Growth and characterization of SSD InP crystals used as substrates for infra-red LED's

Bulk indium phosphide crystals have been grown by the synthesis, solute diffusion (SSD) method. Various growth temperatures and temperature gradients in the indium melt were investigated. The growth temperature of about 850–900°C and the temperature gradient of about 10–15°C cm⁻¹ were found as the most suitable growth conditions. All grown crystals were of the n-type either undoped or doped with Te or Sn. Infrared light-emitting junctions were grown by single LPE process. Characteristic surface structures of InP epitaxial layers as a function of the growth temperature and cooling rate were observed. Efficiencies of LED's have been typically 0.8%. Single LPE process on LEC InP substrates has given LED's with substantially lower efficiencies.     

Growth and characterization of undoped and thallium doped cesium iodide single crystals

Single crystals of pure and thallium (Tl) doped cesium iodide (CsI) have been grown by melt growth (Bridgman) technique. The grown crystals were subjected to powder X-ray diffraction and high-resolution XRD analysis. The cut and polished crystals were characterized for luminescence studies. UV-visible transmission studies have been carried out on the grown crystal in the wavelength range 200–650 nm. From the transmission spectrum it was found that the cut off wavelength increases with increase in Tl concentration and the transmittance is about 70%. The 0.06 mol% of Tl doped CsI crystal shows a good energy resolution of 7.6%. The hardness decreases for increasing the doping concentration. Etching studies have been carried out on doped and undoped crystals using methanol and water as etchant.     

Influence of non-stoichiometry on the recombination activity of dislocations in undoped semi-insulating GaAs crystals

The effect of non-stoichiometry of gallium arsenide melt composition on the recombination activity of dislocations in undoped semi-insulating GaAs crystals is studied and analyzed. It is shown that the deviation from the stoichiometric melt composition is one of the major factors affecting the recombination activity of dislocations in undoped semi-insulating GaAs crystals. namely: the recombination activity of dislocations is increased when the arsenic-rich melt is used, and, on the contrary, is decreased when the gallium-rich melt is used. The regularities observed are explained by the complex processes of interaction of dislocations with the non-stoichiometry-induced intrinsic point defects.     

Growth of the KR3F10 (R = Tb–Er) Compounds by the Vertical Directional Crystallization Method. II. Refinement of the Character of Melting,Growth, and Some Physical Properties of KDy3F10 Crystals

Crystallography Reports - KDy3F10 crystals have been grown from melt by the Bridgman technique. The incongruent character of melting of this compound is confirmed. The optimal melt composition for...     

半绝缘磷化铟中与非化学配比有关的深能级缺陷

在不同的化学配比条件下制备了半绝缘磷化铟材料,其中包括配比和富铟熔体中的铁掺杂以及磷气氛和磷化铁气氛下高温退火非掺杂晶片.在这些半绝缘磷化铟材料中检测到了与非化学配比有关的深能级缺陷.通过对大量的原生掺铁和非掺退火半绝缘磷化铟材料中的缺陷的研究,发现原生深能级缺陷与材料的电学参数质量密切相关.迁移率低、热稳定性差的掺铁半绝缘磷化铟材料中有大量的能级位于0.1～0.4eV之间的缺陷.高温退火非掺磷化铟抑制了这些缺陷的产生,获得了迁移率高、均匀性好的高质量半绝缘材料.根据这些结果,我们提出了一种通过控制化学配比制备高质量半绝缘磷化铟材料的方法.     

Optimisation of chromium doping in LiNbO3 single crystals

Growth of undoped and Cr doped (0.1, 0.25 and 0.5 mol % Cr₂O₃) congruently‐ melting‐composition LiNbO₃ single crystals by Czochralski technique is reported. Chromium doping was optimised to get crystals with potential for an integrated, broadband, tunable laser in the 700‐1100 nm spectral range. Typical sizes of the grown crystals are 25‐30 mm in diameter and 30‐40 mm in length. Symmetrical and sharp conoscopy pictures confirm the optical homogeneity of the crystals. Optical transmission was recorded for both undoped and doped crystals. 70% transmittance was observed. The grown crystals have reasonably good laser damage threshold. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Influence of semi-insulating InP substrates on InAlAs epilayers grown by molecular beam epitaxy

Tensile-strained InAlAs layers have been grown by solid-source molecular beam epitaxy on as-grown Fe-doped semi-insulating (SI) InP substrates and undoped SI InP substrates obtained by annealing undoped conductive InP wafers (wafer-annealed InP). The effect of the two substrates on InAlAs epilayers and InAlAs/InP type II heterostructures has been studied by using a variety of characterization techniques. Our calculation data proved that the out-diffusion of Fe atoms in InP substrate may not take place due to their low diffusion coefficient. Double-crystal X-ray diffraction measurements show that the lattice mismatch between the InAlAs layers and the two substrates is different, which is originated from their different Fe concentrations. Furthermore, photoluminescence results indicate that the type II heterostructure grown on the wafer-annealed InP substrate exhibits better optical and interface properties than that grown on the as-grown Fe-doped substrate. We have also given a physically coherent explanation on the basis of these investigations.     

Radiation hardening studies in KBr-KI mixed crystals

Radiation hardening studies have been made in KBr, KI and in different compositions of KBr-KI mixed crystals, grown from melt by Kyropoulos technique. The irradiation hardness in mixed crystals is found to vary non-linearly with composition, attaining a minimum value at intermediate compositions. Dislocation density measurements have shown a high concentration of dislocations and grain boundaries in mixed crystals as compared to end crystals. The results obtained on radiation hardening of mixed crystals were explained in terms of dislocations present in them.     

Tin segregation and donor compensation in melt-grown gallium arsenide

Radio-tin-doped single crystals of GaAs have been grown by the LEC technique from melts of varying composition. Carrier concentration and Sn distribution determined by radio-counting and autoradiography are reported and analysed to show that Sn-related acceptors are incorporated to give a compensation ratio of N_A/N_D = 0.24+-0.03 independent of doping level and of melt composition. These concentrations are significantly in excess of a non-Sn-related residual acceptor - believed to be C_As - which is shown to be present in the crystals at a level of 1.6x10¹⁶ cm^-3. Modified Sheil plots are used to show that the melt composition appears to move progressively toward As-richness as growth proceeds. The distribution coefficient for tin in crystals growing from a stoichiometric melt is determined to be 4.0x10^-3.     

Photorefractive Properties of Stoichiometric Lithium Niobate Single Crystals

The specific features of photorefractive light scattering in nominally pure stoichiometric (Li/Nb = 1) sin- gle crystals grown from a melt with 58.6 mol % Li₂O (LiNbO₃st) and in the stoichiometric single crystals grown from a melt of congruent composition in the presence of K₂O flux (LiNbO₃stK₂O) have been investi- gated. At an excitation power of 30 mW, LiNbO₃stK₂O single crystals are found to exhibit a stronger photo- refractive effect than LiNbO₃st single crystals.     

TEM investigation of precipitates in VCz GaAs crystals

Bulk GaAs crystals were grown from various Ga‐rich melts by the vapour‐pressure controlled Czochralski method in order to reduce As precipitates. The correlation of the melt composition with both, structural perfection and solid composition was examined by various methods of transmission electron microscopy (TEM). From transmission electron diffraction and diffraction contrast imaging a direct correlation between melt composition and sample properties is missing. High‐resolution TEM imaging hints to inhomogeneities only for the sample grown from a melt with a mole fraction of y = 0.492. Strain analysis of a selected defect reveals a strained crystal lattice in the surrounding of the defect. For the same sample, high angle annular dark‐field imaging and energy dispersive X‐ray spectroscopy verify the formation of precipitates. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Photorefraction Dependent on Composition in LiNbO3 Crystals with and without MgO Doping

The photorefraction in LiNbO₃ single crystals dependent on the melt composition with and without MgO doping was investigated. It was found that 1 mol% MgO-doped crystal with nearly stoichiometric composition has a strong photorefraction resistance. compared with a congruent composition. In an undoped crystal, the photorefraction was shown to be pronounced as incrcasing Li content of a melt from 48.6 to 58 mol% Li₂O. These results were discussed from a viewpoint of the relationship between the photoconductivity and the concentration of cation-site vacancies or Nb on Li-site.     

Influence of growth conditions on microstructure and properties of GaSe crystals

GaSe crystals have been grown from melt. There are several reasons why it is difficult to meet ideal demands for nonlinear optic material, GaSe single crystal. First, these crystals have a tendency towards lamination because of great difference in a and c crystal lattice parameters and very weak Vander der Waals forces in c direction. Next, there is a great difference in saturation vapor pressure of the components, which can cause nonstoichiometry of a melt-grown crystal composition. Another obstacle in the growth of perfect GaSe crystals is dendrite formation caused by instability of the growth front. To overcome this obstacle we used Bridgman technique and have found the temperature and pressure conditions, and growth velocity which provide growth of perfect bulk single crystals of about 100 mm in length and 20 mm in diameter. Sharp Laue patterns and a rocking curve confirm perfect structure of the grown crystals. Electron-probe X-ray microanalysis shows stoichiometric composition of GaSe crystals and X-ray phase analysis reveals presence of single-phased hexagonal structure.     

A Study of Convection,Striations and Interface Shape in InP Crystals Grown by the Double-Crucible LEC Technique

A doublecrucible (DC) Czochralski setup has been used for the pulling of semi-insulating Fe-doped InP. The level of the Fe-doped melt in the growth crucible is replanished with the undoped InP from the reservoir crucible. In this way, since the distribution coefficient of iron is very small (about 0.001), the Fe concentration in the growth crucible is virtually unchanged during the pulling so that the axial Fe concentration is much more uniform than in standard LEC crystals. The use of two concentric crucibles has great implications in terms of convective flows, stability of the melt temperature and interface shape. In this paper we report the results of a study on striations and structural defects in InP grown from a double-crucible LEC arrangement. A dimensionless relationship for correlating striation features with melt motions is also proposed.     

Growth of large doped Bi12SiO20 crystals

The conditions for growing Cr-, Mn-, Fe-, Co-, Ni-, and Cr + Al-doped BSO crystals from a stoichiometric melt by the Czochralski method have been the subject of research. A decrease of the absorption coefficient along the growth axis was observed in undoped crystals of 50 mm diameter and 150 mm long, which is indicative of melt stoichiometry change in the course of the growth run. The transmission and reflection spectra of different crystals were measured and the absorption coefficients was determined in the range 0.38–0.70 μm. When Fe dopant concentration exceeds a limit value, the absorption spectrum is blue-shifted relative to the undoped case and the absorption coefficient decreases. Co, Cr, Mn, and Cr + Al dopants produce a red shift and increase the absorption coefficient. Combined Cr + Al doping shift the absorption spectrum to the blue region as compared to Cr-only doping with the same Cr concentration.     

Study of microdefects in GaP and GaPZn single crystals grown by the liquid-encapsulation Czochralski method

Microdefects in undoped and zinc-doped GaP single crystals grown by the liquid-encapsulation Czochralski method have been studied by X-ray diffuse scattering. In undoped GaP single crystals, deviation from stoichiometry increases from the beginning to the end of an ingot. The ingot end is characterized by enhanced precipitation of excess gallium with formation of platelike microdefects. With an increase in their size, stress relaxation around microdefects begins to manifest itself. Doping with zinc leads to a significant change in the microdefect formation pattern.     

On the Reasons Leading to an Appearance of Correlated and Anticorrelated Dependences of the Minority Carrier Lifetime on the Dislocation Density in Undoped Semi-Insulating “Stoichiometric” GaAs Crystals

It is shown that in undoped semi-insulating GaAs crystals grown under the stoichiometric conditions both correlated and anticorrelated dependences of the minority carrier lifetime τ on the dislocation density N_d could be observed. The above-pointed effect is connected with a slight excess of Ga atoms (then the correlated dependence τ vs Nd appears) or of As atoms (then the anticorrelated dependence τ vs N_d appears) which inevitably exists even in “stoichiometric” GaAs crystals (i.e. in GaAs crystals of “stoichiometric” composition).     

Temperature distribution in growing semi-transparent crystals (III). Conical liquid/solid interface

Temperature distribution in Al₂O₃ and YAG crystals grown by Czochralski method and in the melt layer adjacent to the liquid/solid interface of the conical shape was computed. The results were compared with the quality of the crystals. Using a highly absorbing material, temperature difference near the deeply submerged sharp interface decreases from the edge to the centre of a crystal and it is relatively great and unalterable in the case of a shallowly submerged blunt interface. Sharp interface show the crystals grown from the melt of the same composition (Al₂O₃ or accurately “stoichiometric” YAG), whereas the blunt one is typical of YAG grown from the melt of the “non-stoichiometric” composition, because its solidifying point is below the melting point of YAG phase.     

Growth and properties of Pb[(Zn1/3Nb2/3)0.91Ti0.09]O3 single crystals directly from melt

Pb[(Zn_1/3Nb_2/3)_0.91Ti_0.09]O₃ (PZNT91/9) single crystals were grown by a modified Bridgman method directly from melt using an allomeric Pb[(Mg_1/3Nb_2/3)_0.69Ti_0.31]O₃ (PMNT69/31) single crystal as a seed. X-ray diffraction (XRD) measurement confirmed that the as-grown PZNT91/9 single crystals are of pure perovskite structure. Electrical properties and thermal stabilization of PZNT91/9 crystals grown directly from melt exhibit different characters from those of PZNT91/9 crystals grown from flux, although segregation and the variation of chemical composition are not seriously confirmed by X-ray fluorescence analysis (XPS). The [0 0 1]-oriented PZNT91/9 crystals cut from the middle part of the as-grown crystal boules exhibit broad dielectric-response peaks at around 105 °C, accompanied by apparent frequency dispersion. The values of piezoelectric constant d₃₃, remnant polarization P_r, and induced strain are about 1800–2200 pC/N, 38.8 μC/cm², and 0.3%, respectively, indicating that the quality of PZNT crystals grown directly from melt can be comparable to those of PZNT91/9 single crystals grown from flux. However, further work deserves attention to improve the dielectric properties of PZNT crystals grown directly from melt. Such unusual characterizations of dielectric properties of PZNT crystals grown directly from melt are considered as correlating with defects, microinhomogeneities, and polar regions.     

Influence of F-Anions on the Habit and Growth Mechanism of Potassium-rich Feldspars

Orthoclase-rich alkalic feldspar crystals were grown from melts next to Orthoclase-Albite-Quartz eutectic composition at 2 kb in the presence of a surplus of a supercritical aqueous phase by isobaric cooling at a rate of approximately 10 °C/day. Some runs were made with KF-bearing fluid phase, in two runs the melt was formed during intensive thermoconvection of the fluid phase. Tabular crystals were only formed from F-bearing melts, crystals grown from F-free melt were always fan-shaped. We assume this fact is due to a more easy supply of Al to the growing crystal in melts with F content.