在ZnO／Al2O3衬底上生长高质量GaN单晶薄膜

利用ＬＰ－ＭＯＣＶＤ在ＺｎＯ／Ａｌ２Ｏ３衬底上生长了ＧａＮ。实验发现低温生长ＧａＮ过渡层有利于晶体质量的提高;样品ＰＬ谱主峰红移到蓝光区,这对于研制蓝色ＬＥＤ具有一定的启发意义。     

863计划项目“GaN-based蓝光LED的研制”通过验收

由北京大学承担的８６３计划项目“ＧａＮ－ｂａｓｅｄ蓝光ＬＥＤ的研制”（课题编号：８６３－３０７－０５－０１（０５））已于去年１０月通过８６３计划３０７主题专家组的评审验收。验收专家组认为：（１）该课题组对ＧａＮ－ｂａｓｅｄ蓝光ＬＥＤ材料的生长和特性进...     

GaN的MOVPE生长和m－i－n型蓝光LED的试制

利用自行研制的常压ＭＯＶＰＥ设备和全部国产ＭＯ源，采用低温生长缓冲层技术，在蓝宝石（α－Ａｌ２Ｏ３）衬底上获得了高质量的ＧａＮ外延层。未掺杂的ＧａＮ外延层的室温电子迁移率已达１１４ｃｍ２／Ｖ．ｓ，载流于浓度为２×１０１８。７７Ｋ光致发光谱近带边发射峰波长为３６５ｎｍ，其线宽为４ＤｍｅＶ。Ｘ射线双晶衍射回摆曲线的线宽为３６０ａｒｃｓｅｃ。用Ｚｎ掺杂生长了绝缘的ｉ－ＧａＮ层。在此基础上研制了ｍ－ｉ－ｎ型ＧａＮ的ＬＥＤ，并在室温正向偏压下发出波长为４５５ｎｍ的蓝光。     

氮化镓基电子与光电子器件

ＧａＮ具有宽禁带、高击穿电压、异质结沟道中高峰值电子漂移速度和高薄层电子浓度等特点,是大功率和高温半导体器件的理想化合物半导体材料。宽禁带Ⅲ－Ⅴ族化合物半导体的性能和研究进展已经使大功率紫外光／蓝光／绿光光发射二极管走向商业市场,证明ＩｎＧａＡｓ／ＧａＮ／ＡｌＧａＡｓ紫罗兰色异质结激光器能够在室温和脉冲或连续波条件下工作,是性能优越的光电器件的理想材料。本文综述了上述研究成果。     

GaN光导型紫外探测器

研究了以金属有机物化学气相沉积方法生长在６Ｈ－ＳｉＣ衬底上的ＧａＮ光导型紫外探测器的光电流性质。通过光电流谱的测量，获得了ＧａＮ探测器在波长２５０ｎｍ－３６０ｎｍ范围近于平坦的光电流响应，并且观察到在３６５ｎｍ（￣３．４ｅＶ）带边附近陡峭的截止边。测得ＧａＮ探测器在５Ｖ偏压下在３６０ｎｍ波长处的光电流响应度为１３３Ａ／Ｗ，并得到了其响应度与外加偏压的关系。通过拟合光电信号强度与入射光调制频率的实验     

GaN材料的GSMBE生长

在国内首次用ＮＨ３作氮源的ＧＳＭＢＥ方法在α－Ａｌ２Ｏ３衬底上生长出了ＧａＮ单昌外延膜。ＧａＮ生长速率可达０．５μｍ／ｈ。ＧａＮ外延膜的（０００２）双晶Ｘ射线衍射峰回摆曲线的半高宽最窄为８ａｒｃｍｉｎ。霍尔迁移率为５０ｃｍ＾２／Ｖ．ｓ。对质量好的ＧａＮ膜，室温阴性发光谱上只有一个强而锐的近岸边发光峰，谱峰位于３７２ｎｍ处，谱峰半高宽为１４ｎｍ（１２５ｍｅＶ）。     

高迁移率AlGaN-GaN二维电子气

用金属有机物气相外延方法在（０００１）蓝宝石衬底上生长了ＡｌｘＧａ１－ｘＮ／ＧａＮ二维电子气结构。Ａｌ０．１３Ｇａ０．８７Ｎ（７００ｎｍ）／ＧａＮ（６００ｎｍ）异质结的室温电子迁移率达１０２４ｃｍ＾２／Ｖｓ,而ＧａＮ体材料的室温电子迁移率为３９０ｃｍ＾２／Ｖｓ;该异质结的７７Ｋ电子迁移率达３５００ｃｍ＾２／Ｖｓ,而ＧａＮ体材料的电子迁移率在１８５Ｋ下达到峰值,为４９０ｃｍ＾２／Ｖｓ,７７Ｋ下下降到     

GaN和AlxGa1—xN薄膜材料研究进展

ＧａＮ及ＡｌｘＧａ１－ｘＮ是发兰光的关键材料，是目前光电子材料中最引人注目，必须攻克的课题。本文综述了ＧａＮ及ＡｌｘＧａ１－ｘＮ材料的研究现状重点介绍了ＧａＮ及ＡｌｘＧａ１－ｘＮ材料近年来在性能评价，生长技术和应用开发方面的进展。     

GaN和Al_xGa_(1-x)N薄膜材料研究进展

ＧａＮ及ＡｌｘＧａ１－ｘＮ是发兰光的关键材料，是目前光电子材料中最引人注目、必须攻克的课题。本文综述了ＧａＮ及ＡｌｘＧａ１－ｘＮ材料的研究现状，重点介绍了ＧａＮ及ＡｌｘＧａ１－ｘＮ材料近年来在性能评价、生长技术和应用开发方面的进展     

调制掺杂AlxGa1-xN/GaN异质结中二维电子气的光致发光

研究了调制掺杂ＡｌｘＧａ１－ｘＮ／ＧａＮ异质结中与二维电子气（２ＤＥＧ）有关的光致发光,发现温度４０Ｋ时Ａｌ０．２２Ｇａ０．７８Ｎ／ＧａＮ异质结中２ＤＥＧ与光激发空穴复合形成的发光峰位于３．４４８ｅＶ,低于ＧａＮ自由激子峰４５ｍｅＶ。由于ＡｌｘＧａ１－ｘＮ／ＧａＮ界面极强的压电极化场的影响,光激发空穴很快扩散进ＧａＮ平带区,导致２ＤＥＧ与光激发空穴复合几率很低,在ＧａＮ中接近Ａｌ０．２２Ｇａ０．７     

Reducing Architecture Limitations for Efficient Blue Perovskite Light‐Emitting Diodes

Light‐emitting diodes utilizing perovskite nanocrystals have generated strong interest in the past several years, with green and red devices showing high efficiencies. Blue devices, however, have lagged significantly behind. Here, it is shown that the device architecture plays a key role in this lag and that NiO_x, a transport layer in one of the highest efficiency devices to date, causes a significant reduction in perovskite luminescence lifetime. An alternate transport layer structure which maintains robust nanocrystal emission is proposed. Devices with this architecture show external quantum efficiencies of 0.50% at 469 nm, seven times higher than state‐of‐the‐art devices at that wavelength. Finally, it is demonstrated that this architecture enables efficient devices across the entire blue‐green portion of the spectrum. The improvements demonstrated here open the door to efficient blue perovskite light‐emitting diodes.     

Red emission in Pr doped CaBi4Ti4O15 ferroelectric ceramics

In this paper, Pr doped CaBi₄Ti₄O₁₅ ceramics were prepared by a traditional solid state method. Crystal structure and morphologies of the ceramics were characterized by X-ray diffraction (XRD) and scanning electron microscopy (SEM). The photoluminescence properties of the samples were investigated by a spectrofluorometer. Three excitation bands are located at wide range of wavelength, which are 300-430 nm, 440-510 nm and 550-570 nm respectively. Upon the excitation of 494 nm light, the samples shows an emission peak centered at 614 nm, corresponding to ¹D₂ → ³H₄ transition. A 614 nm red emission excited under the wave with long wavelength of Pr doped CaBi₄Ti₄O₁₅ makes it useful in the white LEDs. In addition, it is an intrinsic ferroelectric and piezoelectric material; the enhanced ferroelectric properties were obtained by Pr doping. As a multifunctional materials, Pr doped CaBi₄Ti₄O₁₅ may be useful in white LEDs, sensor, and optical-electro integration.     

Luminescent properties of Eu-activated nanophosphors Ca3Y0.8Gd0.2(VO4)2.4(PO4)0.6: Eu for light-emitting diodes

Eu³⁺-doped Ca₃Y_0.8Gd_0.2(VO₄)_2.4(PO₄)_0.6 nanophosphors have been prepared by modified solid-state reaction. X-ray powder diffraction, transmission electron microscopy (TEM), photoluminescence excitation and emission spectra were used to characterize the resulting samples. X-ray powder diffraction (XRD) analysis confirmed the formation of YVO₄. Photoluminescence (PL) results showed that the phosphor could be efficiently excited by UV-visible light from 350 to 550 nm, exhibiting bright orange-red emission(excited by 397) and red emission(excited by 467), which has potential application as a phosphor for UV and blue GaN-based light-emitting diodes (LEDs). TEM images show that the grain size of Ca₃Y_0.45Eu_0.35Gd_0.2(VO₄)_2.4(PO₄)_0.6 is about 39 nm, which is in full agreement with the theoretical calculation data from the XRD patterns.     

Progress in discovery and structural design of color conversion phosphors for LEDs

Phosphor materials enable the optical frequency conversion to realize the full-color white emission light-emitting diodes (LEDs). So far much effort has been devoted to the design and discovery of novel LED phosphors for solid state lighting. In this review, firstly, we briefly describe several representative families of LED phosphors. Secondly, we propose the design methodology aimed at discovery of new phosphors with focus on the crystal structural considerations. Thirdly, we review the results of our work and other researchers on the recent advances in discovery and structural design of LED phosphors that exemplify the adopted strategies, including (1) design of the novel phosphors from the existed structural models, (2) discovery of novel phosphors from new crystal materials by doping and (3) structural modification of the known phosphors. The importance on the structure-property relations and recently reported methodologies involved in the crystal chemistry analysis for the discovery of LED phosphors, including mineral-inspired structural model design, exploratory crystal growth via single particle diagnostic approach, chemical unit cosubstitution, and so on, have been summarized in this review. We finally discuss the topics of structure-related active investigations and future opportunities for new and improved host materials for the color conversion applied in LEDs.     

MBE grown InGaN quantum dots and quantum wells: effects of in-plane localization

InGaN/GaN heterostructure samples were grown by molecular beam epitaxy using ammonia as a nitrogen precursor. The growth of InGaN/GaN self-assembled quantum dots was monitored in situ by reflection high energy electron diffraction intensity oscillations. Atomic force microscopy scans showed a very high density of InGaN islands, 1×10¹¹ cm⁻², well above the dislocation density. This could explain the increased radiative efficiency of these samples compared to homogeneous quantum wells. Light emitting diodes (LEDs) with InGaN active layers buried in GaN were realized. Electroluminescence and photocurrent spectra of these LEDs evidence a strong Stokes shift that can be attributed to high localization of carriers in InGaN layers.