Shock-Assisted Superficial Hexagonal-to-Cubic Phase Transition in GaN/Sapphire Interface Induced by Using Ultra-violet Laser Lift-Off Techniques

Ultra-violet （KrF excimer laser,λ =248 nm） laser lift-off （LLO） techniques have been operated to the GaN/sapphire structure to separate GaN from the sapphire substrate. Hexagonal to cubic phase transformation induced by the ultra-violet laser lift-off （UV-LLO） has been characterized by micro-Raman spectroscopy, miero-photoluminescence, along with high-resolution transmission electron microscopy （HRTEM）. HRTEM indicates that UV-LLO induced phase transition takes place above the LLO interface, without phase transition under the LLO interface. The formed cubic GaN often exists as nanocrystal grains attaching on the bulk hexagona/GaN. The half-loop-clusterlike UV-LLO interface indicates that the LLO-indueed shock waves has generated and played an assistant role in the decomposition of the hexagonal GaN and in the formation of cubic GaN grains at the LLO surface.     

Effect of Indium Ambient on Electrical Properties of Mg-Foped AlxGa1-xN

Mg-doped AlxGa1-xN epilayers were grown on AlN/sapphire templates by metal organic chemical vapor depo- sition （MOCVD） using an indium-assisted growth method. At room temperature, the resistivity of Mg-doped Alo.43Gao.57N epilayer grown under indium （In） ambient is of the order of 10^4Ω.cm, while the resistivity of Mg-doped Al0.43Ga0.57N grown without In assistance is of the order of 10^6Ω.cm. The ultraviolet light-emitting diodes （UV-LEDs） using the In-assisted Mg-doped Al0.43Ga0.57N as the p-type layers were fabricated to verify the function of indium ambient. It is found that there are a lower turn-on voltage and a lower diode series resistance in the UV-LEDs fabricated with p-type Al0.43Ga0.57 N layers grown under In-ambient.     

金属有机化学气相淀积技术制备GaMnN薄膜材料光学性质研究

研究由MOCVD 技术制备的 GaMnN 外延薄膜光吸收谱.实验发现Mn掺杂后较未掺杂GaN吸收系数在近紫外区增加,在吸收谱低能区144 eV附近观察到吸收峰,吸收系数随Mn浓度的增加而增大.实验结果与基于密度泛函理论的第一性原理计算结果一致,结合理论计算分析认为144 eV附近的吸收峰源于Mn³⁺离子e态与t₂态间的带内跃迁⁵T₂→⁵E. 关键词： GaMnN MOCVD 密度泛函理论 光学性质     

Role of vacancy-type defects in magnetism of GaMnN

Role of vacancy-type(N vacancy(VN) and Ga vacancy(VGa)) defects in magnetism of GaMnN is investigated by first-principle calculation.Theoretical results show that both the VNand VGainfluence the ferromagnetic state of a system.The VNcan induce antiferromagnetic state and the VGaindirectly modify the stability of the ferromagnetic state by depopulating the Mn levels in GaMnN.The transfer of electrons between the vacancy defects and Mn ions results in converting Mn~(3+)(d~4) into Mn~(2+)(d5).The introduced VNand the ferromagnetism become stronger and then gradually weaker with Mn concentration increasing,as well as the coexistence of Mn~(3+)(d~4) and Mn~(2+)(d~5) are found in GaMnN films grown by metal–organic chemical vapor deposition.The analysis suggests that a big proportion of Mn~(3+)changing into Mn~(2+)will reduce the exchange interaction and magnetic correlation of Mn atoms and lead to the reduction of ferromagnetism of material.     

MOVPE生长m面GaN薄膜的表面吸附研究

采用基于密度泛函理论的Materials Studio中的CASTEP模块,对金属有机物气相外延MOVPE生长m面GaN薄膜的表面反应前体的吸附过程进行研究.针对吸附粒子GaCH3和NH3在m面GaN表面不同的初始吸附位,优化计算了GaCH3和NH3在表面的吸附能、与近邻原子的距离、态密度、电荷密度分布、电子布居.计算结果表明,GaCH3在表面Ga brg2位优化之后的位置最稳定,吸附能最低,GaCH3中的Ga原子与表面邻近的N原子、Ga原子分别形成Ga-N、Ga-Ga共价键.NH3在表面N brg2位最稳定,吸附能最低,NH3中的N原子与表面邻近的Ga原子形成N-Ga共价键.通过对比在最佳吸附位的MMG中的Ga原子和NH3中的N原子与表面原子的电荷分布情况和布居数,证明上述吸附粒子与表面确实存在共价作用,形成共价键.     

Quasi-homoepitaxial GaN-based blue light emitting diode on thick GaN templateQuasi-homoepitaxial GaN-based blue light emitting diode on thick GaN templateQuasi-homoepitaxial GaN-based blue light emitting diode on thick GaN templateQuasi-homoepitaxial GaN-based blue light emitting diode on thick GaN template

The high power GaN-based blue light emitting diode （LED） on an 80%tm-thick GaN template is proposed and even realized by several technical methods like metal organic chemical vapor deposition （MOCVD）, hydride vapor-phase epi- taxial （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%tm- thick 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-~m-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%tin-thick GaN template, which changes the strain in InGaN QWs and leads to InGaN phase separation.     

氮化镓单晶衬底制备技术发展与展望

氮化镓(GaN)是第三代半导体材料中的典型代表.因其良好的物理化学性能与热稳定特性,是制作光电子器件及电力电子器件的理想材料.采用同质外延技术在GaN单晶衬底上制备GaN基器件是实现其高性能的根本途径.本文综述了GaN单晶衬底制备的氢化物气相外延技术、三卤化物气相外延技术、氨热法及助熔剂法(钠流法)的研究进展,并对未来可能的发展方向提出了展望.     

新型含均三氮唑Schiff碱吡唑基Mannich碱的合成

以N-(1-苯基-3-甲基-5-氯)吡唑甲酰肼基二硫代甲酸钾和水合肼为起始原料,经闭环反应制得4-氨基-5-(1-苯基-3-甲基-5-氯吡唑)-1,2,4-三唑-3-硫酮(2);2与对溴苯甲醛经缩合反应得4-(4-溴苯次甲亚胺)-5-(1-苯基-3-甲基-5-氯吡唑)-1,2,4-三唑-3-硫酮(3);以乙醇为溶剂,3在甲醛溶液中与吗啉于75℃反应4 h合成了新化合物——2-(吗啉亚甲基)-4-(4-溴苯次甲亚胺)-5-(1-苯基-3-甲基-5-氯吡唑)-1,2,4-三唑-3-硫酮,总收率37%,其结构经1H NMR,IR和元素分析表征。     

GaN-Based Thin Film Vertical Structure Light Emitting Diodes Fabricated by a Modified Laser Lift-off Process and Transferred to Cu

GaN-based thin film vertical structure light-emitting diodes （VS-LEDs） were fabricated by a modified YAG laser lift-off （LLO） process and transferred to Cu substrates. With a comparison of the electrical and optical properties of conventional LEDs on sapphire substrates and of lateral structure thin film LEDs by a KrF LLO process, the vertical structure of LLO LEDs shows obvious superiority. LLO VSLEDs made by modified YAG LLO process show less increase of leakage current than the devices made by conventional/（rE LLO process. Furthermore, owing to the well current spreading and less current path, the ideality factors and series resistance of vertical structure LEDs reduce greatly and the efficiency increases more obviously than the lateral structure LEDs, which is dso reflected on the relative L - I curves. The output power of vertical structure LEDs is over 3 times greater than that of the lateral structure LLO LEDs within 300mA.     

InGaN/GaN多量子阱热退火的拉曼光谱和荧光光谱

通过拉曼光谱及荧光光谱测量研究了采用低压金属有机化学沉积(MOCVD)方法生长的InGaN／GaN多量子阱高温快速热退火处理对量子阱光学性质的影响。观测到退火后InGaN／GaN量子阱的拉曼光谱E2,A1(LO)模式的峰位置出现了红移,而且该振动峰的半高宽也有微小变化。温度升高退火效果更明显。退火使量子阱内应力部分消除,同时In,Ga原子扩散出现相分离使拉曼谱表现出变化。在常温和低温下的光荧光谱表明,退火处理的量子阱发光主峰都出现了红移;而且低温退火出现红移,退火温度升高相对低温退火出现蓝移;同时在低温荧光光谱里看到经过退火处理后原发光峰中主峰旁边弱的峰消失了。讨论了退火对多量子阱光学性质的影响。