16 results on '"ZHIJIAN YANG"'
Search Results
2. Effects of oxidation by O2 plasma on formation of Ni∕Au ohmic contact to p-GaN
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Quanjie Jia, Zhijian Yang, X. M. Jiang, Z. X. Qin, Xiaodong Hu, Tongjun Yu, G. Y. Zhang, Zhizhong Chen, L. S. Yu, W. L. Zheng, and Y. Z. Tong
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Nickel ,Materials science ,chemistry ,Annealing (metallurgy) ,Nickel oxide ,X-ray crystallography ,Contact resistance ,Analytical chemistry ,General Physics and Astronomy ,chemistry.chemical_element ,Crystallite ,Reactive-ion etching ,Ohmic contact - Abstract
Oxidation of Ni∕Au (5nm∕10nm) contact to p-GaN layer was performed by O2 plasma in a reactive ion etching system. The structural characteristics of the Ni∕Au p-GaN for different oxidation time were investigated by x-ray diffraction (XRD) measurements, using an intense synchrotron x-ray source. The XRD measurements indicated that the grains of nickel oxide polycrystalline in the contact were grown continually when the oxidation time increased in 10min. However, Au showed amorphouslike and the intensities of Bragg diffraction peaks were hardly changed when oxidation time increased to 10min. The nickel oxide formed by O2 plasma without sequent thermal annealing did not reduce the specific contact resistance (ρc) to p-GaN, but it took an important role in lowering ρc followed by thermal annealing in N2 at 500°C for 10min. Optical transmission spectra confirmed that the nickel was easy to be oxidized and few interdiffusions occurred at the metal interface in O2 plasma ambient. Finally, the mechanism of oxidati...
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- 2004
3. Two local vibrational modes related to hydrogen in GaN
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Z. H. Xu, Y. Z. Tong, Xiang Zhang, J. Q. Duan, Liping Wang, Y. X. Zhang, G. Y. Zhang, Zhijian Yang, S. X. Jin, Baoshan Zhang, and Guangzhao Qin
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Materials science ,Absorption spectroscopy ,Hydrogen ,chemistry ,Infrared ,Molecular vibration ,Analytical chemistry ,General Physics and Astronomy ,chemistry.chemical_element ,Infrared spectroscopy ,Irradiation ,Epitaxy ,Absorption (electromagnetic radiation) - Abstract
We have observed two absorption bands located at around 1730 and 2960 cm−1 in the infrared (IR) absorption spectra from undoped GaN samples which are grown using low pressure metalorganic vapor phase epitaxy and irradiated by gamma ray and then exposed to a radio frequency hydrogen plasma. Proton implantation followed by gamma-ray irradiation of the GaN samples can also activate the IR band at around 1730 cm−1. Based on the experimental results, we tentatively ascribe the 1730 cm−1 band to the local vibrational modes of Ga–H complexes in the vicinity of N vacancies and the 2960 cm−1 band to those of either N–H complexes in the vicinity of Ga vacancies or C–H complexes.
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- 1997
4. Different exciton behaviors in blue and green wells of dual-wavelength InGaN/GaN MQWs structures
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Hao Long, Zhijian Yang, G. Y. Zhang, Tongjun Yu, H. Fang, and Li-Min Liu
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Materials science ,Photoluminescence ,business.industry ,Exciton ,Wide-bandgap semiconductor ,General Physics and Astronomy ,Optoelectronics ,Metalorganic vapour phase epitaxy ,Green-light ,business ,Luminescence ,Epitaxy ,Quantum well - Abstract
Staggered structures with blue and green quantum wells (QWs) were grown by metal organic vapor phase epitaxy (MOVPE) and characterized by photoluminescence (PL) and time resolved photoluminescence (TRPL) at various temperatures from 10 K to 300 K. High efficiency green light was observed, accompanying with decreased intensity of blue light. Efficiency of the green band was lower than that of the blue band below 100 K, but became two times greater than the efficiency of blue when temperature increased to room temperature. Three-dimensional and two-dimensional exciton behaviors were observed by TRPL measurements corresponding to blue and green bands, respectively. It is considered that carrier tunneling from blue wells is a key process for high efficiency luminescence in green QWs.
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- 2012
5. Different strain relief behaviors in Al0.35Ga0.65N/GaN multiple quantum wells on GaN/Sapphire templates with AlN/GaN supperlattices and low-temperature AlN interlayers
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Jie Song, Zhijian Yang, Feng Xu, Z. Y. Xu, C. C. Huang, Xinqiang Wang, Jianpu Wang, B. G. Shen, W. J. Lu, Xurong Chen, Gang Chen, and R. Zhu
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Template ,Materials science ,Strain (chemistry) ,business.industry ,Ultimate tensile strength ,Surface roughness ,Sapphire ,Wide-bandgap semiconductor ,General Physics and Astronomy ,Optoelectronics ,Chemical vapor deposition ,Metalorganic vapour phase epitaxy ,business - Abstract
Strain relief behaviors in Al0.35Ga0.65N/GaN multiple quantum wells (MQWs) grown on GaN/sapphire templates with either AlN/GaN supperlattices (SLs) or low-temperature AlN (LT-AlN) interlayers (ILs) between the MQWs and templates have been investigated. These two IL techniques can both effectively relieve the tensile strain in the MQWs, leading to crack-free surfaces and high crystalline quality. Further analysis shows that there are two distinct strain relief channels. In the case of adopting AlN/GaN SLs IL, microcracks and misfit dislocations account for strain relief in the MQWs. Microcracks are first generated in the IL, followed by activating formation of misfit dislocations. Then, the microcracks are immediately filled up by the subsequent epilayers. Contrastively, strain relief by using LT-AlN IL is mainly through the self relaxation process of the MQWs by surface roughening and strain compensation effect of LT-AlN IL.
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- 2012
6. Magnetotransport properties of lattice-matched In0.18Al0.82N/AlN/GaN heterostructures
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Z. L. Miao, C. C. Huang, Tongjun Yu, Xinyu Liu, K. Han, Ke Wei, Jie Song, Xinqiang Wang, N. Tang, Zhijian Yang, Feng Xu, B. G. Shen, L. B. Cen, G. Y. Zhang, and J. Huang
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Condensed Matter::Materials Science ,Materials science ,Condensed matter physics ,Scattering ,Wide-bandgap semiconductor ,General Physics and Astronomy ,Heterojunction ,Scattering theory ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Fermi gas ,Shubnikov–de Haas effect ,Quantum well ,Magnetic field - Abstract
Magnetotransport properties of the two-dimensional electron gas (2DEG) in lattice-matched In0.18Al0.82N/AlN/GaN heterostructures have been studied at low temperatures and high magnetic fields. The double subband occupancy of the 2DEG in the triangular quantum well at the heterointerface is observed. The 2DEG density is determined to be 2.09×1013 cm−2 and the energy separation between the first and the second subbands is 191 meV. Both of them are significantly higher than those in AlxGa1−xN/AlN/GaN heterostructures owing to the stronger spontaneous polarization effect. The evident difference of the quantum scattering times in the two subbands of the 2DEG indicates that the interface roughness scattering plays an important role in the transport properties of the 2DEG in InxAl1−xN/AlN/GaN heterostructures.
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- 2011
7. Polarization modification in InGaN/GaN multiple quantum wells by symmetrical thin low temperature-GaN layers
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F. F. Zhang, L. P. You, Xiangning Kang, S. L. Qi, Tongjun Yu, Zhizhong Chen, Zhijian Yang, Y. B. Tao, C. Y. Jia, G. Y. Zhang, and Dapeng Yu
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Materials science ,business.industry ,Wide-bandgap semiconductor ,General Physics and Astronomy ,Epitaxy ,law.invention ,Blueshift ,Optics ,law ,Optoelectronics ,Metalorganic vapour phase epitaxy ,business ,High-resolution transmission electron microscopy ,Current density ,Quantum well ,Light-emitting diode - Abstract
Light emitting diodes (LEDs) using InGaN/GaN quantum wells (QWs) with thin low temperature GaN (LT-GaN) layers bounding each InGaN layer are grown by metal-organic vapor phase epitaxy. The light output power of such LEDs increases by a factor of 2 at a drive current density of 35 A/cm2 compared to that from reference LEDs without the LT-GaN. The blueshift in the emission wavelength is 5.2 nm when the current density increases from 3 to 50 A/cm2, which is much smaller than the shift 8.1 nm from reference LEDs. Moreover, the efficiency droop at high current injection is also reduced by 28%, and current density at which peak efficiency is observed increases from 1 to 2 A/cm2. High resolution transmission electron microscopy of the QWs bounded with LT-GaN shows higher quality and less strain compared to the reference samples. The better performance of LEDs incorporating the LT-GaN layers is attributed to suppressed polarization from piezoelectric fields.
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- 2010
8. Strain effects on InxAl1−xN crystalline quality grown on GaN templates by metalorganic chemical vapor deposition
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Jie Song, Zhijian Yang, C. C. Huang, Feng Xu, Tongjun Yu, Lin Lu, G. Y. Zhang, Xinqiang Wang, B. G. Shen, X. P. Zhang, Dapeng Yu, and Z. L. Miao
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Crystallography ,Materials science ,Strain (chemistry) ,Transmission electron microscopy ,Wide-bandgap semiconductor ,Surface roughness ,General Physics and Astronomy ,Chemical vapor deposition ,Metalorganic vapour phase epitaxy ,Composite material ,Microstructure ,Hillock - Abstract
InxAl1−xN epilayers (∼200 nm thick) under different strain states were grown on GaN templates by metalorganic chemical vapor deposition. When the strain is small (0.166≤x≤0.208), InxAl1−xN epilayers are almost fully coherent with the GaN templates, and the surface presents similar characteristic of small hillocks and uniform pits. In the case of large tensile strain, cracks emerged on the surface, but the surface morphology is less influenced compared to the samples with small strain. However, with large compressive strain, the surface roughness dramatically increased and additional smaller pits emerged with partial strain relaxation occurring during growth. In addition, the microstructures were further investigated by transmission electron microscopy. It is demonstrated that even slight relaxation of compressive strain can lead to notable influence on the structural quality and surface morphology of InxAl1−xN films.
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- 2010
9. Structural, optical, and magnetic properties of Cu-implanted GaN films
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S. D. Yao, Zhijian Yang, G. Y. Zhang, Chuan-She Wang, Kun Wang, Zhitao Chen, Xiaolong Yang, X. D. Pei, Yuhao Zhang, and Z. B. Ding
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Materials science ,Condensed matter physics ,business.industry ,Wide-bandgap semiconductor ,General Physics and Astronomy ,Magnetic semiconductor ,Magnetic susceptibility ,Condensed Matter::Materials Science ,Magnetization ,Ion implantation ,Semiconductor ,Ferromagnetism ,Atom ,business - Abstract
The structural, optical, and magnetic properties of Cu-implanted GaN films have been investigated. No secondary phase was found within the resolution limit of the instrument but the lattice defects such as vacancies were present in the film. Room temperature ferromagnetism was observed with saturation magnetization of 0.3μB/Cu atom. The field-cooled magnetization curves can be well fitted by a Curie-Weiss model and a standard three-dimensional spin-wave model in the low and high temperature ranges, respectively. Our findings indicate that the vacancylike defects should be considered in understanding the observed magnetic properties of the Cu-implanted GaN films.
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- 2009
10. Microstructure and origin of dislocation etch pits in GaN epilayers grown by metal organic chemical vapor deposition
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Lin Lu, G. Y. Zhang, Yilong Hao, Dapeng Yu, Z. L. Miao, Sen Huang, X. P. Zhang, Z. Y. Gao, Zhijian Yang, Feng Xu, Jianbin Xu, and B. G. Shen
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Crystallography ,Materials science ,Etch pit density ,Transmission electron microscopy ,Scanning electron microscope ,Etching (microfabrication) ,General Physics and Astronomy ,Metalorganic vapour phase epitaxy ,Chemical vapor deposition ,Dislocation ,Composite material ,Microstructure - Abstract
Morphology and microstructure of dislocation etch pits in GaN epilayers etched by molten KOH have been investigated by atomic force microscopy, scanning electron microscopy, and transmission electron microscopy (TEM). Three types of etch pits (α, β, and γ) are observed. The α type etch pit shows an inversed trapezoidal shape, the β one has a triangular shape, and the γ type one has a combination of triangular and trapezoidal shapes. TEM observation shows that α, β, and γ types etch pits originate from screw, edge, and mixed-type threading dislocations (TDs), respectively. For the screw-type TD, it is easily etched along the steps that the dislocation terminates, and consequently, a small Ga-polar plane is formed to prevent further vertical etching. For the edge-type TD, it is easily etched along the dislocation line. Since the mixed-type TDs have both screw and edge components, the γ type etch pit has a combination of α and β type shapes. It is also found that the chemical stabilization of Ga-polar surfac...
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- 2008
11. Morphology and microstructure evolution of AlxGa1−xN epilayers grown on GaN/sapphire templates with AlN interlayers observed by transmission electron microscopy
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Z. L. Miao, Zhijian Yang, Z. X. Qin, Feng Xu, G. Y. Zhang, Dapeng Yu, X. P. Zhang, Lin Lu, Jianbin Xu, B. G. Shen, Bin Gao, and Shaoyun Huang
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Materials science ,Morphology (linguistics) ,business.industry ,Wide-bandgap semiconductor ,General Physics and Astronomy ,Chemical vapor deposition ,Microstructure ,Metal ,Crystallography ,Transmission electron microscopy ,visual_art ,Sapphire ,visual_art.visual_art_medium ,Optoelectronics ,Metalorganic vapour phase epitaxy ,business - Abstract
Morphology and microstructure evolution of Al0.3Ga0.7N epilayers grown on GaN/sapphire templates with low-temperature (LT) AlN interlayers (IL) by means of metal organic chemical vapor deposition have been investigated by transmission electron microscopy and atomic force microscopy. It is found that the IL improves the surface morphology and suppresses edge-type threading dislocations (TDs). When the IL thickness is 20nm, there is the lowest density of the edge-type TD with 8.7×108cm−2. However, the edge-type TD density increases somewhat as IL thickness increases to 40nm. It is believed that two mechanisms determine the microstructure evolution of the AlxGa1−xN epilayers. One is the TD suppression effect of LT-AlN ILs that ILs can provide an interface for edge-type TD termination. Another is the TD introduction effect of ILs that new edge-type TDs are produced. Due to the lattice mismatch between AlN, GaN, and AlxGa1−xN, the strain in AlxGa1−xN epilayers is modified by inserting the AlN IL, and thus chan...
- Published
- 2008
12. Analysis of mass transport mechanism in InGaN epitaxy on ridge shaped selective area growth GaN by metal organic chemical vapor deposition
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H. Fang, Zhijian Yang, L. B. Zhao, Liwen Sang, G. Y. Zhang, T. Dai, Yanjie Wang, and Tongjun Yu
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Surface diffusion ,Materials science ,Analytical chemistry ,General Physics and Astronomy ,chemistry.chemical_element ,Chemical vapor deposition ,Epitaxy ,Molecular physics ,chemistry ,Diffusion process ,Metalorganic vapour phase epitaxy ,Diffusion (business) ,Layer (electronics) ,Indium - Abstract
In this work, the evolution of the InGaN layer growth on the ridge shaped GaN was studied. A mass transport model was presented to simulate the epitaxy process of the InGaN layer. The model consisted of two consecutive components, gas-phase diffusion process and surface diffusion process. The mean lifetime of adatoms on epitaxial surface was associated with their reaction rate in this model. An InGaN layer on ridge shaped GaN, including (0002) and {112¯2} facets, was grown by metal organic chemical vapor deposition to confirm the mass transport model. Gradient indium content distribution and inhomogeneous thickness of the InGaN layer were observed. Simulation of the InGaN layer growth process was performed by finite difference method with the mass transport model. By analyzing the results from calculations and experiments, the origins of the InGaN layer characteristics were attributed to the two diffusion components in the growth process. Surface diffusion resulted in the inhomogeneous thickness and gas-p...
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- 2008
13. Intersubband transitions in asymmetric AlxGa1−xN∕GaN double quantum wells
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Shuang-Ying Lei, Zhijian Yang, L. Cao, B. G. Shen, and G. Y. Zhang
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Condensed matter physics ,Chemistry ,Wide-bandgap semiconductor ,General Physics and Astronomy ,Schrödinger equation ,symbols.namesake ,Wavelength ,Quantum dot ,Attenuation coefficient ,Excited state ,symbols ,Atomic physics ,Absorption (electromagnetic radiation) ,Quantum well - Abstract
Influence of the width and Al composition of one well in asymmetric Al0.85Ga0.15N∕GaN double quantum wells (DQWs) on the absorption coefficients and the wavelengths of the intersubband transitions (ISBTs) has been investigated by solving the Schrodinger and Poisson equations self-consistently. When the well width is chosen to be 1.91nm, the three-energy-level DQWs are realized. The ISBT between the first odd order and the second even order subbands (the 1odd-2even ISBT) has comparable absorption coefficient with the 1odd-2odd ISBT. Their wavelengths are located at 1.3 and 1.54μm, respectively. When the well width is 2.77nm, the four-energy-level DQWs are realized. The 1odd-2even and the 1even-2odd ISBTs have comparable absorption coefficients. Their wavelengths are located at 1.41 and 2.54μm, respectively. The energy separation between the excited subbands is determined to have the minimum value of 144meV due to the band anticrossing interaction. The calculated results give possible application to ultrafa...
- Published
- 2007
14. Modified transmission line model to investigate non-Ohmic contact behavior and its application on GaN
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Q. Y. Wei, Xiaodong Hu, Rui Li, Guoyi Zhang, Weixi Chen, Zhijian Yang, Yanjie Wang, Yaobo Pan, and Weihua Chen
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Materials science ,Electric power transmission ,Condensed matter physics ,Transmission line ,Degenerate energy levels ,Contact resistance ,Analytical chemistry ,Wide-bandgap semiconductor ,General Physics and Astronomy ,Thermionic emission ,Current (fluid) ,Ohmic contact - Abstract
In this article we proposed a modified transmission line model method to analyze non-Ohmic contact. It can differentiate the contact resistance while the current flows into and out of the contact. When the earlier two factors are equal, this method degenerate to traditional method. By this method, we obtained contact parameters for both p-GaN and n-GaN and revealed the validity of this method. To further study the contact characteristics and transportation mechanism between alloyed Ni/Au and p-GaN, we also measured barrier information at different temperature and current. The result indicates the hole passes through the barrier by thermionic emission and the barrier may lowered by image force.
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- 2007
15. Origin of split peaks in the oscillatory magnetoresistance in AlxGa1−xN∕GaN heterostructures
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Ke Xu, Wu Zhou, K. Han, Zhijian Yang, L. Y. Shang, Shaoling Guo, Nujiang Tang, G. Y. Zhang, J. H. Chu, B. Zhu, B. G. Shen, and Tie Lin
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Physics ,Zeeman effect ,Spin polarization ,Condensed matter physics ,Magnetoresistance ,General Physics and Astronomy ,Heterojunction ,Zero field splitting ,Condensed Matter::Mesoscopic Systems and Quantum Hall Effect ,Shubnikov–de Haas effect ,Magnetic field ,Condensed Matter::Materials Science ,symbols.namesake ,symbols ,Condensed Matter::Strongly Correlated Electrons ,Fermi gas - Abstract
The oscillatory magnetoresistance of the two-dimensional electron gas (2DEG) in AlxGa1−xN∕GaN heterostructures has been studied by means of magnetotransport measurements at low temperatures and high magnetic fields. The split peaks of the Shubnikov–de Haas oscillations are observed at high magnetic fields, which are attributed to the spin splitting of the 2DEG. It is found that the spin splitting energy becomes smaller with an increase in magnetic field, indicating that the Zeeman spin splitting is not dominant at measured magnetic field range. Within this magnetic field range, the zero-field spin splitting, as well as Zeeman spin splitting, affects the split peaks in the oscillatory magnetoresistance of the 2DEG in AlxGa1−xN∕GaN heterostructures.
- Published
- 2006
16. Influence of polarization-induced electric field on the wavelength and the absorption coefficient of the intersubband transitions in AlxGa1−xN∕GaN double quantum wells
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L. Cao, Shuang-Ying Lei, Ke Xu, G. Y. Zhang, Zhijian Yang, Feng Xu, and B. G. Shen
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Wavelength ,symbols.namesake ,Condensed matter physics ,Stark effect ,Chemistry ,Electric field ,Attenuation coefficient ,Wide-bandgap semiconductor ,symbols ,Optical communication ,General Physics and Astronomy ,Polarization (waves) ,Quantum well - Abstract
The influence of the polarization-induced electric field on the wavelength and the absorption coefficient of the intersubband transitions (ISBTs) in AlxGa1−xN∕GaN coupled double quantum wells (DQWs) have been investigated by self-consistent calculation. It is found that the wavelength of the ISBT between the first odd order and the second even order subbands (the 1odd-2even ISBT) can be shortened to 1.3μm owing to the Stark shift induced by the polarization effect. The absorption coefficient of the 1odd-2even ISBT decreases by increasing the polarization field discontinuity. On the other hand, a shorter wavelength and a larger absorption coefficient of the ISBTs are obtained by decreasing the width of the central barrier of AlxGa1−xN∕GaN DQWs. The results are beneficial to achieving devices operation within the optical communication wavelength range.
- Published
- 2006
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