中频反应磁控溅射制备AlN薄膜的工艺研究

利用中频反应磁控溅射成功制备了AIN薄膜。研究了过程参数例如靶电流、溅射气压和氮浓度对AIN薄膜沉积速率和光学性能的影响规律。实验结果表明，在优化制备工艺的基础上，能够制备出具有优良光学性能（高折射率、低消光系数、高透射率）的AIN薄膜。     

稀土La、Nd掺杂硅基薄膜光致发光特性

测量了Ｌａ、Ｎｄ稀土离子注入Ｓｉ基晶片,在不同退火条件下的室温光致发光（ＰＬ）谱,结果表明它们均具有蓝、紫发光峰、且发光稳定,在一定范围内发光效率随掺杂浓度的增加而增大,随退火条件的不同而改变。并对样品的发光机理作了初步探讨。     

Cu掺杂ZnO的光致发光光谱

ZnO是宽禁带半导体,室温下禁带宽度为3.37eV,激子束缚能高达60meV,是制备光电器件的优选材料。然而,p型掺杂仍是亟待解决的问题。ⅠB元素Cu被认为在ZnO中产生受主能级,可以实现ZnO的p型掺杂。综述了各种制备方法、制备条件和激发条件下得到的Cu掺杂ZnO薄膜、纳米线和纳米棒的光致发光谱和机理,总结出Cu掺杂ZnO光致发光谱的带边发射会因为Cu的掺杂强度降低,或出现发射中心红移等现象。可见光区域由于Cu掺杂会产生新的蓝光、绿光和橙光发射峰,蓝光发射峰可能与Cu2+-Cu+跃迁或VZn和Zni有关;绿光发射峰可能与Cu杂质或VO-VZn跃迁有关,Cu掺杂还可能引入非辐射复合的点缺陷中心;橙光发射峰则可能由于Cu杂质受主能级向深施主能级跃迁而产生。     

中频磁控反应溅射AlN薄膜及微观结构研究

采用中频磁控反应溅射工艺进行了氮化铝薄膜的制备,对沉积速率、晶体结构和表面形貌与氮气流量和溅射功率之间的变化关系进行了研究。结果表明,通过调节N2流量和溅射功率选择性地获得非晶态和沿着c轴方向择优生长的晶态AlN薄膜。在化合物沉积模式下,增加溅射功率和增加反应气体流量均有利于获得非晶态AlN薄膜,并且减小薄膜表面粗糙度,获得光滑的AlN薄膜,并采用薄膜生长原理对这种现象进行了解释。     

Fe的不同掺杂量对ZnO薄膜光致发光的影响

采用射频磁控溅射在玻璃衬底上制备了不同掺杂量的Fe-ZnO薄膜,分析不同掺杂量对薄膜光学性能的影响.利用X射线衍射仪(XRD)和原子力显微镜(AFM)研究Fe-ZnO薄膜的微观结构和形貌结构.Fe-ZnO薄膜光致发光(PL)性质的研究发现,发光峰主要有蓝光发射和绿光发射,蓝光发射主要是由于电子从导带向锌空位形成的浅受主能级上的跃迁;绿光发射是由于电子从氧空位到锌空位的能级跃迁及导带底到氧错位缺陷能级的跃迁.由透射谱和吸收谱分析,Fe-ZnO薄膜在可见光区的平均透过率为66%,掺杂量为2%Fe的薄膜的禁带宽度最接近于ZnO的禁带宽度.     

一种有机掺杂体系的光致发光及薄膜电致发光研究

将具有薄膜电致发光（ＴＦＥＬ）性能的有机络合染料８－羟基喹啉铝（Ａｌｑ３）掺以染料罗丹明６Ｇ（Ｒ６Ｇ），用真空热蒸发的方法获得了峰值波长５７５ｎｍ的黄色直流电致发光（ＥＬ）。通过对不同掺杂浓度的粉末，溶液，薄膜样品及电致发光器件的光谱及寿命测量和对比，证实了能量传递的存在并初步探讨了可能的途径。同时发现掺杂器件ＥＬ谱的形状随驱动电压升高发生明显的改变，基质（Ａｌｑ３）的发射（相对于掺杂剂Ｒ６Ｇ的发射）明显增强，对这一现象产生的原因作了分析，并由此讨论了有机掺杂ＴＦＥＬ中复合，发射区域等问题。     

Mn掺杂ZnO纳米线的拉曼散射和光致发光特性

研究了不同Mn掺杂含量的ZnO纳米线在室温条件下的拉曼散射和光致发光性能,发现Mn掺杂入ZnO后引入了部分应力,在其拉曼光谱中表现出拉曼峰的位置发生偏移,Mn的掺杂含量越高,峰偏移得越明显.Mn的掺杂对ZnO纳米线的发光性能也有影响,尽管掺杂后仍保持有较为明显的紫外发光峰,但是,随着Mn含量的增加,紫外发光峰的强度降低,并且半峰宽逐渐增大.此外,Mn的掺杂明显地改变了ZnO紫外发光峰的位置.     

电沉积法制备La掺杂ZnO薄膜及其光致发光性能

以乌洛托品为络合剂,采用电化学沉积法成功地制备出La掺杂ZnO薄膜.通过对样品的XRD表征,得出生长的样品为ZnO纤锌矿结构,(002)衍射峰随掺杂La3+浓度的增加而向更小角度方向移动,表明少量La3+掺杂进入了ZnO点阵结构中.EDS测量结果显示,La3+以替代的形式进入ZnO晶格中,掺入量为2.4%(原子分数)左右.由XPS测量结果可知,镧离子在薄膜中以+3价的形式存在,PL测量结果进一步证明了La3+能够取代ZnO晶格中Zn2+的格位.     

Ce掺杂ZnO纳米晶的光致发光特性

以 Zn(NOs)3·6H2O、Ce(NO3)3·6H2O为原料,明胶为模板分散剂,采用凝胶模板燃烧法制备纯ZnO和ZnO:Ce纳米晶,利用XRD、TEM和PL谱研究样品的结构和性能.结果表明:产物粒子形状基本为球形,结晶良好,属六方晶系结构;随着掺杂量的增加,粒子尺寸逐渐减小,说明Ce掺杂能够有效地抑制ZnO晶粒生长.在310nm光的激发下,观察到480～500nm强而宽的可见发射,在此背景上出现487nm和494nm的蓝绿光子发射峰,掺杂样品的发光强度显著增强.蓝光发射主要是由于氧空位与间隙氧之间的跃迁,绿光发射是由于材料表面离子化氧空位中的电子与价带中光激发的空穴之间的复合.     

中频磁控反应溅射制备c轴择优取向AlN薄膜

通过中频磁控反应溅射,在Si(100)衬底上沉积AlN薄膜,并用X射线衍射、扫描电子显微镜和Raman光谱表征AlN薄膜的微观特征.实验中,研究了氮分压、靶基距、溅射功率对AlN薄膜质量的影响,并优化参数制备高质量的c轴取向的AlN薄膜.结果表明,提高溅射功率、降低靶基距以及降低氮分压,有利于c轴择优取向AlN的生长.在优化条件下制备的AlN薄膜具有高度c轴取向,(002)摇摆曲线的半高宽为5.7°,Raman光谱E2(high)声子峰的FWHM为13.8cm-1.     

Effect of substrate temperature and bias voltage on the crystallite orientation in RF magnetron sputtered AlN thin films

The crystal orientation and residual stress of AlN thin films were investigated using X-ray diffraction and substrate curvature method. The AlN films were deposited on Si(100) by RF magnetron sputtering in a mixed plasma of argon and nitrogen under various substrate negative bias V_s (up to − 100 V) and deposition temperature T_s up to 800 °C. The results show that lower temperature and moderate bias favor the formation of (002) plane parallel to the substrate surface. On the contrary, strong biasing beyond − 75 V and deposition temperature higher than 400 °C lead to the growth of (100) plane. At the same time nanoindentation hardness and compressive stress measured by substrate curvature method showed significant enhancement with substrate bias and temperature. The biased samples develop compressive stress while unbiased samples exhibit tensile or compressive stress depending on plasma power and temperature. The relationships between deposition conditions and crystallographic orientation of the films are discussed in terms of surface energy minimization and ion bombardment effects.     

Growth properties of AlN films on sapphire substrates by reactive sputtering

Aluminum nitride (AlN) films were grown on sapphire substrates by radio frequency (RF) magnetron sputtering in plasma containing a mixture of argon and nitrogen, using a pure aluminum target. The effect of RF power was investigated with respect to growth rate, surface roughness, and transmittance of AlN films. As the RF power increases, the growth rate increases and the root mean square of surface roughness decreases while the absorption edge shifts to longer wavelength. This shift is believed to be due to the defects induced by ion bombardment.     

Substrate biasing effects on the microstructure of magnetron-sputtered AlN films investigated by in situ reflectance interferometry

In situ reflectance interferometry (RI) at 400 nm wavelength was used to investigate the effect of the substrate negative bias on the microstructure of aluminium nitride (AlN) films deposited at room temperature on Si substrates by magnetron sputtering. Their surface reflectance recorded during film deposition promptly yields real-time information on the microstructures developed under oxygen contamination and bias change. Specifically, the refractive index n and the extinction coefficient k are deduced from reflectance using appropriate multilayer optical models and validated by spectroscopic ellipsometry. These optical constants correlate appreciably with the microstructure that evolves between columnar-crystallized and purely amorphous phases including in-between amorphous states containing dispersed nano-AlN grains. These microstructures were identified using ex situ energy dispersive X-ray spectroscopy, transmission electron microscopy and diffraction, X-ray diffraction and Auger electron spectroscopy. The simple and cost-effective in situ RI thus appears a powerful tool in controlling the microstructures of thin AlN films for desired applications.     

Surface morphology of AlN films synthesized by pulsed laser deposition

Surface morphology of AlN films, synthesized on Si substrates by pulsed laser deposition, has been examined by recording atomic-force-microscopy (AFM) images. The influence of N₂ ambient pressure, ranging from 5 × 10⁻⁴ Pa to 10 Pa, is reflected well in the alteration of the surface roughness and size of crystallites of the AlN films. A tendency of a decrease in the surface roughness with increasing N₂ pressure was observed, which also correlates with the polycrystalline structure of the films. Deposition in vacuum resulted in the highest surface roughness due to the large size of crystallites emerging from the surface, while increasing the nitrogen pressure yielded smaller crystallites and a smoother film surface. The presented results could be useful for applications of pulsed laser deposited AlN in different optical and acoustic devices, where the crystalline quality of the AlN films and the surface is very important.     

The influence of defects and impurities in polycrystalline AlN films on the violet and blue photoluminescence

The influence of defects and impurities in polycrystalline aluminum nitride films on the violet and blue photoluminescence properties was investigated. The photoluminescence spectra show a broad emission band in the range from 380 nm to 550 nm, which consists of two components of the violet band centered at 400 nm and the blue band centered at 480 nm. When the native defects reduce and the crystal quality is improved by annealing in nitrogen atmosphere, the shoulder band around 480 nm declines. The center of the violet luminescence shifts from 400 nm to about 440 nm as the oxygen content increase from 2.9 at.% to 12.3 at.%. The intensity and the center of the violet emission vary mostly linearly with the oxygen content. Combining the results of X-ray diffraction and Auger Electron Spectroscopy, the violet emission around 400 nm (3.09 eV) can be attributed to the transition from the shallow donor to the deep acceptor related to the oxygen impurity, while the blue emission around 450 nm (2.58 eV) may originate from transition from the shallow donor to the deep acceptor related to the native defect.     

Effect of process parameter changes on the composition of magnetron sputtered and evaporated TiN and AlN films measured by UHV in-situ techniques

TiN and AlN films are deposited on HSS steel substrates in an ultrahigh vacuum magnetron system equipped with in-situ Auger electron spectroscopy (AES) and mass spectrometric sensors for plasma diagnostics. The composition of TiN_x coatings is measured by AES as a function of the N₂ pressure, the bias voltage, and the d.c. power. The flux of ionic particles impinging on the substrate surface and their energies are determined by a quadruple mass analyzer mounted behind a hole in the substrate. In addition, the reactivity of neutral nitrogen molecules in a reactive evaporation process is measured by a quartz crystal microbalance.     

Effects of outgassing on the reactive sputtering of piezoelectric AlN thin films

A series of study of the effects of outgassing on pulsed-DC reactive sputtering of highly (0002)-textured AlN thin film was conducted with systematically adjusted sputtering parameters like working pressure, atmosphere, and temperature. The film quality was evaluated by its rocking curve width and residual stress, both utilizing X-ray diffraction methods, as well as by SEM and XPS analyses. It is found that with lower outgassing all the above-mentioned sputtering parameters become less effective on both rocking curve width and residual stress. The rocking curve FWHM (Full Width at Half Maximum) measurements even exhibit apparently insensitive regions to the sputtering parameters, and accompanied threshold behaviors as well. XPS analysis reveals higher oxygen content while SEM observation shows thinner and slanter columnar structure in the AlN film when outgassing is higher upon sputtering.     

Deposition of AlN films by reactive sputtering: Effect of radiofrequency substrate bias

Piezoelectric AlN thin films were deposited on Silicon substrates by triode reactive sputtering. The variation of residual stress versus bias voltage on the substrate was investigated. A compressive stress was always observed with a maximum value for a negative substrate bias of 50 V. For higher negative bias voltage values, the compressive stress decreases. X-ray diffraction measurements showed two kinds of growth orientation. First, without bias voltage, films are well crystallized and (002) oriented. Second, with bias voltage, the (002) orientation disappears and a small peak appears (situated in the 2θ = 32°-33° range) which can be attributed to (100) orientation. Finally, the influence of compressive stress and ion bombardment on the change of orientation is discussed.     

The effect of silicon on the wettability and interfacial reaction in AlN/Cu alloy systems

Wetting behavior of AlN by Cu alloys has been studied in vacuum through sessile drop technique. The contact angle was determined by high temperature photography and shape analysis software. Pure copper does not wet AlN. The contact angle of the AlN/Cu system at 1200 °C is 138°. Adding 20 at% Si leads to the decrease of the contact angle from 138° to 96°, and a reaction layer forms in the interfacial area. The addition of Si can also improve the wettability of AlN/Cu10Ti (the atomic ratio of Cu:Ti is 90:10) system. The contact angle of the system decreases to the values less than 20° at 1200 °C by adding 20 at% or 27 at% Si. During the wetting experiment, Ti diffuses to and reacts with AlN, leading to the formation of TiN. Addition of Si can retard the reaction between Ti and AlN by forming a Si-rich layer, mainly composed of Ti-Si compound, between the reaction layer, mainly composed of TiN, and the CuSiTi alloy. The Si-rich layer also contributes to the improvement of the wettability of the system. In the meantime, the addition of Si contributes to the decrease of the stress in the interfacial area and to the bonding at the interfaces.