CdZnTe晶片的Raman光谱研究

利用Raman光谱技术研究了CdZnTe晶片表面处理方法、激光功率及波长变化对CdZnTe晶片的Raman谱线影响.研究表明:CdZnTe晶片分别经过机械抛光、Br-MeOH溶液处理以及Br-MeOH溶液+ KOH/甲醇溶液处理后,由于表面晶格完整性的改变, Raman光谱出现了明显变化.采用514.5 nm、632.8 nm及785 nm激光激发CdZnTe晶片时,晶片的Raman波谱也有所不同,其中用785 nm激光激发样品,荧光发光峰位于100～200 cm~(-1)范围,掩盖了晶片Raman特征峰.在对CdZnTe晶片做Raman测试时,尽可能选择较低功率.     

采用低温PL谱研究探测器级CdZnTe晶体

采用低温光致发光谱技术研究了核辐射探测器用高阻CdZnTe晶体。发现PL谱中的三个特征峰均与晶体质量有关,其中(D0,X)峰FWHM值和I DAP/I(D0,X)与晶格完整性和浅能级缺陷密度有关联,D2峰则与位错密度密切相关。采用双晶X射线摇摆曲线和位错腐蚀坑密度对此表征进行了验证。低温PL谱测试结果显示晶体质量较高的CdZnTe晶片,其探测器的能谱分辨率也相对较高。     

高温垂直Bridgman法生长Zn1-xMgxTe晶体

采用高温垂直Bridgman法,以ZnTe(5N)、Mg(5N)和Te(7N)为初始原料,在高温下成功生长出了尺寸为φ15mm×50 mm的Zn1-xMgxTe晶体.分别采用X射线衍射、紫外可见分光光度计和红外光谱仪研究了晶体的结构及光学性质,通过PL谱和化学腐蚀的方法分析了晶体的结晶质量.结果表明:所生长的晶体具有立方相结构,晶格常数为0.61585 nm,略大于ZnTe晶格常数,晶锭中质量最好部分的晶片红外和紫外透过率接近60;,室温下其禁带宽度约为2.37 eV.77 K温度下,PL谱中存在A和B两个主要的发光带,位错腐蚀坑密度在105 cm-2数量级.     

熔融BaB2O4急冷玻璃态光谱性质的分子动力学模拟

实验测定和分子动力学模拟研究了熔融BaB2O4急冷玻璃态结构的Raman光谱.在分子动力学模拟产生的瞬态位移和速度基础上,发展了各种相关函数及其Fourier变换和有关动力学性质的计算程序.计算得到了β-BaB2O4晶态和玻璃态的B-O键长自相关函数和O原子相对位移互相关函数,及其Fourier变换得出的Raman光谱.实验与模拟结果表明,在分子动力学模拟中调节势参数k=0.58时,计算的晶体Raman谱主峰在683cm-1,玻璃态Raman谱中BO3的主峰在768cm-1,BO4的主峰在590cm-1,与实验基本相符.模拟结果表明,玻璃体中存在大量BO3基团及少量BO4基团,虽然模拟体系中很少存在B3O6环,但模拟结果亦能大体上与β-BaB2O4的Raman光谱相符.     

垂直Bridgman法生长Cd1-XMnxTe晶体的缺陷研究

本文采用垂直布里奇曼(Bridgman)法生长了尺寸为Φ30 mm×130mm的Cd1-xMnxTe晶体,利用Nakagawa腐蚀液显示了晶体的位错、Te夹杂相和孪晶缺陷,并采用傅立叶变换红外光谱仪研究了晶体的红外透过率与晶体缺陷之间的关系.结果表明:生长态Cd1-xMnxTe晶体的位错密度为104～105 cm-2,Te夹杂相密度为103～104cm-2,晶体中的孪晶主要为共格孪晶,孪晶面为[111]面,且平行于晶体生长方向.在入射光波数4000～500 cm-1范围,晶体的红外透过率为36.7;～55.3;,红外透过率越大,表明晶体的位错和Te夹杂相密度越低,晶体对该波长范围的红外光表现为晶格吸收和自由载流子吸收.     

CdTe和CdZnTe电子结构及成键机理的第一性原理研究

采用基于密度泛函理论的CASTEP程序软件包,计算了CdTe和CdZnTe的能带结构和态密度,研究对比了CdTe 和CdZnTe的分子内成键机制.结果表明,在CdZnTe中,Cd eg和Te 5s杂化形成较低的价带,Zn t2g和Te 5pz杂化形成的π键等构成中间价带,Zn 4s和Te 5pz杂化形成的σ键等构成导带.Cd 5s和Te 5s不再杂化,导带底向高能级方向移动.     

退火处理对CdZnTe晶体光电性能的影响

研究了生长态CdZnTe晶体在经历了不同温度和时间的Cd/Zn和Te气氛退火后,其光电性能的变化规律.研究表明,在Cd/Zn气氛下退火180 h后,CdZnTe晶体中直径在5μm以上的Te夹杂的密度减小了1个数量级,晶体的体电阻率由1010 Ω·cm减小至～107 Ω· cm.同时发现,Cd/Zn源区的温度决定了退火后晶体在500～4000cm-1范围内红外透过率曲线的平直状态,这可能与晶体中的Cd间隙缺陷浓度相关,而与晶体中的载流子浓度和夹杂/沉淀相状态无关.在Te气氛下退火时,发现晶体的红外透过率的平直状态与晶体电阻率的对数lg(ρ)呈近似线性关系,同样可归因于退火过程中Cd间隙缺陷的浓度变化.     

Cd1-xZnx合金组元分压控制下高阻CdZnTe晶体的熔体生长

本文运用热力学关系估算了CdZnTe熔体平衡分压.尝试以Cd1-xZnx合金源替代Cd源控制Cd分压和Zn分压进行了Cd 0.8Zn 0.2Te晶体熔体生长,探讨了熔体分压与晶体电阻率的关系.获得的Cd 0.8Zn 0.2Te晶体的电阻率接近1010Ω·cm,高于同类方法文献报道1～2个数量级.晶体的结构完整性较好,平均腐蚀坑密度(EPD)为2×105cm-2,纵向组成分布偏离度在4;左右,红外透过率大于60;,晶体中第二相和沉淀物明显减少,优于仅采用Cd分压控制的Cd0.8Zn0.2Te晶体.     

In掺杂对MVB-Te溶剂法生长的ZnTe晶体光电性能的影响

采用Te溶剂结合改进的垂直布里奇曼法(MVB)制备了In:ZnTe与ZnTe晶体,并对晶体的光学与电学特性进行了表征.通过红外透过显微成像技术观察了In:ZnTe与ZnTe中的Te夹杂并进行了统计分析,发现In掺杂未对ZnTe中的Te夹杂的分布和尺寸产生显著影响.红外透过光谱分析表明,In:ZnTe与ZnTe晶体的红外透过率曲线均表现出平直的趋势,且其平均透过率基本相等,约为60;,进一步表明In的掺入并未导致严重的晶格和杂质吸收.然而,Ⅰ-Ⅴ测试分析发现,In掺杂使得ZnTe晶体的电阻率提高了5个数量级.同时Hall测试分析表明,In:ZnTe与ZnTe晶体均为p型导电,In掺杂很大程度上补偿了晶体中的Vzn,使得晶体中的载流子浓度降低了4个数量级.对比了两种晶体的紫外-可见-近红外透过光谱,可以观察到,In掺杂使ZnTe的吸收边从550 nm红移到560nm,这可能是由于In掺杂引入的浅能级导致的吸收边带尾现象造成的.     

Cd0.80Zn0.20Te晶体的生长及性能研究

用本实验室合成的Cd0.80Zn0.20Te多晶料为原料,采用改进的布里奇曼法在镀碳和未镀碳的石英安瓿中生长出Cd0.80Zn0.20Te晶锭。使用X射线衍射仪对合成产物及晶锭进行了分析,生长晶体的X射线衍射峰尖锐,摇摆谱对称,表明晶锭的结晶性能较好;用IRPrestige-21红外光谱仪分析了晶体的红外透射光谱,测试结果表明安瓿镀碳后生长的晶体位错密度小,均匀性较好,电阻率优于未镀碳安瓿生长的晶体;晶体的蚀坑密度在103~104cm-2之间,比未镀碳安瓿生长的晶体低1个数量级。     

Temperature dependence of Raman‐active mode frequencies and linewidths in TlGaSe2 layered crystals

Raman spectra of TlGaSe₂ crystal at different temperatures are discussed. The temperature dependence of frequency shifts and linewidths of the Raman peaks in the frequency region of 10‐320 cm^‐1 have been measured in the range from 50 to 320 K. The analysis of the experimental data showed that the temperature dependencies of phonon frequencies and linewidths are well described by considering the contributions from thermal expansion and lattice anharmonicity. The anharmonic contribution (phonon‐phonon coupling) is found to be due to three‐phonon processes. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Characterization of mixed phase silicon by Raman spectroscopy

We have examined the common methods for determination of the crystallinity of mixed phase silicon thin films from the TO–LO phonon band in Raman spectra. Spectra are decomposed into contributions of amorphous and crystalline phase and empirical formulas are used to obtain crystallinity either from the integral intensities (peak areas) or from magnitudes (peak maxima). Crystallinity values obtained from Raman spectra excited by Ar⁺ laser green line (514.5 nm) for a special sample with a profile of structure from amorphous to fully microcrystalline were compared with surface crystallinity obtained independently from atomic force microscopy (AFM). Analysis of the Raman collection depth in material composed of grains with absorption depth 1000 nm in an amorphous matrix (absorption depth 100 nm), was used to explain reasons for systematic difference between surface and Raman crystallinities. Recommendations are given for obtaining consistent results.     

8英寸导电型4H-SiC单晶衬底制备与表征

使用物理气相传输法(PVT)通过扩径技术制备出直径为209 mm的4H-SiC单晶,并通过多线切割、研磨和抛光等一系列加工工艺制备出标准8英寸SiC单晶衬底。使用拉曼光谱仪、高分辨X射线衍射仪、光学显微镜、电阻仪、偏光应力仪、面型检测仪、位错检测仪等设备,对8英寸衬底的晶型、结晶质量、微管、电阻率、应力、面型、位错等进行了详细表征。拉曼光谱表明8英寸SiC衬底100%比例面积为单一4H晶型;衬底(004)面的5点X射线摇摆曲线半峰全宽分布在10.44″~11.52″;平均微管密度为0.04 cm^-2;平均电阻率为0.020 3 Ω·cm。使用偏光应力仪对8英寸SiC衬底内部应力进行检测表明整片应力分布均匀,且未发现应力集中的区域;翘曲度(Warp)为17.318 μm,弯曲度(Bow)为-3.773 μm。全自动位错密度检测仪对高温熔融KOH刻蚀后的8英寸衬底进行全片扫描,平均总位错密度为3 293 cm^-2,其中螺型位错(TSD)密度为81 cm^-2,刃型位错(TED)密度为3 074 cm^-2,基平面位错(BPD)密度为138 cm^-2。结果表明8英寸导电型4H-SiC衬底质量优良,同比行业标准达到行业先进水平。     

机械磨抛对CdZnTe薄膜阻变特性的影响

采用磁控溅射法在ITO玻璃上制备了CdZnTe薄膜,探究机械磨抛对CdZnTe薄膜阻变特性的影响。通过对XRD图谱、Raman光谱、AFM显微照片等实验结果分析阐明了机械磨抛影响CdZnTe薄膜阻变特性的物理机制。研究结果表明,磁控溅射制备的薄膜为闪锌矿结构,F43m空间群。机械磨抛提高了CdZnTe薄膜的结晶质量;CdZnTe薄膜粗糙度(Ra)由磨抛前的3.42 nm下降至磨抛后的1.73 nm;磨抛后CdZnTe薄膜透过率和162 cm^-1处的类CdTe声子峰振动峰增强;CdZnTe薄膜的阻变开关比由磨抛前的1.2增加到磨抛后的4.9。机械磨抛提高CdZnTe薄膜质量及阻变特性的原因可能是CdZnTe薄膜在磨抛过程中发生了再结晶。     

A comparison between the Raman modes of the tetrahedral network in amorphous and layered crystalline GeSe2

The characteristic A₁ peak at 199 cm⁻¹ in the Raman spectrum of amorphous GeSe₂ were compared with the peaks at 211 and 216 cm⁻¹ in the spectrum of crystalline GeSe₂. It was proved that the crystalline 216 cm⁻¹ peak is an intrinsic mode which is enhanced by the bulk exciton transition. From a model calculation using a valence force field and bond polarizability, the 211 cm⁻¹ peak was assigned to in-phase breathing vibrations extended along the GeSe₄ tetrahedral chain structure, while the 216 cm⁻¹ peak was attributed to in-phase breathing vibrations quasi-localized at the GeSe₄ edge-sharing tetrahedra. The phonon density of states in the crystal has a doublet peak similar to the amorphous Raman spectrum. A correspondence between the amorphous and the crystalline Raman spectra was proposed.     

Raman Study of Molecular Motions in Organic Solids

The paper presents Raman investigation of the nature of phonon motions in various organic solids and discusses chemical, physical as well as some practical applications of phonon studies. In order to characterize the nature of these motions. delocalization and relaxation of phonons are studied using the mixed crystal technique and temperature dependence of phonon spectra. The application of phonon spectra to investigate chemical perturbation of crystal structure in a group of closely related compounds is discussed. Some preliminary studies are presented on application of phonon spectra in solid state reactions. In regard to practical applications, it is shown that phonon spectra can be used to identify truly random solid solutions as well as various polymorphic forms of a given compound.     

Soft‐Mode Spectroscopy in Fe:KTa1‐xNbxO3 Crystals

Fe‐doped potassium tantalite niobate, Fe:KTa_1‐xNb_xO₃ (Fe:KTN), crystallizes with x = 0.48 and a perovskite‐type structure in tetragonal system with point group 4mm, conforming space group P4mm. The paraelectric‐ferroelectric structural transition of the Fe:KTN is studied by Raman scattering investigations. A condensed soft lattice vibrational mode at the phase transition has been analyzed. It originates from the symmetric O2/O3‐Nb/Ta‐O3/O2 in‐plane bending of the Nb/TaO₆ group. The soft optical phonon mode concerns the extraordinary transverse optical phonons propagating along the [110] direction. The Raman spectra measured reflect the crystal disorder. Curie temperature measured by two methods is within 353 and 356.5 K.     

Specificity in Chemical Perturbation of Crystal Structures

The specificity in chemical perturbation of crystal structure is examined by investigating the efffect of the position of particular substituent group on the crystal structure. 1,2,3,5-tetra-halobenzenes are chosen for this study. A comparative study of Raman phonon spectra of 1,2,3,5-tetrachlorobenzene; 1,2,3-trichloro-5-bromobenzene; and 1,3,5-trichloro-2-bromo-benzene crystals reveals that former two have the same crystal structure, while the latter has a different crystal structure. It is inferred that a bromine group substitution in 2-position of 1,2,3,5-tetrachlorbenzene creates a lattice instability which gives rise to a different crystal structure for 1,3,5-trichloro-2-bromobenzene. The nature of this instability is discussed. Mixed crystals of 1,2,3,5-tetrachlorobenzene and 1,2,3-trichloro-5-bromobenzene are studied to establish phonon correlation and deloalization.     

Laser Raman Investigation of Solid State Rearrangement of bis(O-lodobenzoyl) peroxide into 1-(2'-Iodobenzoyloxy)-1, 2-benziodoxolin-3-one

In solid state, the thermal rearrangement of bis(O-iodobenzoyl) peroxide which yields 1-(2'-iodobenzoyloxy)-1,2-benziodoxolin-3-one,is investigated by laser Raman spectroscopy. The intramolecular vibration spectra are used to characterize this chemical rearrangement. The phonon spectra obtained as a function of the rearrangement progress show that, in spite of the reported topotactic nature of the reaction, it proceeds by a heterogeneous mechanism. A temperature dependence study of the phonon spectra reveal no mode-softening for any optical phonons. Therefore, no evidence has been found for this reaction to be phonon-assisted.