Analysis of Er incorporation on GaSb substrates by diffusion

On this work, two different ways of introducing Er ions to GaSb crystals, one bulk doped and the other Er diffused are compared in order to obtain Er luminescence on GaSb matrix. For this objetive, photoluminescence measurements indicate that there is Er luminescence on the diffused sample, while on the bulk doped, not only there is no Er activation, but crystal quality decreases severally. Surface analysis of diffused sample shows the presence of holes all over the surface. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

大尺寸高质量GaSb单晶研究

采用垂直布里奇曼法(VB法)生长2英寸GaSb单晶,分析了GaSb多晶产生的原因,即GaSb原料与覆盖剂中残留水分发生化学反应生成氧化镓残渣,残渣吸附在坩埚内壁导致GaSb多晶形成.通过增加覆盖剂除水工艺,成功生长出2英寸高质量GaSb单晶.此外,研究了单晶内部位错分布特点,结果显示GaSb晶体具有较低的位错密度,EPD≤500 cm-2;同时,对晶体进行XRD摇摆曲线测试,其FWHM值为27 arcsec,表明晶体质量较高;此外,对晶体进行了电学性能测试,结果显示制备的GaSb晶体呈P型导电,晶体迁移率为610 cm2/V·s,载流子浓度达到了1.68×1017cm-3.     

衬底温度对共蒸发制备GaSb多晶薄膜性质的影响

采用共蒸发的方法在玻璃衬底上制备出GaSb多晶薄膜材料.研究了薄膜生长速率与衬底温度、Ga源温度和Sb源温度的关系.通过XRD、UV-Vis、Hall效应和AFM等测试方法,研究了衬底温度对于GaSb薄膜的结构特性、光电性质以及表面形貌的影响.GaSb多晶薄膜具有(111)择优取向,薄膜的吸收系数达到105 cm-1,晶粒尺寸随衬底温度升高逐渐增大;衬底温度为540℃时,薄膜的迁移率达到127 cm2/V·s,空穴浓度为3×1017 cm-3.GaSb薄膜的表面粗糙度随温度增加而增加.     

Modelling of the Transport Processes in Bridgman grown Gallium Antimonide

In this work the thermal, velocity and species fields in the melt during the crystal growth by the vertical Bridgman method, has been studied. The simulations were focused on the special case of GaSb, which is a semiconductor of high technological importance. The simulations have been carried out both in 2 and 3‐D. In both cases the momentum (Navier‐Stockes), energy and mass transport equations were solved. The wall‐to‐wall radiation has also been included. In the two‐dimensional case an axisymmetric global model was developed taking into account the different elements present inside the real Bridgman growth system. In order to study the transport processes in the whole system during a complete growth process, the time dependence has also been considered. In the three‐dimensional case, the mathematical domain is restricted to the melt. These simulations were developed in order to study the influence of the ampoule tilting on the dopant distribution in the melt.     

GaSb薄膜生长的RHEED研究

采用分子束外延技术,在GaAs衬底上生长GaSb薄膜时,利用反射式高能电子衍射仪(RHEED)对衬底表面清洁状况、外延层厚度等进行在线监控.通过RHEED讨论低温缓冲层对GaSb薄膜表面结构和生长机制的作用,可以估算衬底温度,并能计算出薄膜的生长速率.实验测量GaSb的生长周期为1.96s,每秒沉积0.51单分子层.低温缓冲层提高了在GaAs衬底上外延GaSb薄膜的生长质量.     

Ru、Rh、Pd掺杂GaSb的电子结构和光学性质

运用第一性原理计算方法研究了过渡族金属TM(TM=Ru、Rh、Pd)掺杂GaSb的电子结构和光学性质,结果表明:TM掺杂GaSb主要以TM替代Ga(TM @Ga)缺陷存在,并可增强GaSb半导体材料对红外光区光子的响应,使体系光学吸收谱的吸收边红移;TM@Ga所引入的杂质能级分布于零点费米能级附近,这极大地增强了体系的介电性能,促进了电子-空穴对的产生和迁移,因而提升了掺杂体系的光电转换效率;Ru 掺杂对GaSb光学性质的改善最为明显,当掺杂浓度为6.25%(原子数分数)且均匀掺杂时,Ru掺杂GaSb体系对红外光区光子的吸收幅度最大,有效提升了GaSb光电转换效率和光催化活性。     

Observation of individual dislocations in 6H and 4H SiC by means of back‐reflection methods of X‐ray diffraction topography

SiC crystals of high structural perfection were investigated with several methods of X‐ray diffraction topography in Bragg‐case geometry. The methods included section and projection synchrotron white beam topography and monochromatic beam topography. The investigated 6H and 4H samples contained in large regions dislocations of density not exceeding 10³ cm^‐2. Most of them cannot be interpreted as hollow core dislocations (micro‐ or nano‐pipes). The concentration of the latter was lower than 10² cm^‐2. The present investigation confirmed the possibility of revealing dislocations with all used methods. The quality of presently obtained Bragg‐case multi‐crystal and section images of dislocation enabled analysis based on comparison with numerically simulated images. The analysis confirmed the domination of screw‐type dislocations in the investigated crystals. (© 2007 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Dislocations and grain boundaries in semiconducting rubrene single-crystals

Assessing the fundamental limits of the charge carrier mobilities in organic semiconductors is important for the development of organic electronics. Although devices such as organic field effect transistors (OFETs), organic thin film transistors (OTFTs) and organic light emitting diodes (OLEDs) are already used in commercial applications, a complete understanding of the ultimate limitations of performance and stability in these devices is still lacking at this time. Crucial to the determination of electronic properties in organic semiconductors is the ability to grow ultra-pure, fully ordered molecular crystals for measurements of intrinsic charge transport. Likewise, sensitive tools are needed to evaluate crystalline quality. We present a high-resolution X-ray diffraction and X-ray topography analysis of single-crystals of rubrene that are of the quality being reported to show mobilities as high as amorphous silicon. We show that dislocations and grain boundaries, which may limit charge transfer, are prominent in these crystals.     

Single‐crystal sapphire microstructure for high‐resolution synchrotron X‐ray monochromators

We report on the growth and characterization of sapphire single crystals for X‐ray optics applications. Structural defects were studied by means of laboratory double‐crystal X‐ray diffractometry and white‐beam synchrotron‐radiation topography. The investigations confirmed that the main defect types are dislocations. The best quality crystal was grown using the Kyropoulos technique. Therein the dislocation density was 10²–10³ cm⁻² and a small area with approximately 2*2 mm² did not show dislocation contrast in many reflections. This crystal has suitable quality for application as a backscattering monochromator. A clear correlation between growth rate and dislocation density is observed, though growth rate is not the only parameter impacting the quality.     

Activity of a Growth Hill,Generated by Two Crossed Screw Dislocations with Equal Burgers' Vectors at Constant Supersaturation and Temperature

The activity of a growth centre, consisting of two transversal screw dislocations with equal Burgers' vectors at constant supersaturation and temperature, is theoretically discussed. A non-linear squared differential equation of the type describing oscillations in autonomous systems is obtained and solved approximately and numerically. The correlation theory - experiment is analysed and the applicability of the results is assessed.     

DKDP晶体的柱面形貌与缺陷分析

采用原子力显微镜观测全方位生长的DKDP晶体的{100}面形貌,发现有螺旋位错,由此推断DKDP晶体{100}面以螺旋位错机制生长;利用同步辐射X射线白光形貌术观测了DKDP晶体缺陷,探讨了不同生长条件及生长阶段对晶体完整性的影响.     

同步辐射单色光形貌术观察6H-SiC单晶中的微管缺陷

采用同步辐射单色光形貌术观察了6H-SiC单晶中的微管缺陷,发现晶片中Burgers矢量为1c的螺位错具有较高的密度.此外,还观察到对应较大Burgers矢量的微管.基于微管附近的应变场,并根据衍射几何,模拟计算了一系列具有不同Burgers矢量的微管在形貌像中的直径,计算结果与实验观察符合较好.     

Nd:LuVO4晶体缺陷的研究

采用提拉法生长的Nd:LuVO4晶体是一种适合二极管泵浦的新型激光晶体,运用化学腐蚀结合光学显微术和同步辐射白光X射线形貌术对Nd:LuVO4晶体缺陷进行观察,结果表明:晶体的主要缺陷为位错和小角晶界.利用高分辨X射线衍射仪进一步验证了这一结果.并初步讨论了缺陷形成的原因.     

Growth twins in self-frequency doubling laser crystal YbxY1−xAl3(BO3)4

Using chemical etching.method, the growth twins in self-frequency doubling laser crystal Yb_xY_1−xAl₃(BO₃₄ have been observed. The etching pits on both sides of growth twin boundaries in the (10 1) slice are of the triangles with different orientations. The structure of growth twins is investigated by transmission synchrotron topography. In the transmission synchrotron topograph, the growth twins are visible not by ‘domain contrast’ but by ‘boundary contrast’, i.e. the twins appear in the topograph in form of X-ray kinematical diffraction contrast due to the lattice strain stemming from the impurity incorporation in the boundaries. The growth twins in Yb_xY_1−xAl₃(BO₃)₄ crystal are of inversion types, since no domain contrast was observed.     

Growth imperfections in oriented grown KDP crystals by X‐ray topographic analysis

Potassium dihydrogen phosphate (KDP) crystals were restrained to grow in two dimensions only, using a specially designed platform. This enables us to grow the blanks of frequency conversion elements that satisfy type‐II phase matching direction out of a type‐II phase‐matched seed crystal. Synchrotron radiation topography was used to study the growth mechanism of these profiling grown KDP crystals. It is found that both dislocation growth mechanism and layer growth mechanism were involved in the growing process. Inclusions, growth striations and dislocations were the main defects that influenced the crystalline quality of these crystals. High‐resolution X‐ray diffraction was employed to study the lattice integrality of the crystal.     

Growth of GaN single crystals with extremely low dislocation density by two-step dislocation reduction

We have discovered a mechanism which can significantly reduce the dislocation density during the growth of GaN single crystals in the Na flux method. The significant reduction of the dislocation density occurs in the later stage of LPE growth, rather than solely at the seed-LPE interface for which we have already reported evidence indicating the presence of bundling dislocations. The two-step dislocation reduction is the key in achieving extremely low dislocation density using this method.     

Nd:LuVO4晶体的生长及其性能研究

采用提拉(Czochralski)法生长了Nd:LuVO4晶体.利用液相反应法,以V2O5和NH4OH生成NH4VO3,Nd2O3、Lu2O3和HNO3生成Nd(NO3)3和Lu(NO3)3反应制备多晶料;所生长Nd0.01Lu0.99VO4晶体为16×20×21 mm3,质量超过40g.以X射线荧光分析仪测得其生长中各主要元素的分凝系数.其中Nd3+约为0.91,V3+和Lu3+接近1.还测定了其介电常数ε11=27.2,ε33=33.9(30℃,1kHz),以同步辐射X射线白光形貌术观察了其内部质量.     

Structural and electrical properties of GaSb, AlGaSb and their heterostructures grown on GaAs by metalorganic chemical vapor deposition

A systematic study of structural and electrical properties of GaSb and AlGaSb grown on GaAs by metalorganic chemical vapor deposition is reported. In general, the results obtained from surface morphologies, X-ray linewidths and Hall properties are consistent with each other and indicate that the optimal growth conditions for GaSb are at 525°C around V/III = 1. A highest hole mobility of 652 cm²/V · s at RT (3208 cm²/V · s at 77 K) and a lowest concentration of 2.8 × 10¹⁶ cm⁻³ (1.2 × 10¹⁵ cm⁻³ at 77 K) were obtained for GaSb grown under this optimal condition. Compared to the GaSb growth, a smaller V/III ratio is needed for the AlGaSb growth to protect the surface morphology. When Al was incorporated into GaSb growth, mobility decreased and carrier concentration increased sharply. The AlGaSb grown at 600°C had a background concentration about one order of magnitude lower than the AlGaSb grown at 680°C. Room-temperature current-voltage characteristics of GaSb/Al_xGa_{1 − x}Sb/GaSb show a rectifying feature when Al composition x is higher than 0.3, suggesting a valence-band discontinuity at the AlGaSb/GaSb interface. A leakage current much higher than the value predicted by the thermionic emission theory is observed at 77 K, presumably due to a large number of dislocations generated by the huge lattice mismatch between GaSb and GaAs.     

Dislocations in BZS and PMN pyrochlores

The dislocations observed in Bi_3/2ZnSb_3/2O₇ (BZS) and Pb_1.83Mg_0.29Nb_1.71O_6.39 (PMN) pyrochlores are described. An attempt is made to determine the Burgers vectors.     

Growth‐Sector Boundaries and Growth‐Rate Dispersion in Potassium Alum Crystals

Crystals of potassium alum, pure and slightly doped with Cr³⁺, were grown from aqueous solution by slow temperature lowering. In addition, short re‐dissolution periods were introduced in order to provoke growth defects and changes of growth rates. Crystal slices of about 1 mm thickness were studied by conventional LANG X‐ray diffraction topography using MoKα radiation. For Cr‐doped crystals, boundaries between {100}, {100} and {111} growth sectors appear by pronounced dynamical X‐ray topographic contrast similar to that of stacking faults. Re‐dissolution experiments provoke the formation of inclusions on {100} faces, followed by an increase of the {100} growth rate by the factor of about six, relative to the neighboured {111} faces. X‐ray topographs show that this increase is correlated with the formation of dislocations, which interestingly have pure‐edge character. During further growth these dislocations penetrate the {100}‐{111} growth sector boundary and vanish from the {100} face, which slows down and finally adopts its former growth rate before re‐dissolution.