Growth and properties of wide spectral white light emitting diodes

Wide spectral white light emitting diodes have been designed and grown on a sapphire substrate by using a metal-organic chemical vapor deposition system. Three quantum wells with blue-light-emitting, green-light-emitting and red-light-emitting structures were grown according to the design. The surface morphology of the film was observed by using atomic force microscopy. The films were characterized by their photoluminescence measurements. X-ray diffraction θ/2θ scan spectroscopy was carried out on the multi-quantum wells. The secondary fringes of the symmetric ω/2θ X-ray diffraction scan peaks indicate that the thicknesses and the alloy compositions of the individual quantum wells are repeatable throughout the active region. The room temperature photoluminescence spectra of the structures indicate that the white light emission of the multi-quantum wells is obtained. The light spectrum covers 400-700 nm, which is almost the whole visible light spectrum.     

m面GaN平面内结构和光学各向异性研究

采用金属有机物化学气相淀积方法在铝酸锂LiAlO₂衬底上外延生长m面GaN薄膜.X射线衍射测量的结果表明所得薄膜具有较理想的m面晶体取向，并对其各向异性的应变进行了计算，摇摆曲线的测量发现样品存在明显的面内结构各向异性.采用偏振光致发光研究材料的面内光学各向异性，发现随着偏振角度的改变，发光峰的峰位和强度均有明显变化，并用对称性破缺导致价带子带劈裂的理论对结果进行了解释. 关键词： m面GaN 结构各向异性 偏振光致发光     

MOCVD生长的InN薄膜中In分凝现象

利用金属有机物化学气相淀积(MOCVD)方法不同生长条件下在c面蓝宝石衬底上制备了InN薄膜,通过不同的物理表征手段研究了InN薄膜的物理性质,结果表明:合适的生长温度可以抑制InN薄膜表面分凝现象。研究认为较低的生长温度使作为N源的NH3分解率较低,In—N的成键可能性小,导致In在表面聚集出现分凝;而较高生长温度时,InN薄膜中In—N键能较小,易发生断裂,反应活性较强的N和H原子逸离薄膜表面,In滞留在薄膜表面也导致In分凝现象的出现。相对于表面分凝的样品,未出现表面分凝的样品的薄膜晶体质量和表面形貌也得到了提高。同时,通过Raman散射谱研究了晶格振动E2声子模的应力效应。     

Growth studies of m-GaN layers on LiAlO2 by MOCVD

This paper reports that the m-plane GaN layer is grown on （200）-plane LiAlO2 substrate by metal-organic chemical wpour deposition （MOCVD） method. Tetragonal-shaped crystallites appear at the smooth surface. Raman measurement illuminates the compressive stress in the layer which is released with increasing the layer＇s thickness. The high transmittance （80%）, sharp band edge and excitonic absorption peak show that the GaN layer has good optical quality. The donor acceptor pair emission peak located at -3.41 eV with full-width at half maximum of 120 meV and no yellow peaks in the photoluminescence spectra partially show that no Li incorporated into GaN layer from the LiAlO2 substrate.     

Photoresponse of the In0.3Ga0.7N metal-insulator-semiconductor photodetectors

In0.3Ga0.7N metal-insulator-semiconductor （MIS） and metal-semiconductor （MS） surface barrier photodetectors have been fabricated. The In0.3Ga0.7N epilayers were grown on sapphire by metalorganic chemical vapour deposition （MOCVD）. The photoresponse and reverse current-voltage characteristics of the In0.3Ga0.7N MIS and MS photodetectors were measured. A best zero bias responsivity of 0.18 A/W at 450 nm is obtained for the In0.3Ga0.7N MIS photodetector with 10 nm Si3N4 insulator layer, which is more than ten times higher than the In0.3Ga0.7N MS photodetector. The reason is attributed to the decrease of the interface states and increase of surface barrier height by the inserted insulator. The influence of the thickness of the Si3N4 insulator layer on the photoresponsivity of the MIS photodetector is also discussed.     

氢化物气相外延生长的GaN膜中的应力分析

对在c面蓝宝石上用氢化物气相外延法(HVPE)生长的六方相纤锌矿结构的GaN膜中的应力进行了分析。高分辨X射线衍射(002)面和(102)面摇摆曲线扫描(半高宽数值分别为317和358角秒)表明生长的GaN膜具有较好的晶体质量。利用高分辨X射线衍射技术准确测量了制备的GaN膜的晶格常数,并计算得到GaN膜中面内双轴应变和面外双轴应变分别为3.37×10-4和-8.52×10-4,等静压应变为-7.61×10-5。拉曼光谱和激光光致发光谱测试表明HVPE-GaN外延膜具有较好的光学特性,利用拉曼光谱的E2模式特征峰和激光光致发光谱中近带边发射峰的频移定量计算了外延膜中的面内双轴压应力和等静压应力。两种方法得到的面内双轴压应力较为相符。     

GaN薄膜中的马赛克结构随厚度发生的变化

利用高分辨率X射线衍射(HRXRD)对MOCVD系统中生长在c面Al₂O₃上的不 同厚度的GaN薄膜内马赛克结构进行了研究. 在对称面的三轴X射线衍射曲线中, 用两种方法计算得到晶粒的垂直关联长度和水平关联长度, 两者均随着薄膜厚度的增加而增加, 并且垂直关联长度近似膜厚从倒易空间图中得出的横向关联长度也有相同的趋势, 结合非对称面的衍射曲线用Williamson-Hall方法和外推法分 别拟合出晶粒的面外倾斜角和面内扭转角, 他们随着薄膜厚度的增加显著减少, 这一切都表明厚度的增加, 晶粒的单向有序排列越来越整齐, 外延片的质量越来越高. 关键词： GaN薄膜马赛克结构 厚度 HRXRD     

掺Ni的ZnO粉末的Raman光谱研究

利用拉曼(Raman)光谱对掺镍(Ni)氧化锌(ZnO)粉末的声子谱进行了研究.在掺杂样品的Raman光谱中仍能观察到未掺杂ZnO的声子模式,此外还观察到两个额外模式.掺杂粉末中观察到ZnO的E2(h)模式表明掺Ni的ZnO仍然保持六角对称结构.652 cm-1额外模式的起源是掺杂引起的ZnO本底缺陷.为了查明544 cm-1处额外模式的起源,分别对掺Ni,掺钴(Co),和掺锰(Mn)的ZnO粉末的Raman光谱进行了对比研究.结果表明544 cm-1额外模式起源于Ni相关的局域振动模式.对光谱中的其他声子模式的起源也进行了讨论;同时还报告了利用325nm激光作激发源观察到掺Ni样品的多重纵光学(LO)声子模式的结果.     

厚度对MOCVD生长InN薄膜位错特性与光电性质的影响

研究了金属有机物化学气相沉积法制备的不同厚度InN薄膜的位错特性与光电性质.基于马赛克微晶模型,通过X射线衍射非对称面摇摆曲线测量,拟合出样品刃型位错密度分别为4.2×10¹⁰cm^-2和6.3×10¹⁰cm^-2,并发现样品的微晶扭转角与位错密度随薄膜厚度增加而减小.通过室温霍尔效应测量得到样品载流子浓度分别为9×10¹⁸cm^-3和1.2×10¹⁸cm关键词： 氮化铟 位错 载流子起源 局域态     

Epitaxial Growth and Characteristics of Nonpolar a-Plane InGaN Films with Blue-Green-Red Emission and Entire In Content Range

Nonpolar （11■0） plane In_xGa_1-x N epilayers comprising the entire In content （x） range were successfully grown on nanoscale Ga N islands by metal-organic chemical vapor deposition.The structural and optical properties were studied intensively.It was found that the surface morphology was gradually smoothed when x increased from 0.06 to 0.33,even though the crystalline quality was gradually declined,which was accompanied by the appearance of phase separation in the In_x