Characterization of herpetrione amorphous nanoparticles stabilized by hydroxypropylmethyl cellulose and its absorption mechanism in vitro.

Herpetrione(HPE) is an effective compound that has been used in the treatment of liver diseases. To improve its dissolution and absorption, herpetrione nanosuspensions was prepared. Nanosuspensions were proved to achieve intact absorption in vivo. However, the transport mechanisms are not fully understood, especially lack of direct evidence of translocation of particulates. In this study, an environment-responsive dye, P4, was loaded into herpetrione amorphous nanoparticles (HPE-ANPs) to elucidate the absorption and transport mechanism of the nanoparticles. And the amount of HPE and nanoparticles in the samples were quantified using HPLC/LC-MS/MS and IVIS with the model of Caco-2 and Caco-2/HT29-MTX. Results demonstrated that HPE is mainly taken up by passive diffusion in the form of free drugs, while HPE-ANPs are internalized by an energy dependent active transport pathway or intracellular endocytosis. It is speculated that HPE-ANPs may change the original entry pathway of drug molecules. Furthermore, the presence of mucus layer and the use of HPMC E15 may contribute to drug absorption to some extent. Transcellular transport study indicates that HPE-ANPs has a poor absorption. In conclusion, the differences in the absorption behavior trends of HPE-ANPs are caused by the difference in particle properties and the form of existence of the drug.

Herpetetrone nanosuspensions enhance drug solubility and bioavailability to improve anti-hepatic fibrosis effects.

The aim of this study was to enhance the dissolution rate and oral bioavailability of herpetetrone (HPT) by preparing nanosuspensions (NSs) and evaluate the changes in its anti-hepatic fibrosis effect. Herpetetrone nanosuspension (HPT-NS) was prepared using the ultrasound-precipitation technique, and characterised on the basis of mean diameter, zeta potential (ZP), encapsulation efficiency percent (EE%), scanning electron microscopy (SEM), and X-ray powder diffraction (XRPD). In addition, the pharmacokinetics and anti-hepatic fibrosis activity were evaluated. HPT-NS prepared with the optimised formulation was found to be spherical with mean diameter of 177.48 ± 6.13 nm, polydispersity index (PDI) of 0.108 ± 0.002 and ZP of -17.28 ± 2.02 mV. The EE (m/m, %) was 83.25 ± 0.27. XRPD analyses confirmed that the amorphous state of HPT in HPT-NS remained unchanged. The dissolution rate of HPT-NS was significantly higher than that of HPT coarse suspensions (HPT-CSs). Following oral administration, Cmax and AUC0-t of HPT-NS showed a significant increase (p < 0.05). In vitro, HPT inhibited the proliferation of HSC-T6 cells and induced apoptosis by up-regulating the expression of Bax proteins and down-regulating the expression of Bcl-2 and TGF-ß1 proteins. Compared with HPT-CS, HPT-NS exhibited a more pronounced anti-fibrotic effect. HPT-NS, as a new drug formulation designed to improve the solubility and bioavailability of the drug, shows promising potential in enhancing the anti-liver fibrosis effect.

Demonstration of SWIR Silicon-Based Photodetection by Using Thin ITO/Au/Au Nanoparticles/n-Si Structure.

Plasmonic photodetection based on the hot-electron generation in nanostructures is a promising strategy for sub-band detection due to the high conversion efficiencies; however, it is plagued with the high dark current. In this paper, we have demonstrated the plasmonic photodetection with dark current suppression to create a Si-based broadband photodetector with enhanced performance in the short-wavelength infrared (SWIR) region. By hybridizing a 3 nm Au layer with the spherical Au nanoparticles (NPs) formed by rapid thermal annealing (RTA) on Si substrate, a well-behaved ITO/Au/Au NPs/n-Si Schottky photodetector with suppressed dark current and enhanced absorption in the SWIR region is obtained. This optimized detector shows a broad detection beyond 1200 nm and a high responsivity of 22.82 mA/W at 1310 nm at -1 V, as well as a low dark current density on the order of 10-5 A/cm2. Such a Si-based plasmon-enhanced detector with desirable performance in dark current will be a promising strategy for realization of the high SNR detector while keeping fabrication costs low.

Realizing Single Chip White Light InGaN LED via Dual-Wavelength Multiple Quantum Wells.

Dual-wavelength multiple quantum wells (MQWs) have great potential in realizing high quality illumination, monolithic micro light-emitting diode (LED) displays and other related fields. Here, we demonstrate a single chip white light indium gallium nitride (InGaN) LED via the manipulation of the dual-wavelength MQWs. The MQWs contain four pairs of blue light-emitting MQWs and one pair of green light-emitting QW. The fabricated LED chips with nickel/gold (Ni/Au) as the current spreading layer emit white light with the injection current changing from 0.5 mA to 80 mA. The chromaticity coordinates of (0.3152, 0.329) closing to the white light location in the Commission International de I'Eclairage (CIE) 1931 chromaticity diagram are obtained under a 1 mA current injection with a color rendering index (CRI) Ra of 60 and correlated color temperature (CCT) of 6246 K. This strategy provides a promising route to realize high quality white light in a single chip, which will significantly simplify the production process of incumbent white light LEDs and promote the progress of high-quality illumination.

N-polar GaN Film Epitaxy on Sapphire Substrate without Intentional Nitridation.

High-temperature nitridation is commonly thought of as a necessary process to obtain N-polar GaN films on a sapphire substrate. In this work, high-quality N-polar GaN films were grown on a vicinal sapphire substrate with a 100 nm high-temperature (HT) AlN buffer layer (high V/III ratio) and without an intentional nitriding process. The smallest X-ray full width at half maximum (FWHM) values of the (002)/(102) plane were 237/337 arcsec. On the contrary, N-polar GaN film with an intentional nitriding process had a lower crystal quality. In addition, we investigated the effect of different substrate treatments 1 min before the high-temperature AlN layer's growth on the quality of the N-polar GaN films grown on different vicinal sapphire substrates.

High performance visible-SWIR flexible photodetector based on large-area InGaAs/InP PIN structure.

Mechanically flexible optoelectronic devices and systems can enable a much broader range of applications than what their rigid counterparts can do, especially for novel bio-integrated optoelectronic systems, flexible consumer electronics and wearable sensors. Inorganic semiconductor could be a good candidate for the flexible PD when it can keep its high performance under the bending condition. Here, we demonstrate a III-V material-based flexible photodetector operating wavelength from 640 to 1700 nm with the high detectivity of 5.18 × 1011 cm‧Hz1/2/W and fast response speed @1550 nm by using a simply top-to-down fabrication process. The optoelectrical performances are stable as the PDs are exposed to bending cycles with a radius of 15 mm up to 1000 times. Furthermore, the mechanical failure mode of the PD is also investigated, which suggests that the cracking and delamination failure mode are dominant in bending up and bending down direction, respectively. Such a flexible III-V material-based PD and design with stable and high performance could be a promising strategy for the application of the flexible broad spectrum detection.

Opto-electrical and polarization performance of a mesa-structured InGaAs PIN detector integrated with subwavelength aluminum gratings.

Polarization detection in the short-wave infrared (SWIR) region presents broad applications in target-background contrast enhancement, underwater imaging, material classification, etc. A mesa structure can prevent electrical cross talk due to its intrinsic advantages, making it potentially suited to meet the need for manufacturing smaller-sized devices to save cost and shrink volume. In this Letter, mesa-structured InGaAs PIN detectors with a spectral response ranging from 900 nm to 1700 nm and a detectivity of 6.28 × 1011 cm·Hz1/2/W at 1550 nm and -0.1 V bias (room temperature) have been demonstrated. Furthermore, the devices with subwavelength gratings in four orientations show obvious polarization performance. Their extinction ratios (ERs) can reach 18:1 at 1550 nm and their transmittances are over 90%. Such a polarized device with a mesa structure could realize miniaturized SWIR polarization detection.

Enhanced light extraction from AlGaInP-based red light-emitting diodes with photonic crystals.

The photonic crystal (PC) has been demonstrated to be very effective in improving the extraction efficiency of light-emitting diodes (LEDs). In this paper, high-brightness AlGaInP-based vertical LEDs (VLEDs) with surface PC (SPCLED) and embedded PC (EPCLED) were successfully fabricated. Compared with normal LED (NLED), photoluminescence intensities of SPCLED and EPCLED have been improved up to 30% and 60%, respectively. And the reflection patterns of SPCLED and EPCLED were periodic bright points array, showing the ability to control light in PC. Electroluminescent measurements show that three kinds of LEDs have similar threshold voltages. Simultaneously, the light output power (LOP) of SPCLED and EPCLED has been improved up to 24% and 11% at 200 mA, respectively, in comparison to NLEDs. But the LOP decays earlier for EPCLED due to the excessive heat production. Furthermore, it is demonstrated that the SPCLED and EPCLED luminous uniformity is better. This kind of high brightness PCLED is promising in improving the properties of all kinds of LEDs, especially mini LEDs and micro LEDs.

The enhanced photo absorption and carrier transportation of InGaN/GaN Quantum Wells for photodiode detector applications.

We have conducted a series of measurements of resonantly excited photoluminescence, photocurrent and photovoltage on InGaN/GaN quantum wells with and without a p-n junction under reverse bias condition. The results indicate that most of the resonantly excited photo-generated carriers are extracted from the quantum wells when a p-n junction exists, and the photon absorption of quantum wells is enhanced by the p-n junction. Additionally, the carrier extraction becomes more distinct under a reverse bias. Our finding brings better understanding of the physical characteristics of quantum wells with p-n junction, which also suggests that the quantum well is suitable for photodiode detectors applications when a p-n junction is used.

Investigation of temperature-dependent photoluminescence in multi-quantum wells.

Photoluminescence (PL) is a nondestructive and powerful method to investigate carrier recombination and transport characteristics in semiconductor materials. In this study, the temperature dependences of photoluminescence of GaAs-AlxGa1-xAs multi-quantum wells samples with and without p-n junction were measured under both resonant and non-resonant excitation modes. An obvious increase of photoluminescence(PL) intensity as the rising of temperature in low temperature range (T < 50 K), is observed only for GaAs-AlxGa1-xAs quantum wells sample with p-n junction under non-resonant excitation. The origin of the anomalous increase of integrated PL intensity proved to be associated with the enhancement of carrier drifting because of the increase of carrier mobility in the temperature range from 15 K to 100 K. For non-resonant excitation, carriers supplied from the barriers will influence the temperature dependence of integrated PL intensity of quantum wells, which makes the traditional methods to acquire photoluminescence characters from the temperature dependence of integrated PL intensity unavailable. For resonant excitation, carriers are generated only in the wells and the temperature dependence of integrated PL intensity is very suitable to analysis the photoluminescence characters of quantum wells.

Realization of high-luminous-efficiency InGaN light-emitting diodes in the "green gap" range.

Light-emitting diodes (LEDs) in the wavelength region of 535-570 nm are still inefficient, which is known as the "green gap" problem. Light in this range causes maximum luminous sensation in the human eye and is therefore advantageous for many potential uses. Here, we demonstrate a high-brightness InGaN LED with a normal voltage in the "green gap" range based on hybrid multi-quantum wells (MQWs). A yellow-green LED device is successfully fabricated and has a dominant wavelength, light output power, luminous efficiency and forward voltage of 560 nm, 2.14 mW, 19.58 lm/W and 3.39 V, respectively. To investigate the light emitting mechanism, a comparative analysis of the hybrid MQW LED and a conventional LED is conducted. The results show a 2.4-fold enhancement of the 540-nm light output power at a 20-mA injection current by the new structure due to the stronger localization effect, and such enhancement becomes larger at longer wavelengths. Our experimental data suggest that the hybrid MQW structure can effectively push the efficient InGaN LED emission toward longer wavelengths, connecting to the lower limit of the AlGaInP LEDs' spectral range, thus enabling completion of the LED product line covering the entire visible spectrum with sufficient luminous efficacy.

Indium segregation measured in InGaN quantum well layer.

The indium segregation in InGaN well layer is confirmed by a nondestructive combined method of experiment and numerical simulation, which is beyond the traditional method. The pre-deposited indium atoms before InGaN well layer growth are first carried out to prevent indium atoms exchange between the subsurface layer and the surface layer, which results from the indium segregation. The uniform spatial distribution of indium content is achieved in each InGaN well layer, as long as indium pre-deposition is sufficient. According to the consistency of the experiment and numerical simulation, the indium content increases from 16% along the growth direction and saturates at 19% in the upper interface, which cannot be determined precisely by the traditional method.

Temperature-dependent photoluminescence in light-emitting diodes.

Temperature-dependent photoluminescence (TDPL), one of the most effective and powerful optical characterisation methods, is widely used to investigate carrier transport and localized states in semiconductor materials. Resonant excitation and non-resonant excitation are the two primary methods of researching this issue. In this study, the application ranges of the different excitation modes are confirmed by analysing the TDPL characteristics of GaN-based light-emitting diodes. For resonant excitation, the carriers are generated only in the quantum wells, and the TDPL features effectively reflect the intrinsic photoluminescence characteristics within the wells and offer certain advantages in characterising localized states and the quality of the wells. For non-resonant excitation, both the wells and barriers are excited, and the carriers that drift from the barriers can contribute to the luminescence under the driving force of the built-in field, which causes the existing equations to become inapplicable. Thus, non-resonant excitation is more suitable than resonant excitation for studying carrier transport dynamics and evaluating the internal quantum efficiency. The experimental technique described herein provides fundamental new insights into the selection of the most appropriate excitation mode for the experimental analysis of carrier transport and localized states in p-n junction devices.

A novel wavelength-adjusting method in InGaN-based light-emitting diodes.

The pursuit of high internal quantum efficiency (IQE) for green emission spectral regime is referred as "green gap" challenge. Now researchers place their hope on the InGaN-based materials to develop high-brightness green light-emitting diodes. However, IQE drops fast when emission wavelength of InGaN LED increases by changing growth temperature or well thickness. In this paper, a new wavelength-adjusting method is proposed and the optical properties of LED are investigated. By additional process of indium pre-deposition before InGaN well layer growth, the indium distribution along growth direction becomes more uniform, which leads to the increase of average indium content in InGaN well layer and results in a redshift of peak-wavelength. We also find that the IQE of LED with indium pre-deposition increases with the wavelength redshift. Such dependence is opposite to the IQE-wavelength behavior in conventional InGaN LEDs. The relations among the IQE, wavelength and the indium pre-deposition process are discussed.

Analyses of 2-DEG characteristics in GaN HEMT with AlN/GaN super-lattice as barrier layer grown by MOCVD.

GaN-based high-electron mobility transistors (HEMTs) with AlN/GaN super-lattices (SLs) (4 to 10 periods) as barriers were prepared on (0001) sapphire substrates. An innovative method of calculating the concentration of two-dimensional electron gas (2-DEG) was brought up when AlN/GaN SLs were used as barriers. With this method, the energy band structure of AlN/GaN SLs was analyzed, and it was found that the concentration of 2-DEG is related to the thickness of AlN barrier and the thickness of the period; however, it is independent of the total thickness of the AlN/GaN SLs. In addition, we consider that the sheet carrier concentration in every SL period is equivalent and the 2-DEG concentration measured by Hall effect is the average value in one SL period. The calculation result fitted well with the experimental data. So, we proposed that our method can be conveniently applied to calculate the 2-DEG concentration of HEMT with the AlN/GaN SL barrier.