Hongxing Wang

Fabrication of UV Photodetector on TiO2/Diamond Film.

The properties of ultraviolet (UV) photodetector fabricated on TiO2/diamond film were investigated. Single crystal diamond layer was grown on high-pressure-high-temperature Ib-type diamond substrate by microwave plasma chemical vapor deposition method, upon which TiO2 film was prepared directly using radio frequency magnetron sputtering technique in Ar and O2 mixing atmosphere. Tungsten was used as electrode material to fabricate metal-semiconductor-metal UV photodetector. The dark current is measured to be 1.12 pA at 30 V. The photo response of the device displays an obvious selectivity between UV and visible light, and the UV-to-visible rejection ratio can reach 2 orders of magnitude. Compared with that directly on diamond film, photodetector on TiO2/diamond film shows higher responsivity.

A 3 w high-voltage single-chip green light-emitting diode with multiple-cells network

A parallel and series network structure was introduced into the design of the high-voltage single-chip (HV-SC) light-emitting diode to inhibit the effect of current crowding and to improve the yield. Using such a design, a 6.6 × 5mm2 large area LED chip of 24 parallel stages was demonstrated with 3 W light output power (LOP) at the current of 500 mA. The forward voltage was measured to be 83 V with the same current injection, corresponding to 3.5 V for a single stage. The LED chips average thermal resistance was identified to be 0.28 K/W by using infrared thermography analysis.

Fabrication of three dimensional diamond ultraviolet photodetector through down-top method

Three dimensional diamond ultraviolet (UV) photodetector have been fabricated on diamond epitaxial layer through down-top approach, where diamond epitaxial layer was grown between metal electrodes. A thin diamond epitaxial layer was first grown on high-pressure high-temperature single crystal diamond substrate. Then, the diamond epitaxial layer was covered by interdigitated tungsten electrodes. Furthermore, another diamond epitaxial layer was grown on uncovered area. At last, UV-Ozone treatment was used to oxidize the surface. The optoelectronic performance of the photodetector was characterized, exhibiting a large responsivity and a repeatable transient response behavior. Moreover, down-top process is beneficial for the electrode conductivity stability. Also, an ohmic contact could be formed between tungsten and diamond during growth. The results indicate that down-top process is an efficient way for fabrication of three dimensional diamond photodetectors.

Fabrication of diamond microlenses by chemical reflow method

We introduce a chemical reflow method to fabricate diamond microlenses. First, photoresist pillars developed by photolithography are reflowed in organic solvent vapor atmosphere at 20 °C to form spherical segment patterns on diamond substrate. The effects of chemical solvent type and reflow time on photoresist pattern profiles are investigated. Second, via dry etching, diamond microlenses are fabricated by transferring the spherical segment pattern into substrate. Furthermore, these diamond microlenses demonstrate low numerical aperture, well-controllable curvature, and good imaging performance with projecting experiment.

Triple-mode squeezing with dressed six-wave mixing

The theory of proof-of-principle triple-mode squeezing is proposed via spontaneous parametric six-wave mixing process in an atomic-cavity coupled system. Special attention is focused on the role of dressed state and nonlinear gain on triple-mode squeezing process. Using the dressed state theory, we find that optical squeezing and Autler-Towns splitting of cavity mode can be realized with nonlinear gain, while the efficiency and the location of maximum squeezing point can be effectively shaped by dressed state in atomic ensemble. Our proposal can find applications in multi-channel communication and multi-channel quantum imaging.

Diamond based field-effect transistors of Zr gate with SiN x dielectric layers

Investigation of Zr-gate diamond field-effect transistor with SiNx dielectric layers (SD-FET) has been carried out. SD-FET works in normally on depletion mode with p-type channel, whose sheet carrier density and hole mobility are evaluated to be 2.17 × 1013 cm-2 and 24.4 cm2ċV-1ċs-1, respectively. The output and transfer properties indicate the preservation of conduction channel because of the SiNx dielectric layer, which may be explained by the interface bond of C-N. High voltage up to -200 V is applied to the device, and no breakdown is observed. For comparison, another traditional surface channel FET (SC-FET) is also fabricated.

UV-photodetector based on NiO/diamond film

In this study, a NiO/diamond UV-photodetector has been fabricated and investigated. A single crystal diamond (SCD) layer was grown on a high-pressure-high-temperature Ib-type diamond substrate by using a microwave plasma chemical vapor deposition system. NiO films were deposited directly by the reactive magnetron sputtering technique in a mixture gas of oxygen and argon onto the SCD layer. Gold films were patterned on NiO films as electrodes to form the metal-semiconductor-metal UV-photodetector which shows good repeatability and a 2 orders of magnitude UV/visible rejection ratio. Also, the NiO/diamond photodetector has a higher responsivity and a wider response range in contrast to a diamond photodetector.In this study, a NiO/diamond UV-photodetector has been fabricated and investigated. A single crystal diamond (SCD) layer was grown on a high-pressure-high-temperature Ib-type diamond substrate by using a microwave plasma chemical vapor deposition system. NiO films were deposited directly by the reactive magnetron sputtering technique in a mixture gas of oxygen and argon onto the SCD layer. Gold films were patterned on NiO films as electrodes to form the metal-semiconductor-metal UV-photodetector which shows good repeatability and a 2 orders of magnitude UV/visible rejection ratio. Also, the NiO/diamond photodetector has a higher responsivity and a wider response range in contrast to a diamond photodetector.

Two-dimensional Talbot self-imaging via Electromagnetically induced lattice

We propose a lensless optical method for imaging two-dimensional ultra-cold atoms (or molecules) in which the image can be non-locally observed by coincidence recording of entangled photon pairs. In particular, we focus on the transverse and longitudinal resolutions of images under various scanning methods. In addition, the role of the induced nonmaterial lattice on the image contrast is investigated. Our work shows a non-destructive and lensless way to image ultra-cold atoms or molecules that can be further used for two-dimensional atomic super-resolution optical testing and sub-wavelength lithography.

Optically induced atomic lattice with tunable near-field and far-field diffraction patterns

Conventional periodic structures usually have nontunable refractive indices and thus lead to immutable photonic bandgaps. A periodic structure created in an ultracold atoms ensemble by externally controlled light can overcome this disadvantage and enable lots of promising applications. Here, two novel types of optically induced square lattices, i.e., the amplitude and phase lattices, are proposed in an ultracold atoms ensemble by interfering four ordinary plane waves under different parameter conditions. We demonstrate that in the far-field regime, the atomic amplitude lattice with high transmissivity behaves similarly to an ideal pure sinusoidal amplitude lattice, whereas the atomic phase lattices capable of producing phase excursion across a weak probe beam along with high transmissivity remains equally ideal. Moreover, we identify that the quality of Talbot imaging about a phase lattice is greatly improved when compared with an amplitude lattice. Such an atomic lattice could find applications in all-optical switching at the few photons level and paves the way for imaging ultracold atoms or molecules both in the near-field and in the far-field with a nondestructive and lensless approach.

Second-order self-imaging with parametric amplification four-wave mixing

By modulating the emission characteristics of a twin-correlated bright beam in a parametric amplification of the four-wave mixing process, a nondestructive and lensless imaging scheme to image ultra-cold atoms or molecules is proposed. The optical lattice state, which is induced via the coupling between ultra-cold atoms and a standing wave, is used to effectively modulate the dressing-suppressed/enhanced nonlinear susceptibility, and an emission-intensity-modulated grating of a correlated bright beam is formed. The intensity fluctuations of the correlated bright beam are taken as the imaging light to implement second-order coincidence measurement. As an important complementary scheme to a previous self-imaging scheme with spontaneous parametric down-conversion, our scheme has the characteristic of an efficient generation and detection rate. In addition, the visibility of the imaging can be significantly improved by enhanced nonlinear susceptibility. Our work may offer a nondestructive and lensless way to image ultra-cold atoms or molecules.