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Our previous study demonstrated altered glucose metabolism and enhanced phosphorylation of the PI3K/AKT pathway in keloid fibroblasts (KFb) under hypoxic conditions. However, whether the PI3K/AKT pathway influences KFb cell function by regulating glucose metabolism under hypoxic conditions remains unclear. Here, we show that when PI3K/AKT pathway was inactivated with LY294002, the protein expression of glycolytic enzymes decreased, while the amount of mitochondria and mitochondrial membrane potential (MMP) increased. The key parameters of extracellular acidification rate (ECAR) markedly diminished, and those of oxygen consumption rate (OCR) significantly increased after inhibition of the PI3K/AKT pathway. When the PI3K/AKT pathway was suppressed, the levels of ROS and mitochondrial ROS were significantly increased. Meanwhile, cell proliferation, migration, and invasion were inhibited, and apoptosis was increased when the PI3K/AKT pathway was blocked. Additionally, cell proliferation was compromised when KFb were treated with both SC79 (an activator of the PI3K/AKT pathway) and 2-DG (an inhibitor of glycolysis), compared to the SC79 group. Moreover, a positive feedback mechanism was demonstrated between the PI3K/AKT pathway and HIF-1α. Our data collectively demonstrated that the PI3K/AKT pathway promotes proliferation and inhibits apoptosis in KFb under hypoxia by regulating glycolysis, indicating that the PI3K/AKT signaling pathway could be a therapeutic target for keloids. This article is protected by copyright. All rights reserved.

Carrier velocity modulation by asymmetrical concave quantum barriers to improve the performance of AlGaN-based deep-ultraviolet light emitting diodes has been investigated. The concave structure is realized by inserting a low Al composition AlGaN layer in the barrier, and thus forming a concave region on energy band. The measured device performance shows a significant improvement under 0–250 mA operation current, with the maximum external quantum efficiency and light output power of 1.02% and 8.0 mW, which are more than double (2.32 and 2.35 times) of that for the conventional one, respectively. Simulation confirms that the concave quantum barriers make it possible for electrons to be scattered, which reduce the electron energy before being injected into quantum wells, and thus the capability of quantum wells to capture electrons is enhanced. Meanwhile, the vertical transport of holes within the active region is also enhanced because the asymmetrical setting of the concave layer in the quantum barriers helps holes accelerate under the polarization field, and then get more energy to overcome the barrier.

Graphical abstract, Irritable bowel syndrome (IBS) is the most prevalent functional gastrointestinal disorder presenting a high comorbidity with depressive disorder (DD). Many studies have confirmed that these two disease share the similar pathophysiological process, but evidence of the genetic risks is limited. This study aimed to analyze the genetic susceptibilities for IBS and DD in Chinese patients. Pooled whole-exome sequencing (pooled-WES) was performed to identify the candidate variants in the group of diarrhea predominant IBS (IBS-D) patients, DD patients, and healthy controls (HC). Then, targeted sequencing was used to validate the candidate variants in three additional cohorts of IBS-D, DD, and HC. Four variants associated with both IBS-D and DD were identified through pooled-WES, and three of them were validated in targeted sequencing. SYT8 rs3741231 G allele and SSPO rs12536873 TT genotype were associated with both IBS-D and DD. The genes of these variants are important in neurogenesis and neurotransmission. In addition, we found COL6A1 rs13051496, a unique risk variation for IBS-D. It increased the IBS-D risk and had a positive correlation with the scores of abdominal bloating and dissatisfaction of bowel habits. Through the results of this study, it provides a genetic basis for the high comorbidity of IBS-D and DD.

Evolution of crystalline quality of AlN via high-temperature (HT) annealing induced by different sapphire pretreatments is investigated. It is found that after HT annealing at 1700 °C for one hour, an AlN film grown on a nitridation treated sapphire substrate presents a much lower threading dislocation density (TDD) than that grown on an alumination treated one, indicating that the combination of nitridation and HT annealing is a more effective approach to achieve high quality AlN. It is verified that the much greater grain density of the nucleation layer induced by nitridation can produce more columns with much smaller sizes so that they can more easily rotate during the HT annealing to reduce the TDD more effectively. A deep ultraviolet light-emitting diode (285 nm) with an output power over 10 mW has been demonstrated on a HT annealed AlN template with sapphire substrate nitridation pretreatment, showing great potential for applications.

Enhancement of light extraction efficiency (LEE) of AlGaN-based deep-ultraviolet (DUV) light emitting diodes (LEDs) has been attempted by adopting Ag-nanodots/Al reflective electrodes on a highly transparent complex p-type layer. By thinning the p-GaN to several nm, highly DUV transparent p-type layer is achieved, making it meaningful for the application of reflective electrodes composed of Ag-nanodots and Al film to allow most light emitted upward to be reflected back to the sapphire side. By this approach, the maximum light output power and external quantum efficiency of the DUV-LEDs with optimized Ag nanodots/Al electrodes are severally increased by 52% and 58%, respectively, compared to those with traditional Ni/Au electrodes when the current is below 200 mA.

Objective: As an aberrant response to cutaneous wound healing, keloid scarring is a challenge to cure, and its clinical management remains unsatisfactory. The purpose of this study was to investigate whether mitochondrial function and morphology were impaired in keloid pathology. Approach: Keloid fibroblasts (KFs) and normal skin fibroblasts (NFs) were isolated and cultured from excised samples. A real-time extracellular flux analyzer was used to monitor the oxygen consumption rate for evaluating the mitochondrial respiratory function. Real-time PCR or Western blot was performed to detect the levels of mRNAs or proteins, respectively, including those associated with the tricarboxylic acid cycle, mitochondrial fission and fusion, and mitochondrial biogenesis. The reactive oxygen species (ROS) level and the mitochondrial mass were measured by flow cytometry. Mitochondrial ultrastructure was observed by transmission electron microscopy. Results: Compared with NFs, KFs showed reduced basal oxidative respiration (p

Objective: The study aimed to explore the associations of rs4988300 and rs634008 in the low-density lipoprotein receptor–related protein 5 (LRP5) gene with bone mineral density (BMD), bone turnover markers (BTM), and fractures in elderly patients with osteoporosis (OP).Methods: Our study included 328 unrelated OP patients with or without fractures. Genomic DNA was extracted for genotyping. BTM levels were assessed by electrochemiluminescence (ECL). Dual-energy X-ray absorptiometry (DXA) was employed to measure BMD in the lumbar spine (LS) and proximal femur. Basic features between the OP and fracture groups were analyzed using the t-test. The Chi-square test was performed to analyze the differences in allele and genotype frequencies. The associations of single-nucleotide polymorphisms (SNPs) with BMD and BTM in the subgroups were investigated by the analysis of covariance (ANCOVA) adjusted for confounding factors.Results: In both females and males, individuals with fractures exhibited higher BTM levels and lower BMD values than those with OP (P < 0.05). The allele and genotype frequencies of rs4988300 in the subgroups were significantly different (P < 0.05). In both females and males suffering from OP, participants with rs4988300 GG or rs634008 TT presented lower procollagen I N-terminal propeptide (PINP) levels (P < 0.05). Women with OP carrying rs4988300 GG exhibited lower BMD values at FN and TH (P < 0.05). In both females and males with fractures, individuals carrying rs4988300 GG genotype or rs634008 TT genotype exhibited lower PINP levels and BMD values at FN and TH than those with other genotypes (P < 0.05).Conclusions: Rs4988300 and rs634008 polymorphisms in the LRP5 gene are associated with bone phenotypes in the elderly with OP or fractures.

BACKGROUND We investigated levels of the metal elements Ca, Mg, Zn, Fe, and Cu in blood, normal skin (NS), and different types of scar tissue and aimed to elucidate the pathogenesis of hypertrophic scars (HS). MATERIAL AND METHODS Tissue specimens were excised from 3 groups of research participants: scar-free, flat scar (FS), and HS groups. Levels of the study elements were measured in blood, NS, and scar tissues with a spectrophotometer. The levels in plasma or in different types of specimens were compared among subgroups. In the FS and HS groups, levels were compared between the scar tissue and NS of each individual. In addition, element differences in exposed and unexposed areas of NS were investigated in the scar-free group. HS fibroblasts (HFB) were cultured in medium with various reduced levels of metal elements to determine the influence of metal elements on fibroblast growth. RESULTS Levels of trace elements, including Zn, Fe, and Cu, were significantly lower in HS than in FS. The levels of Ca, Zn, Fe, and Cu were markedly lower in HS than in the patients' own NS, while the Cu/Zn ratio was higher. However, no such difference was observed in the FS group. No significant difference in element levels was found in either plasma or NS among the 3 groups. Reduced levels of the elements promoted HFB proliferation within 24 h while an inhibition effect was observed at 72 h. CONCLUSIONS Our findings indicate reduced levels of metal elements in part of the healing microenvironment, suggesting that decreased metal levels may be involved in the pathogenesis of HS.

The crystal quality evolution of AlN films via high-temperature (HT) annealing under nitrogen is investigated. It is found that the best crystal quality can be realized using an optimized combination of the annealing temperature at 1700 °C and an AlN thickness of 540 nm, respectively. Thus the X-ray diffraction ω-scan full width at half maximum (FWHM) values of 59 and 284 arcsec for (0002) and (102) diffractions were achieved, respectively. It is verified that the significant reduction in the threading dislocation density (TDD) via HT annealing starts from the interface zone between AlN and sapphire anterior to the zone far from the interface, which is caused by less energy being required to decrease the larger twist angle among the columns in the interface zone. Benefiting from the low-TDD annealed AlN template, the internal quantum efficiency of the 282-nm AlGaN-based multiple quantum wells reached 57% at 300 K.

In the past few years, exosomes released from adipose-derived stem cells (abbreviated as ADSCs) have shown promises to provide therapeutic benefits in the fields of regenerative medicine. miRNAs, existing in exosomes, are endogenous, small noncoding RNAs that play important roles in a variety of cellular functions and tumor development. Emerging evidences have indicated that miR-21 is one of the important miRNAs associated with tumor angiogenesis. In this study, we identified the role of exosomes from ADSCs overexpressing miR-21 in regulating/promoting vascularization of endothelial cells. Experimental data indicated an elevated miR-21 level in exosomes released by ADSCs overexpressing miR-21. In vitro matrigel angiogenesis assay showed that exosomes secreted by ADSCs overexpressing miR-21 significantly promoted the vascularization of HUVEC cells (an endothelial cell line). Quantitative real-time polymerase chain reaction (qRT-PCR) and western blot (WB) revealed an upregulation of HIF-1α, VEGF, SDF-1, p-Akt, p-ERK1/2 and downregulation of PTEN in response to miR-21 overexpression, indicating that miR-21 enriched exosomes induced angiogenesis through Akt and ERK activation and also HIF-1α and SDF-1 expression. Our work suggests that exosomes from ADSCs that overexpressing miR-21 can potentially promote vascularization and therefore the transplantation of exosomes from their culture may be suitable for clinical effort in regenerative medicine.

Improving the contact characteristics of Ti/Al/Ni/Au on plasma etched n-AlGaN has been attempted by an active pretreatment, which can provide Si and N atoms to occupy the possible metal and N vacancies. It is found that the contacts on both the as-grown and plasma-etched + pretreatment n-Al0.5Ga0.5N present truly Ohmic in nature, whereas the contacts on plasma-etched samples without pretreatment still remain rectifying. Surface atomic concentration analysis indicates that the plasma etching induced N or metal vacancies mostly act as acceptor-like states, leading to a severe compensation. Fortunately, these states can be effectively removed by the presently proposed pretreatment, and thus the Fermi level is raised up toward the conduction band edge, ensuring the formation of Ohmic contacts.

Keloids exhibit metabolic reprogramming including enhanced glycolysis and attenuated oxidative phosphorylation. Hypoxia induces a series of protective responses in mammalian cells. However, the metabolic phenotype of keloid fibroblasts under hypoxic conditions remains to be elucidated. The present study aimed to investigate glycolytic activity, mitochondrial function and morphology, and the HIF1α and PI3K/AKT signaling pathways in keloid fibroblasts (KFB) under hypoxic conditions. Our results showed that hypoxia promoted proliferation, migration invasion and collagen synthesis and inhibited apoptosis in KFB. The mRNA levels, protein expressions and enzyme activities of glycolytic enzymes in KFB were higher than those in normal skin fibroblasts (NFB) under normoxia. Moreover, hypoxia remarkedly upregulated glycolysis in KFB. Decreased activities of mitochondrial complexes and abnormal mitochondria were detected in KFB under normoxic conditions and the damage was aggravated by hypoxia. An intracellular metabolic profile assay suggested hypoxia increased glycolytic parameters except glycolytic reserve but inhibited the key parameters of mitochondrial function apart from H+ leak. Protein levels of HIF1α and phosphorylation levels of the PI3K/AKT signaling pathway were upregulated in the context of 3% oxygen. Enhanced total reactive oxygen species (ROS), mitochondrial ROS (mitoROS) and antioxidant activities of KFB were observed in response to hypoxia. Additionally, autophagy was induced by hypoxia. Our data collectively demonstrated potentiated glycolysis and attenuated mitochondrial function under hypoxia, indicating that altered glucose metabolism regulated by hypoxia could be a therapeutic target for keloids.

We demonstrate the growth of full-composition-graded InxGa1−xN (0 ≤ x ≤ 1) on a GaN/sapphire template using plasma-assisted molecular beam epitaxy. Composition of indium in InxGa1−xN films is controlled by growth temperature and gallium flux. It was found that In composition increases gradually from x = 0 (GaN) to x = 1 (InN) along the growth direction accompanied by a gradual strain relaxation. At the initial stage of growth, multiple quantum wells like structures with low and high In composition InxGa1−xN layers are spontaneously formed, effectively relaxing the in-plane strain. Finally, the graded InxGa1−xN film exhibits a broadband absorption covering the full solar spectrum, which provides a promising path for the design and production of graded InxGa1−xN based photovoltaic devices.

Background: Large-scale muscle tissue engineering remains a major challenge. An axial vascular pedicle and perfusion bioreactor are necessary for the development and maintenance of large-scale engineered muscle to ensure circulation within the construct. We aimed to develop a novel experimental model of a large-scale engineered muscle flap from an existing rat groin fat flap. Methods: A fat flap based on the superficial inferior epigastric vascular pedicle was excised from rats and placed into a perfusion bioreactor. The flaps were kept in the bioreactor for up to 7 weeks, and transdifferentiation of adipose to muscle tissue could have taken place. This system enabled myogenic-differentiation medium flow through the bioreactor at constant pH and oxygen concentration. Assessment of viability was performed by an immunofluorescence assay, histological staining, a calcein-based live/dead test, and through determination of RNA quantity and quality after 1, 3, 5, and 7 weeks. Results: Immunofluorescence staining showed that smooth muscle around vessels was still intact without signs of necrosis or atrophy. The visual assessment of viability by the calcein-based live/dead test revealed viability of the rat adipose tissue preserved in the bioreactor system with permanent perfusion. RNA samples from different experimental conditions were quantified by spectrophotometry, and intact bands of 18S and 28S rRNA were detected by gel electrophoresis, indicating that degradation of RNA was minimal. Conclusions: Flow perfusion maintains the long-term viability of a rat groin engineered muscle flap in vitro, and a large-scale vascularized muscle could be engineered in a perfusion bioreactor. Key words: Culture Ex vivo; Flow Perfusion; Perfusion Bioreactor; Tissue Engineering

We report on a GaN/AlN quantum cascade detector operating in an extended spectral range going from the mid-infrared to visible wavelengths. This broadband detection is achieved thanks to the design of active quantum wells supporting five bound-to-bound intersubband transitions. The photodetector exhibits a broad signal between 4.1 μm and 550 nm. The photocurrent persists up to room temperature. The calibrated responsivity at 77 K under irradiation through a 45° angle polished facet amounts to 7 μA/W at a wavelength of 633 nm and is peaked at 14 μA/W at a wavelength of 720 nm.

The effect of high temperature annealing (HTA) on crystalline quality improvement of h-BN films grown on sapphire substrates has been investigated. It is found that BN grown using conventional molecular beam epitaxy is disordered due to the growth temperature below 1000 °C. By annealing at a temperature of 1700 °C, thermodynamically stable crystalline h-BN could be obtained at wafer scale, where diffusion of atoms in the as-grown BN film is enhanced and the structural defect density decreases. The crystalline h-BN has been confirmed by x-ray diffraction, Raman scattering, and atomic force microscopy measurements. This work demonstrates that HTA is a simple and effective way to achieve wafer-scale crystalline h-BN films, which have numerous potential applications in next-generation two-dimensional devices and flexible III-nitride optoelectronic devices.

To compare the differences of mitochondrial functions between keloid fibroblasts and normal skin fibroblasts and explore its relationship with cell proliferation.Keloid fibroblasts (KFb) and normal skin fibroblasts (NFb) were isolated by explants culture method. KFb and NFb were cultured under normoxia or hypoxia (2％ O2).Differences of cell proliferation were detected by CCK-8.Flow cytometer was used to detect the content of mitochondria and reactive oxygen species (ROS) in KFb and NFb. Ultra-structures of mitochondria in KFb and NFb were observed by transmission electron microscope (TEM).Mitochondria fusion/fission related genes MFN1,MFN2 and FIS1 were detected by RT-PCR. Oxygen consumption rate, lactate production and ATP contents were determined by spectrophotometry.KFb showed a higher proliferation rate compared with NFb, especially under hypoxia. The oxygen consumption rate, ATP content, lactate production and ROS of KFb were lower than NFb under normoxia. After incubated under hypoxia, there was a significant increase in oxygen consumption, ATP content, lactate production and ROS in KFb, while NFb showed less increase compared with KFb. KFb had 15.33％ more mitochondrion than NFb, and expressions of MFN1, MFN2, FIS1 in KFb were 33.27％,113.39％ and 20.34％ higher compared with NFb. Under TEM, KFb showed an increase of enlarged mitochondrion, with disrupted inner membrane and loss of cristae.KFb may have dysfunctions of mitochondrion which lead to changes of cell metabolism and continuous proliferation of KFb.

To explore the effect of simvastatin on the proliferation, apoptosis and protein expressions of keloid fibroblasts under normoxia,hypoxia or TGF-β1 treatment.Keloid fibroblasts (KFs) were isolated by explants culture method. KFs were treated with different concentrations of simvastatin under normoxia or hypoxia (2％ O2) for 24 h and 48 h. The effects of simvastatin on cell proliferation were detected by CCK-8.Flow cytometer was used to detect the apoptosis of KFs treated with 10 μ mol/L simvastatin for 24 h or 48 h under normoxia, hypoxia or 10 ng/ml TGF-β1 treatment. Then the expressions of keloid-related proteins were analyzed by Western Blot.It showed that simvastatin could inhibit the proliferation of KFs in a concentration-and time-dependent manner with the concentration range of 10-500 μ mol/L for 24 h and 0.1-500 μ mol/L for 48 h. This inhibitory effect could be significantly enhanced when cells were incubated under hypoxia for 48h with 10-500 μ mol/L simvastatin.10 μ mol/L simvastatin could not influence the apoptosis of KFs under normoxia or TGF-β1 treatment, neither incubated for 24 h nor 48 h.When incubated under hypoxia,10 μ mol/L simvastatin could significantly induce the apoptosis of KFs, with the rate of 155.6％ for 24 h and 478.8％ for 48 h, compared with no-drug control. There are no significant influences on the expression of type Ⅰ collagen, CTGF or TIMP-1 when KFs were treated with 10 μ mol/L simvastatin under normoxia for 48 h. When incubated with 10 ng/ml TGF-β1 together with 10 μmol/L simvastatin for 48 h, the expression of CTGF was significantly inhibited. KFs treated with 10 μ mol/L simvastatin under hypoxia for 48 h showed a significant decrease of type Ⅰ collagen and CTGF, and a significant increase of TIMP-1.Simvastatin has different effects on the proliferation, apoptosis and protein expressions of KFs in a dosedependent manner under different conditions. The effects are enhanced under hypoxia.

MicroRNAs are endogenous single-stranded non-coding small RNA molecules that can be secreted into the circulation and exist stably. They usually exhibit aberrant expression under different physiological and pathological conditions. Recently, differentially expressed circulating microRNAs were focused on as potential biomarkers for cancer screening. We herein review the role of circulating microRNAs for cancer diagnosis, tumor subtype classification, chemo- or radio-resistance monitoring, and outcome prognosis. Moreover, circulating microRNAs still have several issues hindering their reliability for the practical clinical application. Future studies need to elucidate further potential application of circulating microRNAs as specific and sensitive markers for clinical diagnosis or prognosis in cancers.

Epitaxial growth of AlN films on c-sapphire using a multilayer structure has been investigated by metal–organic chemical vapor deposition adopting multiple alternation cycles of low- and high-temperature (LT–HT) growth. It is found that the surface morphology and crystal quality can be greatly improved using three alternation cycles with X-ray diffraction ω-scan full width at half maximum values of 311 and 548 arcsec for the (0002) and (10−12) peaks, respectively, which are induced by the alternation of the three-dimensional (3D) and two-dimensional (2D) growth modes caused by the LT–HT process. The first 3D–2D cycle is found to play a major role in threading dislocation reduction, while the second and third cycles mainly account for tensile stress relaxation.

Periostin, a secreted extracellular matrix protein, is highly expressed in wound healing and in various types of human cancer and is involved in angiogenesis. Keloids, considered dermal benign tumors, are granulomatous lesions characterized by capillary proliferation. However, the underlying regulatory mechanism of angiogenesis in keloids remains to be elucidated. The present study aimed to examine the effect of periostin on angiogenesis in keloids. The expression of periostin was upregulated and the vessel density was higher in human keloids compared with normal tissue, observed following staining with CD31 and CD105. Periostin demonstrated a markedly positive correlation with blood vessel density, which was assessed using CD31 staining (r=0.711; P

Methods to facilitate topical anesthesia for venipuncture are characterized by substantial limitations. This randomized double-blind study was undertaken to assess whether use of a quickly and painlessly applied microneedle system (functional microarray, FMA) to create punctures in the stratum corneum facilitates topical anesthesia in healthy adults. In 25 volunteers receiving topical dyclonine, FMA was applied to one forearm and a sham device in the other, followed by assessment of pain levels associated with application of a standardized stimulus at 5-minute intervals over an hour. Analysis of the primary end point, time required to achieve a significant degree of pain reduction (13 mm on a 100-mm scale), revealed that FMA significantly sped time to pain reduction (log-rank P = .007). Functional microarray also resulted in a greater degree of pain reduction (Kruskal-Wallis P < .0001). Functional microarray application had no adverse effects, and the device shows promise for facilitation of topical anesthesia.

The influence of the annealing pressure of the nucleation layer (NL) on the resistance of GaN films grown on sapphire by means of metal-organic chemical vapor deposition has been investigated. It is found that the sheet resistance of GaN increases significantly with decreasing the annealing pressure. When the annealing pressure is 10 kPa, GaN with sheet resistance higher than 1011 Ω/sq is achieved. It is determined that the edge-component threading dislocations (ETDs) rather than the screw-component ones are the dominant structural feature responsible for the resistance variation. Based on the analysis of in-situ reflectance and atomic force microscopy, it is believed that the island density and island size in the NL are the key factors accounting for the resistance variation in GaN. The high island density and small island size in the NL not only lead to more ETDs in GaN, which introduce more acceptors to compensate the background electrons, but also enhance the rapid coalescence in GaN and thus effectively limit the diffusion of oxygen impurities into GaN epilayers from GaN/sapphire interfaces.

Tunneling induced electron transfer in SiN x /Al 0.22 Ga 0.78 N/GaN based metal–insulator–semiconductor (MIS) structures has been investigated by means of capacitance–voltage (C–V) measurements at various temperatures. Large clock-wise hysteresis window in C–V profiles indicates the injection of electrons from the two-dimensional electron gas (2DEG) channel to the SiN x layer. Depletion of the 2DEG at positive bias in the negative sweeping direction indicates that the charges injected have a long decay time, which was also observed in the recovery process of the capacitance after injection. The tunneling induced electron transfer effect in SiN x /Al 0.22 Ga 0.78 N/GaN based MIS structure opens up a way to design Al x Ga 1− x N/GaN based variable capacitors and memory devices.

Effects of the passivation of SiN x on the high temperature transport characteristics of the two-dimensional electron gas (2DEG) in unintentionally doped Al x Ga 1− x N/GaN heterostructures have been investigated by means of high temperature Hall measurements. The 2DEG density increases much after SiN x passivation, and the increment is proportional to the Si content in SiN x layer, indicating that the increment is mainly caused by ionized Si atoms at the SiN/Al x Ga 1− x N interface with dangling bonds or by Si atoms incorporated into the Al x Ga 1− x N layer during the SiN x growth, which is approved by strain analysis and X-ray photoemission spectroscopy (XPS). There is lower 2DEG mobility at room temperature in a passivated sample than in an unpassivated one. However, the 2DEG mobility becomes to be higher in a passivated sample than in an unpassivated one when the temperature is above 250 °C, which is suggested to be caused by different subband occupation ratios in the triangular quantum well at the heterointerface before and after passivation.

The barrier effect of Pt and Ni has been investigated in the Ti/Al/Pt/Au and Ti/Al/Ni/Au Ohmic contacts to n-GaN, respectively. Severe indiffusion of Pt and Au has been found in the 800 °C annealed Au/Pt/Al/Ti/n-GaN samples. However, Ni does not penetrate into the n-GaN and shows better barrier effect for preventing Au penetration into Au/Ni/Al/Ti/n-GaN samples. The reaction between Ga and Pt has also been identified in the samples annealed at 600 °C. At the same time, the electrical degradation was found for the Ti/Al/Pt/Au samples aged at 600 °C. However, no obvious degradation was found for the aged Ti/Al/Ni/Au samples. It is suggested that the reaction between Ga and Pt may cause the electrical degradation of the Ti/Al/Pt/Au metallization system.

In this work, InGaN/GaN multiple quantum well (MQW) light emitting diodes (LEDs) wafer with two emission peaks were grown by metalorganic chemical vapor deposition (MOCVD). X-ray diffraction (XRD), Ruthford backscattering (RBS), cathodoluminescence (CL), electroluminescence (EL) and emission microscope (EM) measurements were performed to study the recombination mechanism of InGaN QWs. The green spots and blue floccules in EM images were assigned to In-rich quantum dots (QDs) and modified QW by piezoelectric field. The wavelengths for both blue and green emissions do not shift until the injection level reach to 2×10 4 mA/cm 2 . In CL images, the modified QWs assigned by EM and EL have a broad band tail expanding to 526 nm.

Utilizing the growth temperature controlled epitaxy, high quality GaN/In0.15Ga0.85N multiple quantum wells designed for intersubband transition (ISBT) as novel candidates in III-nitride infrared device applications have been experimentally realized for the first time. Photo-absorption originated from the ISBT has been successfully observed at infrared regime covering the 3–5 μm atmosphere window, where the central absorption wavelength is modulated by adjusting the quantum well width. With increasing the quantum well thickness, the ISBT center wave length blue shifts at thickness less than 2.8 nm and then redshifts with further increase of the well thickness. The non-monotonic trend is most likely due to the polarization induced asymmetric shape of the quantum wells.

The diffusion barrier effect of Pt has been investigated in Ti/Al/Pt/Au ohmic contacts to n-GaN. Severe indiffusion, outdiffusion of Pt and outdiffusion of Ga have been found in 450 ?C annealed samples according to the Rutherford backscattering spectrometry (RBS) results. At the same time, the reaction between Ga and Pt has also been identified by glancing angle synchrotron irradiation x-ray diffraction (GASIXRD) in the samples annealed at 450 ?C. A higher annealing temperature causes Pt to indiffuse into GaN and react with GaN further. As a result, electrical degradation of the Ti/Al/Pt/Au metallization system was found for samples aged at 600 ?C. In contrast, no obvious degradation was found for the aged Ti/Al/Ni/Au samples. According to the RBS and GASIXRD results, it is suggested that the formation of Ga3Pt5 may cause degradation in the electrical properties of the Ti/Al/Pt/Au metallization system.

s The microstructure evolution of oxidized Ni (20 nm)/Au (20 nm) contact to p-GaN with increasing annealing temperature was studied by synchrotron X-ray diffraction (XRD) and powder XRD. With the increase of annealing temperature, it was observed that the Au on the p-GaN gradually grew on the p-GaN with the orientation relationship of Au(1 1 1)//GaN(0 0 0 2). NiO also had such a orientation relationship of NiO(1 1 1)//GaN(0 0 0 2) at 500 °C and gradually turned back to polycrystalline structure at higher temperature. The orientation relationship of Au, NiO and GaN implied that the epitaxial crystallization might occur during annealing. The specific contact resistance also reduced to the minimum 2.73×10−4 Ω cm2 at 500 °C. Therefore, plausibly the epitaxial crystallization is an important mechanism for lowering the contact resistance between oxidized Ni/Au contacts and p-GaN.

The high-power white light emitting diode (LED) is packaged by GaN-based blue LED chip with the size of 1 x 1 mm 2 , YAG:Ce yellow fluorescer, epoxy and an effective heat sinking. The wavelength of the LED chip emission blue-shifts from 482 to 475 nm, while that of the fluorescer emission does not change in electroluminescence (EL) spectrum when the injection current increases from 5 to 200 mA. And the correlated color temperature decreases from 5300 to 4800 K. When the injection current increases to 200 mA, the luminous power (P e ) increases to 13.8 mW, which is about 10 times of those of the normal size (0.3 x 0.3 mm 2 ) diodes fabricated with the same wafer and same injection density. P e and forward bias (V f ) at 200 mA are measured for the aging high-power white LED. At the beginning, P e decreases dramatically 20% and V f decreases about 0.2 V in 2 days. And then P e and V f decrease slowly in the remaining 79 days aging. The contact metals electro migration along the channels induced by the threading dislocations may be the dominant aging mechanism.

Photoluminescence and Raman scattering spectra of InGaN/GaN MQWs on sapphire and membranes free of substrate fabricated by laser lift-off have been studied. It is observed that photoluminescence peak of 850 °C annealed sample red-shifts from that of as grown sample, while in the case of membrane samples, the luminescence peak blue-shifts when annealed at 700 °C. In Raman scattering spectra, InGaN/GaN MQWs film without sapphire substrate has a lower E 2 mode frequency (569.3 cm -1 ) than that of the films with substrate (570.8 cm -1 ), which indicates that compressive stress in the films releases partially when the sapphire substrate is taken off. It is believed that the piezoelectric field decrease leads to the blue-shift in luminescence spectra. Compared with the samples with sapphire substrate, the free-standing membranes showed blue-shift of luminescence peak after relatively low temperature annealing, because the piezoelectric field reduced more easily in the films without substrate.

The thermal annealing effects on Ti/Al/Ni/Au Ohmic contact to n-GaN are investigated by current–voltage (I–V) characteristics and transmission line method (TLM) measurements. The cladding layer of Ni/Au on Ti/Al plays two roles: preventing inter-diffusion of Ti, Al, Au and anti-oxidation of the contacting layer. The specific contact resistance (ρc) of Ti/Al/Ni/Au to n-GaN increases slightly at first with the increasing annealing temperature (Ta). When Ta increases above 500 °C, ρc decreases monotonously in the range of 400–900 °C. However, the morphology of the contact degrades gradually when Ta increases above 600 °C. The minimum of ρc is obtained as 9.65×10−7 Ω cm2 by two-step annealing method in this work. Finally, the roles of two-step annealing method in the formation mechanism of the Ohmic contact to n-GaN are also discussed.

InGaN/GaN layers have been grown under low pressure by metal-organic vapor phase epitaxy on sapphire substrate. X-ray diffraction (XRD), photoluminescence, and optical absorption measurements have been performed to study the radiative recombination mechanisms in the samples. The In composition was determined by XRD measurement using Vegard's law. With increasing In composition, a red shift of absorption edge and a broad Urbach tail in absorption spectra were observed. The InN inclusions in InGaN played a key role in long-wavelength absorption. There existed large Stokes shifts in all thick InGaN layers with different In compositions. The intensities of low-energy emissions were enhanced compared to those of high-energy ones with increasing In composition. We attributed low-energy emissions to deep levels and high-energy emissions to In-rich quantum dots.

Current–voltage (I–V) characteristics, transmission line method (TLM), and optical transmittance measurements are performed to investigate the effects of thermal oxidation and plasma-induced oxidation treatments on Ni/Au contacts to p-type GaN. Whether oxidation and thermal annealing are performed simultaneously or in succession, the specific contact resistances of Au/Ni/p-GaN are reduced. As to plasma-induced oxidation, neither no-oxidation nor long-time oxidation treatments on Ni/Au layers are suitable for obtaining a low-resistance Ohmic contact. The roles of oxidation are believed to activate the Mg acceptor in p-GaN and to form an oxygenous intermediate semiconductor layer, which may lower the Schottky barrier height between the metal layer and p-GaN. (© 2003 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Current–voltage ( I – V ) characteristics, contact resistance, and optical transmittance measurements are performed to investigate the effects of different annealing ambient conditions on properties of contacts of Ni/Au/p-GaN. With increasing annealing temperature in the range from room temperature to 600 °C in air, I – V characteristics become linear, and the specific contact resistance ( ρ c ) reduces continually. ρ c of Ni (20 nm)/Au (50 nm) contact to p-GaN annealed in air at 600 °C is obtained as 2.76×10 − 2 Ω cm 2 . However, in N 2 ambient, ρ c is higher and shows a more complex evolution with increasing annealing temperature. The optical transmittance of the specimens increases and maintains a high value with the annealing temperature in air while it increases first, and then decreases monotonically in N 2 atmosphere. We suggest that formation of low-resistance and high optical transmittance p-type Ohmic contact may be attributed to the oxidized Ni layer. The mechanism of Ohmic contact formation under different ambient conditions is also discussed.

In this work, InGaN/GaN multi-quantum wells (MQWs) high brightness light emitting diode (LED) was grown by metalorganic chemical deposition (MOCVD). Photoluminescence (PL), X-ray diffraction (XRD), cathodoluminescence (CL), transmission electron microscope (TEM) were performed on the LED wafers to investigate the effects of growth temperature, well width and In composition in the InGaN quantum well on the emitting wavelength of LED. It was found that the wavelength of InGaN MQW-LED shifted from about 400–470 nm due to the difference in the In composition introducing into the InGaN well layer at different growth temperature. It was also demonstrated that the wavelength can be changed from 470 nm to 504 nm only by changed the thickness of the InGaN quantum well layer. Combined with the CL image and TEM observation, it was concluded that the change from MQW structure to multi-quantum dot structure would be the cause of the shift from 470 to 504 nm by changed the InGaN well width.

Plasma-induced damage of n-type GaN in Cl2/CH4/Ar reactants and its recovery by the O2/CHF3 plasma in a reactive ion etching (RIE) system were studied by photoluminescence and Hall measurements. The mobility and optical properties of n-type GaN etched in Cl2/CH4/Ar were degraded gradually with increased radio frequency power. The effects of O2/CHF3 plasma treatment on the electrical and optical properties of n-type etched GaN were investigated by changing the ratio of O2/CHF3 flow rate. It was found that the damage caused by the conventional RIE process could be partly recovered by O2/CHF3 plasma treatment. The recovery mechanism was also discussed.

The evolution of wing tilt in laterally and epitaxially overgrown (LEO) GaN thick film was studied using cross-sectional transmission electron microscope (TEM) observation and high-resolution X-ray diffraction (XRD). The LEO GaN film was grown by hydride vapor epitaxy (HVPE) on Si(1 1 1) substrate. Horizontally propagating dislocations (HDs) and low density of threading dislocation (TD) in LEO wings were observed in TEM micrographs. Tilt of LEO wing to the GaN seed region was measured as 3.3° at interface of HVPE–GaN/metal organic vapor phase epitaxy (MOVPE)–GaN by selective area electron diffraction, which is much more than that in the surface region estimated as 0.4° by XRD measurements. With φ-scan XRD technique, we found that there exist many differences of tilts and twists of c-axis between the opposite wings on each mask. Asymmetry growth of the opposite wings on SiO2 mask may be due to the flow asymmetry of precursor in vertical reactor. The tilting generation and diminishing increasing with film thickness was discussed too.

In this paper, the interface structure of GaN/α-Al2O3 (0 0 0 1) is studied by high-resolution transmission electron microscopy on tilted samples around the 〈1 1 2 0〉 Al 2 O 3 axis. Sets of moire fringes are observed. There are many disparities, such as contrast, period, tilt angle, and so on, among these moire fringes located in different regions. These fringes represent magnifying images of the plane distances of (1 1 0 0) GaN and the tilts of c-axis of GaN crystallites to that of the substrate. According to these results, the growth mechanism of GaN buffer layer at the interface is discussed.

The amount of InN included in InGaN films grown by MOCVD (metalorganic chemical vapor deposition) was estimated by X-ray diffraction measurement technology. The In compositions in our InGaN films are measured as 0.1–0.34 by X-ray 2θ scan using Vegard’s law. The inclusion of InN in InGaN layers was obtained as 0.0684–2.6396% by measuring the ratio of the integrated intensity of the InN (0002) peak to that of the InGaN (0002) peak in X-ray rocking curves. The theoretical diffraction intensities from InN and InGaN have been calculated according to the X-ray-diffraction theory. The values of the InN inclusion for all our samples were less than 3%, which indicated that the degree of phase separation of the samples was low. It was also found that the flow rate of N2 carrier gas and the operation pressure strongly affected the InN inclusion in InGaN.