Superhigh gain InGaN/GaN visible-light photodetector using polarization heterointerface barrier and single-carrier superlattices.

Visible-light detection with high sensitivity and strong wavelength selectivity is highly desired in emerging applications. Here, we demonstrate a high-performance visible-light photodetector with an active region composed of a polarization induced barrier and single-carrier superlattices (SCSLs). The barrier at SCSLs/GaN heterointerface brings both a low dark current and a high gain originating from the photoinduced barrier reduction effect. Meanwhile, the designed InGaN/GaN SCSLs allow the photoelectrons in the quantum wells to escape, but photogenerated holes are weakly localized, thus generating the additional photoconductive gain. The resulting devices exhibited a super-high gain of 7.8 × 104, a large detectivity of 1.2 × 1016 jones, and a relatively fast response speed with rise/falling time of 2.5/89.6 ns. Also, a 400/500-nm rejection ratio greater than 3 × 105 was shown at 1 V, indicating excellent wavelength selectivity.

Highly Responsive Gate-Controlled p-GaN/AlGaN/GaN Ultraviolet Photodetectors with a High-Transmittance Indium Tin Oxide Gate.

This work presents highly responsive gate-controlled p-GaN/AlGaN/GaN ultraviolet photodetectors (UVPDs) on Si substrates with a high-transmittance ITO gate. The two-dimensional electron gas (2DEG) in the quantum well of the polarized AlGaN/GaN heterojunction was efficiently depleted by the p-GaN gate, leading to a high photo-to-dark current ratio (PDCR) of 3.2 × 105. The quantum wells of the p-GaN/AlGaN and AlGaN/GaN heterojunctions can trap the holes and electrons excited by the UV illumination, thus efficiently triggering a photovoltaic effect and photoconductive effect, separately. Furthermore, the prepared photodetectors allow flexible adjustment of the static bias point, making it adaptable to different environments. Compared to traditional thin-film semi-transparent Ni/Au gates, indium tin oxide (ITO) exhibits higher transmittance. Under 355 nm illumination, the photodetector exhibited a super-high responsivity exceeding 3.5 × 104 A/W, and it could even exceed 106 A/W under 300 nm illumination. The well-designed UVPD combines both the advantages of the high-transmittance ITO gate and the structure of the commercialized p-GaN/AlGaN/GaN high-electron-mobility transistors (HEMTs), which opens a new possibility of fabricating large-scale, low-cost, and high-performance UVPDs in the future.

Photoelectric characteristics of hydrogen-terminated polycrystalline diamond MESFETs.

In the field of diamond MESFETs, this work is what we believe to be the first to investigate the optoelectronic properties of hydrogen-terminated polycrystalline diamond MESFETs under visible and near-UV light irradiation. It is shown that the diamond MESFETs are well suited for weak light detection in the near-ultraviolet region around the wavelength of 368 nm, with a responsivity of 6.14 × 106 A/W and an external quantum efficiency of 2.1 × 107 when the incident light power at 368.7 nm is only 0.75 µW/cm2. For incident light at 275.1 nm, the device's sensitivity and EQE increase as the incident light power increases; at an incident light power of 175.32 µW/cm2 and a VGS of -1 V, the device's sensitivity is 2.9 × 105 A/W and the EQE is 1.3 × 106. For incident light in the wavelength range of 660 nm to 404 nm with an optical power of 70 µW/cm2, the device achieves an average responsivity of 1.21 × 105 A/W. This indicates that hydrogen-terminated polycrystalline diamond MESFETs are suitable for visible and near-UV light detection, especially for weak near-UV light detection. However, the transient response test of the device shows a long relaxation time of about 0.2 s, so it is not yet suitable for high-speed UV communication or detection.

A Novel p-Type ZnCoxOy Thin Film Grown by Atomic Layer Deposition.

Reported herein is the atomic layer deposition (ALD) of novel ternary ZnCoxOy films possessing p-type semiconducting behavior. The preparation comprises of optimized ZnO and Co3O4 deposition in sub-cycles using the commercially available precursors cyclopentadienylcobalt dicarbonyl (CpCo(CO)2), diethylzinc (DEZ) and ozone (O3). A systematic exploration of the film's microstructure, crystallinity, optical properties and electrical properties was conducted and revealed an association with Zn/Co stoichiometry. The noteworthy results include the following: (1) by adjusting the sub-cycle of ZnO/ Co3O4 to 1/10, a spinel structured ZnCoxOy film was grown at 150 °C, with it exhibiting a smooth surface, good crystallinity and high purity; (2) the material transmittance and bandgap decreased as the Co element concentration increased; (3) the ZnCoxOy film is more stable than its p-type analog Co3O4 film; and (4) upon p-n diode fabrication, the ZnCoxOy film demonstrated good rectification behaviors as well as very low and stable reverse leakage in forward and reverse-biased voltages, respectively. Its application in thin film transistors and flexible or transparent semiconductor devices is highly suggested.

Superfluorescence of Sub-Band States in C-Plane In0.1Ga0.9N/GaN Multiple-QWs.

Superfluorescence is a collective emission from quantum coherent emitters due to quantum fluctuations. This is characterized by the existence of the delay time (τD) for the emitters coupling and phase-synchronizing to each other spontaneously. Here we report the observation of superfluorescence in c-plane In0.1Ga0.9N/GaN multiple-quantum wells by time-integrated and time-resolved photoluminescence spectroscopy under higher excitation fluences of the 267 nm laser and at room temperature, showing a characteristic τD from 79 ps to 62 ps and the ultrafast radiative decay (7.5 ps) after a burst of photons. Time-resolved traces present a small quantum oscillation from coupled In0.1Ga0.9N/GaN multiple-quantum wells. The superfluorescence is attributed to the radiative recombination of coherent emitters distributing on strongly localized subband states, Ee1→Ehh1 or Ee1→Elh1 in 3nm width multiple-quantum wells. Our work paves the way for deepening the understanding of the emission mechanism in the In0.1Ga0.9N/GaN quantum well at a higher injected carrier density.

Preparation and investigation of high solid content PTX-loaded nanoparticles dispersion via nanoprecipitation method.

The improvement of the solid content of the hydrophobic drugs (such as paclitaxel (PTX), etc.) loaded nanoparticles (NPs) dispersion is important for enhancing drug-loaded efficiency and reducing the cost in production and application. A diblock copolymer methoxy poly(ethylene glycol)-b-poly(ε-caprolactone-co-1,4,8-trioxa[4.6]spiro-9-undecanone) (mPECT) is synthesized via the ring-opening polymerization of ε-caprolactone and 1,4,8-trioxa[4.6]spiro-9-undecanone (TOSUO) with methoxy poly(ethyleneglycol) (mPEG） as the initiator. The chemical structures and thermal properties of mPECT are characterized by (1)HNMR, Fourier transform infrared (FT-IR), gel permeation chromatography, differential scanning calorimetry, etc. PEG45.45-b-P(C28.33-co-T5.38) (mPECT-2) is able to self-assemble into stable NPs in water via nanoprecipitation method at a high solid content (≤25 wt%) and their freeze-dried powders can well re-disperse in water. The paclitaxel (PTX) is chosen as a hydrophobic drug model and successfully encapsulate into the mPECT-2 NPs via the same method at a high solid content. The encapsulation efficiency, cytotoxicity and in vitro release of PTX-loaded NPs are investigated. The results suggest that the behavior of the drug-loaded mPECT-2 NPs prepared at a solid content of 25 wt% is similar to that of NPs prepared at a solid content of 1 wt%, which indicate that increasing solid content of polymer has no negative effect on the properties of NPs dispersion in application. In summary, the freeze-dried NPs prepared from the high solid content dispersion (≤25 wt%) has a good redispersibility and exhibits great potential in cost control of preparing NPs dispersion used as drug delivery system.

Thermosensitive in situ hydrogel based on the hybrid of hyaluronic acid and modified PCL/PEG triblock copolymer.

In this work, a new hydrogel was constructed using poly(ɛ-caprolactone-co-1,4,8-trioxa[4.6]spiro-9-undecanone)-poly(ethylene glycol)-poly(ɛ-caprolactone-co-1,4,8-trioxa[4.6]spiro-9-undecanone) tri-block copolymers (PECT) with hyaluronic acid (HA) in order to expand application scopes of PECT hydrogel. The rheological and sol-gel phase transition behaviors were investigated by rheometer and test tube inversion method, and the interior morphologies of hydrogel systems were observed by scanning electron microscope (SEM). With the introduction of HA, certain properties of PECT hydrogel, such as viscosity and morphology, have present trends with regularity. Furthermore, with the participation of HA, the degradation and release of acetylsalicylic acid was slightly affected, however, the drug release mechanism of hydrogel has not been changed. PECT/HA hydrogel is confirmed to be non-toxic through a test to NIH3T3 cells. In conclusion, blending with HA is a feasible and safe method to tune properties of PECT hydrogel.

Drying effects on the antioxidant properties of polysaccharides obtained from Agaricus blazei Murrill.

Three polysaccharides (ABMP-F, ABMP-V, ABMP-A) were obtained from Agaricus blazei Murrill via methods such as freeze drying, vacuum drying and air drying, respectively. Their chemical compositions were examined, and antioxidant activities were investigated on the basis of assay for hydroxyl radical, DPPH radical, ABTS free radical scavenging ability and assay for Fe(2+)-chelating ability. Results showed that the three ABMPs have different physicochemical and antioxidant properties. Compared with air drying and vacuum drying methods, freeze drying method resulted to ABMP with higher neutral sugar, polysaccharide yield, uronic acid content, and stronger antioxidant abilities of hydroxyl radical, DPPH radical, ABTS radical scavenging and Fe(2+)-chelating. As a result, Agaricus blazei Murrill polysaccharides are natural antioxidant and freeze drying method serves as a good choice for the preparation of such polysaccharides and should be used to produce antioxidants for food industry.

Photo-crosslinked poly(ethylene glycol)-b-poly(ϵ-caprolactone) nanoparticles for controllable paclitaxel release.

Novel biodegradable core-crosslinked nanoparticles (CNPs) consisting of methoxy poly(ethylene glycol)-block-poly(ϵ-caprolactone-co-γ-cinnamoyloxy-ϵ-caprolactone) (mPEG-b-P(CL-co-CCL)) were prepared and evaluated for paclitaxel (PTX) delivery. mPEG113-b-P(CL65.2-co-CCL10.1) had a higher drug loading efficiency (95%) compared to mPEG113-b-PCL93.1 (43%). The stability of NPs has been largely improved and PTX release was significantly inhibited by crosslinking via UV irradiation at λ = 254 nm. MTT assays demonstrated that both blank non-crosslinked and crosslinked NPs showed low cytotoxicity to NCL-H460 cells while PTX-loaded non-crosslinked and crosslinked NPs exhibited obvious cytotoxicity against NCL-H460 cells, and the cytotoxicity was both dose-dependent and time-dependent. Furthermore, after 48 h incubation the cell viability of PTX-loaded crosslinked NPs was lower compared to that of PTX-loaded non-crosslinked NPs or free PTX. These properties indicated that CNPs prepared from mPEG-b-P(CL-co-CCL) have great potentials as carriers for drug delivery.

Poly(ethyleneglycol)-b-poly(ε-caprolactone-co-γ-hydroxyl-ε- caprolactone) bearing pendant hydroxyl groups as nanocarriers for doxorubicin delivery.

A novel biodegradable amphiphilic diblock copolymer methoxy poly(ethylene glycol)-b-poly(ε-caprolactone-co-γ-hydroxyl-ε-caprolactone) (mPEG-b-P(CL-co-HCL)) bearing pendant hydroxyl groups on the PCL block was prepared. The hydroxyl groups were formed through the reduction of ketones by sodium borohydride without protection and deprotection. The obtained polymers were well characterized by (1)H NMR, Fourier transform infrared (FT-IR), gel permeation chromatography (GPC), differential scanning calorimetry (DSC), X-ray diffraction (XRD), and contact angle measurement. mPEG-b-P(CL-co-HCL) could self-assemble into stable nanoparticles (NPs) with critical micellar concentrations (CMC) of 6.3 × 10(-4) ∼ 8.1 × 10(-4) mg/mL. The NPs prepared from mPEG-b-P(CL-co-HCL) were spherical in shape with diameters about 100 to 140 nm. The hydrophobic doxorubicin (DOX) was chosen as a drug model and successfully encapsulated into the NPs. The encapsulation efficiency and release kinetics of DOX were investigated. The results indicated that the introduction of hydroxyl groups onto the core-forming block could decrease the hydrophobicity of copolymers, thus improving the storage stability of NPs in aqueous solution. Moreover, higher loading capacity and slower in vitro release of DOX were observed, which was due to the hydrogen-bonding formation between DOX and hydroxyl groups. Meanwhile, the MTT assay demonstrated that the blank NPs were biocompatible to HepG2 cell,s while free DOX and DOX-loaded NPs showed significant cytotoxicity against the cells. Moreover, Compared to the free DOX, the DOX-loaded NPs were more efficiently internalized by HepG2 cells. In sum, the introduction of hydroxyl groups on the polyester block in mPEG-b-P(CL-co-HCL) exhibited great potentials for modifications in the stability, drug solubilization, and release properties of NPs.