ZnO: Mn稀磁薄膜结构和铁磁特性分析

采用脉冲激光沉积技术在蓝宝石衬底上制备了不同Mn掺杂浓度的ZnO薄膜(ZnO: Mn),研究了与生长相关的浅缺陷能级对薄膜磁性的作用.结果表明:所制备的ZnO: Mn薄膜均具有高度c轴择优取向,且具有室温铁磁性.随Mn含量增加,薄膜结晶质量逐渐提高,晶粒尺寸明显增大,单位磁性离子磁矩逐渐减小.薄膜所显示出的铁磁性可归结为材料结构缺陷的本质反映.薄膜导电特性变化反映了薄膜生长过程所决定的晶粒内部和晶粒边界缺陷密度变化的竞争,与此对应,激活能的变化反映了晶粒内部费米能级位置先升高而后降低.薄膜的载流子传输在低温下满足变程跳跃电导机制,该机制和材料的铁磁性紧密相关.近邻Mn离子比例的增加将对薄膜铁磁性的减小产生贡献.     

自然掺杂p型ZnO薄膜的螺旋波等离子体辅助溅射沉积

本工作通过调整工作气压,采用螺旋波等离子体辅助射频磁控溅射技术在Al2O3衬底上成功的制备了自然掺杂的p型ZnO薄膜.Hall测量显示在Ar/O2等离子体辅助下,随气压增加所沉积薄膜表现出从n型到p型再到n型的转变.p型ZnO薄膜载流子浓度为1.30×1016cm-3,电阻率为99.68Ω·cm,霍尔迁移率为4cm2·V-1·s-1.X射线衍射和原子力显微镜的分析结果显示ZnO薄膜的导电类型和薄膜的生长特征相关,等离子体中活性粒子载能的减小导致薄膜表面成核几率增加和ZnO晶粒逐渐减小.较高氧活性粒子浓度有利于自然掺杂p型ZnO薄膜生长,而活性氧粒子种类的变化使薄膜生长质量变差,施主缺陷增加,薄膜转化为n型导电.     

Nanocrystalline silicon films prepared by laser—induced crystallization

The excimer laser-induced crystallization technique has been used to investigate the preparation of nanocrystalline silicon (nc-Si) from amorphous silicon ($\al$-Si) thin films on silicon or glass substrates. The $\al$-Si films without hydrogen grown by pulsed-laser deposition are chosen as precursor to avoid the problem of hydrogen effluence during annealing. Analyses have been performed by scanning electron microscopy, atomic force microscopy, Raman scattering spectroscopy and high-resolution transmission--electron microscopy. Experimental results show that silicon nanocrystals can be formed through laser annealing. The growth characters of nc-Si are strongly dependent on the laser energy density. It is shown that the volume of the molten silicon predominates essentially the grain size of nc-Si, and the surface tension of the crystallized silicon is responsible for the mechanism of nc-Si growth.     

氮气辉光放电阴极鞘层重粒子输运过程研究

采用蒙特卡罗模拟对氮气辉光放电等离子体阴极鞘层内离子(N₂⁺,N⁺)和快中性分子(N_2f)的输运过程进行了研究,计算了阴极鞘层中离子(N₂⁺,N⁺)和快中性分子的能量及角分布的空间变化,较好地解释了实验结果.得到了氮气辉光放电等离子体阴极附近主要存在着能量较低的荷能分子、密度较低的高能原子离子及密度和能量居中的分子离子.诸粒子状态随放电条件而变化.模拟结 关键词：     

Temperature-dependent rectifying and photovoltaic characteristics of an oxygen-deficient Bi_2Sr_2Co_2O_y/Si heterojunction

A Bi2Sr2Co2Oy/Si heterojunction is obtained by growing a layer of p-type oxygen-deficient Bi2Sr2Co2Oy film on a commercial n-type silicon wafer by pulsed laser deposition. Its rectifying and photovoltaic properties are studied in a wide temperature range from 20 K to 300 K. The transport mechanism under the forward bias can be attributed to a trap- filled space-charge-limited current conduction mechanism. Under the irradiation of a 532-nm continuous wave laser, a clear photovoltaic effect is observed and the magnitude ofphotovoltage increases as the temperature decreases, The results demonstrate the potential application of a Bi2SrzCo2Oy-based heterojunction in the photoelectronic devices.     

纳米硅结构薄膜光致发光的温度依赖特性

综合考虑纳米硅结构薄膜的特殊性质,如量子限制效应、光学带隙和光跃迁振子强度对纳米硅粒径的依赖特性以及光学带隙和光辐射的温度依赖特性等,给出了一个解析表达式来分析具有一定粒径分布的纳米硅结构薄膜的光致发光(PL)强度分布,其中选取了两种纳米硅的粒径分布,即高斯分布和对数正态分布。结果表明,随着平均粒径和粒径分布偏差的减小,纳米硅薄膜的PL谱峰蓝移。随着环境温度的升高,纳米硅结构薄膜的PL谱峰红移且相对发光强度减弱。纳米硅结构薄膜光辐射拟合的结果与实验数据的比较分析表明,该模型能够很好地解释纳米硅结构薄膜在不同温度下的PL特性。     

非晶氧化硅薄膜带尾发光特性

采用等离子体增强化学气相沉积技术,通过改变CO2流量制备了不同氧含量的非晶氧化硅薄膜。利用紫外可见吸收谱、傅里叶红外吸收谱和稳态/瞬态光致发光谱等技术研究了薄膜的微观结构和光学特性。实验结果表明,随着氧含量的增加,薄膜的带隙增大,光致发光强度增加、峰值朝高能方向移动、光谱半峰全宽展宽。时间分辨光谱显示薄膜发光峰值处的衰减时间随氧含量的增加从6.2ns单调增加到21ns,而同一样品的发光寿命随发射波长能量增加而减小。综合分析光学吸收、发射及发光衰减特性表明,薄膜的发光机制主要归结为非晶材料带尾态之间的辐射复合。     

后钙钛矿CaRhO3的电子结构和磁学性质的第一性原理研究

采用基于密度泛函理论的投影平面波方法,对后钙钛矿结构(Ppv)的CaRhO₃的电子结构和磁学性质进行了研究.广义梯度(GGA)近似下的计算表明,Ppv-CaRhO₃的基态为铁磁性半金属,Rh⁴⁺离子的磁矩大小为0.57μ_B,具有低自旋态构型;而考虑在位库仑作用修正的GGA+U计算,得到了与实验结果相符的反铁磁绝缘体基态,表明后钙钛矿结构中4d电子之间的关联效应对体 关键词： 电子结构 磁学性质 金属绝缘体转变     

碳化硅薄膜脉冲激光晶化特性研究

采用XeCl准分子激光对非晶碳化硅(a-SiC)薄膜的脉冲激光晶化特性进行了研究.通过原子力显微镜（AFM）和Raman光谱技术对退火前后薄膜样品的形貌、结构及物相特性进行了分析.结果表明，选用合适的激光能量采用激光退火技术能够实现a-SiC薄膜的纳米晶化.退火薄膜中的纳米颗粒大小随着激光能量密度的增加而增大；Raman谱分析结果显示了退火后的薄膜的晶态结构特性并给出了伴随退火过程存在的物相分凝现象.根据以上结果并结合激光退火特性，对a-SiC的脉冲激光晶化机理进行了讨论. 关键词： 激光退火 晶化 碳化硅     

Structural and band tail state photoluminescence properties of amorphous SiC films with different amounts of carbon

Amorphous silicon carbide films are deposited by the plasma enhanced chemical vapour deposition technique,and optical emissions from the near-infrared to the visible are obtained.The optical band gap of the films increases from 1.91 eV to 2.92 eV by increasing the carbon content,and the photoluminescence(PL) peak shifts from 1.51 eV to 2.16 eV.The band tail state PL mechanism is confirmed by analysing the optical band gap,PL intensity,the Stocks shift of the PL,and the Urbach energy of the film.The PL decay times of the samples are in the nanosecond scale,and the dependence of the PL lifetime on the emission energy also supports that the optical emission is related to the radiative recombination in the band tail state.