A tunable grating-coupled external cavity(EC)laser is realized by employing a GaN-based laser diode as the gain device.A tuning range of 4.47 nm from 403.82 to 408.29 nm is achieved.Detailed investigations reveal that...A tunable grating-coupled external cavity(EC)laser is realized by employing a GaN-based laser diode as the gain device.A tuning range of 4.47 nm from 403.82 to 408.29 nm is achieved.Detailed investigations reveal that the injection current strongly influences the performance of the EC laser.Below the free-running lasing threshold,EC laser works stably.While above the free-running lasing threshold,a Fabry–Pérot(F-P)resonance peak in the emission spectrum and a smooth kink in the output power-injection current characteristic curve are observed,suggesting the competition between the inner F-P cavity resonance and EC resonance.Furthermore,the tuning range is found to be asymmetric and occurs predominantly on the longer wavelength side.This is interpreted in terms of the asymmetric gain distribution of GaN-based quantum well material.展开更多
A new interface anisotropic potential,which is proportional to the lattice mismatch of interfaces and has no fitting parameter,has been deduced for(001)zinc-blende semiconductor interfaces.The comparison with other in...A new interface anisotropic potential,which is proportional to the lattice mismatch of interfaces and has no fitting parameter,has been deduced for(001)zinc-blende semiconductor interfaces.The comparison with other interface models is given for GaAs/AlAs and GaAs/InAs interfaces.The strong influence of the interface anisotropic potential on the inplane optical anisotropy of GaAs/AlGaAs low dimensional structures is demonstrated theoretically within the envelope function approximation.展开更多
Activities of space materials science research in China have been continuously supported by two main national programs.One is the China Space Station(CSS)program since 1992,and the other is the Strategic Priority Prog...Activities of space materials science research in China have been continuously supported by two main national programs.One is the China Space Station(CSS)program since 1992,and the other is the Strategic Priority Program(SPP)on Space Science since 2011.In CSS plan in 2019,eleven space materials science experimental projects were officially approved for execution during the construction of the space station.In the SPP Phase Ⅱ launched in 2018,seven pre-research projects are deployed as the first batch in 2018,and one concept study project in 2019.These pre-research projects will be cultivated as candidates for future selection as space experiment projects on the recovery of scientific experimental satellites in the future.A new apparatus of electrostatic levitation system for ground-based research of space materials science and rapid solidification research has been developed under the support of the National Natural Science Foundation of China.In order to promote domestic academic activities and to enhance the advancement of space materials science in China,the Space Materials Science and Technology Division belong to the Chinese Materials Research Society was established in 2019.We also organized scientists to write five review papers on space materials science as a special topic published in the journal Scientia Sinica to provide valuable scientific and technical references for Chinese researchers.展开更多
Helicity-dependent photocurrent(HDPC)of the surface states in a high-quality topological insulator(Bi_(0.7)Sb_(0.3))_(2)Te_(3)nanoplate grown by chemical vapor deposition(CVD)is investigated.By investigating the angle...Helicity-dependent photocurrent(HDPC)of the surface states in a high-quality topological insulator(Bi_(0.7)Sb_(0.3))_(2)Te_(3)nanoplate grown by chemical vapor deposition(CVD)is investigated.By investigating the angle-dependent HDPC,it is found that the HDPC is mainly contributed by the circular photogalvanic effect(CPGE)current when the incident plane is perpendicular to the connection of the two contacts,whereas the circular photon drag effect(CPDE)dominates the HDPC when the incident plane is parallel to the connection of the two contacts.In addition,the CPGE of the(Bi_(0.7)Sb_(0.3))_(2)Te_(3)nanoplate is regulated by temperature,light power,excitation wavelength,the source–drain and ionic liquid top-gate voltages,and the regulation mechanisms are discussed.It is demonstrated that(Bi_(0.7)Sb_(0.3))_(2)Te_(3)nanoplates may provide a good platform for novel opto-spintronics devices.展开更多
Optical reflection anisotropy microscopy mappings of micropipe defects on the surface of a 4H-SiC single crystal are studied by the scanning anisotropy microscopy(SAM)system.The reflection anisotropy(RA)image with a&#...Optical reflection anisotropy microscopy mappings of micropipe defects on the surface of a 4H-SiC single crystal are studied by the scanning anisotropy microscopy(SAM)system.The reflection anisotropy(RA)image with a'butterfly pattern'is obtained around the micropipes by SAM.The RA image of the edge dislocations is theoretically simulated based on dislocation theory and the photoelastic principle.By comparing with the Raman spectrum,it is verified that the micropipes consist of edge dislocations.The different patterns of the RA images are due to the different orientations of the Burgers vectors.Besides,the strain distribution of the micropipes is also deduced.One can identify the dislocation type,the direction of the Burgers vector and the optical anisotropy from the RA image by using SAM.Therefore,SAM is an ideal tool to measure the optical anisotropy induced by the strain field around a defect.展开更多
10-kV 4 H–SiC p-channel insulated gate bipolar transistors(IGBTs) are designed, fabricated, and characterized in this paper. The IGBTs have an active area of 2.25 mm^2 with a die size of 3 mm× 3 mm. A step space...10-kV 4 H–SiC p-channel insulated gate bipolar transistors(IGBTs) are designed, fabricated, and characterized in this paper. The IGBTs have an active area of 2.25 mm^2 with a die size of 3 mm× 3 mm. A step space modulated junction termination extension(SSM-JTE) structure is introduced and fabricated to improve the blocking performance of the IGBTs.The SiC p-channel IGBTs with SSM-JTE termination exhibit a leakage current of only 50 nA at-10 kV. To improve the on-state characteristics of SiC IGBTs, the hexagonal cell(H-cell) structure is designed and compared with the conventional interdigital cell(I-cell) structure. At an on-state current of 50 A/cm^2, the voltage drops of I-cell IGBT and H-cell IGBT are10.1 V and 8.3 V respectively. Meanwhile, on the assumption that the package power density is 300 W/cm^2, the maximum permissible current densities of the I-cell IGBT and H-cell IGBT are determined to be 34.2 A/cm^2 and 38.9 A/cm^2 with forward voltage drops of 8.8 V and 7.8 V, respectively. The differential specific on-resistance of I-cell structure and H-cell structure IGBT are 72.36 m?·cm^2 and 56.92 m?·cm^2, respectively. These results demonstrate that H-cell structure silicon carbide IGBT with SSM-JTE is a promising candidate for high power applications.展开更多
We present a strain-compensated InP-based InGaAs/InAlAs photovoltaic quantum cascade detector grown by solid source molecular beam epitaxy. The detector is based on a vertical intersubband transition and electron tran...We present a strain-compensated InP-based InGaAs/InAlAs photovoltaic quantum cascade detector grown by solid source molecular beam epitaxy. The detector is based on a vertical intersubband transition and electron transfer on a cascade of quantum levels which is designed to provide longitudinal optical phonon extraction stairs. By careful structure design and growth, the whole epilayer has a residual strain toward InP substrate of only -2.8× 10^-4. A clear narrow band detection spectrum centered at 4.5 μm has been observed above room temperature for a device with 200／times 200 ×μm^2 square mesa.展开更多
We report a monolithic integrated dual-wavelength laser diode based on a distributed Bragg reflector （DBR） composite resonant cavity. The device consists of three sections, a DBR grating section, a passive phase sec...We report a monolithic integrated dual-wavelength laser diode based on a distributed Bragg reflector （DBR） composite resonant cavity. The device consists of three sections, a DBR grating section, a passive phase section, and an active gain section. The gain section facet is cleaved to work as a laser cavity mirror. The other laser mirror is the DBR grating, which also functions as a wavelength filter and can control the number of wavelengths involved in the laser action. The reflection bandwidth of the DBR grating is fabricated to have an appropriate value to make the device work at the dual-wavelength lasing state. We adopt the quantum well intermixing （QWI） technique to provide low-absorption loss grating and passive phase section in the fabrication process. By tuning the injection currents on the DBR and the gain sections, the device can generate 0.596 nm-spaced dual-wavelength lasing at room temperature.展开更多
A 7.8-μm surface emitting second-order distributed feedback quantum cascade laser （DFB QCL） structure with metallized surface grating is studied. The modal property of this structure is described by utilizing coupl...A 7.8-μm surface emitting second-order distributed feedback quantum cascade laser （DFB QCL） structure with metallized surface grating is studied. The modal property of this structure is described by utilizing coupled-mode theory where the coupling coefficients are derived from exact Floquet-Bloch solutions of infinite periodic structure. Based on this theory, the influence of waveguide structure and grating topography as well as device length on the laser performance is numerically investigated. The optimized surface emitting second-order DFB QCL structure design exhibits a high surface outcoupling efficiency of 22% and a low threshold gain of 10 cm-1. Using a π phase-shift in the centre of the grating, a high-quality single-lobe far-field radiation pattern is obtained.展开更多
We demonstrate high-performance broadband tunable external-cavity lasers(ECLs) with the metal-organic chemical vapor deposition(MOCVD) grown In As/In P quantum dots(QDs) structures. Without cavity facet coatings, the ...We demonstrate high-performance broadband tunable external-cavity lasers(ECLs) with the metal-organic chemical vapor deposition(MOCVD) grown In As/In P quantum dots(QDs) structures. Without cavity facet coatings, the 3-d B spectral bandwidth of the Fabry–Perot(FP) laser is approximately 10.8 nm, while the tuning bandwidth of ECLs is 45 nm.Combined with the anti-reflection(AR)/high-reflection(HR) facet coating, a 92 nm bandwidth tuning range has been obtained with the wavelength covering from 1414 nm to 1506 nm. In most of the tuning range, the threshold current density is lower than 1.5 k A/cm2. The maximum output power of 6.5 m W was achieved under a 500 m A injection current.All achievements mentioned above were obtained under continuous-wave(CW) mode at room temperature(RT).展开更多
The free carrier density and mobility in n-type 4H-SiC substrates and epilayers were determined by accurately analysing the frequency shift and the full-shape of the longitudinal optic phono-plasmon coupled （LOPC） m...The free carrier density and mobility in n-type 4H-SiC substrates and epilayers were determined by accurately analysing the frequency shift and the full-shape of the longitudinal optic phono-plasmon coupled （LOPC） modes, and compared with those determined by Hall-effect measurement and that provided by the vendors. The transport properties of thick and thin 4H-SiC epilayers grown in both vertical and horizontal reactors were also studied. The free carrier density ranges between 2× 10^18 cm^-3 and 8× 10^18 cm^-3with a carrier mobility of 30-55 cm2/（V.s） for ntype 4H-SiC substrates and 1× 10^16 -3× 10^16 cm^-3 with mobility of 290-490 cm2/（V.s） for both thick and thin 4H-SiC epilayers grown in a horizontal reactor, while thick 4H-SiC epilayers grown in vertical reactor have a slightly higher carrier concentration of around 8.1×10^16 cm^-3 with mobility of 380 cm2/（V.s）. It was shown that Raman spectroscopy is a potential technique for determining the transport properties of 4H-SiC wafers with the advantage of being able to probe very small volumes and also being non-destructive. This is especially useful for future mass production of 4H-SiC epi-wafers.展开更多
ZnO films prepared at different temperatures and annealed at 900^o C in oxygen are studied by photoluminescence （PL） and x-ray photoelectron spectroscopy （XPS）. It is observed that in the PL of the as-grown films ...ZnO films prepared at different temperatures and annealed at 900^o C in oxygen are studied by photoluminescence （PL） and x-ray photoelectron spectroscopy （XPS）. It is observed that in the PL of the as-grown films the green luminescence （GL） and the yellow luminescence （YL） are related, and after annealing the GL is restrained and the YL is enhanced. The 0 ls XPS results also show the coexistence of oxygen vacancy （Vo） and interstitial oxygen （Oi） before annealing and the quenching of the Vo after annealing. By combining the two results it is deduced that the GL and YL are related to the Vo and Oi defects, respectively.展开更多
A monolithically active-passive integrated colliding pulse mode-locked semiconductor laser is demonstrated in the InGaAsP//InP material system. The device is mode locked at the second harmonic passive mode-locking reg...A monolithically active-passive integrated colliding pulse mode-locked semiconductor laser is demonstrated in the InGaAsP//InP material system. The device is mode locked at the second harmonic passive mode-locking regime with a wide mode-locking range. Pulse trains with the repetition rate of 40 GHz, 3-dB rf line width of 25 kHz, the pulse width of 2.5 ps, and a nearly transform-limited time-bandwidth product of 0.53 are obtained.展开更多
AlGaN/GaN high electron mobility transistors （HEMTs） grown on Fe-modulation-doped （MD） and unintentionally doped （UID） GaN buffer layers are investigated and compared. Highly resistive GaN buffers （10^9Ω·...AlGaN/GaN high electron mobility transistors （HEMTs） grown on Fe-modulation-doped （MD） and unintentionally doped （UID） GaN buffer layers are investigated and compared. Highly resistive GaN buffers （10^9Ω·cm） are induced by individual mechanisms for the electron traps＇ formation： the Fe MD buffer （sample A） and the UID buffer with high density of edge-type dislocations （7.24×10^9cm^-2, sample B）. The 300K Hall test indicates that the mobility of sample A with Fe doping （2503cm^2V^-1s^-1） is much higher than sample B （1926cm^2V^-1s^-1） due to the decreased scattering effect on the two-dimensional electron gas. HEMT devices are fabricated on the two samples and pulsed I–V measurements are conducted. Device A shows better gate pinch-off characteristics and a higher threshold voltage （-2.63V） compared with device B （-3.71V）. Lower gate leakage current ｜IGS｜ of device A （3.32×10^-7A） is present compared with that of device B （8.29×10^-7A）. When the off-state quiescent points Q_2 （V GQ2=-8V, V DQ2=0V） are on, V th hardly shifts for device A while device B shows ＋0.21V positive threshold voltage shift, resulting from the existence of electron traps associated with the dislocations in the UID-GaN buffer layer under the gate. Under pulsed I–V and transconductance G m–V GS measurement, the device with the Fe MD-doped buffer shows more potential in improving reliability upon off-state stress.展开更多
Dipolar and quadrupolar resonance wavelengths of SiO_(2)/Au nanoshell surface plasmons are designed at 560 nm to enhance the light trapping in thin film solar cells.In order to quantitatively describe the light trappi...Dipolar and quadrupolar resonance wavelengths of SiO_(2)/Au nanoshell surface plasmons are designed at 560 nm to enhance the light trapping in thin film solar cells.In order to quantitatively describe the light trapping effect,the forward−scattering efficiency(FSE)and the light trapping efficiency(LTE)are proposed by considering the light scattering direction of SiO_(2)/Au nanoshells.Based on the Mie theory,the FSE and the LTE are calculated for SiO_(2)/Au nanoshells of different dimensions,and the contributions of the dipolar and quadrupolar modes to the light trapping effect are analyzed in detail.When the surface coverage of nanoshells is 5%,the LTEs are 21.7%and 46.9%for SiO_(2)/Au nanoshells with sizes of(31 nm,69 nm)and(53 nm,141 nm),respectively.The results indicate that the SiO_(2)/Au nanoshell whose quadrupolar mode peak is designed to the strongest solar energy flux density of the solar spectrum facilitates the further enhancement of light harvesting in thin film solar cells.展开更多
Te-doped GaSb single crystal grown by the liquid encapsulated Czochralski(LEC) method exhibits a lag of compensating progress and a maximum carrier concentration around 8×10^(17) cm^(-3). The reason for this phen...Te-doped GaSb single crystal grown by the liquid encapsulated Czochralski(LEC) method exhibits a lag of compensating progress and a maximum carrier concentration around 8×10^(17) cm^(-3). The reason for this phenomenon has been investigated by a quantity concentration evaluation of the Te donor and native acceptor. The results of glow discharge mass spectrometry(GDMS) and Hall measurement suggest that the acceptor concentration increases with the increase of Te doping concentration, resulting in the enhancement of electrical compensation and free electron concentration reduction.The acceptor concentration variation is further demonstrated by photoluminescence spectra and explained by the principle of Fermi level dependent defect formation energy.展开更多
Monolithic integration of four 1.55-μm-range InGaAsP/InP distributed feedback （DFB） lasers using varied ridge width with a 4 x 1-multimode-interference （MMI） optical combiner and a semiconductor optical amplifier...Monolithic integration of four 1.55-μm-range InGaAsP/InP distributed feedback （DFB） lasers using varied ridge width with a 4 x 1-multimode-interference （MMI） optical combiner and a semiconductor optical amplifier （SOA） is demon- strated. The average output power and the threshold current are 1.8 mW and 35 mA, respectively, when the injection current of the SOA is 100 mA, with a side mode suppression ratio （SMSR） exceeding 40 dB. The four channels have a 1-nm average channel spacing and can operate separately or simultaneously.展开更多
Polarization dependence of the coupling of excitation light to surface plasmon polaritons （SPPs） was investigated in a Ag nanoparticle-nanowire waveguide system （a Ag nanoparticle attached to a Ag nanowire）. It wa...Polarization dependence of the coupling of excitation light to surface plasmon polaritons （SPPs） was investigated in a Ag nanoparticle-nanowire waveguide system （a Ag nanoparticle attached to a Ag nanowire）. It was found that under the illumination of excitation light on the nanoparticle-nanowire junction, the coupling efficiency of light to SPPs depends on the polarization of the excitation light. Theoretical simulations revealed that it is the local near-field coupling between the nanoparticle and the nanowire that enhances the incident light to excite the nanowire SPPs. Because the shapes of the Ag nanoparticles differ, the local field intensity, and thus the excitement of the nanowire SPPs, vary with the polarization of the excitation light.展开更多
The mode splitting induced by electro-optic birefringence in a P-I-N InGaAs/GaAs/A1GaAs vertical-cavity surface- emitting laser （VCSEL） has been studied by polarized electroluminescence （EL） at room temperature. T...The mode splitting induced by electro-optic birefringence in a P-I-N InGaAs/GaAs/A1GaAs vertical-cavity surface- emitting laser （VCSEL） has been studied by polarized electroluminescence （EL） at room temperature. The polarized EL spectra with E｜｜[110] and E ｜｜ [150] directions, are extracted for different injected currents. The mode splitting of the two orthogonal polarized modes for a VCSEL device is determined, and its value increases linearly with the increasing injected current due to electro-optic birefringence; This article demonstrates that the polarized EL is a powerful tool to study the mode splitting and polarization anisotropy of a VCSEL device.展开更多
The interface properties and electrical characteristics of the n-type 4H-SiC planar and trench metal-oxide-semiconductor （MOS） capacitors are investigated by measuring the capacitance voltage and current voltage. Th...The interface properties and electrical characteristics of the n-type 4H-SiC planar and trench metal-oxide-semiconductor （MOS） capacitors are investigated by measuring the capacitance voltage and current voltage. The flat-band voltage and interface state density are evaluated by the quasi-static method. It is not effective on further improving the interface properties annealing at 1250 ℃ in NO ambient for above 1 h due to the increasing interface shallow and fast states. These shallow states reduce the effective positive fixed charge density in the oxide. For the vertical MOS capacitors on the （1120） and （1100） faces, the interface state density can be reduced by approximately one order of magnitude, in comparison to the result of the planar MOS capacitors on the （0001） face under the same NO annealing condition. In addition, it is found that Fowler-Nordheim tunneling current occurs at an oxide electric field of 7 MV/cm for the planar MOS device. However, Poole-Frenkel conduction current occurs at a lower electric field of 4 MV/cm for the trench MOS capacitor. This is due to the local field crowded at the trench corner severely causing the electrons to be early captured at or emitted from the SiO2/SiC interface. These results provide a reference for an in-depth understanding of the mobility-limiting factors and long term reliability of the trench and planar SiO2/SiC interfaces.展开更多
基金Supported by the National Natural Science Foundation of China under grant Nos 91023048,61106044,and 61274052.
文摘A tunable grating-coupled external cavity(EC)laser is realized by employing a GaN-based laser diode as the gain device.A tuning range of 4.47 nm from 403.82 to 408.29 nm is achieved.Detailed investigations reveal that the injection current strongly influences the performance of the EC laser.Below the free-running lasing threshold,EC laser works stably.While above the free-running lasing threshold,a Fabry–Pérot(F-P)resonance peak in the emission spectrum and a smooth kink in the output power-injection current characteristic curve are observed,suggesting the competition between the inner F-P cavity resonance and EC resonance.Furthermore,the tuning range is found to be asymmetric and occurs predominantly on the longer wavelength side.This is interpreted in terms of the asymmetric gain distribution of GaN-based quantum well material.
基金Supported by the National Natural Science Foundation of China under Grant No.69391700.
文摘A new interface anisotropic potential,which is proportional to the lattice mismatch of interfaces and has no fitting parameter,has been deduced for(001)zinc-blende semiconductor interfaces.The comparison with other interface models is given for GaAs/AlAs and GaAs/InAs interfaces.The strong influence of the interface anisotropic potential on the inplane optical anisotropy of GaAs/AlGaAs low dimensional structures is demonstrated theoretically within the envelope function approximation.
基金Supports by the Strategic Priority Research Program on Space Science,the Chinese Academy of Sciences(XDA15013200,XDA15013700,XDA15013800,XDA15051200)the China’s Manned Space Station Project(TGJZ800-2-RW024)and the National Natural Science Foundation of China(51327901)。
文摘Activities of space materials science research in China have been continuously supported by two main national programs.One is the China Space Station(CSS)program since 1992,and the other is the Strategic Priority Program(SPP)on Space Science since 2011.In CSS plan in 2019,eleven space materials science experimental projects were officially approved for execution during the construction of the space station.In the SPP Phase Ⅱ launched in 2018,seven pre-research projects are deployed as the first batch in 2018,and one concept study project in 2019.These pre-research projects will be cultivated as candidates for future selection as space experiment projects on the recovery of scientific experimental satellites in the future.A new apparatus of electrostatic levitation system for ground-based research of space materials science and rapid solidification research has been developed under the support of the National Natural Science Foundation of China.In order to promote domestic academic activities and to enhance the advancement of space materials science in China,the Space Materials Science and Technology Division belong to the Chinese Materials Research Society was established in 2019.We also organized scientists to write five review papers on space materials science as a special topic published in the journal Scientia Sinica to provide valuable scientific and technical references for Chinese researchers.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.62074036,61674038,and 11574302)the Foreign Cooperation Project of Fujian Province,China(Grant No.2023I0005)+2 种基金the Open Research Fund Program of the State Key Laboratory of Low-Dimensional Quantum Physics(Grant No.KF202108)the National Key Research and Development Program of China(Grant No.2016YFB0402303)the Foundation of Fujian Provincial Department of Industry and Information Technology of China(Grant No.82318075)。
文摘Helicity-dependent photocurrent(HDPC)of the surface states in a high-quality topological insulator(Bi_(0.7)Sb_(0.3))_(2)Te_(3)nanoplate grown by chemical vapor deposition(CVD)is investigated.By investigating the angle-dependent HDPC,it is found that the HDPC is mainly contributed by the circular photogalvanic effect(CPGE)current when the incident plane is perpendicular to the connection of the two contacts,whereas the circular photon drag effect(CPDE)dominates the HDPC when the incident plane is parallel to the connection of the two contacts.In addition,the CPGE of the(Bi_(0.7)Sb_(0.3))_(2)Te_(3)nanoplate is regulated by temperature,light power,excitation wavelength,the source–drain and ionic liquid top-gate voltages,and the regulation mechanisms are discussed.It is demonstrated that(Bi_(0.7)Sb_(0.3))_(2)Te_(3)nanoplates may provide a good platform for novel opto-spintronics devices.
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2018YFE0204001,2018YFA0209103,2016YFB0400101,and 2016YFB0402303)the National Natural Science Foundation of China(Grant Nos.61627822,61704121,61991430,and 62074036)Postdoctoral Research Program of Jiangsu Province(Grant No.2021K599C).
文摘Optical reflection anisotropy microscopy mappings of micropipe defects on the surface of a 4H-SiC single crystal are studied by the scanning anisotropy microscopy(SAM)system.The reflection anisotropy(RA)image with a'butterfly pattern'is obtained around the micropipes by SAM.The RA image of the edge dislocations is theoretically simulated based on dislocation theory and the photoelastic principle.By comparing with the Raman spectrum,it is verified that the micropipes consist of edge dislocations.The different patterns of the RA images are due to the different orientations of the Burgers vectors.Besides,the strain distribution of the micropipes is also deduced.One can identify the dislocation type,the direction of the Burgers vector and the optical anisotropy from the RA image by using SAM.Therefore,SAM is an ideal tool to measure the optical anisotropy induced by the strain field around a defect.
基金Project supported by the National Basic Research Program of China(Grant No.2015CB759600)the Science Challenge Project,China(Grant No.TZ2018003)+3 种基金the National Natural Science Foundation of China(Grant Nos.61474113,61574140,and 61804149)the Beijing NOVA Program,China(Grant Nos.2016071and Z181100006218121)the Beijing Municipal Science and Technology Commission Project,China(Grant No.Z161100002116018)the Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant No.2012098)
文摘10-kV 4 H–SiC p-channel insulated gate bipolar transistors(IGBTs) are designed, fabricated, and characterized in this paper. The IGBTs have an active area of 2.25 mm^2 with a die size of 3 mm× 3 mm. A step space modulated junction termination extension(SSM-JTE) structure is introduced and fabricated to improve the blocking performance of the IGBTs.The SiC p-channel IGBTs with SSM-JTE termination exhibit a leakage current of only 50 nA at-10 kV. To improve the on-state characteristics of SiC IGBTs, the hexagonal cell(H-cell) structure is designed and compared with the conventional interdigital cell(I-cell) structure. At an on-state current of 50 A/cm^2, the voltage drops of I-cell IGBT and H-cell IGBT are10.1 V and 8.3 V respectively. Meanwhile, on the assumption that the package power density is 300 W/cm^2, the maximum permissible current densities of the I-cell IGBT and H-cell IGBT are determined to be 34.2 A/cm^2 and 38.9 A/cm^2 with forward voltage drops of 8.8 V and 7.8 V, respectively. The differential specific on-resistance of I-cell structure and H-cell structure IGBT are 72.36 m?·cm^2 and 56.92 m?·cm^2, respectively. These results demonstrate that H-cell structure silicon carbide IGBT with SSM-JTE is a promising candidate for high power applications.
基金Supported by the National Science Fund for Distinguished Young Scholars of China under Grant No 60525406, the National Natural Science Foundation of China under Grant Nos 60736031, 60806018, 60906026 and 10990100, the National Basic Research Program of China under Grant No 2006CB604903, and the National High-tcch R＆D Program of China under Grant Nos 2007AA03Z446 and 2009AA03Z403.
文摘We present a strain-compensated InP-based InGaAs/InAlAs photovoltaic quantum cascade detector grown by solid source molecular beam epitaxy. The detector is based on a vertical intersubband transition and electron transfer on a cascade of quantum levels which is designed to provide longitudinal optical phonon extraction stairs. By careful structure design and growth, the whole epilayer has a residual strain toward InP substrate of only -2.8× 10^-4. A clear narrow band detection spectrum centered at 4.5 μm has been observed above room temperature for a device with 200／times 200 ×μm^2 square mesa.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60736036 and 61021003)the National Basic Research Program of China (Grant No. 2011CB301702)
文摘We report a monolithic integrated dual-wavelength laser diode based on a distributed Bragg reflector （DBR） composite resonant cavity. The device consists of three sections, a DBR grating section, a passive phase section, and an active gain section. The gain section facet is cleaved to work as a laser cavity mirror. The other laser mirror is the DBR grating, which also functions as a wavelength filter and can control the number of wavelengths involved in the laser action. The reflection bandwidth of the DBR grating is fabricated to have an appropriate value to make the device work at the dual-wavelength lasing state. We adopt the quantum well intermixing （QWI） technique to provide low-absorption loss grating and passive phase section in the fabrication process. By tuning the injection currents on the DBR and the gain sections, the device can generate 0.596 nm-spaced dual-wavelength lasing at room temperature.
基金Project supported by the National Science Fund for Distinguished Young Scholars of China (Grant No. 60525406)the National Natural Science Foundation of China (Grant Nos. 60736031,60806018,and 60906026)+1 种基金the National Basic Research Program of China (Grant No. 2006CB604903)the National High Technology Research and Development Program of China (Grant Nos. 2007AA03Z446 and 2009AA03Z403)
文摘A 7.8-μm surface emitting second-order distributed feedback quantum cascade laser （DFB QCL） structure with metallized surface grating is studied. The modal property of this structure is described by utilizing coupled-mode theory where the coupling coefficients are derived from exact Floquet-Bloch solutions of infinite periodic structure. Based on this theory, the influence of waveguide structure and grating topography as well as device length on the laser performance is numerically investigated. The optimized surface emitting second-order DFB QCL structure design exhibits a high surface outcoupling efficiency of 22% and a low threshold gain of 10 cm-1. Using a π phase-shift in the centre of the grating, a high-quality single-lobe far-field radiation pattern is obtained.
基金Project supported by the National Natural Science Foundation of China(Grant No.61974141)Tianjin Municipal Science and Technology BureauScience and Technology Innovation Bureau of China-Singapore Tianjin Eco-City。
文摘We demonstrate high-performance broadband tunable external-cavity lasers(ECLs) with the metal-organic chemical vapor deposition(MOCVD) grown In As/In P quantum dots(QDs) structures. Without cavity facet coatings, the 3-d B spectral bandwidth of the Fabry–Perot(FP) laser is approximately 10.8 nm, while the tuning bandwidth of ECLs is 45 nm.Combined with the anti-reflection(AR)/high-reflection(HR) facet coating, a 92 nm bandwidth tuning range has been obtained with the wavelength covering from 1414 nm to 1506 nm. In most of the tuning range, the threshold current density is lower than 1.5 k A/cm2. The maximum output power of 6.5 m W was achieved under a 500 m A injection current.All achievements mentioned above were obtained under continuous-wave(CW) mode at room temperature(RT).
基金supported by the National Natural Science Foundation of China (Grant No. 60876003)the Knowledge Innovation Project of Chinese Academy of Sciences (Grant Nos. Y072011000 and ISCAS2008T04)the Science and Technology Projects of the State Grid Corporation of China (ZL71-09-001)
文摘The free carrier density and mobility in n-type 4H-SiC substrates and epilayers were determined by accurately analysing the frequency shift and the full-shape of the longitudinal optic phono-plasmon coupled （LOPC） modes, and compared with those determined by Hall-effect measurement and that provided by the vendors. The transport properties of thick and thin 4H-SiC epilayers grown in both vertical and horizontal reactors were also studied. The free carrier density ranges between 2× 10^18 cm^-3 and 8× 10^18 cm^-3with a carrier mobility of 30-55 cm2/（V.s） for ntype 4H-SiC substrates and 1× 10^16 -3× 10^16 cm^-3 with mobility of 290-490 cm2/（V.s） for both thick and thin 4H-SiC epilayers grown in a horizontal reactor, while thick 4H-SiC epilayers grown in vertical reactor have a slightly higher carrier concentration of around 8.1×10^16 cm^-3 with mobility of 380 cm2/（V.s）. It was shown that Raman spectroscopy is a potential technique for determining the transport properties of 4H-SiC wafers with the advantage of being able to probe very small volumes and also being non-destructive. This is especially useful for future mass production of 4H-SiC epi-wafers.
基金Supported by the Special Funds for Major State Basic Research Programme of China under No 2006CB604907, and the National Natural Science Foundation of China under Grant No 60506002.
文摘ZnO films prepared at different temperatures and annealed at 900^o C in oxygen are studied by photoluminescence （PL） and x-ray photoelectron spectroscopy （XPS）. It is observed that in the PL of the as-grown films the green luminescence （GL） and the yellow luminescence （YL） are related, and after annealing the GL is restrained and the YL is enhanced. The 0 ls XPS results also show the coexistence of oxygen vacancy （Vo） and interstitial oxygen （Oi） before annealing and the quenching of the Vo after annealing. By combining the two results it is deduced that the GL and YL are related to the Vo and Oi defects, respectively.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61335009,61274046 and 61474111
文摘A monolithically active-passive integrated colliding pulse mode-locked semiconductor laser is demonstrated in the InGaAsP//InP material system. The device is mode locked at the second harmonic passive mode-locking regime with a wide mode-locking range. Pulse trains with the repetition rate of 40 GHz, 3-dB rf line width of 25 kHz, the pulse width of 2.5 ps, and a nearly transform-limited time-bandwidth product of 0.53 are obtained.
基金Supported by the National Natural Science Foundation of China under Grant Nos 61204017 and 61334002the National Basic Research Program of Chinathe National Science and Technology Major Project of China
文摘AlGaN/GaN high electron mobility transistors （HEMTs） grown on Fe-modulation-doped （MD） and unintentionally doped （UID） GaN buffer layers are investigated and compared. Highly resistive GaN buffers （10^9Ω·cm） are induced by individual mechanisms for the electron traps＇ formation： the Fe MD buffer （sample A） and the UID buffer with high density of edge-type dislocations （7.24×10^9cm^-2, sample B）. The 300K Hall test indicates that the mobility of sample A with Fe doping （2503cm^2V^-1s^-1） is much higher than sample B （1926cm^2V^-1s^-1） due to the decreased scattering effect on the two-dimensional electron gas. HEMT devices are fabricated on the two samples and pulsed I–V measurements are conducted. Device A shows better gate pinch-off characteristics and a higher threshold voltage （-2.63V） compared with device B （-3.71V）. Lower gate leakage current ｜IGS｜ of device A （3.32×10^-7A） is present compared with that of device B （8.29×10^-7A）. When the off-state quiescent points Q_2 （V GQ2=-8V, V DQ2=0V） are on, V th hardly shifts for device A while device B shows ＋0.21V positive threshold voltage shift, resulting from the existence of electron traps associated with the dislocations in the UID-GaN buffer layer under the gate. Under pulsed I–V and transconductance G m–V GS measurement, the device with the Fe MD-doped buffer shows more potential in improving reliability upon off-state stress.
基金by the Natural Science Foundation of Beijing under Grant No 2102042the National Natural Science Foundation of China under Grant No 61006050+1 种基金the Fundamental Research Funds for the Central Universities under Grant No 10QG24the National Basic Research Program of China under Grant No 2010CB933800.
文摘Dipolar and quadrupolar resonance wavelengths of SiO_(2)/Au nanoshell surface plasmons are designed at 560 nm to enhance the light trapping in thin film solar cells.In order to quantitatively describe the light trapping effect,the forward−scattering efficiency(FSE)and the light trapping efficiency(LTE)are proposed by considering the light scattering direction of SiO_(2)/Au nanoshells.Based on the Mie theory,the FSE and the LTE are calculated for SiO_(2)/Au nanoshells of different dimensions,and the contributions of the dipolar and quadrupolar modes to the light trapping effect are analyzed in detail.When the surface coverage of nanoshells is 5%,the LTEs are 21.7%and 46.9%for SiO_(2)/Au nanoshells with sizes of(31 nm,69 nm)and(53 nm,141 nm),respectively.The results indicate that the SiO_(2)/Au nanoshell whose quadrupolar mode peak is designed to the strongest solar energy flux density of the solar spectrum facilitates the further enhancement of light harvesting in thin film solar cells.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61474104 and 61504131)
文摘Te-doped GaSb single crystal grown by the liquid encapsulated Czochralski(LEC) method exhibits a lag of compensating progress and a maximum carrier concentration around 8×10^(17) cm^(-3). The reason for this phenomenon has been investigated by a quantity concentration evaluation of the Te donor and native acceptor. The results of glow discharge mass spectrometry(GDMS) and Hall measurement suggest that the acceptor concentration increases with the increase of Te doping concentration, resulting in the enhancement of electrical compensation and free electron concentration reduction.The acceptor concentration variation is further demonstrated by photoluminescence spectra and explained by the principle of Fermi level dependent defect formation energy.
基金Project supported by the National High Technology Research and Pevelopment Program of China (Grant Nos. 2011AA010303 and 2012AA012203)the National Basic Research Program of China (Grant No. 2011CB301702)the National Natural Science Foundation of China (Grant Nos. 61021003 and 61090392)
文摘Monolithic integration of four 1.55-μm-range InGaAsP/InP distributed feedback （DFB） lasers using varied ridge width with a 4 x 1-multimode-interference （MMI） optical combiner and a semiconductor optical amplifier （SOA） is demon- strated. The average output power and the threshold current are 1.8 mW and 35 mA, respectively, when the injection current of the SOA is 100 mA, with a side mode suppression ratio （SMSR） exceeding 40 dB. The four channels have a 1-nm average channel spacing and can operate separately or simultaneously.
基金supported by the National Basic Research Program of China(Grant Nos.2012CB933004 and 2007CB936801)the National Natural Science Foundation of China(Grant Nos.11374023,61176120,and 60977015)+1 种基金the National Undergraduate Innovational Experimentation Program,Chinathe National Fund for Fostering Talents of Basic Science(NFFTBS),China(Grant Nos.J1030310 and J1103205)
文摘Polarization dependence of the coupling of excitation light to surface plasmon polaritons （SPPs） was investigated in a Ag nanoparticle-nanowire waveguide system （a Ag nanoparticle attached to a Ag nanowire）. It was found that under the illumination of excitation light on the nanoparticle-nanowire junction, the coupling efficiency of light to SPPs depends on the polarization of the excitation light. Theoretical simulations revealed that it is the local near-field coupling between the nanoparticle and the nanowire that enhances the incident light to excite the nanowire SPPs. Because the shapes of the Ag nanoparticles differ, the local field intensity, and thus the excitement of the nanowire SPPs, vary with the polarization of the excitation light.
基金Project supported the National Key Basic Research and Development Program of China (Grant Nos.2012CB921304 and 2013CB632805)the National Natural Science Foundation of China (Grant Nos.60990313,61306120,and 6106003)the Foundation of Fuzhou University (Grant No.022498)
文摘The mode splitting induced by electro-optic birefringence in a P-I-N InGaAs/GaAs/A1GaAs vertical-cavity surface- emitting laser （VCSEL） has been studied by polarized electroluminescence （EL） at room temperature. The polarized EL spectra with E｜｜[110] and E ｜｜ [150] directions, are extracted for different injected currents. The mode splitting of the two orthogonal polarized modes for a VCSEL device is determined, and its value increases linearly with the increasing injected current due to electro-optic birefringence; This article demonstrates that the polarized EL is a powerful tool to study the mode splitting and polarization anisotropy of a VCSEL device.
基金supported by the National Basic Research Program of China(Grant No.2015CB759600)the National Natural Science Foundation of China(Grant Nos.61474113 and 61574140)+3 种基金the Beijing NOVA Program,China(Grant No.Z1611000049161132016071)China Academy of Engineering Physics(CAEP)Microsystem and THz Science and Technology Foundation,China(Grant No.CAEPMT201502)the Beijing Municipal Science and Technology Commission Project,China(Grant Nos.Z161100002116018 and D16110300430000)the Youth Innovation Promotion Association of Chinese Academy of Sciences(Grant No.2012098)
文摘The interface properties and electrical characteristics of the n-type 4H-SiC planar and trench metal-oxide-semiconductor （MOS） capacitors are investigated by measuring the capacitance voltage and current voltage. The flat-band voltage and interface state density are evaluated by the quasi-static method. It is not effective on further improving the interface properties annealing at 1250 ℃ in NO ambient for above 1 h due to the increasing interface shallow and fast states. These shallow states reduce the effective positive fixed charge density in the oxide. For the vertical MOS capacitors on the （1120） and （1100） faces, the interface state density can be reduced by approximately one order of magnitude, in comparison to the result of the planar MOS capacitors on the （0001） face under the same NO annealing condition. In addition, it is found that Fowler-Nordheim tunneling current occurs at an oxide electric field of 7 MV/cm for the planar MOS device. However, Poole-Frenkel conduction current occurs at a lower electric field of 4 MV/cm for the trench MOS capacitor. This is due to the local field crowded at the trench corner severely causing the electrons to be early captured at or emitted from the SiO2/SiC interface. These results provide a reference for an in-depth understanding of the mobility-limiting factors and long term reliability of the trench and planar SiO2/SiC interfaces.
