We propose a novel resonator containing an elliptical microring based on a silicon-on-insulator platform. Simu- lations using the three-dimensional finite-difference time-domain method show that the novel elliptical m...We propose a novel resonator containing an elliptical microring based on a silicon-on-insulator platform. Simu- lations using the three-dimensional finite-difference time-domain method show that the novel elliptical microring can efficiently enhance the mode coupling between straight bus waveguides and resonator waveguides or between adjacent resonators while preserving relatively high intrinsic quality factors with large free spectral range. The proposed resonator would be an alternative choice for future high-density integrated photonic circuits.展开更多
The local density of states （LDOS） of two-dimensional square lattice photonic crystal （PhC） defect cavity is studied. The results show that the LDOS in the centre is greatly reduced, while the LDOS at the point of...The local density of states （LDOS） of two-dimensional square lattice photonic crystal （PhC） defect cavity is studied. The results show that the LDOS in the centre is greatly reduced, while the LDOS at the point off the centre （for example, at the point （0.3a, 0.4a）, where a is the lattice constant） is extremely enhanced. Further, the disordered radii are introduced to imitate the real devices fabricated in our experiment, and then we study the LDOS of PhC cavity with configurations of different disordered radii. The results show that in the disordered cavity, the LDOS in the centre is still greatly reduced, while the LDOS at the point （0.3a, 0.4a） is still extremely enhanced. It shows that the LDOS analysis is useful. When a laser is designed on the basis of the square lattice PhC rod cavity, in order to enhance the spontaneous emission, the active materials should not be inserted in the centre of the cavity, but located at positions off the centre. So LDOS method gives a guide to design the positions of the active materials （quantum dots） in the lasers.展开更多
Quantum key distribution(QKD)system based on passive silica planar lightwave circuit(PLC)asymmetric Mach–Zehnder interferometers(AMZI)is characterized with thermal stability,low loss and sufficient integration scalab...Quantum key distribution(QKD)system based on passive silica planar lightwave circuit(PLC)asymmetric Mach–Zehnder interferometers(AMZI)is characterized with thermal stability,low loss and sufficient integration scalability.However,waveguide stresses,both intrinsic and temperature-induced stresses,have significant impacts on the stable operation of the system.We have designed silica AMZI chips of 400 ps delay,with bend waveguides length equalized for both long and short arms to balance the stresses thereof.The temperature characteristics of the silica PLC AMZI chip are studied.The interference visibility at the single photon level is kept higher than 95%over a wide temperature range of 12℃.The delay time change is 0.321 ps within a temperature change of 40℃.The spectral shift is 0.0011 nm/0.1℃.Temperature-induced delay time and peak wavelength variations do not affect the interference visibility.The experiment results demonstrate the advantage of being tolerant to chip temperature fluctuations.展开更多
A quantum key distribution transmitter chip based on hybrid-integration of silica planar light-wave circuit(PLC)and lithium niobates(LN)modulator PLC is presented.The silica part consists of a tunable directional coup...A quantum key distribution transmitter chip based on hybrid-integration of silica planar light-wave circuit(PLC)and lithium niobates(LN)modulator PLC is presented.The silica part consists of a tunable directional coupler and 400-ps delay line,and the LN part is made up of a Y-branch,with electro-optic modulators on both arms.The two parts are facet-coupled to form an asymmetric Mach-Zehnder interferometer.We successfully encode and decode four BB84 states at 156.25-MHz repetition rate.Fast phase-encoding of 0 orπis achieved,with interference fringe visibilities 78.53%and 82.68%for states|+〉and|-〉,respectively.With the aid of an extra off-chip LN intensity modulator,two time-bin states are prepared and the extinction ratios are 18.65 dB and 15.46 dB for states|0〉and|1〉,respectively.展开更多
High quality Ge was epitaxially grown on Si using ultrahigh vacuum/chemical vapor deposition （UHV/CVD）. This paper demonstrates efficient germanium-on-silicon p-i-n photodetectors with 0.8 μm Ge, with responsivitie...High quality Ge was epitaxially grown on Si using ultrahigh vacuum/chemical vapor deposition （UHV/CVD）. This paper demonstrates efficient germanium-on-silicon p-i-n photodetectors with 0.8 μm Ge, with responsivities as high as 0.38 and 0.21 A/W at 1.31 and 1.55 μm, respectively. The dark current density is 0.37 mA/cm^2 and 29.4 mA/cm^2 at 0 V and a reverse bias of 0.5 V. The detector with a diameter of 30μm, a 3 dB-bandwidth of 4.72 GHz at an incident wavelength of 1550 nm and zero external bias has been measured. At a reverse bias of 3 V, the bandwidth is 6.28 GHz.展开更多
A compact and highly linear quartz-enhanced photoacoustic spectroscopy（QEPAS） sensor for the measurement of water vapor concentration in the air is demonstrated. A cost-effective quartz tuning fork（QTF） is used as...A compact and highly linear quartz-enhanced photoacoustic spectroscopy（QEPAS） sensor for the measurement of water vapor concentration in the air is demonstrated. A cost-effective quartz tuning fork（QTF） is used as the sharp transducer to convert light energy into an electrical signal based on the piezoelectric effect, thereby removing the need for a photodetector. The short optical path featured by the proposed sensing system leads to a decreased size. Furthermore, a pair of microresonators is applied in the absorbance detection module（ADM） for QTF signal enhancement. Compared with the system without microresonators, the detected QTF signal is increased to approximately 7-fold. Using this optimized QEPAS sensor with the proper modulation frequency and depth, we measure the water vapor concentration in the air at atmospheric pressure and room temperature. The experimental result shows that the sensor has a high sensitivity of 1.058parts-per-million.展开更多
Beta-gallium oxide(β-Ga_(2)O_(3))thin films were deposited on c-plane(0001)sapphire substrates with different mis-cut angles along<>by metal-organic chemical vapor deposition(MOCVD).The structural properties an...Beta-gallium oxide(β-Ga_(2)O_(3))thin films were deposited on c-plane(0001)sapphire substrates with different mis-cut angles along<>by metal-organic chemical vapor deposition(MOCVD).The structural properties and surface morphology of as-grownβ-Ga_(2)O_(3)thin films were investigated in detail.It was found that by using thin buffer layer and mis-cut substrate technology,the full width at half maximum(FWHM)of the()diffraction peak of theβ-Ga_(2)O_(3)film is decreased from 2°on c-plane(0001)Al_(2)O_(3)substrate to 0.64°on an 8°off-angled c-plane(0001)Al_(2)O_(3)substrate.The surface root-mean-square(RMS)roughness can also be improved greatly and the value is 1.27 nm for 8°off-angled c-plane(0001)Al_(2)O_(3)substrate.Room temper-ature photoluminescence(PL)was observed,which was attributed to the self-trapped excitons formed by oxygen and gallium vacancies in the film.The ultraviolet-blue PL intensity related with oxygen and gallium vacancies is decreased with the increas-ing mis-cut angle,which is in agreement with the improved crystal quality measured by high resolution X-ray diffraction(HR-XRD).The present results provide a route for growing high qualityβ-Ga_(2)O_(3)film on Al_(2)O_(3)substrate.展开更多
Two series of p-GaN films grown at different temperatures are obtained by metal organic chemical vapor deposition（MOCVD）. And the different variation behaviors of resistivity with growth condition for high- temperat...Two series of p-GaN films grown at different temperatures are obtained by metal organic chemical vapor deposition（MOCVD）. And the different variation behaviors of resistivity with growth condition for high- temperature（HT）-grown and low-temperature（LT）-grown p-GaN films are investigated. It is found that the resistivity of HT-grown p-GaN film is nearly unchanged when the NH_3 flow rate or reactor pressure increases. However, it decreases largely for LT-grown p-GaN film.These different variations may be attributed to the fact that carbon impurities are easy to incorporate into p-GaN film when the growth temperature is low. It results in a relatively high carbon concentration in LT-grown p-GaN film compared with HT-grown one. Therefore, carbon concentration is more sensitive to the growth condition in these samples, ultimately,leading to the different variation behaviors of resistivity for HT- and LT-grown ones.展开更多
In this paper, the temperature-dependent photoluminescence（PL） properties of Ga N grown on Si（111） substrate are studied. The main emission peaks of Ga N films grown on Si（111） are investigated and compared with...In this paper, the temperature-dependent photoluminescence（PL） properties of Ga N grown on Si（111） substrate are studied. The main emission peaks of Ga N films grown on Si（111） are investigated and compared with those grown on sapphire substrates. The positions of free and bound exciton luminescence peaks, i.e., FX A and D0 X peaks, of Ga N films grown on Si（111） substrates undergo red shifts compared with those grown on sapphire. This is attributed to the fact that the Ga N films grown on sapphire are under the action of compressive stress, while those grown on Si（111） substrate are subjected to tensile stress. Furthermore, the positions of these peaks may be additionally shifted due to different stress conditions in the real sample growth. The emission peaks due to stacking faults are found in Ga N films grown on Si（111） and an S-shaped temperature dependence of PL spectra can be observed, owing to the influence of the quantum well（QW） emission by the localized states near the conduction band gap edge and the temperature-dependent distribution of the photo-generated carriers.展开更多
New neuromorphic architectures and memory technologies with low power consumption,scalability and high-speed are in the spotlight due to the von Neumann bottleneck and limitations of Moore’s law.The memristor,a two-t...New neuromorphic architectures and memory technologies with low power consumption,scalability and high-speed are in the spotlight due to the von Neumann bottleneck and limitations of Moore’s law.The memristor,a two-terminal synaptic device,shows powerful capabilities in neuromorphic computing and information storage applications.Active materials with high defect migration speed and low defect migration barrier are highly promising for high-performance memristors.Halide perovskite(HP)materials with point defects(such as gaps,vacancies,and inversions)have strong application potential in memristors.In this article,we review recent advances on HP memristors with exceptional performances.First,the working mechanisms of memristors are described.Then,the structures and properties of HPs are explained.Both electrical and photonic HP-based memristors are overviewed and discussed.Different fabrication methods of HP memristor devices and arrays are described and compared.Finally,the challenges in integrating HP memristors with complementary metal oxide semiconductors(CMOS)are briefly discussed.This review can assist in developing HP memristors for the next-generation information technology.展开更多
We present the growth of CaN epilayer on Si （111） substrate with a single A1GaN interlayer sandwiched between the GaN epilayer and A1N buffer layer by using the metalorganic chemical vapour deposition. The influence...We present the growth of CaN epilayer on Si （111） substrate with a single A1GaN interlayer sandwiched between the GaN epilayer and A1N buffer layer by using the metalorganic chemical vapour deposition. The influence of the AlN buffer layer thickness on structural properties of the GaN epilayer has been investigated by scanning electron microscopy, atomic force microscopy, optical microscopy and high-resolution x-ray diffraction. It is found that an A1N buffer layer with the appropriate thickness plays an important role in increasing compressive strain and improving crystal quality during the growth of AlGaN interlayer, which can introduce a more compressive strain into the subsequent grown GaN layer, and reduce the crack density and threading dislocation density in GaN film.展开更多
A 25-channel 200 GHz arrayed waveguide grating(AWG)based on Si nanowire wavegnides is designed,simulated and fab-ricated.Transfer function method is used in the simulation and error analysis of AWG with width fluctuat...A 25-channel 200 GHz arrayed waveguide grating(AWG)based on Si nanowire wavegnides is designed,simulated and fab-ricated.Transfer function method is used in the simulation and error analysis of AWG with width fluctuations.The 25-channel 200 GHz AWG exhibits central channel insertion loss of 6.7 dB,crosstalk of-13 dB,and central wavelength of 1560.55 nm.The error analysis can explain the experimental results of 25-channel 200 GHz AWG well.By using deep ul-traviolet lithography(DUV)and inductively coupled plasma etching(ICP)technologies,the devices are fabricated on sili-con-on-insulator(SOI)substrate.展开更多
We report our recent progress of investigations on InGaN-based blue-violet laser diodes （LDs）. The roomtemperature （RT） cw operation lifetime of LDs has extended to longer than 15.6 h. The LD structure was grown o...We report our recent progress of investigations on InGaN-based blue-violet laser diodes （LDs）. The roomtemperature （RT） cw operation lifetime of LDs has extended to longer than 15.6 h. The LD structure was grown on a c-plane free-standing （FS） GaN substrate by metal organic chemical vapor deposition （MOCVD）. The typical threshold current and voltage of LD under RT cw operation are 78 mA and 6.8 V, respectively. The experimental analysis of degradation of LD performances suggests that after aging treatment, the increase of series resistance and threshold current can be mainly attributed to the deterioration of p-type ohmic contact and the decrease of internal quantum efticiency of multiple quantum well （MQW）, respectively.展开更多
In traditional semiconductor lasers, it is usual to obtain single lateral mode operation by narrowing the ridge of waveguide, which is sensitive to fabrication inaccuracies. To overcome this shortcoming, a quasi-PT(pa...In traditional semiconductor lasers, it is usual to obtain single lateral mode operation by narrowing the ridge of waveguide, which is sensitive to fabrication inaccuracies. To overcome this shortcoming, a quasi-PT(parity-time)symmetric double ridge semiconductor laser is proposed to reach single lateral mode operation for an intrinsic multi-mode stripe laser. The coupled mode theory is used to analyze the non-Hermitian modulation of the gain(or loss) of the PT symmetric double ridge laser to obtain the coupling coefficient between the two ridge waveguides. Finally, the mode field distributions of the quasi-PT symmetric double ridge laser are simulated before and after the spontaneous PT symmetry breaking, which keep the laser operating in single lateral mode.展开更多
Development of minimally invasive dry electrodes for recording biopotentials is presented. The detailed fabrication process is outlined. A dry electrode is formed by a number of microneedles. The lengths of the micron...Development of minimally invasive dry electrodes for recording biopotentials is presented. The detailed fabrication process is outlined. A dry electrode is formed by a number of microneedles. The lengths of the microneedles are about 150μm and the diameters are about 50μm. The tips of the microneedles are sharp enough to penetrate into the skin. The silver/silver chloride is grown on microneedle arrays and demonstrates good character. The electrocardiogram shows that the dry electrode is suitable for recording biopotentials.展开更多
We combine Cartesian coordinates and polar coordinates wave number eigenvalue equations based on the planewave expansion(PWE)method to calculate and optimize the band structures of the two-dimensional(2D)metal photoni...We combine Cartesian coordinates and polar coordinates wave number eigenvalue equations based on the planewave expansion(PWE)method to calculate and optimize the band structures of the two-dimensional(2D)metal photonic crystals(PhCs).Compared with the traditional PWE methods for metal PhCs,the band structures can be calculated directly in our method and no further procedures are needed to handle the folded band structures.With this method,we optimize the large gap-midgap ratio of the 2D square lattice of square metal rods and circular metal rods.The TM gap-midgap ratio of the 2D square lattice of square metal rods reaches 7.6246%with the side length L=0.71a with a being the lattice constant.The TM gap-midgap ratio of the 2D square lattice of circular metal rods reaches 16.3934%with radius R=0.45a.Our method can be easily used in both square lattice and triangular lattice directly.展开更多
A compact structured illumination chip based on integrated optics is proposed and fabricated on a silicon-on- insulator platform. Based on the simulation of Caussian beam interference, we adopt a chirped diffraction g...A compact structured illumination chip based on integrated optics is proposed and fabricated on a silicon-on- insulator platform. Based on the simulation of Caussian beam interference, we adopt a chirped diffraction grating to achieve a specific interference pattern. The experimental results match well with the simulations. The portability and flexibility of the structured illumination chip can be increased greatly through horizontal encapsulation. High levels of integration, compared with the conventional structured illumination approach, make this chip very compact, with a footprint of only around 1 mm2. The chip has no optical lenses and can be easily combined with a microfluidic system. These properties would make the chip very suitable for portable 3D scanner and compact super-resolution microscopy applications.展开更多
It is important to acquire the composition of Si1-xGex layer, especially that with high Ge content, epitaxied on Si substrate. Two nondestructive examination methods, double crystals X-ray diffraction （DCXRD） and mi...It is important to acquire the composition of Si1-xGex layer, especially that with high Ge content, epitaxied on Si substrate. Two nondestructive examination methods, double crystals X-ray diffraction （DCXRD） and micro-Raman measurement, were introduced comparatively to determine x value in Si1-xGex layer, which show that while the two methods are consistent with each other when x is low, the results obtained from double crystals X-ray diffraction are not credible due to the large strain relaxation occurring in Si1-xGex layers when Ge content is higher than about 20%. Micro-Raman measurement is more appropriate for determining high Ge content than DCXRD.展开更多
Properties of the Ag/Ni/p-GaN structure at different temperatures are studied by Auger electron spectroscopy, scanning electron microscopy and high resolution x-ray diffraction. The effect of Ag in ohmic contact on th...Properties of the Ag/Ni/p-GaN structure at different temperatures are studied by Auger electron spectroscopy, scanning electron microscopy and high resolution x-ray diffraction. The effect of Ag in ohmic contact on the crystalline quality is investigated and the optimized value of annealing temperature is reported. The lowest specific contact resistance of 2.5 × 10^-4 Ωcm^2 is obtained at annealing temperature of 550^o C.展开更多
Models for calculating the sheet densities of two-dimensional electron gas （2DEG） induced by spontaneous and piezoelectric polarization in A1GaN/GaN, A1GaN/A1N/GaN, and GaN/A1GaN/GaN heterostructures are provided. T...Models for calculating the sheet densities of two-dimensional electron gas （2DEG） induced by spontaneous and piezoelectric polarization in A1GaN/GaN, A1GaN/A1N/GaN, and GaN/A1GaN/GaN heterostructures are provided. The detailed derivation process of the expression of 2DEG sheet density is given. A longstanding confusion in a very widely cited formula is pointed out and its correct expression is analyzed in detail.展开更多
基金Project supported by the National Basic Research Program of China (Grant Nos. 2011CB301701, 2012CB933502, and2012CB933504)the National Natural Science Foundation of China (Grant Nos. 60877036 and 61107048)the Knowledge Innovation Program of the Chinese Academy of Sciences (Grant No. KGCX2-EW-102)
文摘We propose a novel resonator containing an elliptical microring based on a silicon-on-insulator platform. Simu- lations using the three-dimensional finite-difference time-domain method show that the novel elliptical microring can efficiently enhance the mode coupling between straight bus waveguides and resonator waveguides or between adjacent resonators while preserving relatively high intrinsic quality factors with large free spectral range. The proposed resonator would be an alternative choice for future high-density integrated photonic circuits.
基金supported by the National Basic Research Program of China (Grant No. 2006CB921705)the National Natural Science Foundation of China (Grant Nos. 10634080,60677046 and 60838003)the National High Technology Research and Development Program of China (Grant Nos. 2007AA03Z410 and 2007AA03Z408)
文摘The local density of states （LDOS） of two-dimensional square lattice photonic crystal （PhC） defect cavity is studied. The results show that the LDOS in the centre is greatly reduced, while the LDOS at the point off the centre （for example, at the point （0.3a, 0.4a）, where a is the lattice constant） is extremely enhanced. Further, the disordered radii are introduced to imitate the real devices fabricated in our experiment, and then we study the LDOS of PhC cavity with configurations of different disordered radii. The results show that in the disordered cavity, the LDOS in the centre is still greatly reduced, while the LDOS at the point （0.3a, 0.4a） is still extremely enhanced. It shows that the LDOS analysis is useful. When a laser is designed on the basis of the square lattice PhC rod cavity, in order to enhance the spontaneous emission, the active materials should not be inserted in the centre of the cavity, but located at positions off the centre. So LDOS method gives a guide to design the positions of the active materials （quantum dots） in the lasers.
基金Project supported by the National Key R&D Program of China (Grant No.2018YFA0306403)the Strategic Priority Research Program of Chinese Academy of Sciences (Grant No.XDB43000000)+1 种基金Innovation Program for Quantum Science and TechnologyComputer Interconnect Technology Alliance Funding (Grant No.20220103)。
文摘Quantum key distribution(QKD)system based on passive silica planar lightwave circuit(PLC)asymmetric Mach–Zehnder interferometers(AMZI)is characterized with thermal stability,low loss and sufficient integration scalability.However,waveguide stresses,both intrinsic and temperature-induced stresses,have significant impacts on the stable operation of the system.We have designed silica AMZI chips of 400 ps delay,with bend waveguides length equalized for both long and short arms to balance the stresses thereof.The temperature characteristics of the silica PLC AMZI chip are studied.The interference visibility at the single photon level is kept higher than 95%over a wide temperature range of 12℃.The delay time change is 0.321 ps within a temperature change of 40℃.The spectral shift is 0.0011 nm/0.1℃.Temperature-induced delay time and peak wavelength variations do not affect the interference visibility.The experiment results demonstrate the advantage of being tolerant to chip temperature fluctuations.
基金supported by the National Key Research and Development Program of China(Grant No.2018YFA0306403)the National Natural Science Foundation of China(Grant Nos.61435013 and 61627820)+1 种基金the Strategic Priority Research Program of the Chinese Academy of Sciences(Grant No.XDB43000000)the K.C.Wong Education Foundation,Anhui Initiative in Quantum Information Technologies,China(Grant No.AHY030000)。
文摘A quantum key distribution transmitter chip based on hybrid-integration of silica planar light-wave circuit(PLC)and lithium niobates(LN)modulator PLC is presented.The silica part consists of a tunable directional coupler and 400-ps delay line,and the LN part is made up of a Y-branch,with electro-optic modulators on both arms.The two parts are facet-coupled to form an asymmetric Mach-Zehnder interferometer.We successfully encode and decode four BB84 states at 156.25-MHz repetition rate.Fast phase-encoding of 0 orπis achieved,with interference fringe visibilities 78.53%and 82.68%for states|+〉and|-〉,respectively.With the aid of an extra off-chip LN intensity modulator,two time-bin states are prepared and the extinction ratios are 18.65 dB and 15.46 dB for states|0〉and|1〉,respectively.
基金Project supported by the National High-Technology Research and Development Program of China (Grant No 2006AA03Z415)the Major State Basic Program of China (Grant No 2007CB613404)the National Natural Science Foundation of China(Grant No 60676005)
文摘High quality Ge was epitaxially grown on Si using ultrahigh vacuum/chemical vapor deposition （UHV/CVD）. This paper demonstrates efficient germanium-on-silicon p-i-n photodetectors with 0.8 μm Ge, with responsivities as high as 0.38 and 0.21 A/W at 1.31 and 1.55 μm, respectively. The dark current density is 0.37 mA/cm^2 and 29.4 mA/cm^2 at 0 V and a reverse bias of 0.5 V. The detector with a diameter of 30μm, a 3 dB-bandwidth of 4.72 GHz at an incident wavelength of 1550 nm and zero external bias has been measured. At a reverse bias of 3 V, the bandwidth is 6.28 GHz.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61107070,61127018,and 61377071)
文摘A compact and highly linear quartz-enhanced photoacoustic spectroscopy（QEPAS） sensor for the measurement of water vapor concentration in the air is demonstrated. A cost-effective quartz tuning fork（QTF） is used as the sharp transducer to convert light energy into an electrical signal based on the piezoelectric effect, thereby removing the need for a photodetector. The short optical path featured by the proposed sensing system leads to a decreased size. Furthermore, a pair of microresonators is applied in the absorbance detection module（ADM） for QTF signal enhancement. Compared with the system without microresonators, the detected QTF signal is increased to approximately 7-fold. Using this optimized QEPAS sensor with the proper modulation frequency and depth, we measure the water vapor concentration in the air at atmospheric pressure and room temperature. The experimental result shows that the sensor has a high sensitivity of 1.058parts-per-million.
基金the National Key Research and Development Program of China(Grant No.2018YFB2200500)the National Natural Science Foundation(Grant Nos.62050073,62090054,61975196).
文摘Beta-gallium oxide(β-Ga_(2)O_(3))thin films were deposited on c-plane(0001)sapphire substrates with different mis-cut angles along<>by metal-organic chemical vapor deposition(MOCVD).The structural properties and surface morphology of as-grownβ-Ga_(2)O_(3)thin films were investigated in detail.It was found that by using thin buffer layer and mis-cut substrate technology,the full width at half maximum(FWHM)of the()diffraction peak of theβ-Ga_(2)O_(3)film is decreased from 2°on c-plane(0001)Al_(2)O_(3)substrate to 0.64°on an 8°off-angled c-plane(0001)Al_(2)O_(3)substrate.The surface root-mean-square(RMS)roughness can also be improved greatly and the value is 1.27 nm for 8°off-angled c-plane(0001)Al_(2)O_(3)substrate.Room temper-ature photoluminescence(PL)was observed,which was attributed to the self-trapped excitons formed by oxygen and gallium vacancies in the film.The ultraviolet-blue PL intensity related with oxygen and gallium vacancies is decreased with the increas-ing mis-cut angle,which is in agreement with the improved crystal quality measured by high resolution X-ray diffraction(HR-XRD).The present results provide a route for growing high qualityβ-Ga_(2)O_(3)film on Al_(2)O_(3)substrate.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61474110,61377020,61376089,61223005,and 61176126)the National Natural Science Fund for Distinguished Young Scholars,China(Grant No.60925017)+1 种基金the One Hundred Person Project of the Chinese Academy of Sciencesthe Basic Research Project of Jiangsu Province,China(Grant No.BK20130362)
文摘Two series of p-GaN films grown at different temperatures are obtained by metal organic chemical vapor deposition（MOCVD）. And the different variation behaviors of resistivity with growth condition for high- temperature（HT）-grown and low-temperature（LT）-grown p-GaN films are investigated. It is found that the resistivity of HT-grown p-GaN film is nearly unchanged when the NH_3 flow rate or reactor pressure increases. However, it decreases largely for LT-grown p-GaN film.These different variations may be attributed to the fact that carbon impurities are easy to incorporate into p-GaN film when the growth temperature is low. It results in a relatively high carbon concentration in LT-grown p-GaN film compared with HT-grown one. Therefore, carbon concentration is more sensitive to the growth condition in these samples, ultimately,leading to the different variation behaviors of resistivity for HT- and LT-grown ones.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61474110,61377020,61376089,61223005,and 61176126)the National Science Fund for Distinguished Young Scholars of China(Grant No.60925017)
文摘In this paper, the temperature-dependent photoluminescence（PL） properties of Ga N grown on Si（111） substrate are studied. The main emission peaks of Ga N films grown on Si（111） are investigated and compared with those grown on sapphire substrates. The positions of free and bound exciton luminescence peaks, i.e., FX A and D0 X peaks, of Ga N films grown on Si（111） substrates undergo red shifts compared with those grown on sapphire. This is attributed to the fact that the Ga N films grown on sapphire are under the action of compressive stress, while those grown on Si（111） substrate are subjected to tensile stress. Furthermore, the positions of these peaks may be additionally shifted due to different stress conditions in the real sample growth. The emission peaks due to stacking faults are found in Ga N films grown on Si（111） and an S-shaped temperature dependence of PL spectra can be observed, owing to the influence of the quantum well（QW） emission by the localized states near the conduction band gap edge and the temperature-dependent distribution of the photo-generated carriers.
基金the financial support from the National Key Research and Development Program of China(Grant Nos.2018YFA0209000,2017YFB0403603)the National Natural Science Foundation of China(Grant Nos.61904173,61634006,61675191,61674050,61874158)+1 种基金the Hundred Persons Plan of Hebei Province(Grant No.E2018050004,E2018050003)the Supporting Plan for 100 Excellent Innovative Talents in Colleges and Universities of Hebei Province(SLRC2019018).
文摘New neuromorphic architectures and memory technologies with low power consumption,scalability and high-speed are in the spotlight due to the von Neumann bottleneck and limitations of Moore’s law.The memristor,a two-terminal synaptic device,shows powerful capabilities in neuromorphic computing and information storage applications.Active materials with high defect migration speed and low defect migration barrier are highly promising for high-performance memristors.Halide perovskite(HP)materials with point defects(such as gaps,vacancies,and inversions)have strong application potential in memristors.In this article,we review recent advances on HP memristors with exceptional performances.First,the working mechanisms of memristors are described.Then,the structures and properties of HPs are explained.Both electrical and photonic HP-based memristors are overviewed and discussed.Different fabrication methods of HP memristor devices and arrays are described and compared.Finally,the challenges in integrating HP memristors with complementary metal oxide semiconductors(CMOS)are briefly discussed.This review can assist in developing HP memristors for the next-generation information technology.
基金Project supported by the National Natural Science Foundation of China (Grant Nos. 60506001,60476021,60576003,60776047and 60836003)the National Basic Research Program of China (Grant No. 2007CB936700)the Project of Technological Research and Development of Hebei Province,China (Grant No. 07215134)
文摘We present the growth of CaN epilayer on Si （111） substrate with a single A1GaN interlayer sandwiched between the GaN epilayer and A1N buffer layer by using the metalorganic chemical vapour deposition. The influence of the AlN buffer layer thickness on structural properties of the GaN epilayer has been investigated by scanning electron microscopy, atomic force microscopy, optical microscopy and high-resolution x-ray diffraction. It is found that an A1N buffer layer with the appropriate thickness plays an important role in increasing compressive strain and improving crystal quality during the growth of AlGaN interlayer, which can introduce a more compressive strain into the subsequent grown GaN layer, and reduce the crack density and threading dislocation density in GaN film.
基金supported by the National Key Research and Development Program of China(No.2016YFB0402504)the National Natural Science Foundation of China(Nos.61435013 and 61405188)
文摘A 25-channel 200 GHz arrayed waveguide grating(AWG)based on Si nanowire wavegnides is designed,simulated and fab-ricated.Transfer function method is used in the simulation and error analysis of AWG with width fluctuations.The 25-channel 200 GHz AWG exhibits central channel insertion loss of 6.7 dB,crosstalk of-13 dB,and central wavelength of 1560.55 nm.The error analysis can explain the experimental results of 25-channel 200 GHz AWG well.By using deep ul-traviolet lithography(DUV)and inductively coupled plasma etching(ICP)technologies,the devices are fabricated on sili-con-on-insulator(SOI)substrate.
基金Supported by the National Natural Science Foundation of China under Grant Nos 60976045, 60506001, 60776047 and 60836003, and the National Basic Research Program of China under Grant No 2007CB936700.
文摘We report our recent progress of investigations on InGaN-based blue-violet laser diodes （LDs）. The roomtemperature （RT） cw operation lifetime of LDs has extended to longer than 15.6 h. The LD structure was grown on a c-plane free-standing （FS） GaN substrate by metal organic chemical vapor deposition （MOCVD）. The typical threshold current and voltage of LD under RT cw operation are 78 mA and 6.8 V, respectively. The experimental analysis of degradation of LD performances suggests that after aging treatment, the increase of series resistance and threshold current can be mainly attributed to the deterioration of p-type ohmic contact and the decrease of internal quantum efticiency of multiple quantum well （MQW）, respectively.
基金Supported by the National Key R&D Program of China(Grant Nos.2016YFB0401804 and 2016YFA0301102)the National Natural Science Foundation of China(Grant Nos.91850206,61535013,and 11981260014).
文摘In traditional semiconductor lasers, it is usual to obtain single lateral mode operation by narrowing the ridge of waveguide, which is sensitive to fabrication inaccuracies. To overcome this shortcoming, a quasi-PT(parity-time)symmetric double ridge semiconductor laser is proposed to reach single lateral mode operation for an intrinsic multi-mode stripe laser. The coupled mode theory is used to analyze the non-Hermitian modulation of the gain(or loss) of the PT symmetric double ridge laser to obtain the coupling coefficient between the two ridge waveguides. Finally, the mode field distributions of the quasi-PT symmetric double ridge laser are simulated before and after the spontaneous PT symmetry breaking, which keep the laser operating in single lateral mode.
基金Supported by the National Natural Science Foundation of China under Grant Nos 60776024, 60877035 and 90820002, tile National High-Technology Research and Development Program of China under Grant Nos 2007AA03Z427, 2007AA04Z329 and 2007AA04Z254.
文摘Development of minimally invasive dry electrodes for recording biopotentials is presented. The detailed fabrication process is outlined. A dry electrode is formed by a number of microneedles. The lengths of the microneedles are about 150μm and the diameters are about 50μm. The tips of the microneedles are sharp enough to penetrate into the skin. The silver/silver chloride is grown on microneedle arrays and demonstrates good character. The electrocardiogram shows that the dry electrode is suitable for recording biopotentials.
基金Supported by the National Basic Research Program of China under Grant No 2006CB921705the National Natural Science Foundation of China under Grant Nos 10634080,60677046 and 60838003the National High Technology Research and Development Program of China under Grant Nos 2007AA03Z410 and 2007AA03Z408.
文摘We combine Cartesian coordinates and polar coordinates wave number eigenvalue equations based on the planewave expansion(PWE)method to calculate and optimize the band structures of the two-dimensional(2D)metal photonic crystals(PhCs).Compared with the traditional PWE methods for metal PhCs,the band structures can be calculated directly in our method and no further procedures are needed to handle the folded band structures.With this method,we optimize the large gap-midgap ratio of the 2D square lattice of square metal rods and circular metal rods.The TM gap-midgap ratio of the 2D square lattice of square metal rods reaches 7.6246%with the side length L=0.71a with a being the lattice constant.The TM gap-midgap ratio of the 2D square lattice of circular metal rods reaches 16.3934%with radius R=0.45a.Our method can be easily used in both square lattice and triangular lattice directly.
基金Supported by the National Natural Science Foundation of China under Grant No 61334008the National High-Technology Research and Development Program of China under Grant No 2015AA016904the Instrument Developing Project of the Chinese Academy of Sciences under Grant No YZ201301
文摘A compact structured illumination chip based on integrated optics is proposed and fabricated on a silicon-on- insulator platform. Based on the simulation of Caussian beam interference, we adopt a chirped diffraction grating to achieve a specific interference pattern. The experimental results match well with the simulations. The portability and flexibility of the structured illumination chip can be increased greatly through horizontal encapsulation. High levels of integration, compared with the conventional structured illumination approach, make this chip very compact, with a footprint of only around 1 mm2. The chip has no optical lenses and can be easily combined with a microfluidic system. These properties would make the chip very suitable for portable 3D scanner and compact super-resolution microscopy applications.
基金This work is supported by the National Natural Science Foundation of China （Grant Nos. 60336010 ＆ 90401001）973 Program （Grant No. TG 2000036603）the Student Innovation Program of CAS （No. 1731000500010）.
文摘It is important to acquire the composition of Si1-xGex layer, especially that with high Ge content, epitaxied on Si substrate. Two nondestructive examination methods, double crystals X-ray diffraction （DCXRD） and micro-Raman measurement, were introduced comparatively to determine x value in Si1-xGex layer, which show that while the two methods are consistent with each other when x is low, the results obtained from double crystals X-ray diffraction are not credible due to the large strain relaxation occurring in Si1-xGex layers when Ge content is higher than about 20%. Micro-Raman measurement is more appropriate for determining high Ge content than DCXRD.
文摘Properties of the Ag/Ni/p-GaN structure at different temperatures are studied by Auger electron spectroscopy, scanning electron microscopy and high resolution x-ray diffraction. The effect of Ag in ohmic contact on the crystalline quality is investigated and the optimized value of annealing temperature is reported. The lowest specific contact resistance of 2.5 × 10^-4 Ωcm^2 is obtained at annealing temperature of 550^o C.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61377020,61376089,61223005,and 61176126)the National Science Fund for Distinguished Young Scholars,China(Grant No.60925017)
文摘Models for calculating the sheet densities of two-dimensional electron gas （2DEG） induced by spontaneous and piezoelectric polarization in A1GaN/GaN, A1GaN/A1N/GaN, and GaN/A1GaN/GaN heterostructures are provided. The detailed derivation process of the expression of 2DEG sheet density is given. A longstanding confusion in a very widely cited formula is pointed out and its correct expression is analyzed in detail.
