In order to investigate the inherent polarization intensity in InGaN/GaN multiple quantum well(MQW) structures,the electroluminescence(EL) spectra of three samples with different GaN barrier thicknesses of 21.3 nm, 11...In order to investigate the inherent polarization intensity in InGaN/GaN multiple quantum well(MQW) structures,the electroluminescence(EL) spectra of three samples with different GaN barrier thicknesses of 21.3 nm, 11.4 nm, and 6.5 nm are experimentally studied. All of the EL spectra present a similar blue-shift under the low-level current injection,and then turns to a red-shift tendency when the current increases to a specific value, which is defined as the turning point.The value of this turning point differs from one another for the three InGaN/GaN MQW samples. Sample A, which has the GaN barrier thickness of 21.3 nm, shows the highest current injection level at the turning point as well as the largest value of blue-shift. It indicates that sample A has the maximum intensity of the polarization field. The red-shift of the EL spectra results from the vertical electron leakage in InGaN/GaN MQWs and the corresponding self-heating effect under the high-level current injection. As a result, it is an effective approach to evaluate the polarization field in the InGaN/GaN MQW structures by using the injection current level at the turning point and the blue-shift of the EL spectra profiles.展开更多
A novel organic electroluminescent device was made with the structure of ITO/PVK：Tb0.5Eu0.5（TTA）3 Dipy/ BCP/Alq3/Al（a） which utilized the rare earth complex Tb0.5Eu0.5（TTA）3 Dipy as the emitting layer. When it ...A novel organic electroluminescent device was made with the structure of ITO/PVK：Tb0.5Eu0.5（TTA）3 Dipy/ BCP/Alq3/Al（a） which utilized the rare earth complex Tb0.5Eu0.5（TTA）3 Dipy as the emitting layer. When it was driven under a direct electric field, 612 nm emission from EU^3＋ and 410 nm emission from PVK were observed. In addition, in the EL spectrum a new peak at 490 nm appeared. From the analysis of different devices, the mechanism of the new emission was studied. It was concluded that the new emission was the electroplex originating from the interface between the ligand （TTA）3Dipy and BCP.展开更多
A novel binuclear europium P-diketone complex with squaric acid ligand was synthesized for the first time. Its structure was elucidated by IR, UV, and Elemental Analysis. Red light emitting diode (LED) was fabricated ...A novel binuclear europium P-diketone complex with squaric acid ligand was synthesized for the first time. Its structure was elucidated by IR, UV, and Elemental Analysis. Red light emitting diode (LED) was fabricated by using the novel europium complex as an emitting layer, tris(8-quinolinolate) aluminum (III) (Alq(3)) as an electron-transporting layer, N, N'-diphenyl-N, N'-(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) as a hole-transporting layer. A cell structure of indium-tin-oxide/TPD/Eu-complex/Alq(3)/Mg: Ag was employed. Red electroluminescence was observed at room temperature with dc bias voltage of 2 V in this cell. 2 Red emission peaks at about 613 nm with maximum luminance of over 106 cd/m(2). Compared with the EL luminance from those europium complexes reported before, one from the Eu-complex is best in the same cells.展开更多
A GaN/Si nanoheterojunction is prepared through growing Ga N nanocrystallites（nc-GaN） on a silicon nanoporous pillar array（Si-NPA） by a chemical vapor deposition（CVD） technique at a relatively low temperature. T...A GaN/Si nanoheterojunction is prepared through growing Ga N nanocrystallites（nc-GaN） on a silicon nanoporous pillar array（Si-NPA） by a chemical vapor deposition（CVD） technique at a relatively low temperature. The average size of nc-Ga N is determined to be ~10 nm. The spectral measurements disclose that the photoluminescence（PL） from GaN/SiNPA is composed of an ultraviolet（UV） band and a broad band spanned from UV to red region, with the feature that the latter band is similar to that of electroluminescence（EL）. The electron transition from the energy levels of conduction band and, or, shallow donors to that of deep acceptors of Ga N is indicated to be responsible for both the broad-band PL and the EL luminescence. A study of the I-V characteristic shows that at a low forward bias, the current across the heterojunction is contact-limited while at a high forward bias it is bulk-limited, which follows the thermionic emission model and space-charge-limited current（SCLC） model, respectively. The bandgap offset analysis indicates that the carrier transport is dominated by electron injection from n-GaN into the p-Si-NPA, and the EL starts to appear only when holes begin to be injected from Si-NPA into GaN with biases higher than a threshold voltage.展开更多
The SrS∶HoF 3 Electroluminescent (EL) thin films are prepared at the different substrate temperature by electron beam evaporation. The crystallinity and EL characteristics of the samples are analyzed. It is found th...The SrS∶HoF 3 Electroluminescent (EL) thin films are prepared at the different substrate temperature by electron beam evaporation. The crystallinity and EL characteristics of the samples are analyzed. It is found that the main diffraction peak is (200) at the higher substrate temperature and the main diffraction peak is (111) at the lower substrate temperature. The blue emission intensity and EL brightness of the SrS∶HoF 3 thin films increase with the increase of the substrate temperature. Annealing the samples can change the cyrstal phase and strengthen the blue emission of EL thin film.展开更多
The increasing use of color terminals for personal computers has raised a demand for video graphic adapter(VGA)-format panel displays. Since only monochrome(ZnS∶Mn) electroluminescence(EL) displays of suitable size a...The increasing use of color terminals for personal computers has raised a demand for video graphic adapter(VGA)-format panel displays. Since only monochrome(ZnS∶Mn) electroluminescence(EL) displays of suitable size and speed are available, lack of colors has to be replaced by grayscale in the first place. There are two basic driving methods to achieve grayscale in thin-film EL displays: pulse amplitude modulation(PAM) method and pulse width modulation(PWM) method. But there are serious disadvantages of the two traditional methods. For the former method, the high voltage PAM ICs are too expensive to produce the grayscale EL display in bulks and the driver integrated circuit(IC) is complex. Though the PWM method has good grayscale display quality, the hardware implementation is too complex. A new driving method with which the width and the amplitude of the pulse can be modulated and simultaneously the challenge can be solved efficaciously is presented.展开更多
This work applied the ultrasonic bonding to package flip chip GaN-based light emitting diodes （flip chip LEDs） on Si substrates. The effects of ultrasonic bonding parameters on the reliability of flip chip GaN-based...This work applied the ultrasonic bonding to package flip chip GaN-based light emitting diodes （flip chip LEDs） on Si substrates. The effects of ultrasonic bonding parameters on the reliability of flip chip GaN-based LED were investigated. In the sequent aging tests, samples were driven with a constant current of 80 mA for hundreds hours at the room temperature. It was found that the electroluminescence （EL） intensity variation had a large correlation to the ultrasonic power, and then to the bonding temperature and force. A high bonding temperature and ultrasonic power and a proper bonding force improved the EL intensity significantly. It was contributed to a strong atom inter-diffusion forming a stable joint at the bonding interface, The temperature fluctuation in the aging test was the main factor to generate a high inner stress forming delamination at the interface between the chip and Au bump. As a result, delamination had retarded the photons to emit out of the LED packaging and decay its EL intensity.展开更多
A new structure containing negative refractive index dielectric layer(NRIDL) is introduced into microcavity. The properties of the new microcavity organic light-emitting devices(MOLEDs) are investigated. In the experi...A new structure containing negative refractive index dielectric layer(NRIDL) is introduced into microcavity. The properties of the new microcavity organic light-emitting devices(MOLEDs) are investigated. In the experiment, the transfer matrix method is adopted. The dependence of reflectance and transmittance on the refractive index and thickness of NRIDL are analyzed in detail. Compared with the electroluminescence spectra of non-NRIDL diodes, the line widths of the spectra of the MOLEDs are narrower and all the peaks enhance. The results show that the new structure is beneficial to improve the performance and reduce the thickness of microcavity devices.展开更多
基金Project supported by the National Key Research and Development Program of China(Grant Nos.2016YFB0400803 and 2016YFB0401801)the National Natural Science Foundation of China(Grant Nos.61674138,61674139,61604145,61574135,and 61574134)。
文摘In order to investigate the inherent polarization intensity in InGaN/GaN multiple quantum well(MQW) structures,the electroluminescence(EL) spectra of three samples with different GaN barrier thicknesses of 21.3 nm, 11.4 nm, and 6.5 nm are experimentally studied. All of the EL spectra present a similar blue-shift under the low-level current injection,and then turns to a red-shift tendency when the current increases to a specific value, which is defined as the turning point.The value of this turning point differs from one another for the three InGaN/GaN MQW samples. Sample A, which has the GaN barrier thickness of 21.3 nm, shows the highest current injection level at the turning point as well as the largest value of blue-shift. It indicates that sample A has the maximum intensity of the polarization field. The red-shift of the EL spectra results from the vertical electron leakage in InGaN/GaN MQWs and the corresponding self-heating effect under the high-level current injection. As a result, it is an effective approach to evaluate the polarization field in the InGaN/GaN MQW structures by using the injection current level at the turning point and the blue-shift of the EL spectra profiles.
基金Foundation ite m:Project supported bythe National Natural Science Foundation of China (60576016 ,10374001 ,10434030) "973"NationalKey Basic Research Foundation of China (2003CB314707)
文摘A novel organic electroluminescent device was made with the structure of ITO/PVK：Tb0.5Eu0.5（TTA）3 Dipy/ BCP/Alq3/Al（a） which utilized the rare earth complex Tb0.5Eu0.5（TTA）3 Dipy as the emitting layer. When it was driven under a direct electric field, 612 nm emission from EU^3＋ and 410 nm emission from PVK were observed. In addition, in the EL spectrum a new peak at 490 nm appeared. From the analysis of different devices, the mechanism of the new emission was studied. It was concluded that the new emission was the electroplex originating from the interface between the ligand （TTA）3Dipy and BCP.
基金This work was supported by National Natural Science Foundation of China (29972032) and Provincial Natural Science Foundation of Hunan (00JJY2043).
文摘A novel binuclear europium P-diketone complex with squaric acid ligand was synthesized for the first time. Its structure was elucidated by IR, UV, and Elemental Analysis. Red light emitting diode (LED) was fabricated by using the novel europium complex as an emitting layer, tris(8-quinolinolate) aluminum (III) (Alq(3)) as an electron-transporting layer, N, N'-diphenyl-N, N'-(3-methylphenyl)-1,1'-biphenyl-4,4'-diamine (TPD) as a hole-transporting layer. A cell structure of indium-tin-oxide/TPD/Eu-complex/Alq(3)/Mg: Ag was employed. Red electroluminescence was observed at room temperature with dc bias voltage of 2 V in this cell. 2 Red emission peaks at about 613 nm with maximum luminance of over 106 cd/m(2). Compared with the EL luminance from those europium complexes reported before, one from the Eu-complex is best in the same cells.
基金Project supported by the National Natural Science Foundation of China(Grant No.61176044)
文摘A GaN/Si nanoheterojunction is prepared through growing Ga N nanocrystallites（nc-GaN） on a silicon nanoporous pillar array（Si-NPA） by a chemical vapor deposition（CVD） technique at a relatively low temperature. The average size of nc-Ga N is determined to be ~10 nm. The spectral measurements disclose that the photoluminescence（PL） from GaN/SiNPA is composed of an ultraviolet（UV） band and a broad band spanned from UV to red region, with the feature that the latter band is similar to that of electroluminescence（EL）. The electron transition from the energy levels of conduction band and, or, shallow donors to that of deep acceptors of Ga N is indicated to be responsible for both the broad-band PL and the EL luminescence. A study of the I-V characteristic shows that at a low forward bias, the current across the heterojunction is contact-limited while at a high forward bias it is bulk-limited, which follows the thermionic emission model and space-charge-limited current（SCLC） model, respectively. The bandgap offset analysis indicates that the carrier transport is dominated by electron injection from n-GaN into the p-Si-NPA, and the EL starts to appear only when holes begin to be injected from Si-NPA into GaN with biases higher than a threshold voltage.
文摘The SrS∶HoF 3 Electroluminescent (EL) thin films are prepared at the different substrate temperature by electron beam evaporation. The crystallinity and EL characteristics of the samples are analyzed. It is found that the main diffraction peak is (200) at the higher substrate temperature and the main diffraction peak is (111) at the lower substrate temperature. The blue emission intensity and EL brightness of the SrS∶HoF 3 thin films increase with the increase of the substrate temperature. Annealing the samples can change the cyrstal phase and strengthen the blue emission of EL thin film.
文摘The increasing use of color terminals for personal computers has raised a demand for video graphic adapter(VGA)-format panel displays. Since only monochrome(ZnS∶Mn) electroluminescence(EL) displays of suitable size and speed are available, lack of colors has to be replaced by grayscale in the first place. There are two basic driving methods to achieve grayscale in thin-film EL displays: pulse amplitude modulation(PAM) method and pulse width modulation(PWM) method. But there are serious disadvantages of the two traditional methods. For the former method, the high voltage PAM ICs are too expensive to produce the grayscale EL display in bulks and the driver integrated circuit(IC) is complex. Though the PWM method has good grayscale display quality, the hardware implementation is too complex. A new driving method with which the width and the amplitude of the pulse can be modulated and simultaneously the challenge can be solved efficaciously is presented.
基金supported by the National Natural Science Foundation of China(Grant No.50675130)the National Key Technology Research and Development Program of the Ministry of Science and Technology of China(Grant No.2011BAE01B14)the Program for the New Century Excellent Talents in University(Grant No.NCET-07-0535)
文摘This work applied the ultrasonic bonding to package flip chip GaN-based light emitting diodes （flip chip LEDs） on Si substrates. The effects of ultrasonic bonding parameters on the reliability of flip chip GaN-based LED were investigated. In the sequent aging tests, samples were driven with a constant current of 80 mA for hundreds hours at the room temperature. It was found that the electroluminescence （EL） intensity variation had a large correlation to the ultrasonic power, and then to the bonding temperature and force. A high bonding temperature and ultrasonic power and a proper bonding force improved the EL intensity significantly. It was contributed to a strong atom inter-diffusion forming a stable joint at the bonding interface, The temperature fluctuation in the aging test was the main factor to generate a high inner stress forming delamination at the interface between the chip and Au bump. As a result, delamination had retarded the photons to emit out of the LED packaging and decay its EL intensity.
基金Natural Science Research Item of Education Department of Henan Province(2008A430009)Doctor Foundation of Henan Polytechnic University(B2008-22)
文摘A new structure containing negative refractive index dielectric layer(NRIDL) is introduced into microcavity. The properties of the new microcavity organic light-emitting devices(MOLEDs) are investigated. In the experiment, the transfer matrix method is adopted. The dependence of reflectance and transmittance on the refractive index and thickness of NRIDL are analyzed in detail. Compared with the electroluminescence spectra of non-NRIDL diodes, the line widths of the spectra of the MOLEDs are narrower and all the peaks enhance. The results show that the new structure is beneficial to improve the performance and reduce the thickness of microcavity devices.
