A novel source-connected field plate structure, featuring the same photolithography mask as the gate electrode, is proposed as an improvement over the conventional field plate （FP） techniques to enhance the frequenc...A novel source-connected field plate structure, featuring the same photolithography mask as the gate electrode, is proposed as an improvement over the conventional field plate （FP） techniques to enhance the frequency performance in GaN-based HEMTs. The influences of the field plate on frequency and breakdown performance are investigated simul- taneously by using a two-dimensional physics-based simulation. Compared with the conventional T-gate structures with a field plate length of 1.2 gm, this field plate structure can induce the small signal power gain at 10 GHz to increase by 5-9.5 dB, which depends on the distance between source FP and dramatically shortened gate FE This technique minimizes the parasitic capacitances, especially the gate-to-drain capacitance, showing a substantial potential for millimeter-wave, high power applications.展开更多
A novel Ga N-based vertical heterostructure field effect transistor（HFET） with nonuniform doping superjunctions（non-SJ HFET） is proposed and studied by Silvaco-ATLAS,for minimizing the specific on-resistance（RonA...A novel Ga N-based vertical heterostructure field effect transistor（HFET） with nonuniform doping superjunctions（non-SJ HFET） is proposed and studied by Silvaco-ATLAS,for minimizing the specific on-resistance（RonA） at no expense of breakdown voltage（BV）.The feature of non-SJ HFET lies in the nonuniform doping concentration from top to bottom in the n-and p-pillars,which is different from that of the conventional Ga N-based vertical HFET with uniform doping superjunctions（un-SJ HFET）.A physically intrinsic mechanism for the nonuniform doping superjunction（non-SJ） to further reduce RonA at no expense of BV is investigated and revealed in detail.The design,related to the structure parameters of non-SJ,is optimized to minimize the RonA on the basis of the same BV as that of un-SJ HFET.Optimized simulation results show that the reduction in RonA depends on the doping concentrations and thickness values of the light and heavy doping parts in non-SJ.The maximum reduction of more than 51% in RonA could be achieved with a BV of 1890 V.These results could demonstrate the superiority of non-SJ HFET in minimizing RonA and provide a useful reference for further developing the Ga N-based vertical HFETs.展开更多
Driven by the urgent demands for information technology,energy,and intelligent industry,third-generation semiconductor GaN has emerged as a pivotal component in electronic and optoelectronic devices.Fundamentally,piez...Driven by the urgent demands for information technology,energy,and intelligent industry,third-generation semiconductor GaN has emerged as a pivotal component in electronic and optoelectronic devices.Fundamentally,piezoelectric polarization is the most essential feature of GaN materials.Incorporating piezotronics and piezo-phototronics,GaN materials synergize mechanical signals with electrical and optical signals,thereby achieving multi-field coupling that enhances device performance.Piezotronics regulates the carrier transport process in micro-nano devices,which has been proven to significantly improve the performance of devices(such as high electron mobility transistors and microLEDs)and brings many novel applications.This review examines GaN material properties and the theoretical foundations of piezotronics and phototronics.Furthermore,it delves into the fabrication and integration processes of GaN devices to achieve state-of-the-art performance.Additionally,this review analyzes the impact of introducing three-dimensional stress and regulatory forces on the electrical and optical output performance of devices.Moreover,it discusses the burgeoning applications of GaN devices in neural sensing,optoelectronic output,and energy harvesting.The potential of piezotroniccontrolled GaN devices provides valuable insights for future research and the development of multi-functional,diversified electronic devices.展开更多
In recent years,the development of wafer-level GaN nanowires photocatalyst loaded onto silicon substrates has progressed rapidly depending on its simplicity of instrumentation,collection and separation from the water....In recent years,the development of wafer-level GaN nanowires photocatalyst loaded onto silicon substrates has progressed rapidly depending on its simplicity of instrumentation,collection and separation from the water.Accordingly,the wafer-level GaN-based nanowires(GaN NWs)photocatalyst can be a fabulous candidate for the application in the field of photocatalytic hydrogen evolution reaction(PHER)and provides a novel route to address the environmental and energy crisis.Herein,a range of innovative strategies to improve the performance of GaN NWs photocatalyst are systematically summarized.Then,the solar-to-hydrogen conversion efficiency,the characteristics of GaN NWs system,the cost of the origin material required,as well as the stability,activity and the corrosion resistance to seawater are discussed in detail as some of the essential conditions for advancing its large-scale industry-friendly application.Last but not least,we provide the potential application of this system for splitting seawater to produce hydrogen and point out the direction for overcoming the barriers to future industrial-scale implementation.展开更多
In this paper, we present a two-dimensional （2D） fully analytical model with consideration of polarization effect for the channel potential and electric field distributions of the gate field-plated high electron mob...In this paper, we present a two-dimensional （2D） fully analytical model with consideration of polarization effect for the channel potential and electric field distributions of the gate field-plated high electron mobility transistor （FP-HEMT） on the basis of 2D Poisson＇s solution. The dependences of the channel potential and electric field distributions on drain bias, polarization charge density, FP structure parameters, A1GaN/GaN material parameters, etc. are investigated. A simple and convenient approach to designing high breakdown voltage FP-HEMTs is also proposed. The validity of this model is demonstrated by comparison with the numerical simulations with Silvaco-Atlas. The method in this paper can be extended to the development of other analytical models for different device structures, such as MIS-HEMTs, multiple-FP HETMs, slant-FP HEMTs, etc.展开更多
In this work,we design and fabricate AlGaN/GaN-based Schottky barrier diodes(SBDs)on a silicon substrate with a trenched n^(+)-GaN cap layer.With the developed physical models,we find that the n^(+)-GaN cap layer prov...In this work,we design and fabricate AlGaN/GaN-based Schottky barrier diodes(SBDs)on a silicon substrate with a trenched n^(+)-GaN cap layer.With the developed physical models,we find that the n^(+)-GaN cap layer provides more electrons into the AlGaN/GaN channel,which is further confirmed experimentally.When compared with the reference device,this increases the two-dimensional electron gas(2DEG)density by two times and leads to a reduced specific ON-resistance(Ron,sp)of~2.4 mΩ·cm^(2).We also adopt the trenched n^(+)-GaN structure such that partial of the n^(+)-GaN is removed by using dry etching process to eliminate the surface electrical conduction when the device is set in the off-state.To suppress the surface defects that are caused by the dry etching process,we also deposit Si_(3)N_(4)layer prior to the deposition of field plate(FP),and we obtain a reduced leakage current of~8×10^(−5)A·cm^(−2)and breakdown voltage(BV)of 876 V.The Baliga’s figure of merit(BFOM)for the proposed structure is increased to~319 MW·cm^(−2).Our investigations also find that the pre-deposited Si_(3)N_(4)layer helps suppress the electron capture and transport processes,which enables the reduced dynamic R_(on,sp).展开更多
Stimulated emission and lasing of GaN-based laser diodes(LDs)were reported at 1995[1]and 1996[2],right after the breakthrough of p-type doping[3−5],material quality[6]and the invention of high-brightness GaN-based LED...Stimulated emission and lasing of GaN-based laser diodes(LDs)were reported at 1995[1]and 1996[2],right after the breakthrough of p-type doping[3−5],material quality[6]and the invention of high-brightness GaN-based LEDs[7,8].However,it took much longer time for GaN-based LDs to achieve high power,high wall plug efficiency,and long lifetime.Until 2019,Nichia reported blue LDs with these performances[9],which open wide applications with GaN-based blue LDs.展开更多
Ridge InGaN multi-quantum-well-structure （MQW） edge-emitting laser diodes （LDs） were grown on （0001） sapphire substrates by low-pressure metal-organic chemical vapour deposition （MOCVD）. The dielectric TiO2/Si...Ridge InGaN multi-quantum-well-structure （MQW） edge-emitting laser diodes （LDs） were grown on （0001） sapphire substrates by low-pressure metal-organic chemical vapour deposition （MOCVD）. The dielectric TiO2/SiO2 front and back facet coatings as cavity mirror facets of the LDs have been deposited with electron-beam evaporation method. The reflectivity of the designed front coating is about 50% and that of the back high reflective coating is as high as 99.9%. Under pulsed current injection at room temperature, the influences of the dielectric facets were discussed. The threshold current of the ridge GaN-based LDs was decreased after the deposition of the back high reflective dielectric mirrors and decreased again after the front facets were deposited. Above the threshold, the slope efficiency of the LDs with both reflective facets was larger than those with only back facets and without any reflective facets. It is important to design the reflectivity of the front facets for improving the performance of GaN-based LDs.展开更多
In order to suppress the electron leakage to p-type region of near-ultraviolet GaN/In_xGa_（1-x ）N/GaN multiple-quantumwell（MQW） laser diode（LD）, the Al composition of inserted p-type AlxGa_（1-x）N electron bloc...In order to suppress the electron leakage to p-type region of near-ultraviolet GaN/In_xGa_（1-x ）N/GaN multiple-quantumwell（MQW） laser diode（LD）, the Al composition of inserted p-type AlxGa_（1-x）N electron blocking layer（EBL） is optimized in an effective way, but which could only partially enhance the performance of LD. Here, due to the relatively shallow GaN/In_（0.04）Ga_（0.96）N/GaN quantum well, the hole leakage to n-type region is considered in the ultraviolet LD. To reduce the hole leakage, a 10-nm n-type Al_xGa_（1-x）N hole blocking layer（HBL） is inserted between n-type waveguide and the first quantum barrier, and the effect of Al composition of Al_xGa_（1-x）N HBL on LD performance is studied. Numerical simulations by the LASTIP reveal that when an appropriate Al composition of Al_xGa_（1-x）N HBL is chosen, both electron leakage and hole leakage can be reduced dramatically, leading to a lower threshold current and higher output power of LD.展开更多
GaN-based continuous-wave operated blue-violet laser diodes(LDs) with long lifetime are demonstrated, which are grown on a c-plane GaN substrate by metal organic chemical vapor deposition with a 10 × 600 μm^2 ri...GaN-based continuous-wave operated blue-violet laser diodes(LDs) with long lifetime are demonstrated, which are grown on a c-plane GaN substrate by metal organic chemical vapor deposition with a 10 × 600 μm^2 ridge waveguide structure.The electrical and optical characteristics of a blue-violet LD are investigated under direct-current injection at room temperature(25 °C). The stimulated emission wavelength and peak optical power of the LD are around 413 nm and over 600 mW, respectively.In addition, the threshold current density and voltage are as small as 1.46 kA/cm^2 and 4.1 V, respectively. Moreover, the lifetime is longer than 1000 hours under room-temperature continuous-wave operation.展开更多
The upper waveguide （UWG） has direct influences on the optical and electrical characteristics of the violet laser diode （LD） by changing the optical field distribution or barrier of the electron blocking layer （...The upper waveguide （UWG） has direct influences on the optical and electrical characteristics of the violet laser diode （LD） by changing the optical field distribution or barrier of the electron blocking layer （EBL）. In this study, a series of InGaN-based violet LDs with different UWGs are investigated systematically with LASTIP software. It is found that the output light power （OLP） under an injecting current of 120 mA or the threshold current （Ith） is deteriorated when the UWG is u-In0.02Ga0.98N/GaN or u-In0.02Ga0.98N/AlxGa1-xN （0 ≤ x ≤ 0.1）, which should be attributed to small optical confinement factor （OCF） or severe electron leakage. Therefore, a new violet LD structure with u-In0.02Ga0.98N/GaN/Al0.05Ga0.95N multiple layer UWG is proposed to reduce the optical loss and increase the barrier of EBL. Finally, the output light power under an injecting current of 120 mA is improved to 176.4 mW.展开更多
GaN-based light-emitting diodes （LEDs） with surface-textured indium tin oxide （ITO） as a transparent current spreading layer were fabricated. The ITO surface was textured by inductively coupled plasma （ICP） etch...GaN-based light-emitting diodes （LEDs） with surface-textured indium tin oxide （ITO） as a transparent current spreading layer were fabricated. The ITO surface was textured by inductively coupled plasma （ICP） etching technology using a monolayer of nickel （Ni） nanoparticles as the etching mask. The luminance intensity of ITO surface-textured GaN-based LEDs was enhanced by about 34% compared to that of conventional LED without textured ITO layer. In addition, the fabricated ITO surface-textured GaN-based LEDs would present a quite good performance in electrical characteristics. The results indicate that the scattering of photons emitted in the active layer was greatly enhanced via the textured ITO surface, and the ITO surface-textured technique could have a potential application in improving photoelectric characteristics for manufacturing GaN-based LEDs of higher brightness.展开更多
Gallium nitride(Ga N)-based high electron mobility transistors(HEMTs)that work in aerospace are exposed to particles radiation,which can cause the degradation in electrical performance.We investigate the effect of pro...Gallium nitride(Ga N)-based high electron mobility transistors(HEMTs)that work in aerospace are exposed to particles radiation,which can cause the degradation in electrical performance.We investigate the effect of proton irradiation on the concentration of two-dimensional electron gas(2 DEG)in Ga N-based HEMTs.Coupled Schr¨odinger’s and Poisson’s equations are solved to calculate the band structure and the concentration of 2 DEG by the self-consistency method,in which the vacancies caused by proton irradiation are taken into account.Proton irradiation simulation for Ga N-based HEMT is carried out using the stopping and range of ions in matter(SRIM)simulation software,after which a theoretical model is established to analyze how proton irradiation affects the concentration of 2 DEG.Irradiated by protons with high fluence and low energy,a large number of Ga vacancies appear inside the device.The results indicate that the ionized Ga vacancies in the Ga N cap layer and the Al Ga N layer will affect the Fermi level,while the Ga vacancies in the Ga N layer will trap the two-dimensional electrons in the potential well.Proton irradiation significantly reduced the concentration of 2 DEG by the combined effect of these two mechanisms.展开更多
Although the 5G wireless network has made significant advances,it is not enough to accommodate the rapidly rising requirement for broader bandwidth in post-5G and 6G eras.As a result,emerging technologies in higher fr...Although the 5G wireless network has made significant advances,it is not enough to accommodate the rapidly rising requirement for broader bandwidth in post-5G and 6G eras.As a result,emerging technologies in higher frequencies including visible light communication(VLC),are becoming a hot topic.In particular,LED-based VLC is foreseen as a key enabler for achieving data rates at the Tb/s level in indoor scenarios using multi-color LED arrays with wavelength division multiplexing(WDM)technology.This paper proposes an optimized multi-color LED array chip for high-speed VLC systems.Its long-wavelength GaN-based LED units are remarkably enhanced by V-pit structure in their efficiency,especially in the“yellow gap”region,and it achieves significant improvement in data rate compared with earlier research.This work investigates the V-pit structure and tries to provide insight by introducing a new equivalent circuit model,which provides an explanation of the simulation and experiment results.In the final test using a laboratory communication system,the data rates of eight channels from short to long wavelength are 3.91 Gb/s,3.77 Gb/s,3.67 Gb/s,4.40 Gb/s,3.78 Gb/s,3.18 Gb/s,4.31 Gb/s,and 4.35 Gb/s(31.38 Gb/s in total),with advanced digital signal processing(DSP)techniques including digital equalization technique and bit-power loading discrete multitone(DMT)modulation format.展开更多
The kink effect in current-voltage （IV） characteristic s seriously deteriorates the performance of a GaN-based HEMT. Based on a series of direct current （DC） IV measurements in a GaN-based HEMT with an AlGaN back ...The kink effect in current-voltage （IV） characteristic s seriously deteriorates the performance of a GaN-based HEMT. Based on a series of direct current （DC） IV measurements in a GaN-based HEMT with an AlGaN back barrier, a possible mechanism with electron-trapping and detrapping processes is proposed. Kink-related deep levels are activated by a high drain source voltage （Vds） and located in a GaN channel layer. Both electron trapping and detrapping processes are accomplished with the help of hot electrons from the channel by impact ionization. Moreover, the mechanism is verified by two other DC IV measurements and a model with an expression of the kink current.展开更多
GaN-based multiple quantum well light-emitting diodes （LEDs） with conventional and superlattice barriers have been investigated numerically. Simulation results demonstrate using InGaN/GaN superlattices as barriers c...GaN-based multiple quantum well light-emitting diodes （LEDs） with conventional and superlattice barriers have been investigated numerically. Simulation results demonstrate using InGaN/GaN superlattices as barriers can effectively enhance performances of the GaN-Based LEDs, mainly owing to the improvement of hole injection and transport among the MQW active region. Meanwhile, the improved electron capture decreases the electron leakage and alleviates the efficiency droop. The weak polarization field induced by the superlattice structure strengthens the intensity of the emission spectrum and leads to a blue-shift relative to the conventional one.展开更多
In the GaN-based heterostructures, this paper reports that the strong electric fields induced by polarization effects at the structure boundaries complicate the electric-static equilibrium and the boundary conditions....In the GaN-based heterostructures, this paper reports that the strong electric fields induced by polarization effects at the structure boundaries complicate the electric-static equilibrium and the boundary conditions. The basic requirements of electric-static equilibrium for the heterostructure systems are discussed first, and it is deduced that in the application of the coupled Schroedinger-Poisson model to the heterostructures of electric static equilibrium state, zero external electric field guarantees the overall electric neutrality, and there is no need to introduce the charge balance equation. Then the relation between the screening of the polar charges in GaN-based heterostructures and the possible boundary conditions of the Poisson equation is analysed, it is shown that the various boundary conditions are equivalent to each other, and the surface charge, which can be used in studying the screening of the polar charges, can be precisely solved even if only the conduction band energy is correctly known at the surface. Finally, through the calculations on an AlGaN/GaN heterostructure with typical structure parameters by the coupled Schroedinger-Poisson model under the various boundary conditions, the correctness of the above analyses are validated.展开更多
The effects of dielectric thin films on the performance of GaN-based high-electron-mobility transistors （HEMTs） were reviewed in this work. Firstly, the nonpolar dielectric thin films which act as both the surface p...The effects of dielectric thin films on the performance of GaN-based high-electron-mobility transistors （HEMTs） were reviewed in this work. Firstly, the nonpolar dielectric thin films which act as both the surface passivation layers and the gate insulators of the high-frequency GaN-based high-electron-mobility transistors were presented. Furthermore, the influences of dielectric thin films on the electrical properties of two-dimensional electron gas （2DEG） in the A1GaN/GaN hetero-structures were ana- lyzed. It was found that the additional in-plane biaxial tensile stress was another important factor besides the change in surface potential profile for the device perfor- mance improvement of the A1GaN/GaN HEMTs with dielectric thin films as both passivation layers and gate dielectrics. Then, two kinds of polar gate dielectric thin films, the ferroelectric LiNbO3 and the fluorinated A1203, were compared for the enhancement-mode GaN-based HEMTs, and an innovative process was proposed. At last, high-permittivity dielectric thin films were adopted as passivation layers to modulate the electric field and accordingly increase the breakdown voltage of GaN-based HEMTs. Moreover, the polyimide embedded with Cr particles effectively increased the breakdown voltage of GaNbased HEMTs. Finally, the effects of high-permittivity dielectric thin films on the potential distribution in the drift region were simulated, which showed an expanded electric field peak at the drain-side edge of gate electrode.展开更多
The influences of InGaN/GaN multiple quantum wells (MQWs) and AlGaN electron-blocking layers (EBL) on the performance of GaN-based violet laser diodes are investigated. Compared with the InGaN/GaN MQWs grown at two di...The influences of InGaN/GaN multiple quantum wells (MQWs) and AlGaN electron-blocking layers (EBL) on the performance of GaN-based violet laser diodes are investigated. Compared with the InGaN/GaN MQWs grown at two different temperatures, the same-temperature growth of InGaN well and GaN barrier layers has a positive effect on the threshold current and slope efficiency of laser diodes, indicating that the quality of MQWs is improved. In addition, the performance of GaN laser diodes could be further improved by increasing Al content in the AlGaN EBL due to the fact that the electron leakage current could be reduced by properly increasing the barrier height of AlGaN EBL. The violet laser diode with a peak output power of 20 W is obtained.展开更多
基金supported by the Program for New Century Excellent Talents in University, China (Grant No. NCET-12-0915)the National Natural Science Foundation of China (Grant No. 61106106)the Fundamental Research Funds for the Central Universities, China (Grant No. K5051225013)
文摘A novel source-connected field plate structure, featuring the same photolithography mask as the gate electrode, is proposed as an improvement over the conventional field plate （FP） techniques to enhance the frequency performance in GaN-based HEMTs. The influences of the field plate on frequency and breakdown performance are investigated simul- taneously by using a two-dimensional physics-based simulation. Compared with the conventional T-gate structures with a field plate length of 1.2 gm, this field plate structure can induce the small signal power gain at 10 GHz to increase by 5-9.5 dB, which depends on the distance between source FP and dramatically shortened gate FE This technique minimizes the parasitic capacitances, especially the gate-to-drain capacitance, showing a substantial potential for millimeter-wave, high power applications.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61574112,61334002,61474091,and 61574110)the Natural Science Basic Research Plan in Shaanxi Province,China(Grant No.605119425012)
文摘A novel Ga N-based vertical heterostructure field effect transistor（HFET） with nonuniform doping superjunctions（non-SJ HFET） is proposed and studied by Silvaco-ATLAS,for minimizing the specific on-resistance（RonA） at no expense of breakdown voltage（BV）.The feature of non-SJ HFET lies in the nonuniform doping concentration from top to bottom in the n-and p-pillars,which is different from that of the conventional Ga N-based vertical HFET with uniform doping superjunctions（un-SJ HFET）.A physically intrinsic mechanism for the nonuniform doping superjunction（non-SJ） to further reduce RonA at no expense of BV is investigated and revealed in detail.The design,related to the structure parameters of non-SJ,is optimized to minimize the RonA on the basis of the same BV as that of un-SJ HFET.Optimized simulation results show that the reduction in RonA depends on the doping concentrations and thickness values of the light and heavy doping parts in non-SJ.The maximum reduction of more than 51% in RonA could be achieved with a BV of 1890 V.These results could demonstrate the superiority of non-SJ HFET in minimizing RonA and provide a useful reference for further developing the Ga N-based vertical HFETs.
基金the support from the National Natural Science Foundation of China(Grant Nos.52173298,52192611 and 61904012)the National Key R&D Project from Minister of Science and Technology(2021YFA1201603)+1 种基金Beijing Natural Science Foundation(Z230024)the Fundamental Research Funds for the Central Universities。
文摘Driven by the urgent demands for information technology,energy,and intelligent industry,third-generation semiconductor GaN has emerged as a pivotal component in electronic and optoelectronic devices.Fundamentally,piezoelectric polarization is the most essential feature of GaN materials.Incorporating piezotronics and piezo-phototronics,GaN materials synergize mechanical signals with electrical and optical signals,thereby achieving multi-field coupling that enhances device performance.Piezotronics regulates the carrier transport process in micro-nano devices,which has been proven to significantly improve the performance of devices(such as high electron mobility transistors and microLEDs)and brings many novel applications.This review examines GaN material properties and the theoretical foundations of piezotronics and phototronics.Furthermore,it delves into the fabrication and integration processes of GaN devices to achieve state-of-the-art performance.Additionally,this review analyzes the impact of introducing three-dimensional stress and regulatory forces on the electrical and optical output performance of devices.Moreover,it discusses the burgeoning applications of GaN devices in neural sensing,optoelectronic output,and energy harvesting.The potential of piezotroniccontrolled GaN devices provides valuable insights for future research and the development of multi-functional,diversified electronic devices.
基金supported by the Natural Science Foundation of China(No.51902101,22479079)Innovation Support Programme(Soft Science Research)Project Achievements of Jiangsu Province(BK20231514)+3 种基金the Youth Natural Science Foundation of Hunan Province(No.2021JJ40044)Natural Science Foundation of Jiangsu Province(No.BK20201381)Science Foundation of Nanjing University of Posts and Telecommunications(Nos.NY219144,NY221046)the National College Student Innovation and Entrepre-neurship Training Program(No.202210293083Y).
文摘In recent years,the development of wafer-level GaN nanowires photocatalyst loaded onto silicon substrates has progressed rapidly depending on its simplicity of instrumentation,collection and separation from the water.Accordingly,the wafer-level GaN-based nanowires(GaN NWs)photocatalyst can be a fabulous candidate for the application in the field of photocatalytic hydrogen evolution reaction(PHER)and provides a novel route to address the environmental and energy crisis.Herein,a range of innovative strategies to improve the performance of GaN NWs photocatalyst are systematically summarized.Then,the solar-to-hydrogen conversion efficiency,the characteristics of GaN NWs system,the cost of the origin material required,as well as the stability,activity and the corrosion resistance to seawater are discussed in detail as some of the essential conditions for advancing its large-scale industry-friendly application.Last but not least,we provide the potential application of this system for splitting seawater to produce hydrogen and point out the direction for overcoming the barriers to future industrial-scale implementation.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61204085 and 61334002)the Fundamental Research Funds for the Central Universities,China(Grant No.K5051225013)
文摘In this paper, we present a two-dimensional （2D） fully analytical model with consideration of polarization effect for the channel potential and electric field distributions of the gate field-plated high electron mobility transistor （FP-HEMT） on the basis of 2D Poisson＇s solution. The dependences of the channel potential and electric field distributions on drain bias, polarization charge density, FP structure parameters, A1GaN/GaN material parameters, etc. are investigated. A simple and convenient approach to designing high breakdown voltage FP-HEMTs is also proposed. The validity of this model is demonstrated by comparison with the numerical simulations with Silvaco-Atlas. The method in this paper can be extended to the development of other analytical models for different device structures, such as MIS-HEMTs, multiple-FP HETMs, slant-FP HEMTs, etc.
基金supported by National Natural Science Foundation of China under grant U23A20361Key Area R&D Program of Guangdong Province under grant 2022B0701180001.
文摘In this work,we design and fabricate AlGaN/GaN-based Schottky barrier diodes(SBDs)on a silicon substrate with a trenched n^(+)-GaN cap layer.With the developed physical models,we find that the n^(+)-GaN cap layer provides more electrons into the AlGaN/GaN channel,which is further confirmed experimentally.When compared with the reference device,this increases the two-dimensional electron gas(2DEG)density by two times and leads to a reduced specific ON-resistance(Ron,sp)of~2.4 mΩ·cm^(2).We also adopt the trenched n^(+)-GaN structure such that partial of the n^(+)-GaN is removed by using dry etching process to eliminate the surface electrical conduction when the device is set in the off-state.To suppress the surface defects that are caused by the dry etching process,we also deposit Si_(3)N_(4)layer prior to the deposition of field plate(FP),and we obtain a reduced leakage current of~8×10^(−5)A·cm^(−2)and breakdown voltage(BV)of 876 V.The Baliga’s figure of merit(BFOM)for the proposed structure is increased to~319 MW·cm^(−2).Our investigations also find that the pre-deposited Si_(3)N_(4)layer helps suppress the electron capture and transport processes,which enables the reduced dynamic R_(on,sp).
基金supported by the Natural Science Foundation of Jiangsu Province(Grant.BK20232042).
文摘Stimulated emission and lasing of GaN-based laser diodes(LDs)were reported at 1995[1]and 1996[2],right after the breakthrough of p-type doping[3−5],material quality[6]and the invention of high-brightness GaN-based LEDs[7,8].However,it took much longer time for GaN-based LDs to achieve high power,high wall plug efficiency,and long lifetime.Until 2019,Nichia reported blue LDs with these performances[9],which open wide applications with GaN-based blue LDs.
基金supported by the National High Technology Program of China (Grant No 2007AA03Z403)the National Natural Science Foundation of China (Grant Nos 60776042 and 60477011)National Basic Research Program of China (Grand No2006CB921607)
文摘Ridge InGaN multi-quantum-well-structure （MQW） edge-emitting laser diodes （LDs） were grown on （0001） sapphire substrates by low-pressure metal-organic chemical vapour deposition （MOCVD）. The dielectric TiO2/SiO2 front and back facet coatings as cavity mirror facets of the LDs have been deposited with electron-beam evaporation method. The reflectivity of the designed front coating is about 50% and that of the back high reflective coating is as high as 99.9%. Under pulsed current injection at room temperature, the influences of the dielectric facets were discussed. The threshold current of the ridge GaN-based LDs was decreased after the deposition of the back high reflective dielectric mirrors and decreased again after the front facets were deposited. Above the threshold, the slope efficiency of the LDs with both reflective facets was larger than those with only back facets and without any reflective facets. It is important to design the reflectivity of the front facets for improving the performance of GaN-based LDs.
基金Project supported by the Science Challenge Project,China(Grant No.Z2016003)the National Key R&D Program of China(Grant Nos.2016YFB0400803and 2016YFB0401801)+1 种基金the National Natural Science Foundation of China(Grant Nos.61674138,61674139,61604145,61574135,61574134,61474142,61474110,61377020,and 61376089)the Beijing Municipal Science and Technology Project,China(Grant No.Z161100002116037)
文摘In order to suppress the electron leakage to p-type region of near-ultraviolet GaN/In_xGa_（1-x ）N/GaN multiple-quantumwell（MQW） laser diode（LD）, the Al composition of inserted p-type AlxGa_（1-x）N electron blocking layer（EBL） is optimized in an effective way, but which could only partially enhance the performance of LD. Here, due to the relatively shallow GaN/In_（0.04）Ga_（0.96）N/GaN quantum well, the hole leakage to n-type region is considered in the ultraviolet LD. To reduce the hole leakage, a 10-nm n-type Al_xGa_（1-x）N hole blocking layer（HBL） is inserted between n-type waveguide and the first quantum barrier, and the effect of Al composition of Al_xGa_（1-x）N HBL on LD performance is studied. Numerical simulations by the LASTIP reveal that when an appropriate Al composition of Al_xGa_（1-x）N HBL is chosen, both electron leakage and hole leakage can be reduced dramatically, leading to a lower threshold current and higher output power of LD.
基金supported by the National Key R&D Program of China (Nos. 2016YFB0401801, 2016YFB0400803)the Science Challenge Project (No. TZ2016003)+1 种基金the National Natural Science Foundation of China (Nos. 61674138, 61674139, 61604145, 61574135, 61574134, 61474142, 61474110)the Beijing Municipal Science and Technology Project (No. Z161100002116037)
文摘GaN-based continuous-wave operated blue-violet laser diodes(LDs) with long lifetime are demonstrated, which are grown on a c-plane GaN substrate by metal organic chemical vapor deposition with a 10 × 600 μm^2 ridge waveguide structure.The electrical and optical characteristics of a blue-violet LD are investigated under direct-current injection at room temperature(25 °C). The stimulated emission wavelength and peak optical power of the LD are around 413 nm and over 600 mW, respectively.In addition, the threshold current density and voltage are as small as 1.46 kA/cm^2 and 4.1 V, respectively. Moreover, the lifetime is longer than 1000 hours under room-temperature continuous-wave operation.
基金Project supported by the National Key R&D Program of China(Grant Nos.2016YFB0400803 and 2016YFB0401801)the National Natural Science Foundation of China(Grant Nos.61674138,61674139,61604145,61574135,61574134,61474142,61474110,61377020,and 61376089)+1 种基金the Science Challenge Project,China(Grant No.TZ2016003)the Beijing Municipal Science and Technology Project,China(Grant No.Z161100002116037)
文摘The upper waveguide （UWG） has direct influences on the optical and electrical characteristics of the violet laser diode （LD） by changing the optical field distribution or barrier of the electron blocking layer （EBL）. In this study, a series of InGaN-based violet LDs with different UWGs are investigated systematically with LASTIP software. It is found that the output light power （OLP） under an injecting current of 120 mA or the threshold current （Ith） is deteriorated when the UWG is u-In0.02Ga0.98N/GaN or u-In0.02Ga0.98N/AlxGa1-xN （0 ≤ x ≤ 0.1）, which should be attributed to small optical confinement factor （OCF） or severe electron leakage. Therefore, a new violet LD structure with u-In0.02Ga0.98N/GaN/Al0.05Ga0.95N multiple layer UWG is proposed to reduce the optical loss and increase the barrier of EBL. Finally, the output light power under an injecting current of 120 mA is improved to 176.4 mW.
基金Project supported by the Production and Research Program of Guangdong Province and Ministry of Education (Grant No.2009B090300338)Guangdong Natural Science Foundation of China (Grant No.8251063101000007)+1 种基金Guangdong Science and Technology Plan of China (Grant No.2008B010200004)the Student Research Project of South China Normal University (Grant No.09XXKC03)
文摘GaN-based light-emitting diodes （LEDs） with surface-textured indium tin oxide （ITO） as a transparent current spreading layer were fabricated. The ITO surface was textured by inductively coupled plasma （ICP） etching technology using a monolayer of nickel （Ni） nanoparticles as the etching mask. The luminance intensity of ITO surface-textured GaN-based LEDs was enhanced by about 34% compared to that of conventional LED without textured ITO layer. In addition, the fabricated ITO surface-textured GaN-based LEDs would present a quite good performance in electrical characteristics. The results indicate that the scattering of photons emitted in the active layer was greatly enhanced via the textured ITO surface, and the ITO surface-textured technique could have a potential application in improving photoelectric characteristics for manufacturing GaN-based LEDs of higher brightness.
基金Project supported by the National Natural Science Foundation of China(Grant No.61874108)the Gansu Province Natural Science Foundation,China(Grant Nos.18JR3RA285 and 20JR5RA287)the Fundamental Research Funds for the Central Universities,China(Grant Nos.lzujbky-2020-kb06 and lzujbky-2020-cd02)。
文摘Gallium nitride(Ga N)-based high electron mobility transistors(HEMTs)that work in aerospace are exposed to particles radiation,which can cause the degradation in electrical performance.We investigate the effect of proton irradiation on the concentration of two-dimensional electron gas(2 DEG)in Ga N-based HEMTs.Coupled Schr¨odinger’s and Poisson’s equations are solved to calculate the band structure and the concentration of 2 DEG by the self-consistency method,in which the vacancies caused by proton irradiation are taken into account.Proton irradiation simulation for Ga N-based HEMT is carried out using the stopping and range of ions in matter(SRIM)simulation software,after which a theoretical model is established to analyze how proton irradiation affects the concentration of 2 DEG.Irradiated by protons with high fluence and low energy,a large number of Ga vacancies appear inside the device.The results indicate that the ionized Ga vacancies in the Ga N cap layer and the Al Ga N layer will affect the Fermi level,while the Ga vacancies in the Ga N layer will trap the two-dimensional electrons in the potential well.Proton irradiation significantly reduced the concentration of 2 DEG by the combined effect of these two mechanisms.
基金This research was funded by the National Key Research and Development Program of China(2022YFB2802803)the Natural Science Foundation of China Project(No.61925104,No.62031011,No.62201157,No.62074072).
文摘Although the 5G wireless network has made significant advances,it is not enough to accommodate the rapidly rising requirement for broader bandwidth in post-5G and 6G eras.As a result,emerging technologies in higher frequencies including visible light communication(VLC),are becoming a hot topic.In particular,LED-based VLC is foreseen as a key enabler for achieving data rates at the Tb/s level in indoor scenarios using multi-color LED arrays with wavelength division multiplexing(WDM)technology.This paper proposes an optimized multi-color LED array chip for high-speed VLC systems.Its long-wavelength GaN-based LED units are remarkably enhanced by V-pit structure in their efficiency,especially in the“yellow gap”region,and it achieves significant improvement in data rate compared with earlier research.This work investigates the V-pit structure and tries to provide insight by introducing a new equivalent circuit model,which provides an explanation of the simulation and experiment results.In the final test using a laboratory communication system,the data rates of eight channels from short to long wavelength are 3.91 Gb/s,3.77 Gb/s,3.67 Gb/s,4.40 Gb/s,3.78 Gb/s,3.18 Gb/s,4.31 Gb/s,and 4.35 Gb/s(31.38 Gb/s in total),with advanced digital signal processing(DSP)techniques including digital equalization technique and bit-power loading discrete multitone(DMT)modulation format.
基金Project supported by the Program for New Century Excellent Talents in University,China (Grant No.NCET-12-0915)
文摘The kink effect in current-voltage （IV） characteristic s seriously deteriorates the performance of a GaN-based HEMT. Based on a series of direct current （DC） IV measurements in a GaN-based HEMT with an AlGaN back barrier, a possible mechanism with electron-trapping and detrapping processes is proposed. Kink-related deep levels are activated by a high drain source voltage （Vds） and located in a GaN channel layer. Both electron trapping and detrapping processes are accomplished with the help of hot electrons from the channel by impact ionization. Moreover, the mechanism is verified by two other DC IV measurements and a model with an expression of the kink current.
基金Project supported by the National Natural Science Foundation of China(Grant No.60877069)the Science and Technology Key Program of Guangdong Province,China(Grant Nos.2011A081301004 and 2012A080304006)
文摘GaN-based multiple quantum well light-emitting diodes （LEDs） with conventional and superlattice barriers have been investigated numerically. Simulation results demonstrate using InGaN/GaN superlattices as barriers can effectively enhance performances of the GaN-Based LEDs, mainly owing to the improvement of hole injection and transport among the MQW active region. Meanwhile, the improved electron capture decreases the electron leakage and alleviates the efficiency droop. The weak polarization field induced by the superlattice structure strengthens the intensity of the emission spectrum and leads to a blue-shift relative to the conventional one.
文摘In the GaN-based heterostructures, this paper reports that the strong electric fields induced by polarization effects at the structure boundaries complicate the electric-static equilibrium and the boundary conditions. The basic requirements of electric-static equilibrium for the heterostructure systems are discussed first, and it is deduced that in the application of the coupled Schroedinger-Poisson model to the heterostructures of electric static equilibrium state, zero external electric field guarantees the overall electric neutrality, and there is no need to introduce the charge balance equation. Then the relation between the screening of the polar charges in GaN-based heterostructures and the possible boundary conditions of the Poisson equation is analysed, it is shown that the various boundary conditions are equivalent to each other, and the surface charge, which can be used in studying the screening of the polar charges, can be precisely solved even if only the conduction band energy is correctly known at the surface. Finally, through the calculations on an AlGaN/GaN heterostructure with typical structure parameters by the coupled Schroedinger-Poisson model under the various boundary conditions, the correctness of the above analyses are validated.
基金financially supported by the National Nature Science Foundation of China(No.50932002)the Research Foundation for the Doctoral Program of Higher Education of China(No.2012018530003)
文摘The effects of dielectric thin films on the performance of GaN-based high-electron-mobility transistors （HEMTs） were reviewed in this work. Firstly, the nonpolar dielectric thin films which act as both the surface passivation layers and the gate insulators of the high-frequency GaN-based high-electron-mobility transistors were presented. Furthermore, the influences of dielectric thin films on the electrical properties of two-dimensional electron gas （2DEG） in the A1GaN/GaN hetero-structures were ana- lyzed. It was found that the additional in-plane biaxial tensile stress was another important factor besides the change in surface potential profile for the device perfor- mance improvement of the A1GaN/GaN HEMTs with dielectric thin films as both passivation layers and gate dielectrics. Then, two kinds of polar gate dielectric thin films, the ferroelectric LiNbO3 and the fluorinated A1203, were compared for the enhancement-mode GaN-based HEMTs, and an innovative process was proposed. At last, high-permittivity dielectric thin films were adopted as passivation layers to modulate the electric field and accordingly increase the breakdown voltage of GaN-based HEMTs. Moreover, the polyimide embedded with Cr particles effectively increased the breakdown voltage of GaNbased HEMTs. Finally, the effects of high-permittivity dielectric thin films on the potential distribution in the drift region were simulated, which showed an expanded electric field peak at the drain-side edge of gate electrode.
基金Supported by the National Key Research and Development Program of China under Grant No 2016YFB0401801the National Natural Science Foundation of China under Grant Nos 61574135,61574134,61474142,61474110,61377020,61376089,and 61223005the One Hundred Person Project of the Chinese Academy of Sciences
文摘The influences of InGaN/GaN multiple quantum wells (MQWs) and AlGaN electron-blocking layers (EBL) on the performance of GaN-based violet laser diodes are investigated. Compared with the InGaN/GaN MQWs grown at two different temperatures, the same-temperature growth of InGaN well and GaN barrier layers has a positive effect on the threshold current and slope efficiency of laser diodes, indicating that the quality of MQWs is improved. In addition, the performance of GaN laser diodes could be further improved by increasing Al content in the AlGaN EBL due to the fact that the electron leakage current could be reduced by properly increasing the barrier height of AlGaN EBL. The violet laser diode with a peak output power of 20 W is obtained.
