Well-width dependence of the emission linewidth in ZnO/MgZnO quantum wells

Photoluminescence (PL) spectra were measured as a function of well width (L(W)) and temperature in ZnO/Mg(0.1)Zn(0.9)O single quantum wells (QWs) with graded thickness. The emission linewidth (full width at half maximum) was extracted from the emission spectra, and its variation as a function of L(W) was studied. The inhomogeneous linewidth obtained at 5 K was found to decrease with increasing L(W) from 1.8 to 3.3 nm due to the reduced potential variation caused by the L(W) fluctuation. Above 3.3 nm, however, the linewidth became larger with increasing L(W), which was explained by the effect related with defect generation due to strain relaxation and exciton expansion in the QW. For the homogenous linewidth broadening, longitudinal optical (LO) phonon scattering and impurity scattering were taken into account. The LO phonon scattering coefficient Γ(LO) and impurity scattering coefficient Γ(imp) were deduced from the temperature dependence of the linewidth of the PL spectra. Evident reduction of Γ(LO) with decreasing L(W) was observed, which was ascribed to the confinement-induced enhancement of the exciton binding energy. Different from Γ(LO), a monotonic increase in Γ(imp) was observed with decreasing L(W), which was attributed to the enhanced penetration of the exciton wave function into the barrier layers

Fabrication and Characteristics of GaN-based Blue VCSEL

利用金属有机物气相沉积技术(MOCVD)在(0001)蓝宝石衬底上生长了Ga N基垂直腔面发射激光器(VCSEL)的多量子阱腔层结构。X射线衍射测量显示该多量子阱具有良好周期结构和平整界面。运用键合及激光剥离技术将该外延片制作成VCSEL,顶部和底部反射镜为极高反射率的介质膜分布布拉格反射镜(DBR)。在室温、紫外脉冲激光的泵浦条件下,观察到了VCSEL明显的激射现象,峰值波长位于447.7 nm,半高宽为0.11 nm,自发辐射因子约为6.0×10-2,阈值能量密度约为8.8 m J/cm2。在大幅度降低制作难度的情况下,得到目前国际最好结果同样数量级的激射阈值。降低器件制作难度有利于制备的重复性,有利于器件的产品化。Ga N-based multiple quantum wells( MQWs) were epitaxially grown on( 0001)-oriented sapphire substrate by metal organic chemical vapor deposition( MOCVD) technique. X-ray diffraction measurements indicated that the MQWs had good periodic structure and smooth interface. By employing bonding and laser lift-off techniques,the MQW structure was sandwiched between two high reflectivity dielectric distributed Bragg reflectors( DBRs),forming a vertical-cavity surfaceemitting laser( VCSEL). Under optical pumping,the VCSEL achieved laser action at room temperature with a threshold pumping energy density of about 8. 8 m J / cm2. The laser emitted a blue light at 447. 7 nm with a narrow linewidth of 0. 11 nm,and had a high spontaneous emission factor of about 6. 0 × 10- 2.国家自然科学基金(61307115);; 福建省教育厅A类科技项目(JA12249);; 厦门理工学院高校高层次人才基金(YKJ11026R);; 福建省自然科学基金(2013J05104)资助项

Polishing of Laser Lift-off-Induced GaN Surface

激光剥离(llO)技术是研制新型氮化镓(gAn)基谐振腔结构光电子器件的关键技术。然而llO后的gAn表面往往具有较大的粗糙度,而制作谐振腔结构器件需要很高的表面平整度,因此需要对llO后的gAn表面进行抛光。分别采用金刚石粉抛光液和胶粒二氧化硅抛光液进行机械抛光和化学机械抛光(CMP),并对比了两种方法获得的抛光结果,研究发现前者会在抛光后的gAn表面引入划痕,而采用后者可以得到亚纳米级平整度的表面。进一步的实验结果表明,胶粒二氧化硅抛光液同样适用于图形化衬底外延片激光剥离后的gAn表面抛光。Laser lift-off( LLO) is a key technology in development of new GaN-based resonant-cavity optoelectronic devices.For cavity-dependent devices,a smooth surface is highly required.However,the GaN surface after LLO is usually rough,and the polishing is necessary.The mechanical polishing of diamond powder and the chemical mechanical polishing of colloidal silica were compared.It is found that diamond powder leads to scratches on the GaN surface whereas colloidal silica leads to smooth surface with sub-nanometer roughness.The experiment results indicate that polishing with colloidal silica solutions can be applied to smoothen the LLO-produced GaN surface from an epitaxial wafer grown on patterned-sapphire substrate.国家自然科学基金资助项目(61274052;61106044); 中国科学院纳米器件与应用重点实验室开放课题资助项目(14ZS02

Influence of p-GaN Annealing on Optical Properties of InGaN MQWs

近年来,n2退火和O2退火均被用于激活P-gAn中的Mg受主以提高P-gAn中的空穴浓度。基于两种退火技术,系统地研究了n2退火和O2退火对lEd样品电学性能及光学性能的影响。电流电压特性的测试结果显示,在较低温度(500℃)下O2退火就可以达到与n2高温退火(800℃)相似的电学特性。变温光致发光测试表明,n2高温退火会在IngAn量子阱中形成In团簇,In团簇作为深的势阱增加了对载流子的束缚,能够将载流子更好地局限在势阱中。然而In团簇形成的同时也伴随着大量位错的产生,使其IngAn量子阱中的位错密度大幅度提高,因此室温下n2退火样品的辐射复合效率低于O2退火样品的辐射复合效率。In recent years,thermal annealing in either N2 ambient or O2 ambient was used to activate the Mg-doped GaN epilayer and thus improve the density of holes in p-GaN.The electrical and optical properties of LED samples annealed in different ambient were systematically investigated.The test results of I-V characteristics show that samples annealed at low temperature(500 ℃) in O2 ambient and high temperature(800 ℃)in N2 ambient show similar current-voltage characteristics.The temperature-dependent photoluminescence(PL)measurement shows that high-temperature thermal annealing in N2 ambient can induce In clusters in InGaN multiple quantum well(MQWs).The deep traps induced by In clusters can work as localized centers which can enhance the confinement of carriers,the cavriers can be better boanded in well.However,there are much more dislocations out of the trap centers caused by high-temperature annealing,the dislocation density of InGaN MQWs increased significantly.Therefore,at room temperature,the radiative efficiency of the sample annealed in N2 ambient was lower than that annealed in O2 ambient.国家自然科学基金(10974165;91023048;61106044); 高等学校博士学科点专项科研基金(20110121110029

Effect of Laser Pulse Width on the Laser Lift-off Process of GaN Films

Major Research Plan of the National Natural Science Foundation of China [91023048]; National Natural Science Foundation of China [61106044, 10974165]; Doctoral Program Foundation of Institutions of Higher Education of China [20110121110029]Laser lift-off (LLO), by which GaN is separated from sapphire, is demonstrated to be a promising technique for advanced GaN-based optoelectronic devices. Its physical insight, however, is still not fully understood. We study systematically the effect of laser pulse width on the LLO process and the property of GaN. To estimate accurately the temperature distribution and the decomposed thickness of GaN, fluctuation in the pulse laser energy is taken into account. It is found that the temperature at the interface is increased in a higher speed for a narrower pulse width. In addition, less damage to the GaN film is expected for a narrower pulse width owing to the smaller heated area, lower transient temperature and lower N-2 vapor pressure encountered during LLO. Some experimental results reported in literature are explained well. Our results are useful in understanding the effect of laser pulse width and can be taken as references in LLO of GaN/sapphire structures

MOCVD growth of high-reflectivity AlN/GaN distributed Bragg reflectors

利用金属有机物化学气相沉积(MOCVD)方法在蓝宝石c面衬底上制备出高反射率AlN/GaN分布布拉格反射镜(DBR)。利用分光光度计测量,在418 nm附近最大反射率达到99%。样品表面显微照片显示,有圆弧形缺陷和少量裂纹出现;在缺陷和裂纹以外的区域,DBR具有较为平坦的表面,其粗糙度在10μm×10μm面积上为3.3 nm左右。样品的截面扫描电镜(SEM)照片显示,DBR具有良好的周期性。对反射率和表面分析的结果表明,该样品达到了制备GaN基垂直腔面发射激光器(VCSEL)的要求。A high reflectivity AlN/GaN distributed Bragg reflector(DBR) is grown on c-plane sapphire substrate by metalorganic chemical vapor deposition(MOCVD).A peak reflectivity of 99% is observed around 418 nm by spectrophotometer.Compass-shape defects and a few cracks are observed on the surface.The surface root mean square(RMS) of roughness in the flat area is around 3.3 nm over a 10 μm×10 μm area.The cross-sectional scanning electron microscope(SEM) image reveals the good periodicity of DBR.Considering the peak reflectivity and surface morphology,the DBR can be used to fabricate GaN-based vertical cavity surface emitting laser(VCSEL).国家高技术研究“863”计划资助项目(2006AA03Z409

Tuning Properties of External Cavity Violet Semiconductor Laser

National Natural Science Foundation of China [91023048, 61106044, 61274052]A tunable grating-coupled external cavity (EC) laser is realized by employing a GaN-based laser diode as the gain device. A tuning range of 4.47 nm from 403.82 to 408.29 nm is achieved. Detailed investigations reveal that the injection current strongly influences the performance of the EC laser. Below the free-running lasing threshold, EC laser works stably. While above the free-running lasing threshold, a Fabry-Perot (F-P) resonance peak in the emission spectrum and a smooth kink in the output power-injection current characteristic curve are observed, suggesting the competition between the inner F-P cavity resonance and EC resonance. Furthermore, the tuning range is found to be asymmetric and occurs predominantly on the longer wavelength side. This is interpreted in terms of the asymmetric gain distribution of GaN-based quantum well material

Influence of barrier thickness on the structural and optical properties of InGaN/GaN multiple quantum wells

National Natural Science Foundation of China [61106044, 61274052]; Specialized Research Fund for the Doctoral Program of Higher Education of China [20110121110029]; Fundamental Research Funds for the Central Universities of Ministry of Education of China [2013121024]; Natural Science Foundation of Fujian Province of China [2013J05096]The structural and optical properties of InGaN/GaN multiple quantum wells (MQWs) with different barrier thicknesses are studied by means of high resolution X-ray diffraction (HRXRD), a cross-sectional transmission electron microscope (TEM), and temperature- dependent photoluminescence (PL) measurements. HRXRD and cross-sectional TEM measurements show that the interfaces between wells and barriers are abrupt and the entire MQW region has good periodicity for all three samples. As the barrier thickness is increased, the temperature of the turning point from blueshift to redshift of the S-shaped temperature- dependent PL peak energy increases monotonously, which indicates that the localization potentials due to In-rich clusters is deeper. From the Arrhenius plot of the normalized integrated PL intensity, it is found that there are two kinds of nonradiative recombination processes accounting for the thermal quenching of photoluminescence, and the corresponding activation energy (or the localization potential) increases with the increase of the barrier thickness. The dependence on barrier thickness is attributed to the redistribution of In-rich clusters during the growth of barrier layers, i.e., clusters with lower In contents aggregate into clusters with higher In contents

The Effects of NS-lactobacillus Complex on Productivity Performance, Plasma Biochemical Indexes and Dilarrhea Rate in Weaned Piglets

选择二元杂交(杜/长)的(28)日龄断奶仔猪90头,平均断奶体重(8.99±1.60)kg,按体重和性别分成3个处理组,每处理3个重复。A组为对照组,饲喂玉米、豆粕基础日粮;B组为添加0.2%(m/m)NS复合乳酸菌制剂到基础日粮中;C组为添加0.2%(m/m)金霉素、0.025%(m/m)阿莫西林和0.012 5%(m/m)的支原净。试验分为3个阶段:试验共30 d,研究微生态制剂NS复合乳酸菌对断奶仔猪生产性能、血液生化指标和减少腹泻率的影响。结果表明,NS复合乳酸菌能显著提高断奶仔猪的生产性能,平均末重、平均增重、平均日增重分别比A组高9.12%,7.64%和7.67%,差异显著(P<0.05);料肉比降低9.70%,差异显著(P<0.05);有效降低断奶仔猪的腹泻率50%,差异极显著(P<0.01);B组的血糖(GLU)含量比A组高20%、超氧化物歧化酶(SOD)活性高10.9%,差异显著(P<0.05),对增强机体抗氧化功能,减少应激作用具有良好效果

Infrared Image Non-uniformity Correction Based on Joint Surface of Radiation and Environment Temperature

在传统红外图像非均匀性校正方法中,探测器均处在常温环境下,当探测器的环温在一个较宽的范围内变化时,这些方法的校正效果便会恶化、不适应。针对此问题,本文在原常温多点标定法的基础上提出了一种基于曲面拟合的校正方法,把原先标定曲线加上探测器环温维度扩展成标定曲面。随后的纵向对比实验和横向对比实验表明该方法能够显著降低非均匀性,并能适应环温变化的情况