Si-based materials and devices for light emission in silicon

We report on the fabrication and performances of extremely efficient Si-based light sources. The devices consist of MOS structures with erbium (Er) implanted in the thin gate oxide. The devices exhibit strong 1.54 μm electroluminescence (EL) at 300 K with a 10% external quantum efficiency, comparable to that of standard light-emitting diodes using III–V semiconductors. Er excitation is caused by hot electrons impact and oxide wearout limits the reliability of the devices. Much more stable light-emitting MOS devices have been fabricated using Er-doped silicon rich oxide (SRO) films as gate dielectric. These devices show a high stability, with an external quantum efficiency reduced to 1%. In these devices, Er pumping occurs by energy transfer from the Si nanostructures to the rare-earth ions. Finally, we have also fabricated MOS structures with Tb- and Yb-doped SiO₂ which show room temperature EL at 540 nm (Tb) and 980 nm (Yb) with an external quantum efficiency of a 10% and 0.1%, respectively.     

电致发光色纯性增强的硅基有机微腔

报道了硅基有机微腔的电致发光（EL）.该微腔由上半透明金属膜、中心有源多层膜和多孔硅分布Bragg反射镜（PS DBR）组成.半透明金属膜由Ag（２０nm）构成，充当发光器件的负电极和微腔的上反射镜.有源多层膜由Al (1 nm) / LiF(05 nm) /Alq3/Alq3:DCJTB/NPB/CuPc/ITO/SiO2组成，其中的Al/LiF为电子注入层，ITO为正电极，SiO2为使正、负电极电隔离的介质层.该PS DBR是采用设备简单、成本低廉且非常省时的电化学腐蚀法用单晶Si来制备的；该PS 关键词： 电化学腐蚀 电致发光 窄峰发射 硅基有机微腔     

Design and electro-optical characterization of Si-based resonant cavity light emitting devices at 850 nm

We report on the fabrication and characterization of Si/SiO₂ Fabry-Perot microcavities. These structures are used to enhance the external quantum efficiency along the cavity axis and the spectral purity of emission from silicon rich oxide films that are used as active media to fabricate a Si based RCLED (resonant cavity light emitting devices). A new structure to electrically pump the active media in the resonant cavity has been designed. These structures are fabricated by chemical vapour deposition on a silicon substrate. The microcavities are tuned at 850 nm and present a quality factor ranging from 17 to 150 depending on the number of pairs constituting the dielectric mirrors. An enhancement of the electro and photoluminescence (PL) signal of 20 times is achieved for the selected emission wavelength. These cavities are characterized by TEM analysis to evaluate film uniformity, thicknesses and the densification after annealing processes for temperature ranging from 800 to 1100 °C. The electrical properties of the active media are analyzed. The electroluminescence spectral features are compared with PL spectra correlated with the quality factor of the cavities. The photometric diagram shows also a high directionality of the emitted light within a 30° cone from the sample normal.     

Tunable photoluminescence and electroluminescence of size-controlled silicon nanocrystals in nanocrystalline-Si/SiO2 superlattices

We present photoluminescence and electroluminescence of silicon nanocrystals deposited by plasma-enhanced chemical vapor deposition (PECVD) using nanocrystalline silicon/silicon dioxide (nc-Si/SiO₂) superlattice approach. This approach allows us to tune the nanocrystal emission wavelength by varying the thickness of the Si layers. We fabricate light emitting devices (LEDs) with transparent indium tin oxide (ITO) contacts using these superlattice materials. The current-voltage characteristics of the LEDs are measured and compared to Frenkel-Poole and Fowler-Nordheim models for conduction. The EL properties of the superlattice material are studied, and tuning, similar to that of the PL spectra, is shown for the EL spectra. Finally, we observe the output power and calculate the quantum efficiency and power conversion efficiency for each of the devices.     

有机电致发光器件中新型芴类小分子材料的光谱特性

针对新型芴类小分子材料6,6′-(9H-fluoren-9,9-diyl)bis(2,3-bis (9,9-dihexyl-9H-fluoren-2-yl) quinoxaline) (BFLBBFLYQ)和空穴传输材料N,N′-biphenyl-N,N′-bis-(3-methylphenyl)-1, 1′-biphenyl-4,4′-diamine(TPD)及二者混合体系的荧光光谱和吸收光谱进行了测试表征,制备了结构为indium-tin oxide (ITO)/BFLBBFLYQ∶TPD/Alq/Mg∶Ag的双层有机电致发光器件。研究发现,BFLBBFLYQ∶TPD混合薄膜存在一个不同于单独分子薄膜的低能量发射光谱,发光峰在530 nm处,与tris(8-hydroxyquinolinato)aluminum(Alq)薄膜的荧光光谱相同,亦与结构为BFLBBFLYQ∶TPD/Alq双层器件的电致发光光谱相同。鉴于荧光染料4-(dicyanomethylene)-2-tert-butyl-6(1,1,7,7-tetramethyljulolidyl-9-enyl) -4H-pyran(DCJTB)的吸收光谱与Alq的荧光光谱有很好的重叠,利用Forster能量传递理论,将DCJTB红色染料引入双层器件,通过调节掺杂位置,考察器件的发光光谱情况,进而对BFLBBFLYQ∶TPD/Alq双层器件的载流子复合区域进行了研究。结果表明,双层器件的载流子复合区域位于BFLBBFLYQ∶TPD/Alq界面附近的Alq层内。     

Alq_3发光层厚度对有机电致发光器件性能的影响

文章以MoO3为空穴注入层,NPB为空穴传输层,改变发光/电子传输层Alq3的厚度,考察了器件电学和光学性能的变化。结果表明,随着Alq3层增加厚度,器件的电流逐步减小,由此获得Alq3薄膜的电场分布情况;器件发光光谱有少量红移,但长波端明显展宽,短波端强度下降。该文拟合了器件电致发光谱,与实验曲线吻合较好。同时拟合结果也表明,干涉效应主要影响光谱在长波端的强度分布,发光区域分布决定光谱在短波端的强度分布。     

Light-emitting structures based on nanocrystalline (Si/CaF2) multiquantum wells

Periodic nanocrystalline (Si/CaF₂) multilayers, deposited on (111) silicon by Molecular Beam Epitaxy (MBE) at room temperature, were used to fabricate simple light emitting structures and to study their electrical and optoelectronic properties. Photoluminescence (PL) and electroluminescence (EL) spectra from the same area of the devices are approximately the same, indicative of the same emission mechanism. Current–voltage characteristics reveal important phenomena in vertical carrier transport. Regions of negative differential resistance and current oscillations were observed and were tentatively attributed to resonant tunneling at high electric fields under field domain formation.     

硅表面硅镱键合与量子级联结构的发光

用纳秒强激光脉冲制备了纳米硅和硅表面的硅镱键合结构,检测了纳米硅表面硅镱键合的发光特性,并对这种结构相应的光致发光(PL)和电致发光(EL)的动力学机理进行了研究。观察到纳米硅表面硅镱键合在700nm附近尖锐的强发光峰,结合第一性原理计算认为是硅镱键合在弯曲纳米硅表面的局域态发光;利用纳秒脉冲激光沉积技术(PLD)制备多晶硅薄膜,发现由硅镱界面的失配形成表面的突触,其上的硅镱键合产生带隙中的电子局域态,该局域态发光分布在1250~1650nm波长范围,有增强的EL发光;用PLD方法制备硅镱多层膜量子级联结构,测量到光通信窗口的多个发光峰,并观察到随膜层数增加且发光峰增多。     

Origin of strong white electroluminescence from dense Si nanodots embedded in silicon nitride

Strong white electroluminescence (EL) from SiN-based devices containing Si nanodots with a density of more than 4.6×10(12)cm(2) was investigated. The white EL illustrates enhanced light emission with increasing applied voltage and can be divided into two components, a dominant peak at ~710 nm and weak one at ~550 nm, which are close to those of the PL spectra optically pumped by the 325 and 488 nm lines, respectively. Based on the PL characteristics, we propose that the dominant EL band arises from the band-to-band recombination in the dense Si nanodots where quantum confinement plays a decisive role in the light emission, whereas the weak EL band originates from the radiative Si dangling bond (K⁰) centers in the silicon nitride matrix.     

Light emitting devices based on silicon nanostructures

In this paper, we summarize the results of an extensive investigation on the properties of MOS-type light emitting devices based on silicon nanostructures. The performances of crystalline, amorphous and Er-doped Si nanostructures are presented and compared. We show that all devices are extremely stable and robust, resulting in an intense room temperature electroluminescence (EL) at around 900 nm or at 1.54 μm. Amorphous nanostructures may constitute an interesting system for the monolithic integration of optical and electrical functions in Si ULSI technology. In fact, they exhibit an intense room temperature EL with the advantage to be formed at a temperature of only 900 °C, remarkably lower than the temperature needed for the formation of Si nanocrystals (1100 °C or higher). To improve the extraction of the light, we coupled the emitting system with a 2D photonic crystal structure properly fabricated with ULSI technology to reduce the total internal reflection of the emitted light. We demonstrate that the extraction efficiency is increased by a factor of 4. Finally, the light emission from devices based on Er-doped Si nanoclusters has been studied and in particular we have investigated the luminescence quenching processes limiting quantum efficiency in these devices. In fact the carrier injection, that determines the excitation of Er ions through electron–hole recombination, at the same time produces an efficient non-radiative Auger de-excitation with trapped carriers. These data are presented and the implications on the device performances discussed.     

掺杂聚合物薄膜的蓝色电致发光

有机薄膜电致发光(OTFEL)自从Tangu[1,2],发表了高效、高亮度的双层结构器件以来,因其驱动电压低、直流驱动、亮度高、效率高、可制成大面积的平板显示而成为当前发光器件研究的热点.但由于有机膜的稳定性差,因此人们逐渐把注意力转向具有稳定结构的聚合物.     

用荧光法研究茶叶防癌抗癌的效用

近年来,由于保健医疗的兴起,有关茶叶防癌的研究受到了极大的关注.美国迈阿密大学一位教授曾周游世界并研究各个地区的茶叶,他发现中国的茶叶是最好的保健饮料,所以这位教授建议饮用中国茶.     

Efficient visible electroluminescence from porous silicon diodes with low driven voltage

By using n-butylamine as carbon resource, diamond-like carbon film (DLCF) was deposited on the p-n porous silicon (PS) surface by means of a radio-frequency glow discharge plasma system. Electroluminescent (EL) spectra show that EL intensity of the passivated PS diodes increases by 4.5 times and 30-nm blue-shift of EL peak occurs compared with the diodes without treatment and both of them are stable while the passivated diodes are exposed to the air indoor. The current-voltage (Ⅰ-Ⅴ) characteristics exhibit that the passivated diodes have a smaller series resistance and a lower onset voltage. The EL intensityvoltage (ⅠEL-Ⅴ) relations of the PS devices with different DLCF thicknesses show that only medium DLCF thickness is optimum. These experimental phenomena have been explained based on Raman spectra and IR spectra of the diamond-like carbon films and IR spectra of the passivated PS samples.     

掺杂8－羟基喹啉铝薄膜的电致发光特性研究

在具有电致发光（ＥＬ）的有机整合染料８－羟基喹啉铝（Ａｌｑ３）中接以染料罗丹明６Ｇ（Ｒ６Ｇ）,用真空热蒸发的方法制备器件,获得了峰值波长５７５ｎｍ的黄色直流薄膜电致发光,从而通过掺杂改变了发光颜色．并在Ａｌｑ３发光层不同区域插入一掺杂薄层（Ａｌｑ３：Ｒ６Ｇ）,利用其发光波长与未掺杂部分（Ａｌｑ３）的不同,以此作为“探测层”,通过对器件光谱及电学特性的测量与分析,探讨了有关发光区域,发光机理,界面对发光影响等基本问题．     

掺杂8-羟基喹啉铝薄膜的电致发光特性研究

在具有电致发光(EL)的有机整合染料8-羟基喹啉铝(Alq3)中接以染料罗丹明6G(R6G),用真空热蒸发的方法制备器件,获得了峰值波长575nm的黄色直流薄膜电致发光,从而通过掺杂改变了发光颜色.并在Alq3发光层不同区域插入一掺杂薄层(Alq3:R6G),利用其发光波长与未掺杂部分(Alq3)的不同,以此作为“探测层”,通过对器件光谱及电学特性的测量与分析,探讨了有关发光区域,发光机理,界面对发光影响等基本问题.     

硅基1.55 μm可调谐共振腔窄带光电探测器的研究

制作了一种低成本硅基1.55 μm可调谐共振腔增强型探测器.首次获得硅基长波长可调谐共振腔探测器的窄带响应,共振峰量子效率达44％,峰值半高宽为12.5nm,调谐范围14.5nm,并且获得1.8 GHz的高频响应.本制作工艺不复杂,成本低,有望用于工业生产.     

ZnS:ErF3电致发光薄膜2H11/2,4S3/2→4I15/2发光的猝灭过程

本文通过ZnS:ErF3交流电致发光薄膜发光光谱和发光衰减特性研究了Er3+离子2H11/2,3S3/2发光的猝灭过程,实验结果表明由于Er3+离子间多极矩相互作用,一个激发的Er3+离子从2H11/2态无辐射弛豫到4F9/2态,同时另一个激发的Er3+离子从4F7/2或4F5/2+4F3/2态跃迁到2H9/2或4G11/2态的交叉弛豫过程是2H11/2,4S3/2发光浓度猝灭的一个主要机制,交叉弛豫几率随着掺杂浓度的增加而增大,根据在固定掺杂浓度下2H11/2,4S3/2、4F9/2发光衰减时间不随激发密度而改变的实验结果,排除了处于激发的Er3+离子之间直接能量传递的可能性,这结果与扩散限制的能量传递理论相符。     

Blue photo- and electroluminescence of silicon dioxide layers ion-implanted with group IV elements

The microstructural, optical and electrical properties of Si-, Ge- and Sn-implanted silicon dioxide layers were investigated. It was found, that these layers exhibit strong photoluminescence (PL) around 2.7 eV (Si) and between 3 and 3.2 eV (Ge, Sn) at room temperature (RT), which is accompanied by an UV emission around 4.3 eV. This PL is compared with that of Ar-implanted silicon dioxide and that of Si- and Ge-rich oxide made by rf magnetron sputtering. Based on PL and PL excitation (PLE) spectra we tentatively interpret the blue–violet PL as due to a T₁→S₀ transition of the neutral oxygen vacancy typical for Si-rich SiO₂ and similar Ge- or Sn-related defects in Ge- and Sn-implanted silicon dioxide. The differences between Si, Ge and Sn will be explained by means of the heavy atom effect. For Ge-implanted silicon dioxide layers a strong electroluminescence (EL) well visible with the naked eye and with a power efficiency up to 5×10^-4 was achieved. The EL spectrum correlates very well with the PL one. Whereas the EL intensity shows a linear dependence on the injection current over three orders of magnitude, the shape of the EL spectrum remains unchanged. The I-V dependence exhibiting the typical behavior of Fowler–Nordheim tunneling shows an increase of the breakdown voltage and the tunnel current in comparison to the unimplanted material. Finally, the suitability of Ge-implanted silicon dioxide layers for optoelectronic applications is briefly discussed. Received: 9 March 2000 / Published online: 30 June 2000     

Low-voltage blue light emission from n-ZnO/p-GaN heterojunction formed by RF magnetron sputtering method

High quality n-ZnO/p-GaN heterojunction was fabricated by growing highly crystalline ZnO epitaxial films on commercial p-type GaN substrates via radio frequency (RF) magnetron sputtering. Low-voltage blue light emitting diode with a turn-on voltage of ∼2.5 V from the n-ZnO/p-GaN heterojunction was demonstrated. The diode gives a bright blue light emission located at ∼460 nm and a low threshold voltage of 2.7 V for emission. Based on the results of the photoluminescence (PL) and electroluminescence (EL) spectra, the origins of the EL emissions were studied in the light of energy band diagrams of ZnO–GaN heterojunction, and may attribute to the radiative recombination of the holes in p-GaN and the electrons injected from n-ZnO, which almost happened on the side of p-GaN layer. These results may have important implications for developing short wavelength optoelectronic devices.     

Er-doped edge emitting devices with a SiGe waveguide

Er-doped Si edge emitting devices have been fabricated using layer structures grown by molecular beam epitaxy (MBE). Both oxygen and carbon were used as co-dopant in the Er-doped layer. In order to achieve a waveguiding effect, a SiGe layer has been placed next to the Er-doped layer. Intense electroluminescence (EL) at 1.54 μm has been observed from edge emission of such a device at room temperature and even up to 50°C at low excitation power under reverse bias. The value of an activation energy (125 meV) for dominating luminescence intensity quenching, as derived from temperature-dependent EL measurements, was 30 meV lower than that observed from our previous Er/O-doped structures (155 meV), which is likely caused by the band gap narrowing induced by C-doping. The estimated external quantum efficiency of these Er-doped Si edge emitting LEDs is 5×10⁻⁵ at room temperature.