and injection of the holes from the p-type ZnO.