bluuebunny/crossref_metadata_2025 huggingface dataset:
Thick InGaN Growth by Metal Organic Vapor Phase Epitaxy with Sputtered InGaN Buffer Layer
Authors: Ohata Toshiya , Honda Yoshio , Yamaguchi Masahito , Amano Hiroshi
Published: May 2013

A thick InGaN film was grown on a sapphire substrate by metal organic vapor phase epitaxy using a thin buffer layer of sputter-deposited InGaN. A thick film of highly luminescent In0.2Ga0.8N can be successfully grown at a rate as high as 2 µm/h. The crystal quality of InGaN grown on the sputter-deposited InGaN buffer layer was better than that of InGaN grown directly on the sapphire substrate. The sample showed n-type conduction with a carrier concentration and mobility of 5×1018 cm-3 and 3 cm2/(V·s), respectively.
Correlations between Epitaxy Recipe, Characteristics, and Performance of Nitride Light Emitting Diode Structures
Authors: Yakovlev Eugene V. , Segal Alexander S. , Bulashevich Kirill A. , Karpov Sergey Yu. , Talalaev Roman A.
Published: May 2013

Metal–organic vapor phase epitaxy of III–nitride light-emitting diode (LED) structures is analyzed by coupled process-device modeling. Different recipes to grow active regions of the structures are examined. The major attention is given to the impact of process recipe on indium composition profile in the active region. Correlations between the composition profiles and device characteristics are discussed. We have focused on the analysis of LED structures with short-period superlattice active regions providing improved efficiency, reduced efficiency droop, and high emission wavelength stability with current. Performances of the structures grown with various recipes are compared to find the most promising growth procedure and evaluate its impact on the operation of the LED heterostructure.
New Model of Fe Diffusion in Highly Resistive Fe-Doped Buffer Layer for GaN High-Electron-Mobility Transistor
Authors: Ishiguro Tetsuro , Yamada Atsushi , Kotani Junji , Nakamura Norikazu , Kikkawa Toshihide , Watanabe Keiji , Imanishi Kenji
Published: May 2013

We demonstrated the suppression of Fe incorporation into undoped GaN layers grown on an Fe-doped GaN layer by metal organic chemical vapor deposition (MOCVD). Our systematic study of the depth profile of Fe doping by secondary-ion mass spectrometry (SIMS) revealed that Fe segregation on the growth surface is responsible for Fe incorporation into the upper undoped GaN layer. Moreover, we confirmed from the Fe doping profiles of strain-varied undoped GaN layers grown on an Fe-doped Al
x
Ga1-x
N layer that the compressive strain on the growth surface could effectively suppress Fe segregation. In this study, we propose a new model showing that the suppression is due to an increase in the extent of thermal desorption of Fe from the growth surface by compressive strain.
Improving the Quality of GaN on Si(111) Substrate with a Medium-Temperature/High-Temperature Bilayer AlN Buffer
Authors: Xiang Peng , Liu Minggang , Yang Yibin , Chen Weijie , He Zhiyuan , Leung Ka Kuen , Surya Charles , Han Xiaobiao , Wu Zhisheng , Liu Yang , Zhang Baijun
Published: May 2013

A medium-temperature/high-temperature (MT/HT) bilayer AlN buffer was introduced for GaN grown on Si(111) by metal organic chemical vapor deposition. The properties of the GaN films with a MT/HT bilayer AlN buffer and those with a single-layer HT-AlN buffer were compared and the influence of the growth temperature of the MT-AlN layer was investigated. With a MT-AlN layer grown in the temperature range from 800 to 1000 °C, the crystalline qualities of the subsequent HT-AlN layer and the GaN film were improved. According to the X-ray diffraction results and the transmission electron microscopy images, the dislocation density in GaN film was reduced with a MT/HT bilayer AlN buffer as compared to those with a single-layer HT-AlN buffer. Moreover, photoluminescence and Raman spectra exhibit enhanced optical properties and less tensile stresses of the GaN film. Better surface morphology of GaN was also obtained with a MT/HT bilayer AlN buffer.
Catalyst Temperature Dependence of NH3 Decomposition for InN Grown by Metal Organic Vapor Phase Epitaxy
Authors: Sugita Kenichi , Hironaga Daizo , Mihara Akihiro , Hashimoto Akihiro , Yamamoto Akio
Published: May 2013

In this paper, we report an independent catalyst heating system on the Pt-catalyst metal organic vapor phase epitaxy (MOVPE) for Indium nitride (InN) growth, and the dependence of the NH3 decomposition rate on the Pt catalyst temperature (RT to 1000 °C) using a quadrupole mass spectrometer (Q-MS). When the catalyst temperature is increased above the growth temperature of InN, the NH3 decomposition rate is enhanced. The grain size of InN becomes larger and the full width at half maximum (FWHM) of the X-ray rocking curve (XRC) was drastically decreased. The increase of N atoms results in the incorporation of nitrogen into the InN layer and thus improves the crystal quality of InN. However, active H increases sharply when the catalyst heater temperature is over about 850 °C. Therefore, a great improvement in the crystal quality of InN film is expected by optimizing the growth condition including a catalyst temperature not exceeding 850 °C.
Thickness Dependence of Structural and Electrical Properties of Thin InN Grown by Radio-Frequency Plasma-Assisted Molecular Beam Epitaxy
Authors: Sakaguchi Junichi , Araki Tsutomu , Fujishima Tatsuya , Matioli Elison , Palacios Tomás , Nanishi Yasushi
Published: May 2013

We have succeeded in achieving high-quality thin InN films (<500 nm) by low-plasma-power growth. In this study, we investigated the thickness dependence of the structural and electrical properties of relatively thin InN films grown by radio-frequency plasma-assisted molecular beam epitaxy (RF-MBE). InN films were grown by RF-MBE on GaN/sapphire templates at 80 W, which is lower than that for conventional InN growth (200 W). The films had thicknesses of 5, 20, 100, 200, and 460 nm. The mobility and carrier concentration of InN degraded with decreasing InN film thickness, although even 200-nm-thick InN demonstrated relatively good characteristics (µ= 1540 cm2 V-1 s-1 and n= 2.1 ×1018 cm-3). On the other hand, the FWHM values of the (002) and (302) X-ray rocking curves (XRCs) were minimum in 5-nm-thick InN and increased with film thickness up to approximately 100–200 nm. This seems to be due to the formation of small grains with better crystal quality at the initial stage. It is also suggested that these grain structures with poor coalescence and roughness caused the deterioration of InN electronic properties in a very thin region.
A Comparative Study of Hydrogen Implantation Induced Blistering and Exfoliation in GaN and AlN
Authors: Dadwal Uday , Singh Rajendra
Published: May 2013

GaN and AlN epitaxial layers were implanted with 100 keV H+ ions at implantation temperatures of RT and 300 °C. The GaN and AlN were H-implanted with fluence of 2.5 ×1017 and 1 ×1017 cm-2, respectively, in order to observe the surface blistering. The morphological investigations revealed that post-implantation annealing resulted in the formation of small size surface blisters with lower exfoliation depth in GaN compared to AlN for the implantation at RT. However, for the implantation at 300 °C, blistering occurred in the as-implanted GaN, whereas large area exfoliation was observed in AlN after annealing. Transmission electron microscopy (TEM) images showed formation of narrower damage band in AlN (as compared to GaN) filled with H-induced nanovoids. This comparative study has shown that H-induced damage and depth distribution of the implanted hydrogen was responsible for the nature of surface buckling in H-implanted GaN and AlN.
ZnO Thick Film Growth on n-GaN by Photoassisted Electrodeposition
Authors: Uno Kazuyuki , Tauchi Yasuhiro , Tanaka Ichiro
Published: May 2013

Zinc oxide (ZnO) thick film growth on n-GaN using an electrodeposition technique was investigated. Although the reaction temperature is about 70 °C in cathodic electrodeposition, ZnO can grow epitaxially on GaN owing to their small lattice mismatch. However, the quality of grown ZnO is too high for electrons to be supplied from the substrate. As a consequence, the electrodeposition can continue for only 50 min. On the other hand, in the case of the growth of ZnO on highly oriented pyrolytic graphite (HOPG), the electrochemical reaction can continue for over 15 h owing to the supply of electrons via grain boundaries or defects. For a long continuous electrochemical reaction, we supply electrons to the surface by light excitation using a Xe lamp. A stable electrochemical reaction is realized and a 5-µm-thick ZnO film with high uniformity is obtained.
Photocurrent Phenomena in Nanoribbon InAlN/GaN High Electron Mobility Transistors
Authors: González-Posada Fernando , Azize Mohamed , Gao Xiang , Guo Shiping , Monroy Eva , Palacios Tomás
Published: May 2013

High electron mobility transistors (HEMTs) based on InAlN/GaN nanoribbon (NR) structures appear as a new technology which can deliver record current densities. Ultraviolet (UV) photodetectors based on ungated InAlN/GaN NR HEMT structures have a gain in the range of the 105–107, a sublinear behaviour with the excitation power and a UV/visible contrast of more than three orders of magnitude. In spite of the larger surface-to-volume ratio, sublinearities and persistent photocurrent effects are less intense in NR structures compared to planar devices, and they decrease at higher excitation power. The asymmetric NR morphology does not induce a preferential coupling of polarized light in the NR structure; since light is mostly absorbed in the GaN buffer layer and photogenerated charges are efficiently collected by the HEMT channel.
Temperature and Light Intensity Dependence of Photocurrent Transport Mechanisms in InGaN p–i–n Homojunction Solar Cells
Authors: Sang Liwen , Liao Meiyong , Koide Yasuo , Sumiya Masatomo
Published: May 2013

The photovoltaic (PV) properties of the InGaN p–i–n homojunction solar cell are investigated at different temperatures and light intensities. With increasing temperature, the dark current–voltage (I–V) behaviors display a large variation especially at the forward voltage near the open-circuit voltage (Voc) region, which leads to a great degradation of theVocat high temperatures. The short-circuit current density (Jsc) first increases and then decreases as temperature increases. The photocurrent transport mechanisms at different temperatures and light intensities are analyzed by fitting theI–Vcurves using different carriers transport models. The traps inside the p–i–n junction especially in the p-type region tend to be activated at elevated temperatures above 338 K, which increase the recombination and reduceJsc. The conversion efficiencies of the solar cell are mainly affected byVoc, which degrades rapidly with elevated temperatures.
Electrical and Optical Properties of a High-Voltage Large Area Blue Light-Emitting Diode
Authors: Wang Wang , Wei Wei , Cai Cai , Yong Yong , Huang Huang , Wei Wei , Li Li , Hai-ou Hai-ou , Zhang Zhang , Bao-shun Bao-shun
Published: May 2013

In this paper, we report a single-chip large area (5×5 mm2) InGaN/GaN blue LED with the optical output power of 4.3 W. This device consists of 24-stages small LED-cells that are connected in series. Driven at 500 mA, the forward voltage is measured to be 87.2 V with a reverse current of 2.63×10-9 A at -120 V. The comparison of two different cooling schemes, i.e., with/without fan cooling, was made; the results suggest that the thermal convection between the heat sink and air is more critical. A simple white LED package was also tried by covering silicone gel mixed with yttrium aluminum garnet (YAG) phosphor. The luminous flux and the correlated color temperature (CCT) were measured to be 1090 lm and 5082 K, when the device was driven at 500 mA. This report also demonstrated the feasibility of the application for camera flash.
Electroluminescence Analysis and Simulation of the Effects of Injection and Temperature on Carrier Distribution in InGaN-Based Light-Emitting Diodes with Color-Coded Quantum Wells
Authors: Meneghini Matteo , Vaccari Simone , Garbujo Alessio , Trivellin Nicola , Zhu Dandan , Humphreys Colin J. , Calciati Marco , Goano Michele , Bertazzi Francesco , Ghione Giovanni , Bellotti Enrico , Meneghesso Gaudenzio , Zanoni Enrico
Published: May 2013

This paper reports on an extensive analysis of the electroluminescence characteristics of InGaN-based LEDs with color-coded structure, i.e., with a triple quantum well structure in which each quantum well has a different indium content. The analysis is based on combined electroluminescence measurements and two-dimensional simulations, carried out at different current and temperature levels. Results indicate that (i) the efficiency of each of the quantum wells strongly depends on device operating conditions (current and temperature); (ii) at low current and temperature levels, only the quantum well closer to the p-side has a significant emission; (iii) emission from the other quantum wells is favored at high current levels. The role of carrier injection, hole mobility, carrier density and non-radiative recombination in determining the relative intensity of the quantum wells is discussed in the text.
Green and Red Light-Emitting Diodes Based on Multilayer InGaN/GaN Dots Grown by Growth Interruption Method
Authors: Lv Wenbin , Wang Lai , Wang Jiaxing , Xing Yuchen , Zheng Jiyuan , Yang Di , Hao Zhibiao , Luo Yi
Published: May 2013

We have successfully implemented green and red light-emitting diodes (LEDs) based on InGaN/GaN quantum dots (QDs) grown by controlling the process of the growth interruption method using metal organic vapor phase epitaxy (MOVPE). It is found that the three-step growth interruption method and the underlying InGaN/GaN superlattice structure are beneficial for achieving greater indium incorporation in InGaN QDs. As a result, green and red LEDs with electroluminescence (EL) peak energies of 2.28 eV at 20 mA and 1.70 eV at 80 mA, respectively, are demonstrated. The EL emission energy blue shift of the green QD LEDs is 140 meV as injection current increases from 5 to 50 mA, while that of the red LED is 70 meV as injection current increases from 75 to 100 mA.
Substrate Lifted-off AlGaN/AlGaN Lateral Conduction Thin-Film Light-Emitting Diodes Operating at 285 nm
Authors: Asif Fatima , Chen Hung-Chi , Coleman Antwon , Lachab Mohamed , Ahmad Iftikhar , Zhang Bin , Fareed Qhalid , Adivarahan Vinod , Khan Asif
Published: May 2013

We report on the substrate laser lift-off (LLO) in lateral conduction flip-chip (FC) deep-UV light-emitting diodes (LEDs) with peak emission wavelength at 285 nm. The AlGaN-based LED epilayer structure was grown on a low-defect 2 µm-thick AlN/sapphire template and processed into 3×3 small periphery pixel-LED arrays. The total p-contact area of the 9 pixel, single chip devices was 180 ×180 µm2. Our results show that the use of FC die assembly with epoxy underfilling the gap between the chip and the submount dramatically increase the yield of damage-free debonding of sapphire and the overlying AlN layer. Equally important, no noticeable degradation of the electrical and optical characteristics of the thin-film light emitters was observed following the LLO process.
1-µm Micro-Lens Array on Flip-Chip Light-Emitting Diode
Authors: Li Kwai Hei , Zhang Qian , Choi Hoi Wai
Published: May 2013

The fabrication of hexagonally close-packed micro-lens array on sapphire face of flip-chip bonded LED by nanosphere lithography is demonstrated. Self-assembled silica spheres serve as an etch mask to transfer hemispherical geometry onto the sapphire. The optical and electrical properties are evaluated. Without degrading the current–voltage (I–V) properties, the lensed LED shows an enhancement of 27.8% on light output power, compared with unpatterned LED. The emission characteristic is also investigated by performing finite-difference time-domain simulation, which is found to be consistent with the experimental results.
Effect of Inductively Coupled Plasma Etching in p-Type GaN Schottky Contacts
Authors: Shiojima Kenji , Takahashi Toshifumi , Kaneda Naoki , Mishima Tomoyoshi , Nomoto Kazuki
Published: May 2013

The effects of inductively coupled plasma (ICP) etching damage on the electrical characteristics of low-Mg-doped p-GaN Schottky contacts were evaluated. The ICP etching greatly reduced the memory effect in the current–voltage characteristics and the difference between the depletion layer capacitances before and after forward current injection. These reductions indicate that acceptor-type interfacial defects were passivated by H atoms during ICP etching. Additionally, photoresponse (PR) measurements revealed that Schottky barrier height was increased from 2.08 to 2.63 eV by the etching. Because of the surface state change, the Fermi level position would be moved toward the conduction band edge slightly by the etching. After annealing, the memory effect and the capacitance change were partially restored, and the PR spectra showed less variation. Absorbed H atoms on the p-GaN surface might be released by annealing.
Direct Observation of Charge Carrier Diffusion and Localization in an InGaN Multi Quantum Well
Authors: Solowan Hans-Michael , Danhof Julia , Schwarz Ulrich T.
Published: May 2013

The temperature dependence of the diffusion constant of an InGaN/GaN multi quantum well (MQW) emitting at 465 nm is studied by time of flight measurements. Utilizing a confocal microscopy setup and scanning the pinhole across the image plane allows us to observe charge carrier diffusion in real space with submicron resolution and to determine the diffusion constant by fitting the time delays of the spatially dependent photoluminescence signal using a simple diffusion model. We see direct evidence for a strong decrease of charge carrier mobility below 110 K and for localization of charge carriers at 10 K. The diffusion constant increases continuously with temperature up to about 0.27 cm2 s-1 at 293 K.
Femtosecond Laser Etching of GaN and InGaN Thin Films Grown by Metal Organic Chemical Vapor Deposition
Authors: Ščiuka Mindaugas , Grinys Tomas , Dmukauskas Mantas , Plerpaitė Viktorija , Melninkaitis Andrius
Published: May 2013

In this work a possibility of selective GaN and InGaN layer etching via femtosecond laser ablation was investigated. The samples of different indium concentrations were grown by metal organic chemical vapor deposition (MOCVD) technique on sapphire substrates. Prior to the laser treatment all samples were characterized by the means of photoluminescence and X-ray diffraction techniques. Further the laser-induced damage thresholds (LIDT) were estimated in multiple pulse (S-on-1) and single pulse (1-on-1) regimes for 1030, 515, and 343 nm wavelengths covering NIR–UV spectral regions. Experimental results indicated a strong interrelation between LIDT, indium concentration and band-gap. An abrupt change in single pulse LIDT is observed when the multi-photon absorption experiences transition from three to two photon absorption. Furthermore an overview of typical laser induced damage morphologies is performed and discussed. A selective smooth etching of GaN and InGaN layers was obtained when exposing with multiple pulses in UV range.
High Internal Quantum Efficiency Blue-Green Light-Emitting Diode with Small Efficiency Droop Fabricated on Low Dislocation Density GaN Substrate
Authors: Sano Tomotaka , Doi Tomohiro , Inada Shunko Albano , Sugiyama Tomohiko , Honda Yoshio , Amano Hiroshi , Yoshino Takashi
Published: May 2013

We fabricated blue (∼450 nm), blue-green (∼500 nm), and green (∼525 nm) light-emitting diodes (LEDs) of different dislocation densities (DD) and characterized their internal quantum efficiency (IQE). The IQE of the blue LEDs fabricated using GaN substrate exceeded 90% (DD: ∼106cm-2), however, when we used a GaN-on-sapphire substrate (DD: ∼108cm-2), IQE was limited to ∼60%. Droop was reduced by use of the GaN substrate. The junction temperature of the GaN-on-sapphire substrate was found to be ∼200 °C although the junction temperature of the GaN substrate was ∼50 °C when a forward current of 100 A/cm2was driven. A lowering of IQE in green LEDs to ∼60% was observed, even though we used a low-dislocation-density substrate [DD: (1–2)×107cm-2]. The junction temperature of blue-green and green LEDs was about 100 °C when a forward current of 177 A/cm2was driven, which indicated that junction temperature is not a major factor for IQE suppression in green LEDs.
Carrier Density Dependent Localization and Consequences for Efficiency Droop in InGaN/GaN Quantum Well Structures
Authors: Badcock Tom J. , Hammersley Simon , Watson-Parris Duncan , Dawson Phil , Godfrey Mike J. , Kappers Menno J. , McAleese Clifford , Oliver Rachel A. , Humphreys Colin J.
Published: May 2013

We report on the observation of a reduction in the depth of the S-shape in the temperature dependence of the photoluminescence peak energy with increasing excitation power density. Over the range of excitation power density where the depth of the S-shape is reduced, we also observe a reduction in the integrated photoluminescence intensity per unit excitation power, i.e., efficiency droop. Hence, the onset of efficiency droop occurs at the same carrier density as the onset of carrier delocalization. We correlate these experimental results with the predictions of a theoretical model of the effects of carrier localization due to local variations in the concentration of the randomly distributed In atoms on the optical properties of InGaN/GaN quantum wells. On the basis of this comparison of theory with experiment we attribute the reduction in the S-shape temperature dependence to the saturation of the available localized states. We propose that this saturation of the localized states is a contributory factor to efficiency droop whereby nonlocalized carriers recombine non-radiatively.
Photoluminescence Study of Plasma-Induced Damage of GaInN Single Quantum Well
Authors: Izumi Shouichiro , Minami Masaki , Kamada Michiru , Tatsumi Tetsuya , Yamaguchi Atsushi A. , Ishikawa Kenji , Hori Masaru , Tomiya Shigetaka
Published: May 2013

Plasma-induced damage (PID) due to Cl2/SiCl4/Ar plasma etching of the GaN capping layer (CAP)/GaInN single quantum well (SQW)/GaN structure was investigated by conventional photoluminescence (PL), transmission electron microscopy (TEM), and time-resolved and temperature-dependent photoluminescence (TRPL). SQW PL intensity remained constant initially, although plasma etching of the CAP layer proceeded, but when the etching thickness reached a certain amount (∼60 nm above the SQW), PL intensity started to decrease sharply. On the other hand, TEM observations show that the physical damage (structural damage) was limited to the topmost surface region. These findings can be explained by the results of TRPL studies, which revealed that there exist two different causes of PID. One is an increase in the number of nonradiative recombination centers, which mainly affects the PL intensity. The other is an increase in the quantum level fluctuation owing mainly to physical damage.
Investigation of Quantum-Well Shapes and Their Impacts on the Performance of InGaN/GaN Light-Emitting Diodes
Authors: Shin Dong-Soo , Han Dong-Pyo , Shim Jong-In , Han Dae-Seob , Moon Yong-Tae , Park Joong Seo
Published: May 2013

We investigate the impacts of quantum-well (QW) shapes on the performance of InGaN/GaN light-emitting diodes (LEDs) grown on c-plane sapphire substrates. Three different QW shapes are utilized, namely, rectangular, staircase, and trapezoidal QWs of thicknesses of 4, 5, and 6 nm. Various optoelectronic measurements are conducted on these samples to determine the correlation of the effect of piezoelectric field with device performances. It is found that the staircase QW consistently shows the reduced effect of piezoelectric field, which agrees well with the simulation results of the increased electron–hole overlap integral over the conventional rectangular QW. The nonconventional QW can reduce the effect of piezoelectric field and improve the LED performance accordingly.
Evidence for Dark States in the Temperature Dependent Recombination Dynamics of InGaN/GaN Quantum Wells
Authors: Badcock Tom J. , Dawson Phil , Oliver Rachel A. , Kappers Menno J. , Humphreys Colin J.
Published: May 2013

The photoluminescence (PL) transients in two highly efficient blue and cyan emitting InGaN/GaN multiple quantum well structures are studied as a function of recombination energy, temperature and excitation density. Based on the form and spectral dependence of the PL decay, the emission is attributed to the recombination of independently localised electron hole pairs throughout the investigated temperature range (10–300 K). To account for the variation of the decay time across the PL linewidth, the T = 10 K detection energies are purposely shifted according to the predicted change in InGaN bandgap with increasing temperature. In this way, we monitor the temperature dependence of the recombination lifetime in separate subsets of localised states. We suggest that the observed reduction in decay rate with increasing temperature above ∼80 K is caused by the thermally induced occupation of optically inactive “dark” states. The reduced temperature sensitivity of the PL decay time under high levels of excitation is consistent with the nature of the dark states being other, higher energy (more weakly) localised states within the distribution.
Quantum Efficiency Analysis of Near-Ultraviolet Emitting AlGaN and AlInGaN Structures
Authors: Netzel Carsten , Knauer Arne , Weyers Markus
Published: May 2013

The quantum efficiency ofc-plane AlxGa1-xN and AlxInyGa1-x-yN structures (x= 0.06–0.21,y= 0.015–0.05) emitting in the UV spectral range between 320 and 350 nm was analyzed using temperature-dependent and polarization-resolved photoluminescence measurements. We found increasing bandgap fluctuation and charge carrier localization in case of higher aluminum or higher indium content. Improved suppression of nonradiative recombination was observed only in case of indium incorporation. The light polarization changed fromE⊥ctoE∥cwith increasing aluminum content in AlGaN. It switched back toE⊥cby the incorporation of indium in AlInGaN. Light polarization significantly contributes to the photoluminescence intensity measured from the top, and the degree of light polarization decreases with increasing temperature. Thus, temperature-dependent photoluminescence measured via thec-plane surface was found to depend both on internal quantum efficiency and on extraction efficiency.
Control of Eu Luminescence Centers by Codoping of Mg and Si into Eu-Doped GaN
Authors: Lee Dong-gun , Wakamatsu Ryuta , Koizumi Atsushi , Terai Yoshikazu , Fujiwara Yasufumi
Published: May 2013

The effects of Mg and Si codoping on Eu luminescence properties have been investigated in Eu-doped GaN (GaN:Eu). The Mg codoping into GaN:Eu produced novel luminescence centers consisting of Eu and Mg, and increased photoluminescence (PL) intensity in Eu,Mg-codoped GaN (GaN:Eu,Mg). However, this increased PL intensity was quenched by thermal annealing in N2 ambient, which is due to activation of Mg acceptors. In GaN:Eu,Mg codoped additionally with Si (GaN:Eu,Mg,Si), on the other hand, the Eu–Mg centers disappeared, while an additional luminescence center appeared. Furthermore, the additional luminescence center showed no quenching under N2 annealing because Si donors compensated for the Mg acceptors in GaN. Thermal quenching of the luminescence center was also approximately half of that in GaN:Eu. These results indicate that the codoping with additional impurities in GaN:Eu is a powerful technique to control Eu luminescence centers for realization of improved device performance in red light-emitting diodes using GaN:Eu.
Bandgap Engineering and Optical Constants of YxAl1-xN Alloys
Authors: Sedrine Nebiha Ben , Zukauskaite Agne , Birch Jens , Hultman Lars , Darakchieva Vanya
Published: May 2013

We study wurtzite YxAl1-xN (0≤x≤0.22) films with (0001) orientation deposited by magnetron sputtering epitaxy on Si(100) substrates and we determine the alloys band gap energies and optical constants. Room temperature spectroscopic ellipsometry (SE) is employed in the energy range from 1 to 6.3 eV, and data modeling based on the standard dielectric function model is used. As a result of the SE data analysis the YxAl1-xN refractive index and extinction coefficient are determined. The band gap of YxAl1-xN is found to decrease linearly from 6.2 eV (x= 0) down to 4.5 eV (x= 0.22). We further observe an increase of the refractive index with increasing Y content; from 1.93 to 2.20 (at 2 eV) forx= 0 and 0.22, respectively, reflecting the increase in material density.
(In)AlGaN Heterojunction Field Effect Transistors and Circuits for High-Power Applications at Microwave and Millimeter-Wave Frequencies
Authors: Maroldt Stephan , Quay Rüdiger , Dennler Philippe , Schwantuschke Dirk , Musser Markus , Dammann Michael , Aidam Rolf , Waltereit Patrick , Tessmann Axel , Ambacher Oliver
Published: May 2013

The suitability of the AlGaN/GaN heterostructure for applications up to 20 GHz is demonstrated based on a technically mature process. A broadband power amplifier integrated circuit is designed and fabricated in order to monitor the technology performance. Further, a 100 W power transistor for mobile communications is realized with an efficiency of 70% and an operation frequency of up to 3 GHz. We also demonstrate the performance of a 60 W switch-mode power amplifier module with 75% efficiency for industrial, scientific and medical applications at 2.4 GHz. To push the technology towards higher millimeter-wave frequencies an InAlGaN-based heterostructure was developed. This structure yields high sheet carrier concentration and mobility of 1.9×1013 cm-2 and 1590 cm2 V-1 s-1, respectively. An excellent f
T of 110 GHz and f
max of 190 GHz were achieved with HFETs with a gate length of 100 nm. This allowed the realization of InAlGaN-based power amplifier monolithic microwave integrated circuits (MMICs) operating at millimeter-wave frequencies of 60 and 94 GHz.
Ultrascaled InAlN/GaN High Electron Mobility Transistors with Cutoff Frequency of 400 GHz
Authors: Yue Yuanzheng , Hu Zongyang , Guo Jia , Sensale-Rodriguez Berardi , Li Guowang , Wang Ronghua , Faria Faiza , Song Bo , Gao Xiang , Guo Shiping , Kosel Thomas , Snider Gregory , Fay Patrick , Jena Debdeep , Xing Huili Grace
Published: May 2013

We report on 30-nm-gate-length InAlN/AlN/GaN/SiC high-electron-mobility transistors (HEMTs) with a record current gain cutoff frequency (f
T) of 400 GHz. Although the high drain-induced barrier lowering (DIBL) value is indicative of significant short-channel effects, more than seven orders of magnitude in the current on/off ratio was observed. The high f
T is a result of minimized parasitic effects and at the expense of a low power gain cutoff frequency (f
MAX). The gate length dependence and temperature dependence of f
T were also measured.
Electrical and Electroluminescence Characteristics of AlGaN/GaN High Electron Mobility Transistors Operated in Sustainable Breakdown Conditions
Authors: Meneghini Matteo , Zanandrea Alberto , Rampazzo Fabiana , Stocco Antonio , Bertin Marco , Cibin Giulia , Pogany Dionyz , Zanoni Enrico , Meneghesso Gaudenzio
Published: May 2013

This paper reports on an extensive analysis of the electrical and optical properties of GaN-based high electron mobility transistors (HEMTs) biased in a non-destructive breakdown regime. By means of a number of measurements carried out with varying voltage and temperature conditions, we show that: (i) HEMTs can reach a sustainable breakdown condition, when they are biased in current-controlled mode, with a gate voltage smaller than the pinch-off voltage; (ii) when biased in sustainable breakdown, HEMTs can emit a weak luminescence signal, localized in proximity of the drain edge; (iii) the breakdown voltage (BDV) is strongly dependent on temperature. Through a careful investigation of the drain, source and gate current components, we demonstrate that breakdown originates from two different mechanisms, depending on the gate voltage: for gate voltages close to the pinch-off, breakdown current originates from the space charge injection of electrons from the source to the drain. On the other hand, for more negative gate voltages, breakdown current originates from the injection of electrons from the gate. Finally, the analysis of the temperature dependence of the breakdown current confirms that two different mechanisms significantly contribute to current conduction at high drain voltage levels.
Analysis of Lags and Current Collapse in Source-Field-Plate AlGaN/GaN High-Electron-Mobility Transistors
Authors: Hanawa Hideyuki , Onodera Hiraku , Horio Kazushige
Published: May 2013

A two-dimensional transient analysis of source-field-plate AlGaN/GaN high-electron-mobility transistors (HEMTs) is performed by considering a deep donor and a deep acceptor in a buffer layer, and the results are compared with those in the case of gate-field-plate structures. It is shown that the reduction rate of drain lag obtained by introducing a field plate is quantitatively similar between source- and gate-field-plate structures. However, the gate-lag rate is rather higher in the source-field-plate structure because the electric field at the drain edge of the gate is higher in the off state, and hence electron injection into the buffer layer and the resulting trapping effects are more significant. Hence, current collapse is slightly larger in the source-field-plate structure. It is also shown that an optimum SiN passivation layer thickness is required to minimize buffer-related current collapse in source-field-plate AlGaN/GaN HEMTs.
Determination of Lateral Extension of Extrinsic Photon Recycling in p-GaN by Using Transmission-Line-Model Patterns Formed with GaN p–n Junction Epitaxial Layers
Authors: Mochizuki Kazuhiro , Mishima Tomoyoshi , Ishida Yuya , Hatakeyama Yoshitomo , Nomoto Kazuki , Kaneda Naoki , Tshuchiya Tadayoshi , Terano Akihisa , Tsuchiya Tomonobu , Uchiyama Hiroyuki , Tanaka Shigehisa , Nakamura Tohru
Published: May 2013

The effect of extrinsic photon recycling (EPR) in p-type gallium nitride (p-GaN), namely, increased ionization ratio (R) of magnesium acceptors owing to radiative recombination, was quantitatively investigated. The lateral extension (L) of EPR was determined by using transmission-line-model (TLM) patterns, formed with GaN p–n junction epitaxial layers on free-standing substrates, as well as by using device simulation. With increasing vertical current (I
V) of the p–n junction, lateral current (I
L) in the p-GaN layer (magnesium concentration: N
Mg = 5×1017 cm-3) was found to increase within L of 10 µm from the edge of the TLM electrodes; the measured I
L corresponded to a large R, namely, 30%. This lateral extension will contribute to reducing base resistance and enhancing conductivity modulation of GaN bipolar power-switching devices for power-electronics applications.
Plasma Instability and Wave Propagation in Gate-Controlled GaN Conduction Channels
Authors: Rudin Sergey , Rupper Greg
Published: May 2013

The plasma wave in the conduction channel of a semiconductor heterostructure high electron mobility transistor (HEMT) can be excited at frequencies significantly higher than the cut-off frequency in a short channel device. The hydrodynamic model predicts a resonance response to applied harmonic signal at the plasma oscillation frequency. When either the ac voltage induced in the channel by the signal at the gate or the current applied at the drain or source contact are not very small, the plasma waves in the semiconductor channel will propagate as a shock wave. The device can be used either as a detector or a tunable source of terahertz range radiation. Using the parameters appropriate for the GaN channel we show that in both configurations the charge flow develops shock waves due to hydrodynamic nonlinearities. In a sufficiently wide channel the wave propagation separates into two or more different bands giving a two-dimensional structure to the waves.
The Polarity Effect on the Photoelectrochemical Properties of Ga- and N-Face Free-Standing GaN Substrate
Authors: Bae Hyojung , Park Jaehyoung , Jung Ki-Chang , Nakamura Akihiro , Fujii Katsushi , Park Hyung-Jo , Jeong Tak , Lee Hyo-Jong , Moon Young Boo , Ha Jun-Seok
Published: May 2013

The band-edge potential and photocurrent density of N-face GaN were experimentally determined to be more negative and greater than those of Ga-face GaN, respectively, in this photoelectrochemical experiment. These results indicate that the N-face GaN could generate much more hydrogen than Ga-face GaN. Although the time dependence of the photocurrent density of N-face GaN was almost constant, that of Ga-face GaN stabilized only after 260 min of reaction time. From these results, we conclude that N-face GaN, which has a more negative band-edge potential and a more stable photocurrent density, could be suitable for higher-photocurrent generation than Ga-face GaN.
Patient Out-of-Pocket Costs for Type 2 Diabetes Medications When Aging Into Medicare
Authors: Barthold Douglas , Li Jing , Basu Anirban
Published: July 2024

Importance

For people with type 2 diabetes (T2D), out-of-pocket medication costs may influence medication choice, adherence, and overall diabetes management and progression. Little is known about how these costs change as insured people enter Medicare at age 65 years, when coinsurance in the coverage gap and catastrophic phases of Part D coverage can be increased greatly by use of insulin and newer, branded medications (eg, dipeptidyl peptidase 4 inhibitors, glucagon-like peptide 1 agonists, and sodium-glucose cotransporter 2 inhibitors).

Objective

To identify whether reaching age 65 years is associated with T2D medication out-of-pocket costs and utilization.

Design, Setting, and Participants

This retrospective cohort study (2012-2020) featuring 7 years of follow-up used prescription drug claims data from the TriNetX Diamond Network. Participants included people in the US with diagnosed T2D, and claims for T2D medications were observed both before and after age 65 years. Data analysis was performed from October 2022 to September 2023.

Exposure

Reaching age 65 years, according to participants’ year of birth.

Main Outcomes and Measures

The primary outcome was patient out-of-pocket costs for T2D drugs per quarter (inflation adjusted to 2020 dollars). Utilization, measured as binary utilization of specific classes, and the number of claims for mutually exclusive classes and combinations of classes were also examined. All outcomes were examined using regression discontinuity design.

Results

In claims data for 129 997 individuals with T2D diagnosed at ages 58 to 72 years (mean [SD] age, 65.50 [2.95] years; 801 235 female [50.9%]), reaching age 65 years was associated with an increase of $23.04 (95% CI, $19.86-$26.22) in mean quarterly out-of-pocket costs for T2D drugs, and an increase of $56.36 (95% CI, $51.48-$61.23) at the 95th percentile of spending, after utilization adjustment. Utilization decreased by 5.3% at age 65 years, from 3.40 claims per quarter (95% CI, 3.38-3.42 claims per quarter) to 3.22 claims per quarter (95% CI, 3.21-3.24 claims per quarter), but a shift in composition of utilization, including increased insulin use, was associated with additional increases in patient costs.

Conclusions and Relevance

In this cohort study of individuals with T2D, the increase in spending upon reaching age 65 years (when most people enroll in Medicare) was associated with patient coinsurance in the coverage gap and catastrophic coverage phases of Medicare Part D. The increased patient cost burden at age 65 years and a modest reduction in overall T2D drug utilization suggest that as people with T2D age into Medicare, there is potentially an increase in nonadherence and diabetes complications.
PRRX1 silencing is required for metastatic outgrowth in melanoma and is an independent prognostic of reduced survival in patients
Authors: Ferreres Josep R. , Vinyals Antònia , Campos‐Martin Rafael , Espín Roderic , Podlipnik Sebastian , Ramos Raquel , Bertran Esther , Carrera Cristina , Marcoval Joaquim , Malvehy Josep , Fabregat Isabel , Puig Susana , Fabra Àngels
Published: July 2024

Paired related homeobox 1 (PRRX1) is an inducer of epithelial‐to‐mesenchymal transition (EMT) in different types of cancer cells. We detected low PRRX1 expression in nevus but increased levels in primary human melanoma and cell lines carrying the BRAFV600E mutation. High expression of PRRX1 correlates with invasiveness and enrichment of genes belonging to the EMT programme. Conversely, we found that loss of PRRX1 in metastatic samples is an independent prognostic predictor of poor survival for melanoma patients. Here, we show that stable depletion of PRRX1 improves the growth of melanoma xenografts and increases the number of distant spontaneous metastases, compared to controls. We provide evidence that loss of PRRX1 counteracts the EMT phenotype, impairing the expression of other EMT‐related transcription factors, causing dysregulation of the ERK and signal transducer and activator of transcription 3 (STAT3) signaling pathways, and abrogating the invasive and migratory properties of melanoma cells while triggering the up‐regulation of proliferative/melanocytic genes and the expression of the neural‐crest‐like markers nerve growth factor receptor (NGFR; also known as neurotrophin receptor p75NTR) and neural cell adhesion molecule L1 (L1CAM). Overall, our results indicate that loss of PRRX1 triggers a switch in the invasive programme, and cells de‐differentiate towards a neural crest stem cell (NCSC)‐like phenotype that accounts for the metastatic aggressiveness.
Breast Cancer Cells Exhibit Mesenchymal–Epithelial Plasticity Following Dynamic Modulation of Matrix Stiffness
Authors: Sankhe Chinmay S. , Sacco Jessica L. , Lawton Jacob , Fair Ryan A. , Soares David Vidotto Rezende , Aldahdooh Mohammed K.R. , Gomez Enrique D. , Gomez Esther W.
Published: July 2024

Mesenchymal–epithelial transition (MET) is essential for tissue and organ development and is thought to contribute to cancer by enabling the establishment of metastatic lesions. Despite its importance in both health and disease, there is a lack of in vitro platforms to study MET and little is known about the regulation of MET by mechanical cues. Here, hyaluronic acid‐based hydrogels with dynamic and tunable stiffnesses mimicking that of normal and tumorigenic mammary tissue are synthesized. The platform is then utilized to examine the response of mammary epithelial cells and breast cancer cells to dynamic modulation of matrix stiffness. Gradual softening of the hydrogels reduces proliferation and increases apoptosis of breast cancer cells. Moreover, breast cancer cells exhibit temporal changes in cell morphology, cytoskeletal organization, and gene expression that are consistent with mesenchymal–epithelial plasticity as the stiffness of the matrix is reduced. A reduction in matrix stiffness attenuates the expression of integrin‐linked kinase, and inhibition of integrin‐linked kinase impacts proliferation, apoptosis, and gene expression in cells cultured on stiff and dynamic hydrogels. Overall, these findings reveal intermediate epithelial/mesenchymal states as cells move along a matrix stiffness‐mediated MET trajectory and suggest an important role for matrix mechanics in regulating mesenchymal–epithelial plasticity.
Spatiotemporally Controllable Covalent Bonding of RNA for Multi‐Protein Interference
Authors: Fang Hao , Wang Tingting , Dai Jun , Hu Jing‐Jing , Chen Zhaojun , Yuan Lizhen , Hong Yuning , Xia Fan , Lou Xiaoding
Published: July 2024

Many diseases are associated with genetic mutation and expression of mutated proteins, such as cancers. Therapeutic approaches that selectively target the synthesis process of multiple proteins show greater potential compared to single‐protein approaches in oncological diseases. However, conventional agents to regulate the synthesis of multiple protein still suffer from poor spatiotemporal selectivity and stability. Here, a new method using a dye‐peptide conjugate, PRFK, for multi‐protein interference with spatiotemporal selectivity and reliable stability, is reported. By using the peptide sequence that targets tumor cells, PRFK can be efficiently taken up, followed by specific binding to the KDELR (KDEL receptor) protein located in the endoplasmic reticulum (ER). The dye generates 1O2 under light irradiation, enabling photodynamic therapy. This process converts the furan group into a cytidine‐reactive intermediate, which covalently binds to mRNA, thereby blocking protein synthesis. Upon treating 4T1 cells, the proteomics data show alterations in apoptosis, ferroptosis, proliferation, migration, invasion, and immune infiltration, suggesting that multi‐protein interference leads to the disruption of cellular physiological activities, ultimately achieving tumor treatment. This study presents a multi‐protein interference probe with the potential for protein interference within various subcellular organelles in the future.
Construction of Iron‐Scavenging Hydrogel via Thiol–Ene Click Chemistry for Antibiotic‐Free Treatment of Bacterial Wound Infection
Authors: Xie Tian‐Qiu , Yan Xiao , Yan Jian‐Hua , Yu Yun‐Jian , Liu Xin‐Hua , Feng Jun , Liu Chuan‐Jun , Zhang Xian‐Zheng
Published: July 2024

Bacteria, especially drug‐resistant strains, can quickly cause wound infections, leading to delayed healing and fatal risk in clinics. With the growing need for alternative antibacterial approaches that rely less on antibiotics or eliminate their use altogether, a novel antibacterial hydrogel named Ovtgel is developed. Ovtgel is formulated by chemically crosslinking thiol‐modified ovotransferrin (Ovt), a member of the transferrin family found in egg white, with olefin‐modified agarose through thiol–ene click chemistry. Ovt is designed to sequester ferric ions essential for bacterial survival and protect wound tissues from damages caused by the reactive oxygen species (ROS) generated in Fenton reactions. Experimental data have shown that Ovtgel significantly enhances wound healing by inhibiting bacterial growth and shielding tissues from ROS‐induced harms. Unlike traditional antibiotics, Ovtgel targets essential trace elements required for bacterial survival in the host environment, preventing the development of drug resistance in pathogenic bacteria. Ovtgel exhibits excellent biocompatibility due to the homology of Ovt to mammalian transferrin. This hydrogel has the potential to serve as an effective antibiotic‐free solution for combating bacterial infections.
Bioengineered Abiotic Nanomaterials Through Cell Membrane‐Camouflaging: Advancements and Challenges in Lung Cancer
Authors: Jin Xuru , Lopes Daniela , Lopes Joana , Hua Zhidan , Lei Ying , Ghanbari Roham , Nazarzadeh Zare Ehsan , Borzacchiello Assunta , Karimi Male Hassan , Iravani Siavash , Sillanpää Mika , Prakash Chander , Wang Xiangdong , Cláudia Paiva‐Santos Ana , Makvandi Pooyan , Xu Yi
Published: July 2024

Lung cancer remains a major global health concern with high mortality rates and poor prognosis. Bridging the gap between the chemical and cellular understanding of cell‐decorated biomimetic nanocomposites and their clinical translation is crucial for developing effective therapies. Nanocomposites show promise in targeted drug delivery and diagnostics, but their clinical application is hindered by biocompatibility and clearance issues. To overcome these challenges, biomimetic approaches utilizing cell membrane‐coated nanomaterials emerge. By camouflaging nanomaterials with cell membranes, the biointerfaces are enhanced, and the inherent properties of the donor cell membranes are acquired. This review provides an overview of recent advancements on cell membrane‐coated nanocomposites for lung cancer diagnosis and treatment. It discusses fabrication techniques, biomedical applications, challenges, and future prospects. The incorporation of cell membranes into nanocomposites holds potential for improved lung cancer therapy, but further development and refinement are needed for precise tumor targeting. Addressing the identified challenges will pave the way for clinical translation of these biomimetic nanoplatforms and advance lung cancer diagnosis and treatment.