陈弘 男 汉族 博导 中国科学院物理所
电子邮件：hchen@aphy.iphy.ac.cn
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部门/实验室：清洁能源实验室
研究领域
教育背景
学历西安交通大学电子工程系 学士 1980－1984 大学毕业
物理所 硕士 博士 1987 研究生毕业
学位 物理所 硕士 博士 1987 博士
工作经历
工作简历1984-1987年电子部第五研究所工作
1992年至今 物理所工作
社会兼职电子学会电子材料分会副主任委员
河北省半导体照明工程技术委员
教授课程
专利与奖励
奖励信息
专利成果授予发明专利10多项
出版信息
发表论文发表SCI文章100篇以上，引用400次以上
发表著作
科研活动
科研项目GaN、GaAs基发光二极管、探测器、HEMT材料研究
SiGe材料的带隙研究
主持863、院方向性项目等10多项
附两篇Compoundsemiconductor杂志发表关于我组文章的 research news
NewsApr 14, 2009
Strain tunes quantum-dot LED wavelengthLattice relaxation controls indium precipitation in the quantum well, altering the emission of InGaN dice from green to white.
Researchers in China are now able to exert control over a chanced-upon technique that allows individual semiconductor die to emit white light.
The LEDs made by Hong Chen and colleagues at the Chinese Academy of Sciences in Beijing produce white emission thanks to precipitation of indium quantum dots in their InGaN quantum wells.
In a paper published online on March 20 in Applied Physics Letters Chen and colleagues show how to vary the extent of indium precipitation.
Multiple Emission
The quantum well emits approximately 440nm light in each device, while the quantum dots emit at 545nm and above.
Additional indium precipitation increases the size and density of quantum dots produced. This raises the wavelength of the original quantum dot emission peak and adds another at around 495nm.
The team’s original intention was to use an InGaN layer at the bottom of the GaN/InGaN quantum well to collect carriers and consequently enhance light emission.
“Based on the question ’What will happen if partly relaxed InGaN is used?’, white emission was found in an LED wafer with a thick underlayer,” Chen told compoundsemiconductor.net.
Now Chen’s team has found that varying the thickness of this underlayer changes the strain in the GaN semiconductor crystal, and in turn the concentration of quantum dots.
Dice with 160nm, 190nm and 220nm underlayers below the quantum well emitted green, yellow-green and white light, respectively.
Electroluminescence spectra of the different LEDs show that the first sample emits light at two wavelengths, while the others emit at three.
The thinnest underlayer retains the highest amount of biaxial strain, with Chen and colleagues deducing that the lattice is about 9.6percent relaxed. The thickest, by contrast, is 64.4percent relaxed, while all the LEDs have around 4.4percent indium in their underlayers.
Indium Precipitation
Using transmission electron microscopy the researchers saw that the strain in the thinner layers prevents precipitation of In-rich quantum dots.
One downside of the approach is that electroluminescent intensity decreases as the thickness of the underlayer increases. Chen suggests that this is because dislocations introduced at a higher level of relaxation act as non-radiative recombination centers.
He concedes that uniformity and reproducibility are issues for the commercial exploitation of this approach to white emission.
“The wavelength reproducibility closely depends on the composition and thickness of the InGaN underlayer, which is sensitive to growth temperature,” Chen commented.
As long as devices emit at the same wavelengths, light emission performance is “well reproducible”, he added.
Dec 10, 2007
Research Review
Dots deliver phosphor-free white light
White LEDs featuring indium-rich quantum dots, rather than a yellow-emitting phosphor, have been built by Hong Chen’s team from the
"Our work provides a novel approach to casting off the limitations of a [down-converting] phosphor," said Chen. According to him, phosphor-free devices promise to deliver longer lifetimes and higher output efficiencies than conventional LED designs.
The researchers fabricated their 300 µm × 300 µm LED chips by low-pressure MOCVD growth on sapphire substrates. A 3 µm thick buffer was grown, followed by 220 nm of InGaN, a four-period active region comprising 3 nm InGaN quantum wells and 14 nm GaN barriers, and a p-type region.
Transmission electron microscopy revealed spinodial decomposition of InGaN in the quantum wells. This phase separation – enhanced by the InGaN underlayer – leads to indium-rich quantum dots with a diameter of 3–4 nm and a density of 1012 cm–2.
At LED drive currents of less than 5 mA, yellow emission from the dots dominates the device’s output. However, blue emission kicks in at higher currents and the ratio of blue-to-yellow emission intensity is almost constant between 20 and 60 mA.
This leads to a stable white light output over this current range, which makes the chip suitable for LED lighting applications. In fact, Chen says that the device can overcome the unwanted color change that plagues many phosphor-converted white LEDs when the drive current is changed.
If quantum-dot LEDs were to replace the light bulb, then their ratio of blue-to-yellow emission intensity would have to be maintained at higher drive currents. However, this should not be a major obstacle, because the current density through the team’s chip at 60 mA is almost identical to that of a 1 × 1 mm power chip operating at 700 mA.
One downside of the phosphor-free device is its efficacy, which is lower than 10 lm/W. The researchers are planning to develop new technology to increase quantum efficiency.
"We also need to investigate how to control the ratio of blue and yellow light intensities, and see whether yellow emission can be shifted to longer wavelengths," explained Chen. If this is possible, it would improve the device’s color-rendering index.
•Journal reference
X HWang 2007 Appl. Phys. Lett. 91 161912.
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