High-quality AlN/sapphire templates were fabricated by the combination of sputtering and high-temperature(HT)annealing.The influence of sputtering parameters including nitrogen flux,radio frequency power,and substrate...High-quality AlN/sapphire templates were fabricated by the combination of sputtering and high-temperature(HT)annealing.The influence of sputtering parameters including nitrogen flux,radio frequency power,and substrate temperature on the crystalline quality and surface morphology of annealed AlN films were investigated.With lower substrate temperature,lower power,and lower N2 flux,the full width at half maximum of the X-ray rocking curve for AlN(0002)and(102)were improved to 97.2 and 259.2 arcsec after high-temperature annealing.This happens because the increased vacancy concentration of sputtered AlN films can facilitate the annihilation of dislocations by increasing the recovery rate during HT annealing.Step and step-bunching morphologies were clearly observed with optimized sputtering conditions.展开更多
This paper conducts a research on modulation characteristics of blue light-emitting diodes (LEDs) used in a visible-light communication (VLC) system. Through analysis of the modulation characteristics of LEDs with dif...This paper conducts a research on modulation characteristics of blue light-emitting diodes (LEDs) used in a visible-light communication (VLC) system. Through analysis of the modulation characteristics of LEDs with different emitting sizes, we find that there is a similar linear relationship between LED’s 3dB bandwidth and the operation current density. This experiment also shows that high series resistance is one major issue that limits our LED's modulation speed. To further improve the LED bandwidth, the resistance can be reduced by optimizing device layout as well as reducing material bulk resistance. Clearly, this study provides an approach to increase the modulation bandwidth of GaN-based LEDs for VLC systems.展开更多
Metallic nanotextured reflectors have been widely used in light emitting diodes(LEDs) to enhance the light extraction efficiency. However, the light absorption loss for the metallic reflectors with nanotexture structu...Metallic nanotextured reflectors have been widely used in light emitting diodes(LEDs) to enhance the light extraction efficiency. However, the light absorption loss for the metallic reflectors with nanotexture structure is often neglected. Here, the influence of absorption loss of metallic nanotextured reflectors on the LED optoelectronic properties were studied. Two commonly used metal reflectors Ag and Al were applied to green GaN-based LEDs. By applying a Ag nanotextured reflector, the light output power of the LEDs was enhanced by 78% due to the improved light extraction. For an Al nanotextured reflector, however,only a 6% enhancement of the light output power was achieved. By analyzing the metal absorption using finite-difference timedomain(FDTD) and the metal reflectivity spectrum, it is shown that the surface plasmon(SP) intrinsic absorption of metallic reflectors with nanotexture structure play an important role. This finding will aid the design of the high-performance metal nanotextured reflectors and optoelectronics devices.展开更多
In recent years,materials and devices operating in the ultraviolet(UV)regime have attracted significant attention and therefore experienced rapid development.On the one hand,following the thriving advancement of GaN-b...In recent years,materials and devices operating in the ultraviolet(UV)regime have attracted significant attention and therefore experienced rapid development.On the one hand,following the thriving advancement of GaN-based blue and white LEDs,which have brought a revolution in lighting sources,various groups are expanding their research work in Al(Ga)N materials and Al(Ga)N-based UV devices with the aim to explore more potential applications in shorter wavelength regime of group III-nitrides.While on the other hand,some binary alloys such as SiC,Ga2O3,BN,etc,whose bandgaps lie in the UV region,have been accomplished for a variety of applications.The development of UV materials laid the foundation for UV devices.Nevertheless,each material has its own benefits and constraints.More efforts should be devoted to overcoming the obstacles and challenges,in order to improve the material quality and devices performance.展开更多
This study focused on the evolution of growth front about AlN growth on nano-patterned sapphire substrate by metal-organic chemical vapor deposition.The substrate with concave cones was fabricated by nano-imprint lith...This study focused on the evolution of growth front about AlN growth on nano-patterned sapphire substrate by metal-organic chemical vapor deposition.The substrate with concave cones was fabricated by nano-imprint lithography and wet etching.Two samples with different epitaxy procedures were fabricated,manifesting as two-dimensional growth mode and three-dimensional growth mode,respectively.The results showed that growth temperature deeply influenced the growth modes and thus played a critical role in the coalescence of AlN.At a relatively high temperature,the AlN epilayer was progressively coalescence and the growth mode was two-dimensional.In this case,we found that the inclined semi-polar facets arising in the process of coalescence were{112^-1}type.But when decreasing the temperature,the{112^-2}semi-polar facets arose,leading to inverse pyramid morphology and obtaining the three-dimensional growth mode.The 3 D inverse pyramid AlN structure could be used for realizing 3 D semi-polar UV-LED or facet-controlled epitaxial lateral overgrowth of AlN.展开更多
The nanorod structure is an alternative scheme to develop high-efficiency deep ultraviolet light-emitting diodes(DUV LEDs). In this paper, we first report the electrically injected 274-nm AlGaN nanorod array DUV LEDs ...The nanorod structure is an alternative scheme to develop high-efficiency deep ultraviolet light-emitting diodes(DUV LEDs). In this paper, we first report the electrically injected 274-nm AlGaN nanorod array DUV LEDs fabricated by the nanosphere lithography and dry-etching technique. Nanorod DUV LED devices with good electrical properties are successfully realized. Compared to planar DUV LEDs, nanorod DUV LEDs present>2.5 times improvement in light output power and external quantum efficiency. The internal quantum efficiency of nanorod LEDs increases by 1.2 times due to the transformation of carriers from the exciton to the free electron–hole, possibly driven by the interface state effect of the nanorod sidewall surface. In addition, the nanorod array significantly facilitates photons escaping from the interior of LEDs along the vertical direction, contributing to improved light extraction efficiency. A three-dimensional finite-different time-domain simulation is performed to analyze further in detail the TE-and TM-polarized photon extraction mechanisms of the nanostructure. Our results demonstrate the nanorod structure is a good candidate for high-efficiency DUV emitters.展开更多
Fast and uniform growth of high-quality graphene on conventional glass is of great importance for practical applications of graphene glass. We report herein a confined-flow chemical vapor deposition （CVD） approach f...Fast and uniform growth of high-quality graphene on conventional glass is of great importance for practical applications of graphene glass. We report herein a confined-flow chemical vapor deposition （CVD） approach for the high- efficiency fabrication of graphene glass. The key feature of our approach is the fabrication of a 2-4 μm wide gap above the glass substrate, with plenty of stumbling blocks; this gap was found to significantly increase the collision probability of the carbon precursors and reactive fragments between one another and with the glass surface. As a result, the growth rate of graphene glass increased remarkably, together with an improvement in the growth quality and uniformity as compared to those in the conventional gas flow CVD technique. These high-quality graphene glasses exhibited an excellent defogging performance with much higher defogging speed and higher stability compared to those previously reported. The graphene sapphire glass was found to be an ideal substrate for growing uniform and ultra-smooth aluminum nitride thin films without the tedious pre-deposition of a buffer layer. The presented confined- flow CVD approach offers a simple and low-cost route for the mass production of graphene glass, which is believed to promote the practical applications of various graphene glasses.展开更多
To achieve high quality lighting and visible light communication(VLC)simultaneously,Ga N based white light emitting diodes(WLEDs)oriented for lighting in VLC has attracted great interest.However,the overall bandwidth ...To achieve high quality lighting and visible light communication(VLC)simultaneously,Ga N based white light emitting diodes(WLEDs)oriented for lighting in VLC has attracted great interest.However,the overall bandwidth of conventional phosphor converted WLEDs is limited by the long lifetime of phosphor,the slow Stokes transfer process,the resistance-capacitance(RC)time delay,and the quantum-confined Stark effect(QCSE).Here by adopting a self-assembled In Ga N quantum dots(QDs)structure,we have fabricated phosphor-free single chip WLEDs with tunable correlated color temperature(CCT,from 1600 K to 6000 K),a broadband spectrum,a moderate color rendering index(CRI)of 75,and a significantly improved modulation bandwidth(maximum of150 MHz)at a low current density of 72 A∕cm^2.The broadband spectrum and high modulation bandwidth are ascribed to the capture of carriers by different localized states of In Ga N QDs with alleviative QCSE as compared to the traditional In Ga N/Ga N quantum well(QW)structures.We believe the approach reported in this work will find its potential application in Ga N WLEDs and advance the development of semiconductor lighting-communication integration.展开更多
The energy-efficient deep ultraviolet(DUV)optoelectronic devices suffer from critical issues associated with the poor quality and large strain of nitride material system caused by the inherent mismatch of heteroepitax...The energy-efficient deep ultraviolet(DUV)optoelectronic devices suffer from critical issues associated with the poor quality and large strain of nitride material system caused by the inherent mismatch of heteroepitaxy.In this work,we have prepared the strain-free AlN film with low dislocation density(DD)by graphene(Gr)-driving strain-pre-store engineering and a unique mechanism of strain-relaxation in quasi-van der Waals(QvdW)epitaxy is presented.The DD in AlN epilayer with Gr exhibits an anomalous sawtooth-like evolution during the whole epitaxy process.Gr can help to enable the annihilation of the dislocations originated from the interface between AlN and Gr/sapphire by impelling a lateral two-dimensional growth mode.Remarkably,it can induce AlN epilayer to pre-store sufficient tensile strain during the early growth stage and thus compensate the compressive strain caused by hetero-mismatch.Therefore,the low-strain state of the DUV light-emitting diode(DUV-LED)epitaxial structure is realized on the strain-free AlN template with Gr.Furthermore,the DUV-LED with Gr demonstrate 2.1 times enhancement of light output power and a better stability of luminous wavelength compared to that on bare sapphire.An in-depth understanding of this work reveals diverse beneficial impacts of Gr on nitride growth and provides a novel strategy of relaxing the vital requirements of hetero-mismatch in conventional heteroepitaxy.展开更多
In this study, the effect of double superlattices on GaN-based blue light-emitting diodes(LEDs) is analyzed numerically. One of the superlattices is composed of InGaN/GaN, which is designed before the multiple quantum...In this study, the effect of double superlattices on GaN-based blue light-emitting diodes(LEDs) is analyzed numerically. One of the superlattices is composed of InGaN/GaN, which is designed before the multiple quantum wells(MQWs). The other one is AlInGaN/AlGaN, which is inserted between the last QB(quantum barriers) and p-GaN. The crucial characteristics of double superlattices LEDs structure, including the energy band diagrams, carrier concentrations in the active region, light output power, internal quantum efficiency, respectively,were analyzed in detail. The simulation results suggest that compared with the conventional AlGaN electronblocking layer(EBL) LED, the LED with double superlattices has better performance due to the enhancement of electron confinement and the increase of hole injection. The double superlattices can make it easier for the carriers tunneling to the MQWs, especially for the holes. Furthermore, the LED with the double superlattices can effectively suppress the electron overflow out of multiple quantum wells simultaneously. From the result, we argue that output power is enhanced dramatically, and the efficiency droop is substantially mitigated when the double superlattices are used.展开更多
High-quality AlN layers with low-density threading dislocations are indispensable for high-efficiency deep ultraviolet light-emitting diodes（UV-LEDs）. In this work, a high-temperature AlN epitaxial layer was grown o...High-quality AlN layers with low-density threading dislocations are indispensable for high-efficiency deep ultraviolet light-emitting diodes（UV-LEDs）. In this work, a high-temperature AlN epitaxial layer was grown on sputtered AlN layer（used as nucleation layer, SNL） by a high-yield industrial metalorganic vapor phase epitaxy（MOVPE）. The full width half maximum（FWHM） of the rocking curve shows that the AlN epitaxial layer with SNL has good crystal quality. Furthermore, the relationships between the thickness of SNL and the FWHM values of（002） and（102） peaks were also studied. Finally, utilizing an SNL to enhance the quality of the epitaxial layer, deep UV-LEDs at 282 nm were successfully realized on sapphire substrate by the high-yield industrial MOVPE. The light-output power（LOP） of a deep UV-LED reaches 1.65 mW at 20 mA with external quantum efficiency of 1.87%. In addition, the saturation LOP of the deep UV-LED is 4.31 mW at an injection current of 60 mA. Hence, our studies supply a possible process to grow commercial deep UV-LEDs in high throughput industrial MOVPE, which can increase yield, at lower cost.展开更多
Slow and smooth etching of gallium nitride（GaN） by BCl;/Cl;-based inductively coupled plasma（ICP）is investigated in this paper. The effects of etch parameters, including ICP power, radio frequency（RF） power, the...Slow and smooth etching of gallium nitride（GaN） by BCl;/Cl;-based inductively coupled plasma（ICP）is investigated in this paper. The effects of etch parameters, including ICP power, radio frequency（RF） power, the flow rate of Cl;and BCl;, on GaN etch rate and etch surface roughness RMS are discussed. A new model is suggested to explain the impact mechanism of the BCl;flow rate on etch surface roughness. An optimized etch result of a slow and smooth etch surface was obtained; the etch rate and RMS were 0.36 ?/s and 0.9 nm, respectively.展开更多
We investigate the effect of AlN/AlGaN superlattices（SLs） on crystal and optical properties of AlGN epitaxial layers. The result indicates that the crystal quality of AlGaN layers is consistent within a wide range o...We investigate the effect of AlN/AlGaN superlattices（SLs） on crystal and optical properties of AlGN epitaxial layers. The result indicates that the crystal quality of AlGaN layers is consistent within a wide range of SLs thicknesses, while the optical properties are opposite. With SLs thickness decreasing from 20/44 to 17/36 and 15/29 nm, the full-width at half maximum of X-ray rocking curves for （0002）- and（1012）-plane of n-AlGaN layers grown on SLs are consistent of around 250 arcsec and 700 arcsec, respectively. Meanwhile, the center of the low optical transmittance band decreases from 326 to 279 nm and less than 266 nm as the SLs thickness decreases.280 nm deep ultraviolet light-emitting diodes（DUV-LEDs） structures are further regrown on the n-AlGaN layers.The electroluminescent intensities of samples are 30% higher than that of the sample whose low optical transmittance band appears around 279 nm. Optical simulations reveal that the SLs acts as distributed Bragg reflectors, thus less photons of the corresponding wavelength escape from the sapphire backside.展开更多
Positive type photosensitive polyimide is used as the modification layer in the thin film transistors production process. The photosensitive polyimide is not only used as the second insulating layer, it can also be us...Positive type photosensitive polyimide is used as the modification layer in the thin film transistors production process. The photosensitive polyimide is not only used as the second insulating layer, it can also be used instead of a mask because of the photosensitivity. A suitable curing condition can help photosensitive polyimide form the high performance polyimide with orderly texture inside, and the performance of imidization depends on the precise control of temperature, time, and heat control during the curing process. Therefore, experiments of different stepped up heating tests are made, and the ability of protecting silicon dioxide is analyzed.展开更多
基金This work was supported by the National Key R&D Program of China(Nos.2016YFB0400800 and 2017YFB0404202)the National Natural Sciences Foundation of China(Grant Nos.61527814,61674147,61904176,U1505253)+1 种基金Beijing Nova Program Z181100006218007Youth Innovation Promotion Association CAS 2017157.
文摘High-quality AlN/sapphire templates were fabricated by the combination of sputtering and high-temperature(HT)annealing.The influence of sputtering parameters including nitrogen flux,radio frequency power,and substrate temperature on the crystalline quality and surface morphology of annealed AlN films were investigated.With lower substrate temperature,lower power,and lower N2 flux,the full width at half maximum of the X-ray rocking curve for AlN(0002)and(102)were improved to 97.2 and 259.2 arcsec after high-temperature annealing.This happens because the increased vacancy concentration of sputtered AlN films can facilitate the annihilation of dislocations by increasing the recovery rate during HT annealing.Step and step-bunching morphologies were clearly observed with optimized sputtering conditions.
文摘This paper conducts a research on modulation characteristics of blue light-emitting diodes (LEDs) used in a visible-light communication (VLC) system. Through analysis of the modulation characteristics of LEDs with different emitting sizes, we find that there is a similar linear relationship between LED’s 3dB bandwidth and the operation current density. This experiment also shows that high series resistance is one major issue that limits our LED's modulation speed. To further improve the LED bandwidth, the resistance can be reduced by optimizing device layout as well as reducing material bulk resistance. Clearly, this study provides an approach to increase the modulation bandwidth of GaN-based LEDs for VLC systems.
基金supported by the National Key Research and Development Program of China (No. 2017YFB0402900)the National Natural Science Foundation of China (No. 61504132, 61505197)
文摘Metallic nanotextured reflectors have been widely used in light emitting diodes(LEDs) to enhance the light extraction efficiency. However, the light absorption loss for the metallic reflectors with nanotexture structure is often neglected. Here, the influence of absorption loss of metallic nanotextured reflectors on the LED optoelectronic properties were studied. Two commonly used metal reflectors Ag and Al were applied to green GaN-based LEDs. By applying a Ag nanotextured reflector, the light output power of the LEDs was enhanced by 78% due to the improved light extraction. For an Al nanotextured reflector, however,only a 6% enhancement of the light output power was achieved. By analyzing the metal absorption using finite-difference timedomain(FDTD) and the metal reflectivity spectrum, it is shown that the surface plasmon(SP) intrinsic absorption of metallic reflectors with nanotexture structure play an important role. This finding will aid the design of the high-performance metal nanotextured reflectors and optoelectronics devices.
文摘In recent years,materials and devices operating in the ultraviolet(UV)regime have attracted significant attention and therefore experienced rapid development.On the one hand,following the thriving advancement of GaN-based blue and white LEDs,which have brought a revolution in lighting sources,various groups are expanding their research work in Al(Ga)N materials and Al(Ga)N-based UV devices with the aim to explore more potential applications in shorter wavelength regime of group III-nitrides.While on the other hand,some binary alloys such as SiC,Ga2O3,BN,etc,whose bandgaps lie in the UV region,have been accomplished for a variety of applications.The development of UV materials laid the foundation for UV devices.Nevertheless,each material has its own benefits and constraints.More efforts should be devoted to overcoming the obstacles and challenges,in order to improve the material quality and devices performance.
基金supported by the National Key R&D Program of China (No. 2016YFB0400800)the National Natural Sciences Foundation of China (Grant Nos. 61875187, 61527814, 61674147, U1505253)+1 种基金Beijing Nova Program Z181100006218 007Youth Innovation Promotion Association CAS 2017157
文摘This study focused on the evolution of growth front about AlN growth on nano-patterned sapphire substrate by metal-organic chemical vapor deposition.The substrate with concave cones was fabricated by nano-imprint lithography and wet etching.Two samples with different epitaxy procedures were fabricated,manifesting as two-dimensional growth mode and three-dimensional growth mode,respectively.The results showed that growth temperature deeply influenced the growth modes and thus played a critical role in the coalescence of AlN.At a relatively high temperature,the AlN epilayer was progressively coalescence and the growth mode was two-dimensional.In this case,we found that the inclined semi-polar facets arising in the process of coalescence were{112^-1}type.But when decreasing the temperature,the{112^-2}semi-polar facets arose,leading to inverse pyramid morphology and obtaining the three-dimensional growth mode.The 3 D inverse pyramid AlN structure could be used for realizing 3 D semi-polar UV-LED or facet-controlled epitaxial lateral overgrowth of AlN.
基金National Key R&D Program of China(2016YFB0400800)National Natural Science Foundation of China(61875187,61527814,61674147,U1505253)+1 种基金Beijing Nova Program(Z181100006218007)Youth Innovation Promotion Association of the Chinese Academy of Sciences(2017157)
文摘The nanorod structure is an alternative scheme to develop high-efficiency deep ultraviolet light-emitting diodes(DUV LEDs). In this paper, we first report the electrically injected 274-nm AlGaN nanorod array DUV LEDs fabricated by the nanosphere lithography and dry-etching technique. Nanorod DUV LED devices with good electrical properties are successfully realized. Compared to planar DUV LEDs, nanorod DUV LEDs present>2.5 times improvement in light output power and external quantum efficiency. The internal quantum efficiency of nanorod LEDs increases by 1.2 times due to the transformation of carriers from the exciton to the free electron–hole, possibly driven by the interface state effect of the nanorod sidewall surface. In addition, the nanorod array significantly facilitates photons escaping from the interior of LEDs along the vertical direction, contributing to improved light extraction efficiency. A three-dimensional finite-different time-domain simulation is performed to analyze further in detail the TE-and TM-polarized photon extraction mechanisms of the nanostructure. Our results demonstrate the nanorod structure is a good candidate for high-efficiency DUV emitters.
基金This work was financially supported by the National Basic Research Program of China （Nos. 2016YFA0200103, 2013CB932603, 2012CB933404, and 2013CB934600）, the National Natural Science Foundation of China （Nos. 51520105003 and 51432002）, the Ministry of Education （No. 20120001130010）, and the Beijing Municipal Science and Technology Planning Project （No. Z151100003315013）.
文摘Fast and uniform growth of high-quality graphene on conventional glass is of great importance for practical applications of graphene glass. We report herein a confined-flow chemical vapor deposition （CVD） approach for the high- efficiency fabrication of graphene glass. The key feature of our approach is the fabrication of a 2-4 μm wide gap above the glass substrate, with plenty of stumbling blocks; this gap was found to significantly increase the collision probability of the carbon precursors and reactive fragments between one another and with the glass surface. As a result, the growth rate of graphene glass increased remarkably, together with an improvement in the growth quality and uniformity as compared to those in the conventional gas flow CVD technique. These high-quality graphene glasses exhibited an excellent defogging performance with much higher defogging speed and higher stability compared to those previously reported. The graphene sapphire glass was found to be an ideal substrate for growing uniform and ultra-smooth aluminum nitride thin films without the tedious pre-deposition of a buffer layer. The presented confined- flow CVD approach offers a simple and low-cost route for the mass production of graphene glass, which is believed to promote the practical applications of various graphene glasses.
基金National Key Research and Development Program of China(2018YFB0406702)Professorship Startup Funding(217056)+2 种基金Innovation-Driven Project of Central South University,China(2018CX001)Project of State Key Laboratory of High-Performance Complex Manufacturing,Central South University,China(ZZYJKT2018-01)Fundamental Research Funds for the Central Universities of Central South University(2018zzts147)。
文摘To achieve high quality lighting and visible light communication(VLC)simultaneously,Ga N based white light emitting diodes(WLEDs)oriented for lighting in VLC has attracted great interest.However,the overall bandwidth of conventional phosphor converted WLEDs is limited by the long lifetime of phosphor,the slow Stokes transfer process,the resistance-capacitance(RC)time delay,and the quantum-confined Stark effect(QCSE).Here by adopting a self-assembled In Ga N quantum dots(QDs)structure,we have fabricated phosphor-free single chip WLEDs with tunable correlated color temperature(CCT,from 1600 K to 6000 K),a broadband spectrum,a moderate color rendering index(CRI)of 75,and a significantly improved modulation bandwidth(maximum of150 MHz)at a low current density of 72 A∕cm^2.The broadband spectrum and high modulation bandwidth are ascribed to the capture of carriers by different localized states of In Ga N QDs with alleviative QCSE as compared to the traditional In Ga N/Ga N quantum well(QW)structures.We believe the approach reported in this work will find its potential application in Ga N WLEDs and advance the development of semiconductor lighting-communication integration.
基金financially supported by the National Key R&D Program of China(No.2019YFA0708203)the National Natural Science Foundation of China(Nos.61974139,52192614 and 12074369)Beijing Natural Science Foundation(No.4222077)。
文摘The energy-efficient deep ultraviolet(DUV)optoelectronic devices suffer from critical issues associated with the poor quality and large strain of nitride material system caused by the inherent mismatch of heteroepitaxy.In this work,we have prepared the strain-free AlN film with low dislocation density(DD)by graphene(Gr)-driving strain-pre-store engineering and a unique mechanism of strain-relaxation in quasi-van der Waals(QvdW)epitaxy is presented.The DD in AlN epilayer with Gr exhibits an anomalous sawtooth-like evolution during the whole epitaxy process.Gr can help to enable the annihilation of the dislocations originated from the interface between AlN and Gr/sapphire by impelling a lateral two-dimensional growth mode.Remarkably,it can induce AlN epilayer to pre-store sufficient tensile strain during the early growth stage and thus compensate the compressive strain caused by hetero-mismatch.Therefore,the low-strain state of the DUV light-emitting diode(DUV-LED)epitaxial structure is realized on the strain-free AlN template with Gr.Furthermore,the DUV-LED with Gr demonstrate 2.1 times enhancement of light output power and a better stability of luminous wavelength compared to that on bare sapphire.An in-depth understanding of this work reveals diverse beneficial impacts of Gr on nitride growth and provides a novel strategy of relaxing the vital requirements of hetero-mismatch in conventional heteroepitaxy.
基金Project supported by the National Key Research and Development Program of China(No.2016YFB0400102)the Beijing Municipal Science and Technology Project(Nos.Z161100002116032,D12110300140000)+3 种基金the National Basic Research Program of China(No.2011CB301902)the Guangzhou Science & Technology Planning Project of Guangdong Province,China(Nos.201604016095,201604030035)the Zhongshan Science & Technology Planning Project of Guangdong Province,China(No.2017A1008)the Science & Technology Planning Project of Guangdong Province(No.2015B010112002)
文摘In this study, the effect of double superlattices on GaN-based blue light-emitting diodes(LEDs) is analyzed numerically. One of the superlattices is composed of InGaN/GaN, which is designed before the multiple quantum wells(MQWs). The other one is AlInGaN/AlGaN, which is inserted between the last QB(quantum barriers) and p-GaN. The crucial characteristics of double superlattices LEDs structure, including the energy band diagrams, carrier concentrations in the active region, light output power, internal quantum efficiency, respectively,were analyzed in detail. The simulation results suggest that compared with the conventional AlGaN electronblocking layer(EBL) LED, the LED with double superlattices has better performance due to the enhancement of electron confinement and the increase of hole injection. The double superlattices can make it easier for the carriers tunneling to the MQWs, especially for the holes. Furthermore, the LED with the double superlattices can effectively suppress the electron overflow out of multiple quantum wells simultaneously. From the result, we argue that output power is enhanced dramatically, and the efficiency droop is substantially mitigated when the double superlattices are used.
基金Project supported by the National Natural Sciences Foundation of China(Nos.61334009,61474109,61306050)
文摘High-quality AlN layers with low-density threading dislocations are indispensable for high-efficiency deep ultraviolet light-emitting diodes（UV-LEDs）. In this work, a high-temperature AlN epitaxial layer was grown on sputtered AlN layer（used as nucleation layer, SNL） by a high-yield industrial metalorganic vapor phase epitaxy（MOVPE）. The full width half maximum（FWHM） of the rocking curve shows that the AlN epitaxial layer with SNL has good crystal quality. Furthermore, the relationships between the thickness of SNL and the FWHM values of（002） and（102） peaks were also studied. Finally, utilizing an SNL to enhance the quality of the epitaxial layer, deep UV-LEDs at 282 nm were successfully realized on sapphire substrate by the high-yield industrial MOVPE. The light-output power（LOP） of a deep UV-LED reaches 1.65 mW at 20 mA with external quantum efficiency of 1.87%. In addition, the saturation LOP of the deep UV-LED is 4.31 mW at an injection current of 60 mA. Hence, our studies supply a possible process to grow commercial deep UV-LEDs in high throughput industrial MOVPE, which can increase yield, at lower cost.
基金supported by the National Key R&D Program of China(No.2017YFB0403001)the National Natural Sciences Foundation of China(No.61404134)
文摘Slow and smooth etching of gallium nitride（GaN） by BCl;/Cl;-based inductively coupled plasma（ICP）is investigated in this paper. The effects of etch parameters, including ICP power, radio frequency（RF） power, the flow rate of Cl;and BCl;, on GaN etch rate and etch surface roughness RMS are discussed. A new model is suggested to explain the impact mechanism of the BCl;flow rate on etch surface roughness. An optimized etch result of a slow and smooth etch surface was obtained; the etch rate and RMS were 0.36 ?/s and 0.9 nm, respectively.
基金Project supported in part by the National High Technology Program of China(No.2014AA032608)the National Key R&D Program of China(Nos.2016YFB0400800,2016YFB0400083,2016YFB0400082)+3 种基金in part by the National Natural Sciences Foundation of China(Nos.6136047,61206090,61527814,61674147,61204053)the Beijing Municipal Science and Technology Project(No.D161100002516002)the National 1000 Young Talents Programthe Youth Innovation Promotion Association,CAS
文摘We investigate the effect of AlN/AlGaN superlattices（SLs） on crystal and optical properties of AlGN epitaxial layers. The result indicates that the crystal quality of AlGaN layers is consistent within a wide range of SLs thicknesses, while the optical properties are opposite. With SLs thickness decreasing from 20/44 to 17/36 and 15/29 nm, the full-width at half maximum of X-ray rocking curves for （0002）- and（1012）-plane of n-AlGaN layers grown on SLs are consistent of around 250 arcsec and 700 arcsec, respectively. Meanwhile, the center of the low optical transmittance band decreases from 326 to 279 nm and less than 266 nm as the SLs thickness decreases.280 nm deep ultraviolet light-emitting diodes（DUV-LEDs） structures are further regrown on the n-AlGaN layers.The electroluminescent intensities of samples are 30% higher than that of the sample whose low optical transmittance band appears around 279 nm. Optical simulations reveal that the SLs acts as distributed Bragg reflectors, thus less photons of the corresponding wavelength escape from the sapphire backside.
文摘Positive type photosensitive polyimide is used as the modification layer in the thin film transistors production process. The photosensitive polyimide is not only used as the second insulating layer, it can also be used instead of a mask because of the photosensitivity. A suitable curing condition can help photosensitive polyimide form the high performance polyimide with orderly texture inside, and the performance of imidization depends on the precise control of temperature, time, and heat control during the curing process. Therefore, experiments of different stepped up heating tests are made, and the ability of protecting silicon dioxide is analyzed.
