脉冲Nd:YAG激光器选区晶化制备多晶硅薄膜

采用三倍频后的Nd:YAG固体脉冲激光系统(波长为355 nm)选区诱导晶化非晶硅薄膜,以制备多晶硅薄膜。分别测试了激光晶化前后薄膜的表面形貌和拉曼光谱。在文中分析了400 nm厚薄膜在激光扫描前后的表面形貌变化。拉曼光谱显示薄膜的晶化程度随着激光能量的增加而提高。最优的激光晶化能量密度与薄膜的厚度相关。对于300 nm和400 nm厚的非晶硅薄膜,有效晶化非晶硅的能量密度分别在440-634 mJ/cm²,777-993 mJ/cm²之间。在激光能量密度分别为634 mJ/cm²,975 mJ/cm²和1571 mJ/cm²时,300 nm、400 nm和500 nm厚薄膜达到最好的晶化效果。     

激光晶化形成纳米硅基电致发光材料及其性质研究

为实现基于硅基材料的高效光源,提出激光晶化形成纳米硅基电致发光材料性能研究,来明确了激光晶化形成纳米硅基电致发光材料的基本性能。主要以选择的纳米硅基电致发光材料作为研究对象,首先采用激光晶化技术完成制备工作,其次设计对电致发光材料性能计算方法,最后设计吸收光谱、固态与薄膜态量子产量、发光寿命、发光率四方面的测定环节,依此对晶化处理和未晶化的两个样本进行电致发光材料测定。结果表明：晶化后的电致发光材料中存在尺寸可控的纳米硅量子,且当氧气量充足时,晶化后的致电发光材料的硅粒子产出量会逐渐增加;光学带隙要比原始沉积样本要小,且当精光密度增加时光学带隙发生进一步缩减;晶化后的样本发光寿命有、无氧两种状态均为1 200 ns,发光率可达到99%。以上结果说明激光晶化形成纳米硅基电致发光材料性能优越,具有较强的发展潜力。以期可为日后的纳米硅基电致发光材料研究与制作过程中提供理论支撑,在此基础上制备出性能更加优异的电致发光材料。     

非晶硅薄膜的准分子激光晶化研究

利用Kr准分子激光器晶化非晶硅薄膜, 研究了不同的激光能量密度和脉冲次数对非晶硅薄膜晶化效果的影响.利用X 射线衍射(XRD)和扫描电子显微镜(SEM)对晶化前后的样品的物相结构和表面形貌进行了表征和分析.实验结果表明, 在激光频率为1 Hz 的条件下, 能量密度约为180 mJ/cm2时,准分子激光退火处理实现了薄膜由非晶结构向多晶结构的转变;当大于晶化阈值180 mJ/cm2小于能量密度230 mJ/cm2时, 随着激光能量密度增大, 薄膜晶化效果越来越好;激光能量密度为230 mJ/cm2时, 晶化效果最好、晶粒尺寸最大, 约60 nm, 并且此时薄膜沿Si(111)面择优生长;脉冲次数50 次以后对晶化的影响不大.     

纳米硅上等离子体激元与光子相互作用对电子局域态及发光的调控

用脉冲激光制备纳米硅的过程中,在Purcell腔中会形成等离子体晶格结构,这是等离子体激元与光子相互作用的结果,其形成的等离子体晶格与Wigner晶体结构很相似。利用光致发光光谱研究局域态发光特征从而去控制纳米硅结构的发光,在氧气或氮气环境下制备纳米硅样品,由于表面键合作用形成电子局域态会产生几个特征发光峰,分别位于560、600和700 nm附近。在氧气环境下用激光照射硅晶片形成硅量子点,可以观察到样品的拉曼光谱随着测量温度的增加而产生频谱移动,这个过程伴随着声子能量的变化。温度较高时,光致发光峰强度下降,同时发射频谱变宽。在77 K时,可以观察到光致发光峰的红移,这表明局域态发光在纳米硅发光的激活起着重要作用。在带隙中产生的局域态取决于表面键合的情况,表面键合可以激活硅量子点而增强发光。在硅薄膜上掺入稀土金属镱会形成电子局域态发光,可将电致发光的波长调控进入光通讯窗口。     

微腔中nc-Si/SiN超晶格的光致发光

研究了一维光子晶体微腔结构对nc-Si/a-SiNz超晶格发射的调制.一维光子晶体微腔采用两种具有不同折射率的非化学组分非晶氮化硅的周期调制结构,腔中嵌入采用激光晶化方法制备的硅量子点阵列,从Raman谱和透射电子显微镜分析得到其尺寸约为3～4 nm.从光致发光谱上观察到明显的选模作用、明显变窄的发光峰以及约两个量级的发光强度的增强.微腔对硅量子点阵列发光的调制主要表现在两个方面:共振模式的增强和非共振模式的抑制.硅量子点中位于腔共振模式的辐射跃迁被增强,非共振模式的辐射跃迁被抑制,因此位于腔共振频率处的跃迁通道成为硅量子点中唯一的辐射跃迁通道,导致光致发光谱的窄化和强度的增强.因此,在提高硅材料发光效率方面,光子晶体微腔具有非常大的应用前景.     

微腔中nc-Si/SiN超晶格的光致发光

研究了一维光子晶体微腔结构对nc-Si/a-SiNz超晶格发射的调制.一维光子晶体微腔采用两种具有不同折射率的非化学组分非晶氮化硅的周期调制结构,腔中嵌入采用激光晶化方法制备的硅量子点阵列,从Raman谱和透射电子显微镜分析得到其尺寸约为3～4 nm.从光致发光谱上观察到明显的选模作用、明显变窄的发光峰以及约两个量级的发光强度的增强.微腔对硅量子点阵列发光的调制主要表现在两个方面:共振模式的增强和非共振模式的抑制.硅量子点中位于腔共振模式的辐射跃迁被增强,非共振模式的辐射跃迁被抑制,因此位于腔共振频率处的跃迁通道成为硅量子点中唯一的辐射跃迁通道,导致光致发光谱的窄化和强度的增强.因此,在提高硅材料发光效率方面,光子晶体微腔具有非常大的应用前景.     

本征非晶硅薄膜的准分子激光晶化

为了减低非晶硅薄膜太阳能电池的光致衰减效应和提高其光电转换效率,用等离子体化学气相沉积系统制备了本征非晶硅薄膜,用波长为248nm的KrF准分子激光器激光晶化了非晶硅表层,用共焦显微喇曼测试技术研究了非晶硅薄膜在不同的激光能量密度和不同的频率下的晶化状态,并用扫描电子显微镜测试晶化前后薄膜的形貌。结果表明,随着激光能量密度的增大,薄膜晶化效果越来越好,能量密度达到268.54mJ/cm2时晶化效果最好,此时结晶比约为76.34%;最佳的激光能量密度范围是204.99mJ/cm2~268.54mJ/cm2,这时薄膜表面晶化良好;在1Hz~10Hz范围内,激光频率越大晶化效果越好;晶化后薄膜明显出现微晶和多晶颗粒,从而达到了良好的晶化效果。     

金纳米颗粒增强富硅氮化硅发光特性的研究

采用时域有限差分(FDTD)方法,对Au纳米颗粒的尺寸和形貌对于其光学特性的影响进行了系统的理论研究。通过采用等离子体增强化学气相沉积(PECVD)、晶化处理、电子束蒸发和高温退火等工艺,制备基于局域表面等离子共振(LSPR)效应的富硅氮化硅发光芯片。利用拉曼光谱仪、扫描电子显微镜(SEM)、奥林巴斯显微镜等对不同结构Au纳米颗粒富硅氮化硅发光器件的特性进行了表征。研究表明,通过对Au纳米颗粒的大小、形状和分布合理优化,富硅氮化硅芯片的发光强度在570nm波长附近提升了7倍,增强峰的位置红移了10nm。     

微腔中nc-Si/SiN超晶格的光致发光

研究了一维光子晶体微腔结构对nc-Si/a-SiNz超晶格发射的调制. 一维光子晶体微腔采用两种具有不同折射率的非化学组分非晶氮化硅的周期调制结构，腔中嵌入采用激光晶化方法制备的硅量子点阵列，从Raman谱和透射电子显微镜分析得到其尺寸约为 3～4nm. 从光致发光谱上观察到明显的选模作用、明显变窄的发光峰以及约两个量级的发光强度的增强. 微腔对硅量子点阵列发光的调制主要表现在两个方面：共振模式的增强和非共振模式的抑制. 硅量子点中位于腔共振模式的辐射跃迁被增强，非共振模式的辐射跃迁被抑制，因此位于腔共振频率处的跃迁通道成为硅量子点中唯一的辐射跃迁通道，导致光致发光谱的窄化和强度的增强. 因此，在提高硅材料发光效率方面，光子晶体微腔具有非常大的应用前景.     

非晶硅薄膜激光晶化及其结构分析

以射频(频率为13.6MHz)磁控溅射系统制备的非晶硅薄膜为前驱物,采用激光晶化技术实现从非晶硅薄膜到纳米晶硅薄膜的相变过程。采用拉曼光谱仪和高分辨透射电镜对激光晶化薄膜的组织结构进行了研究。结果表明:薄膜由非晶硅结构转变为微晶硅结构,微晶硅晶粒尺寸在纳米级。激光晶化存在一个最佳工艺参数,功率太高或太低都不利于晶化。     

富Si的SiN薄膜光致发光及电致发光研究

采用等离子体化学气相沉积法(PECVD)制备了三种不同化学计量比的富Si的SiN薄膜,并对其光致发光及电致发光性能进行了研究.研究发现,随着Si含量的增加,薄膜的光致发光峰位从460 nm红移到610 nm,且半高宽不断增加;而薄膜的电致发光峰位并没有随着Si含量的改变而变化,始终处于600 nm附近,这主要是由于富Si的SiN薄膜的光致发光与电致发光的机理是不同的.光致发光来源于SiN薄膜缺陷态能级之间辐射复合,而电致发光则是由注入的裁流子先迟豫到较低的缺陷态能级,然后经过辐射复合而得到.     

在SiO2中掺Al对Au/纳米(SiO2/Si/SiO2)/p-Si 结构电致发光的影响

利用射频磁控溅射方法,制成纳米SiO2层厚度一定而纳米Si层厚度不同的纳米(SiO2/Si/SiO2)/p-Si结构和纳米(SiO2∶Al/Si/SiO2∶Al)/p-Si结构,用磁控溅射制备纳米SiO2∶Al时所用的SiO2/Al复合靶中的Al的面积百分比为1%．上述两种结构中Si层厚度均为1—3nm,间隔为0.2nm．为了对比研究,还制备了Si层厚度为零的样品．这两种结构在900℃氮气下退火30min,正面蒸半透明Au膜,背面蒸Al作欧姆接触后,都在正向偏置下观察到电致发光（EL）．在一定的正向偏置下,EL强度和峰位以及电流都随Si层厚度的增加而同步振荡,位相相同．但掺Al结构的发光强度普遍比不掺Al结构强．另外,这两种结构的EL具体振荡特性有明显不同．对这两种结构的电致发光的物理机制和SiO2中掺Al的作用进行了分析和讨论．     

非晶Fe73.5Cu1Nb3Si13.5B9合金的激光纳米晶化研究

在相同激光扫描速度(20mm／s)和不同激光功率(150W，200W，250W，300W)工艺条件下，利用CO2激光对铁磁Fe73．5Cu1Nb3Si13．5B9非晶带进行了辐照处理，诱导非晶带样品发生纳米晶化。应用穆斯堡尔(Mossbauer)谱(MS)、透射电镜(TEM)和X射线衍射(XRD)对实验样品的晶化工艺、纳米晶相的组织结构、晶化量和纳米晶化机理等进行了研究。结果表明，晶化析出相是α-Fe(Si)单相固溶体，具有4种超精细结构；其晶粒尺寸约为10～20nm；纳米晶均匀分布在非晶基体上，形成非晶相与纳米晶化相的双相组织结构。随着激光功率的增加，纳米晶化量随着增加，可通过控制激光处理工艺参量，来实现纳米晶化量的控制。     

Electroluminescence from Au/Si/SiO2/p-Si structure

Si/SiO₂ films have been grown using the two-target alternation magnetron sputtering technique. The thickness of the SiO₂ layer in all the films was 8 nm and that of the Si layer in five types of the films ranged from 4 to 20 nm in steps of 4 nm. Visible electroluminescence (EL) has been observed from the Au/Si/SiO₂/p-Si structures at a forward bias of 5 V or larger. A broad band with one peak 650–660 nm appears in all the EL spectra of the structures. The effects of the thickness of the Si layer in the Si/SiO₂ films and of input electrical power on the EL spectra are studied systematically.     

Effect of surface passivation by SiN/SiO2 of AlGaN/GaN high-electron mobility transistors on Si substrate by deep level transient spectroscopy method

Device performance and defects in AlGaN/GaN high-electron mobility transistors have been correlated. The effect of SiN/SiO₂ passivation of the surface of AlGaN/GaN high-electron mobility transistors on Si substrates is reported on DC characteristics. Deep level transient spectroscopy (DLTS) measurements were performed on the device after the passivation by a (50/100 nm) SiN/SiO₂ film. The DLTS spectra from these measurements showed the existence of the same electron trap on the surface of the device.     

Textured silicon surface passivation by high‐rate expanding thermal plasma deposited SiN and thermal SiO2/SiN stacks for crystalline silicon solar cells

Expanding thermal plasma (ETP) deposited silicon nitride (SiN) with optical properties suited for the use as antireflection coating (ARC) on silicon solar cells has been used as passivation layer on textured monocrystalline silicon wafers. The surface passivation behavior of these high‐rate (>5 nm/s) deposited SiN films has been investigated for single layer passivation schemes and for thermal SiO₂/SiN stack systems before and after a thermal treatment that is normally used for contact‐firing. It is shown that as‐deposited ETP SiN used as a single passivation layer almost matches the performance of a thermal oxide. Furthermore, the SiN passivation behavior improves after a contact‐firing step, while the thermal oxide passivation degrades which makes ETP SiN a better alternative for single passivation layer schemes in combination with a contact‐firing step. Moreover, using the ETP SiN as a part of a thermal SiO₂/SiN stack proves to be the best alternative by realizing very low dark saturation current densities of <20 fA/cm² on textured solar‐grade FZ silicon wafers and this is further improved to <10 fA/cm² after the anneal step. Optical and electrical film characterizations have also been carried out on these SiN layers in order to study the behavior of the SiN before and after the thermal treatment. Copyright © 2008 John Wiley & Sons, Ltd.     

Amorphous Si/Si heterojunction microwave transistors

Because the emitter-base junctions of amorphous Si/Si heterojunction bipolar transistors (HBTs) with a conventional structure are inside the amorphous Si (a-Si) layer, their high-frequency performance is limited due to very low electron velocity in a-Si. An improved structure, the two-dimensional-electron-gas (2DEG) emitter structure, is proposed to overcome these problems, and a-Si/Si HBTs with good high-frequency performance are fabricated. Their low-temperature fabrication technology can be extended to other III-V-compound HBTs     

Analyses of interface adhesion between porous SiO2 low-k film and SiC/SiN layers by nanoindentation and nanoscratch tests

In this study, the interface adhesion between porous SiO₂ low-dielectric-constant film and SiN capping layer as well as SiC etch stop layer has been investigated. The SiN capping layer was found mostly composed of Si to N bonds, and the porous SiO₂ film composed of Si to O bonds. Elements of Si, O, and N constructed an interlayer mixing region of about 20 nm at the interface between the porous SiO₂ film and SiN capping layer. Under nanoindentation and nanoscratch tests, interface delamination between the porous SiO₂ film and both SiN capping layer and SiC etch stop layer occurred around the indented regions, and the interface adhesion strengths were accordingly obtained. The interface adhesion energy between the porous SiO₂ film and SiN capping layer was measured as about 3.7 and 0.9 J/m² by nanoindentation and nanoscratch tests, respectively, and that between the porous SiO₂ film and SiC etch stop layer was about 8.3 and 1.2 J/m².     

基于ZnS/SiO2量子点的EL器件及宽谱发射

将ZnS/SiO2量子点与PVP在甲醇溶液中充分混合作为活性层材料,通过匀胶方法制备了ITO//ZnS/SiO2∶PVP//Al结构的电致发光(EL)薄膜器件。器件的EL光谱由510～560nm波段的绿光发射和相对较弱的蓝紫光(400nm左右)发射组成,通过对发光光谱的分析发现,上述两个区域的发射均来自ZnS的缺陷能级。其中,绿色发光峰来源于较低能态的缺陷能级;而高能区域的蓝色发光则是由于高能态的缺陷能级俘获电子的几率增大,在这过程中,PVP形成的能级阶梯有效增加了高能态缺陷能级俘获电子的几率,提升了高能波段的发光效率,相应地,器件的色坐标也随之从(0.37,0.42)变化到(0.30,0.34),趋于白光发射。     

Effect of plasma treatments on interface chemistry and adhesion strength between porous SiO2 low-k film and SiC/SiN layers

In this study, the interface chemistry and adhesion strengths between porous SiO₂ low-dielectric-constant film and SiN capping layer as well as SiC etch stop layer have been investigated under different plasma treatments. Elements of Si, O, and N constructed an interlayer region with mixing Si-N and Si-O bonds at the interface between the porous SiO₂ film and SiN capping layer. After plasma treatments especially O₂ plasma, the oxygen content at the interface increased, and the binding energy obviously shifted to a higher level. Under nanoindentation and nanoscratch tests, interface delamination occurred, and the interface adhesion strength was accordingly measured. After plasma treatments especially the O₂ plasma, more Si-O bonds of high binding energy existed at the interface, and thus the interface adhesion strength was effectively improved. The adhesion energy of SiO₂/SiN and SiC/SiO₂ interfaces was enhanced to 4.7 and 10.5 J/m² measured by nanoindentation test, and to 1.3 and 2.0 J/m² by nanoscratch test, respectively.