The effect of a self-organized SiNs interlayer on the defect density of （1122） semipolar GaN grown on 7n-plane sapphire is studied by transmission electron microscopy, atomic force microscopy and high resolution x-r...The effect of a self-organized SiNs interlayer on the defect density of （1122） semipolar GaN grown on 7n-plane sapphire is studied by transmission electron microscopy, atomic force microscopy and high resolution x-ray diffrac- tion. The SiNx interlayer reduces the c-type dislocation density from 2.5 ×10^10 cm^-2 to 5 ×10^8 cm 2. The SiNx interlayer produces regions that are free from basal plane stacking faults （BSFs） and dislocations. The overall BSF density is reduced from 2.1×10^5 cm-1 to 1.3×10^4 cm^-1. The large dislocations and BSF reduction in semipolar （1122） GaN with the SiNx, interlayer result from two primary mechanisms. The first mechanism is the direct dislocation blocking by the SiNx interlayer, and the second mechanism is associated with the unique structure character of （1122） semipolar GaN.展开更多
YBa2Cu3O7-x（YBCO） films with co-doping BaTiO3（BTO） and Y2O3 nanostructures were prepared by metal organic deposition using trifluoroacetates（TFA-MOD）. The properties of the BTO/Y2O3co-doped YBCO films with diffe...YBa2Cu3O7-x（YBCO） films with co-doping BaTiO3（BTO） and Y2O3 nanostructures were prepared by metal organic deposition using trifluoroacetates（TFA-MOD）. The properties of the BTO/Y2O3co-doped YBCO films with different excess yttrium have been systematically studied by x-ray diffraction（XRD）, Raman spectra, and scanning electron microscope（SEM）. The optimized content of yttrium excess in the BTO/Y2O3co-doped YBCO films is 10 mol.%, and the critical current density is as high as - 17 mA/cm^2（self-field, 65 K） by the magnetic signal. In addition, the Y2Cu2O5 was formed when the content of yttrium excess increases to 24 mol.%, which may result in the deterioration of the superconducting properties and the microstructure. The unique combination of the different types of nanostructures of BTO and Y2O3 in the doped YBCO films, compared with the pure YBCO films and BTO doped YBCO films, enhances the critical current density（JC） not only at the self-magnetic field, but also in the applied magnetic field.展开更多
In this work, the wafer bowing during growth can be in-situ measured by a reflectivity mapping method in the 3×2 Thomas Swan close coupled showerhead metal organic chemical vapor deposition（MOCVD） system. The r...In this work, the wafer bowing during growth can be in-situ measured by a reflectivity mapping method in the 3×2 Thomas Swan close coupled showerhead metal organic chemical vapor deposition（MOCVD） system. The reflectivity mapping method is usually used to measure the film thickness and growth rate. The wafer bowing caused by stresses（tensile and compressive） during the epitaxial growth leads to a temperature variation at different positions on the wafer, and the lower growth temperature leads to a faster growth rate and vice versa. Therefore, the wafer bowing can be measured by analyzing the discrepancy of growth rates at different positions on the wafer. Furthermore, the wafer bowings were confirmed by the ex-situ wafer bowing measurement. High-resistivity and low-resistivity Si substrates were used for epitaxial growth. In comparison with low-resistivity Si substrate, Ga N grown on high-resistivity substrate shows a larger wafer bowing caused by the highly compressive stress introduced by compositionally graded Al Ga N buffer layer. This transition of wafer bowing can be clearly in-situ measured by using the reflectivity mapping method.展开更多
High-performance low-leakage-current A1GaN/GaN high electron mobility transistors （HEMTs） on silicon （111） sub- strates grown by metal organic chemical vapor deposition （MOCVD） with a novel partially Magnesium ...High-performance low-leakage-current A1GaN/GaN high electron mobility transistors （HEMTs） on silicon （111） sub- strates grown by metal organic chemical vapor deposition （MOCVD） with a novel partially Magnesium （Mg）-doped GaN buffer scheme have been fabricated successfully. The growth and DC results were compared between Mg-doped GaN buffer layer and a unintentionally onμe. A 1μ m gate-length transistor with Mg-doped buffer layer exhibited an OFF-state drain leakage current of 8.3 × 10-8 A/mm, to our best knowledge, which is the lowest value reported for MOCVD-grown A1GaN/GaN HEMTs on Si featuring the same dimension and structure. The RF characteristics of 0.25-μ m gate length T-shaped gate HEMTs were also investigated.展开更多
The high power GaN-based blue light emitting diode(LED) on an 80-μm-thick GaN template is proposed and even realized by several technical methods like metal organic chemical vapor deposition(MOCVD), hydride vapor-pha...The high power GaN-based blue light emitting diode(LED) on an 80-μm-thick GaN template is proposed and even realized by several technical methods like metal organic chemical vapor deposition(MOCVD), hydride vapor-phase epitaxial(HVPE), and laser lift-off(LLO). Its advantages are demonstrated from material quality and chip processing. It is investigated by high resolution X-ray diffraction(XRD), high resolution transmission electron microscope(HRTEM), Rutherford back-scattering(RBS), photoluminescence, current-voltage and light output-current measurements. The width of(0002) reflection in XRD rocking curve, which reaches 173 for the thick GaN template LED, is less than that for the conventional one, which reaches 258. The HRTEM images show that the multiple quantum wells(MQWs) in 80-μmthick GaN template LED have a generally higher crystal quality. The light output at 350 mA from the thick GaN template LED is doubled compared to traditional LEDs and the forward bias is also substantially reduced. The high performance of 80-μm-thick GaN template LED depends on the high crystal quality. However, although the intensity of MQWs emission in PL spectra is doubled, both the wavelength and the width of the emission from thick GaN template LED are increased. This is due to the strain relaxation on the surface of 80-μm-thick GaN template, which changes the strain in InGaN QWs and leads to InGaN phase separation.展开更多
CaN nanorods are successfully fabricated by adjusting the flow rate ratio of hydrogen （H2）/nitrogen （N2） and growth temperature of the selective area growth （SAG） method with metal organic chemical vapor deposit...CaN nanorods are successfully fabricated by adjusting the flow rate ratio of hydrogen （H2）/nitrogen （N2） and growth temperature of the selective area growth （SAG） method with metal organic chemical vapor deposition （MOCVD）. The SAG template is obtained by nanospherical-lens photolithography. It is found that increasing the flow rate of 1-12 will change the CaN crystal shape from pyramid to vertical rod, while increasing the growth temperature will reduce the diameters of GaN rods to nanometer scale. Finally the CaN nanorods with smooth lateral surface and relatively good quality are obtained under the condition that the H2：N2 ratio is 1：1 and the growth temperature is 1030℃. The good crystal quality and orientation of GaN nanorods are confirmed by high resolution transmission electron microscopy. The cathodoluminescence spectrum suggests that the crystal and optical quality is also improved with increasing the temperature.展开更多
Deposition patterns of tetracyanoquinodimethane （TCNQ） molecules on different surfaces are investigated by atomic force microscopy. A homemade physical vapour deposition system allows the better control of molecule ...Deposition patterns of tetracyanoquinodimethane （TCNQ） molecules on different surfaces are investigated by atomic force microscopy. A homemade physical vapour deposition system allows the better control of molecule deposition. Taking advantage of this system, we investigate TCNQ thin film growth on both SiO2 and mica surfaces. It is found that dense island patterns form at a high deposition rate, and a unique seahorse-like pattern forms at a low deposition rate. Growth patterns on different substrates suggest that the fractal pattern formation is dominated by molecule-molecule interaction. Finally, a phenomenal ＂two-branch＂ model is proposed to simulate the growth process of the seahorse pattern.展开更多
We report the growth of Al N epilayers on c-plane sapphire substrates by pulsed metal organic chemical vapor deposition（MOCVD）. The sources of trimethylaluminium（TMAl） and ammonia were pulse introduced into the re...We report the growth of Al N epilayers on c-plane sapphire substrates by pulsed metal organic chemical vapor deposition（MOCVD）. The sources of trimethylaluminium（TMAl） and ammonia were pulse introduced into the reactor to avoid the occurrence of the parasitic reaction. Through adjusting the duty cycle ratio of TMAl to ammonia from 0.8 to 3.0, the growth rate of Al N epilayers could be controlled in the range of 0.24 m/h to 0.93 m/h. The high-resolution x-ray diffraction（HRXRD） measurement showed that the full width at half maximum（FWHM） of the（0002） and（10-12） reflections for a sample would be 194 arcsec and 421 arcsec, respectively. The step-flow growth mode was observed in the sample with the atomic level flat surface steps, in which a root-mean-square（RMS） roughness was lower to 0.2 nm as tested by atomic force microscope（AFM）. The growth process of Al N epilayers was discussed in terms of crystalline quality, surface morphology,and residual stress.展开更多
We directly grow a lattice matched GalnP/GalnAs/GalnNAs/Ge （1.88 eVil .42 eVil .05 eV/0.67eV） four-junction （4J） solar cell on a Ge substrate by the metal organic chemical vapor deposition technology. To solve the...We directly grow a lattice matched GalnP/GalnAs/GalnNAs/Ge （1.88 eVil .42 eVil .05 eV/0.67eV） four-junction （4J） solar cell on a Ge substrate by the metal organic chemical vapor deposition technology. To solve the current limit of the GalnNAs sub cell, we design three kinds of anti-reflection coatings and adjust the base region thickness of the GalnNAs sub cell. Developed by a series of experiments, the external quantum efficiency of the GalnNAs sub cell exceeds 80%, and its current density reaches 11.24 mA/cm2. Therefore the current limit of the 4J solar cell is significantly improved. Moreover, we discuss the difference of test results between 4J and GalnP/GalnAs/Ge solar cells under the 1 sun AMO spectrum.展开更多
Nearly lattice-matched InAIGaN/GaN heterostructure is grown on sapphire substrates by pulsed metal organic chemical vapor deposition and excellent high electron mobility transistors are fabricated on this heterostruct...Nearly lattice-matched InAIGaN/GaN heterostructure is grown on sapphire substrates by pulsed metal organic chemical vapor deposition and excellent high electron mobility transistors are fabricated on this heterostructure. The electron mobility is 1668.08cm2/V.s together with a high two-dimensional-electron-gas density of 1.43 × 10^13 cm-2 for the InAlCaN/CaN heterostructure of 2Onto InAlCaN quaternary barrier. High electron mobility transistors with gate dimensions of 1 × 50 μm2 and 4μm source-drain distance exhibit the maximum drain current of 763.91 mA/mm, the maximum extrinsic transconductance of 163.13 mS/mm, and current gain and maximum oscillation cutoff frequencies of 11 GHz and 21 GHz, respectively.展开更多
Pulsed metal organic chemical vapor deposition is introduced into the growth of InGaN channel heterostructure for improving material qualities and transport properties. High-resolution transmission electron microscopy...Pulsed metal organic chemical vapor deposition is introduced into the growth of InGaN channel heterostructure for improving material qualities and transport properties. High-resolution transmission electron microscopy imaging shows the phase separation free InGaN channel with smooth and abrupt interface. A very high two-dimensional electron gas density of approximately 1.85 x 10^13 cm-2 is obtained due to the superior carrier confinement. In addition, the Hall mobility reaches 967 cruZ/V-s, owing to the suppression of interface roughness scattering. Furthermore, temperature-dependent Hall measurement results show that InGaN channel heterostructure possesses a steady two-dimensional electron gas density over the tested temperature range, and has superior transport properties at elevated temperatures compared with the traditional GaN channel heterostructure. The gratifying results imply that InGaN channel heterostructure grown by pulsed metal organic chemical vapor deposition is a promising candidate for microwave power devices.展开更多
Orthogonal experiments of Ga Sb films growth on Ga As（001） substrates have been designed and performed by using a low-pressure metal–organic chemical vapor deposition（LP-MOCVD） system. The crystallinities and mic...Orthogonal experiments of Ga Sb films growth on Ga As（001） substrates have been designed and performed by using a low-pressure metal–organic chemical vapor deposition（LP-MOCVD） system. The crystallinities and microstructures of the produced films were comparatively analyzed to achieve the optimum growth parameters. It was demonstrated that the optimized Ga Sb thin film has a narrow full width at half maximum（358 arc sec） of the（004） ω-rocking curve, and a smooth surface with a low root-mean-square roughness of about 6 nm, which is typical in the case of the heteroepitaxial single-crystal films. In addition, we studied the effects of layer thickness of Ga Sb thin film on the density of dislocations by Raman spectra. It is believed that our research can provide valuable information for the fabrication of high-crystalline Ga Sb films and can promote the integration probability of mid-infrared devices fabricated on mainstream performance electronic devices.展开更多
Nonpolar a-plane GaN epilayers are grown on several r-plane sapphire substrates by metal organic chemical vapour deposition using different nucleation layers： （A） a CaN nucleation layer deposited at low temperature...Nonpolar a-plane GaN epilayers are grown on several r-plane sapphire substrates by metal organic chemical vapour deposition using different nucleation layers： （A） a CaN nucleation layer deposited at low temperature （LT）; （B） an A1N nucleation layer deposited at high temperature; or （C） an LT thin AIN nucleation layer with an AIN layer and an A1N/A1CaN superlattice both subsequently deposited at high temperature. The samples have been characterized by Xray diffraction （XRD）, atomic force microscopy and photoluminescence. The GaN layers grown using nucleation layers B and C show narrower XRD rocking curves than that using nucleation layer A, indicating a reduction in crystal defect density. Furthermore, the GaN layer grown using nucleation layer C exhibits a surface morphology with triangular defect pits eliminated completely. The improved optical property, corresponding to the enhanced crystal quality, is also confirmed by temperature-dependent and excitation power-dependent photoluminescence measurements.展开更多
InGaN/GaN multiple quantum well （MQW） solar cells with stepped-thickness quantum wells （SQW） are designed and grown by metal-organic chemical vapor deposition. The stepped-thickness quantum wells structure, in whi...InGaN/GaN multiple quantum well （MQW） solar cells with stepped-thickness quantum wells （SQW） are designed and grown by metal-organic chemical vapor deposition. The stepped-thickness quantum wells structure, in which the well thickness becomes smaller and smaller along the growth direction, reveals better crystalline quality and better spectral overlap with the solar spectrum. Consequently, the short-circuit current density （Jsc） and conversion efficiency of the solar cell are enhanced by 27.12% and 56.41% compared with the conventional structure under illumination of AM1.5G （100 mW/cm2）. In addition, approaches to further promote the performance of InGaN/GaN multiple quantum well solar cells are discussed and presented.展开更多
This paper studied the low-resistance ohmic contacts on InAlN/GaN with metal–organic chemical vapor deposition(MOCVD)regrowth technique.The 150-nm regrown n-InGaN exhibits a low sheet resistance of 31Ω/□,resulting ...This paper studied the low-resistance ohmic contacts on InAlN/GaN with metal–organic chemical vapor deposition(MOCVD)regrowth technique.The 150-nm regrown n-InGaN exhibits a low sheet resistance of 31Ω/□,resulting in an extremely low contact resistance of 0.102Ω·mm between n^(+)-InGaN and InAlN/GaN channels.Mask-free regrowth process was also used to significantly improve the sheet resistance of InAlN/GaN with MOCVD regrown ohmic contacts.Then,the diffusion mechanism between n^(+)-InGaN and InAlN during regrowth process was investigated with electrical and structural characterizations,which could benefit the further process optimization.展开更多
基金Supported by the National Natural Science Foundation of China under Grant Nos 61204006 and 61574108the Fundamental Research Funds for the Central Universities under Grant No JB141101the Foundation of Key Laboratory of Nanodevices and Applications of Suzhou Institute of Nano-Tech and Nano-Bionics of Chinese Academy of Sciences under Grant No 15CS01
文摘The effect of a self-organized SiNs interlayer on the defect density of （1122） semipolar GaN grown on 7n-plane sapphire is studied by transmission electron microscopy, atomic force microscopy and high resolution x-ray diffrac- tion. The SiNx interlayer reduces the c-type dislocation density from 2.5 ×10^10 cm^-2 to 5 ×10^8 cm 2. The SiNx interlayer produces regions that are free from basal plane stacking faults （BSFs） and dislocations. The overall BSF density is reduced from 2.1×10^5 cm-1 to 1.3×10^4 cm^-1. The large dislocations and BSF reduction in semipolar （1122） GaN with the SiNx, interlayer result from two primary mechanisms. The first mechanism is the direct dislocation blocking by the SiNx interlayer, and the second mechanism is associated with the unique structure character of （1122） semipolar GaN.
基金Project supported by the National Natural Science Foundation of China(Grant No.51272250)the National Basic Research Program of China(Grant No.2011CBA00105)+1 种基金the National High Technology Research and Development Program of China(Grant No.2014AA032702)the Natural Science Foundation of Beijing,China(Grant No.2152035)
文摘YBa2Cu3O7-x（YBCO） films with co-doping BaTiO3（BTO） and Y2O3 nanostructures were prepared by metal organic deposition using trifluoroacetates（TFA-MOD）. The properties of the BTO/Y2O3co-doped YBCO films with different excess yttrium have been systematically studied by x-ray diffraction（XRD）, Raman spectra, and scanning electron microscope（SEM）. The optimized content of yttrium excess in the BTO/Y2O3co-doped YBCO films is 10 mol.%, and the critical current density is as high as - 17 mA/cm^2（self-field, 65 K） by the magnetic signal. In addition, the Y2Cu2O5 was formed when the content of yttrium excess increases to 24 mol.%, which may result in the deterioration of the superconducting properties and the microstructure. The unique combination of the different types of nanostructures of BTO and Y2O3 in the doped YBCO films, compared with the pure YBCO films and BTO doped YBCO films, enhances the critical current density（JC） not only at the self-magnetic field, but also in the applied magnetic field.
基金Project supported by the National Natural Science Foundation of China(Grant Nos.61274039 and 51177175)the National Basic Research Program of China(Grant No.2011CB301903)+5 种基金the Ph.D.Programs Foundation of Ministry of Education of China(Grant No.20110171110021)the International Science and Technology Collaboration Program of China(Grant No.2012DFG52260)the International Science and Technology Collaboration Program of Guangdong Province,China(Grant No.2013B051000041)the Science and Technology Plan of Guangdong Province,China(Grant No.2013B010401013)the National High Technology Research and Development Program of China(Grant No.2014AA032606)the Opened Fund of the State Key Laboratory on Integrated Optoelectronics,China(Grant No.IOSKL2014KF17)
文摘In this work, the wafer bowing during growth can be in-situ measured by a reflectivity mapping method in the 3×2 Thomas Swan close coupled showerhead metal organic chemical vapor deposition（MOCVD） system. The reflectivity mapping method is usually used to measure the film thickness and growth rate. The wafer bowing caused by stresses（tensile and compressive） during the epitaxial growth leads to a temperature variation at different positions on the wafer, and the lower growth temperature leads to a faster growth rate and vice versa. Therefore, the wafer bowing can be measured by analyzing the discrepancy of growth rates at different positions on the wafer. Furthermore, the wafer bowings were confirmed by the ex-situ wafer bowing measurement. High-resistivity and low-resistivity Si substrates were used for epitaxial growth. In comparison with low-resistivity Si substrate, Ga N grown on high-resistivity substrate shows a larger wafer bowing caused by the highly compressive stress introduced by compositionally graded Al Ga N buffer layer. This transition of wafer bowing can be clearly in-situ measured by using the reflectivity mapping method.
文摘High-performance low-leakage-current A1GaN/GaN high electron mobility transistors （HEMTs） on silicon （111） sub- strates grown by metal organic chemical vapor deposition （MOCVD） with a novel partially Magnesium （Mg）-doped GaN buffer scheme have been fabricated successfully. The growth and DC results were compared between Mg-doped GaN buffer layer and a unintentionally onμe. A 1μ m gate-length transistor with Mg-doped buffer layer exhibited an OFF-state drain leakage current of 8.3 × 10-8 A/mm, to our best knowledge, which is the lowest value reported for MOCVD-grown A1GaN/GaN HEMTs on Si featuring the same dimension and structure. The RF characteristics of 0.25-μ m gate length T-shaped gate HEMTs were also investigated.
基金Project supported by the National Basic Research Foundation of China （Grant Nos. TG2011CB301905 and TG2012CB619304） and the National Natural Science Foundation of China （Grant Nos. 60876063 and 61076012）.
文摘The high power GaN-based blue light emitting diode(LED) on an 80-μm-thick GaN template is proposed and even realized by several technical methods like metal organic chemical vapor deposition(MOCVD), hydride vapor-phase epitaxial(HVPE), and laser lift-off(LLO). Its advantages are demonstrated from material quality and chip processing. It is investigated by high resolution X-ray diffraction(XRD), high resolution transmission electron microscope(HRTEM), Rutherford back-scattering(RBS), photoluminescence, current-voltage and light output-current measurements. The width of(0002) reflection in XRD rocking curve, which reaches 173 for the thick GaN template LED, is less than that for the conventional one, which reaches 258. The HRTEM images show that the multiple quantum wells(MQWs) in 80-μmthick GaN template LED have a generally higher crystal quality. The light output at 350 mA from the thick GaN template LED is doubled compared to traditional LEDs and the forward bias is also substantially reduced. The high performance of 80-μm-thick GaN template LED depends on the high crystal quality. However, although the intensity of MQWs emission in PL spectra is doubled, both the wavelength and the width of the emission from thick GaN template LED are increased. This is due to the strain relaxation on the surface of 80-μm-thick GaN template, which changes the strain in InGaN QWs and leads to InGaN phase separation.
基金Supported by the Key Program of the National Natural Science Foundation of China under Grant No 61334009the National High Technology Research and Development Program of China under Grant No 2014AA032604
文摘CaN nanorods are successfully fabricated by adjusting the flow rate ratio of hydrogen （H2）/nitrogen （N2） and growth temperature of the selective area growth （SAG） method with metal organic chemical vapor deposition （MOCVD）. The SAG template is obtained by nanospherical-lens photolithography. It is found that increasing the flow rate of 1-12 will change the CaN crystal shape from pyramid to vertical rod, while increasing the growth temperature will reduce the diameters of GaN rods to nanometer scale. Finally the CaN nanorods with smooth lateral surface and relatively good quality are obtained under the condition that the H2：N2 ratio is 1：1 and the growth temperature is 1030℃. The good crystal quality and orientation of GaN nanorods are confirmed by high resolution transmission electron microscopy. The cathodoluminescence spectrum suggests that the crystal and optical quality is also improved with increasing the temperature.
基金Project supported by the National Natural Science Foundation of China(Grant No.10774176)the National Basic Research Program of China(Grant No.2006CB806202)
文摘Deposition patterns of tetracyanoquinodimethane （TCNQ） molecules on different surfaces are investigated by atomic force microscopy. A homemade physical vapour deposition system allows the better control of molecule deposition. Taking advantage of this system, we investigate TCNQ thin film growth on both SiO2 and mica surfaces. It is found that dense island patterns form at a high deposition rate, and a unique seahorse-like pattern forms at a low deposition rate. Growth patterns on different substrates suggest that the fractal pattern formation is dominated by molecule-molecule interaction. Finally, a phenomenal ＂two-branch＂ model is proposed to simulate the growth process of the seahorse pattern.
基金Project supported by the National High Technology Research and Development Program of China(Grant No.2015AA016801)Guangdong Provincial Scientific and Technologic Planning Program,China(Grant No.2014B010119002)
文摘We report the growth of Al N epilayers on c-plane sapphire substrates by pulsed metal organic chemical vapor deposition（MOCVD）. The sources of trimethylaluminium（TMAl） and ammonia were pulse introduced into the reactor to avoid the occurrence of the parasitic reaction. Through adjusting the duty cycle ratio of TMAl to ammonia from 0.8 to 3.0, the growth rate of Al N epilayers could be controlled in the range of 0.24 m/h to 0.93 m/h. The high-resolution x-ray diffraction（HRXRD） measurement showed that the full width at half maximum（FWHM） of the（0002） and（10-12） reflections for a sample would be 194 arcsec and 421 arcsec, respectively. The step-flow growth mode was observed in the sample with the atomic level flat surface steps, in which a root-mean-square（RMS） roughness was lower to 0.2 nm as tested by atomic force microscope（AFM）. The growth process of Al N epilayers was discussed in terms of crystalline quality, surface morphology,and residual stress.
文摘We directly grow a lattice matched GalnP/GalnAs/GalnNAs/Ge （1.88 eVil .42 eVil .05 eV/0.67eV） four-junction （4J） solar cell on a Ge substrate by the metal organic chemical vapor deposition technology. To solve the current limit of the GalnNAs sub cell, we design three kinds of anti-reflection coatings and adjust the base region thickness of the GalnNAs sub cell. Developed by a series of experiments, the external quantum efficiency of the GalnNAs sub cell exceeds 80%, and its current density reaches 11.24 mA/cm2. Therefore the current limit of the 4J solar cell is significantly improved. Moreover, we discuss the difference of test results between 4J and GalnP/GalnAs/Ge solar cells under the 1 sun AMO spectrum.
基金Supported by the National Science and Technology Major Project of China under Grant No 2013ZX02308-002the National Natural Sciences Foundation of China under Grant Nos 61574108,61334002,61474086 and 61306017
文摘Nearly lattice-matched InAIGaN/GaN heterostructure is grown on sapphire substrates by pulsed metal organic chemical vapor deposition and excellent high electron mobility transistors are fabricated on this heterostructure. The electron mobility is 1668.08cm2/V.s together with a high two-dimensional-electron-gas density of 1.43 × 10^13 cm-2 for the InAlCaN/CaN heterostructure of 2Onto InAlCaN quaternary barrier. High electron mobility transistors with gate dimensions of 1 × 50 μm2 and 4μm source-drain distance exhibit the maximum drain current of 763.91 mA/mm, the maximum extrinsic transconductance of 163.13 mS/mm, and current gain and maximum oscillation cutoff frequencies of 11 GHz and 21 GHz, respectively.
基金supported by the National Natural Science Foundation of China(Grant Nos.61306017,61334002,61474086,and 11435010)the Young Scientists Fund of the National Natural Science Foundation of China(Grant No.61306017)
文摘Pulsed metal organic chemical vapor deposition is introduced into the growth of InGaN channel heterostructure for improving material qualities and transport properties. High-resolution transmission electron microscopy imaging shows the phase separation free InGaN channel with smooth and abrupt interface. A very high two-dimensional electron gas density of approximately 1.85 x 10^13 cm-2 is obtained due to the superior carrier confinement. In addition, the Hall mobility reaches 967 cruZ/V-s, owing to the suppression of interface roughness scattering. Furthermore, temperature-dependent Hall measurement results show that InGaN channel heterostructure possesses a steady two-dimensional electron gas density over the tested temperature range, and has superior transport properties at elevated temperatures compared with the traditional GaN channel heterostructure. The gratifying results imply that InGaN channel heterostructure grown by pulsed metal organic chemical vapor deposition is a promising candidate for microwave power devices.
基金Project supported by the National Natural Science Foundation of China(Grant No.61076010)the International Science and Technology Cooperation Program of Science and Technology Bureau of Changchun,China(Grant No.12ZX68)
文摘Orthogonal experiments of Ga Sb films growth on Ga As（001） substrates have been designed and performed by using a low-pressure metal–organic chemical vapor deposition（LP-MOCVD） system. The crystallinities and microstructures of the produced films were comparatively analyzed to achieve the optimum growth parameters. It was demonstrated that the optimized Ga Sb thin film has a narrow full width at half maximum（358 arc sec） of the（004） ω-rocking curve, and a smooth surface with a low root-mean-square roughness of about 6 nm, which is typical in the case of the heteroepitaxial single-crystal films. In addition, we studied the effects of layer thickness of Ga Sb thin film on the density of dislocations by Raman spectra. It is believed that our research can provide valuable information for the fabrication of high-crystalline Ga Sb films and can promote the integration probability of mid-infrared devices fabricated on mainstream performance electronic devices.
基金Project supported by the National Key Science & Technology Major Project of the Ministry of Science and Technology of China(Grant No. 2008ZX01002-002)the Major Program and the Key Program of the National Natural Science Foundation of China(Grant Nos. 60890191 and 60736033)
文摘Nonpolar a-plane GaN epilayers are grown on several r-plane sapphire substrates by metal organic chemical vapour deposition using different nucleation layers： （A） a CaN nucleation layer deposited at low temperature （LT）; （B） an A1N nucleation layer deposited at high temperature; or （C） an LT thin AIN nucleation layer with an AIN layer and an A1N/A1CaN superlattice both subsequently deposited at high temperature. The samples have been characterized by Xray diffraction （XRD）, atomic force microscopy and photoluminescence. The GaN layers grown using nucleation layers B and C show narrower XRD rocking curves than that using nucleation layer A, indicating a reduction in crystal defect density. Furthermore, the GaN layer grown using nucleation layer C exhibits a surface morphology with triangular defect pits eliminated completely. The improved optical property, corresponding to the enhanced crystal quality, is also confirmed by temperature-dependent and excitation power-dependent photoluminescence measurements.
基金the National Natural Science Foundation of China(Grant No.51172079)the Science and Technology Program of Guangdong Province,China(Grant Nos.2010B090400456 and 2010A081002002)the Science and Technology Program of Guangzhou,China(Grant No.2011J4300018)
文摘InGaN/GaN multiple quantum well （MQW） solar cells with stepped-thickness quantum wells （SQW） are designed and grown by metal-organic chemical vapor deposition. The stepped-thickness quantum wells structure, in which the well thickness becomes smaller and smaller along the growth direction, reveals better crystalline quality and better spectral overlap with the solar spectrum. Consequently, the short-circuit current density （Jsc） and conversion efficiency of the solar cell are enhanced by 27.12% and 56.41% compared with the conventional structure under illumination of AM1.5G （100 mW/cm2）. In addition, approaches to further promote the performance of InGaN/GaN multiple quantum well solar cells are discussed and presented.
基金the Fundamental Research Funds for the National Key Research and Development Project of China(Grant No.2020YFB1807403)the National Natural Science Foundation of China(Grant Nos.62174125 and 62131014)+1 种基金the Fundamental Research Funds for the Central Universities(Grant Nos.QTZX22022 and YJS2213)the Innovation Fund of Xidian University.
文摘This paper studied the low-resistance ohmic contacts on InAlN/GaN with metal–organic chemical vapor deposition(MOCVD)regrowth technique.The 150-nm regrown n-InGaN exhibits a low sheet resistance of 31Ω/□,resulting in an extremely low contact resistance of 0.102Ω·mm between n^(+)-InGaN and InAlN/GaN channels.Mask-free regrowth process was also used to significantly improve the sheet resistance of InAlN/GaN with MOCVD regrown ohmic contacts.Then,the diffusion mechanism between n^(+)-InGaN and InAlN during regrowth process was investigated with electrical and structural characterizations,which could benefit the further process optimization.
