Gettering Properties of Praseodymium in GaAs,In0.53Ga0.47As,and InP Grown by Liquid Phase Epitaxy

The incorporation of praseodymium (Pr) into GaAs, In_0.53Ga_0.47As, and InP during liquid-phase epitaxy were investigated by double crystal x-ray diffraction, Hall effect, low temperature photoluminescence (PL) measurements. The lattice mismatch slightly vary with Pr concentration in the growth melts. Examinations of the electrical property illustrate that the lower carriers concentrations and a higher mobilities are obtain from Pr-doped epilayers than undoped sample (In_0.53Ga_0.47As and InP). The PL spectra (15-K) show that the intensity of the impurity related peaks decreases and the near-band-to-band luminescence intensity increase. They also reveal that the impurities are gettered by Pr ions during LPE growth. Thus, for the purpose of purification, proper amount of Pr in the growth melts is suggested. No intra-4f-shell transition line is observed from the Pr-doped GaAs, In_0.53Ga_0.47As, and InP layers.     

Heterointerface study of perturbed LPE growth of AlGaAs/InGaP single heterostructure

This paper presents the perturbed growth of Al_0.7Ga_0.3As/In_0.5Ga_0.5P single heterostructure on a GaAs substrate by liquid-phase epitaxy. The AlGaAs-InGaP heterointerface was characterized by scanning electron microscopy, photoluminescence, Auger electron spectroscopy, and transmission electron microscopy. Evidence is provided showing that a small amount of droplets, after the slider operation of the In_0.5Ga_0.5P epitaxial growth, mixed with the Ga-rich AlGaAs melt, is sufficient to attack the In_0.5Ga_0.5P underlying layer. Even with complete melt removal, there is still a partial dissolution at the “flat” Al_0.7Ga_0.3As-In_0.5Ga_0.5P heterojunction. The Auger depth profiles reveal the composition-depth transition width at this interface to be 560Å from the 90%-10% of Al (or Ga, As, and In) Auger profile; however, the P atoms penetrate deeply into the Al_0.7Ga_0.3As layer due to the partial dissolution of In_0.5Ga_0.5P layer. By high-resolution electron-micrograph analysis, some dislocations are observed at the heterojunction leading to nonradiative recombination and to poor optical device performance, even though the heterointerface observed by scanning electron microscopy is very flat.     

Gettering properties of PrO2 in In0.53Ga0.47As LPE growth

Praseodymium oxide was used for the gettering of background impurities from the melt, during In_0.53Ga_0.47As/InP LPE growth. The low amount of PrO₂ in the growth solution enables one to prepare n-type In_0.53Ga_0.47As epitaxial layers with electron concentration in the range of 2 × 10¹⁴ to 2 × 10¹⁶ cm^-3 and electron mobilities of 11,000 and 8400 cm²/V·s, respectively. These results were achieved without long time baking of the melt; homogenization lasted only 1 h. The electrical parameters and photoluminescence spectra of the grown layers are presented.     

A Multipurpose Graphite Boat for LPE Growth of Multilayer Heterostructures

In the paper the results of the authors' work are summarized on the preparation of multilayer A³B⁵ heterostructures with the use of originally designed graphite boat. The main scheme of the boat design is described in detail and it is shown that the growth apparatus combine the favourable features of the known LPE growth techniques: epitaxy from thin solution layer, sliding boat technique and the technique based upon the displacement of one melt by another.     

LPE Growth of Ga1 – xInxSb Multi-grading Layers

Electronegativity difference approach (ENDA) has been successfully employed to obtain good prediction of the In atomic fraction, energy bandgap and lattice constant of the Ga_{1 – x}In_xSb/Ga_{1 – y}In_ySb/GaSb system. Nearly lattice-matched GalnSb epilayers with In atomic fraction of 0.42 have been obtained by the liquid phase epitaxy. The cut-off wavelength was 2.2 μm at room temperature.     

多孔硅吸杂对单晶硅片电性能的影响

多孔硅吸杂是减少晶体硅中杂质和缺陷,提高太阳能电池转换效率的有效方法.本文采用电化学腐蚀方法在单晶硅片上制备多孔硅.通过观察多孔硅的形貌、孔隙率、多孔层厚度及单晶硅片的电阻率变化,研究不同的腐蚀时间对制备多孔硅的吸杂效果的影响,并分析多孔硅吸杂的机理.结果表明,在J=100 mA/cm2条件下腐蚀时间为30 min、40 min、50 min、60 min吸杂处理后,电阻率均提高,且随着腐蚀时间的增加,电阻率相应增加,与多孔硅的形貌、孔隙率和多孔层厚度的变化趋势一致.多孔硅形成伴随弹性机械应力出现,随腐蚀时间增加,应力增加,晶格常数相应增加,这都有利于缺陷和金属杂质在多孔硅层-基底界面处迁移和富集,导致单晶硅吸杂后电阻率增大.     

Experimental Evidence for a Step Growth Mechanism of Garnet LPE Films

Experimental observations suggesting a lateral growth mode at {110} and {211} garnet LPE films are reported. Growth steps are revealed using a gold decoration technique and a new decoration method based on the condensation of PbO nuclei is developed which allows to image the step structure of the whole film surface using light optical interference contrast. The step velocity reduced per K undercooling of spiral steps having step distances larger than 100 nm amounts to (0.70 ± 0.10) μm/min ± K independently of step density. Spiral rotation rates and critical nuclei radii are in the order of 1 s⁻¹ and 10 nm respectively.     

重掺硅衬底片的内吸除效应

本文研究了重掺p型(B)和重掺n型(P、As、Sb)硅单晶的内吸除效应.发现在本实验条件下,经过改进的内吸杂(IG)处理后,不同掺杂剂的重掺硅单晶片都出现了氧沉淀增强现象,但不同掺杂剂的重掺硅单晶中氧沉淀形态不同.且发现砷增强了硅片近表层区氧的外扩散.在相同的热处理条件下,不同掺杂剂的重掺硅清洁区宽度不同,重掺硼硅片的清洁区最窄,重掺砷的最宽.     

Calculations of LPE layer thickness

Three basic cases of LPE growth with and without nucleation were examined. The expressions for layer thickness and growth efficiency calculations were developed. Criteria for LPE growth classification were obtained. It was shown the nucleation takes place at critical values of supersaturation of the solution. The values of critical supersaturation may be calculated from growth efficiency experimental data for LPE growth.     

Heat and mass transfer in LPE processes

Current LPE processes for the preparation of magnetic oxide films for “bubble” technology have been developed empirically. However, control of layer perfection and properties can only be achieved by a better understanding of the growth process which involves heat and mass transfer and necessitates consideration of hydrodynamic factors in solution. Solution stability and flow processes which can occur are characterised by the use of dimensionless numbers; the most relevant are the Prandtl and Grashof numbers, which together define the better known Rayleigh number. Until recently, lack of data has restricted the application of hydrodynamic principles to fluxed melt systems. However, many of the important parameters such as solubility, density, viscosity, thermal and mass diffusivity, and their variations with temperature, can be determined using simple experimental techniques.     

Defect Engineering and Gettering in a High-voltage Substrate Technolgy

Defect engineering in the CZ-silicon high-voltage substrate technology with a polycrystalline support needs very deep denuded zones, which enclose the whole volume of the monocrystalline islands. The formation of crystal defects is compared in the substrate fabrication process with and without an outdiffusion annealing (15 h at 1250°C), respectively. The gettering efficiency of the polycrystalline support and of the buried layer at the island bottom has been studied. The influence of the defect density and the heavy metal contamination on the device parameters has been investigated at a high voltage p-n-p lateral transistor.     

液相外延生长Pb(Zn1/3Nb2/3)O3-PbTiO3膜及生长机理研究

采用PbO作助溶剂,我们在钛酸锶(STO)衬底上用液相外延方法生长了一层具有特定取向的PZNT岛状外延膜,并通过引入c轴取向的PZT过渡层后,使原来的岛状三维生长转变为二维生长,显著改善了外延膜的质量,获得了几个微米厚、较完整的PZNT膜.实验证明:在氧化镁和铝酸镧(001)基片以及STO(110)/(111)衬底上,PZNT晶粒以自发形核为主,外延生长膜主要呈现岛状形貌;取STO(001)衬底,膜颗粒取向一致性好,并可获得完整的PZNT膜.     

Phase Formation,Crystal Structure and Electrical Properties of La212 Type Compound Substituted by Silver or Praseodymium

The La212 type compounds substituted by silver or praseodymium are prepared by solid state reaction method. It is found that compounds La_2‐xSr_xCa_0.5Pr_0.5Cu₂O₆, La_1.6Pr_0.4Ca_1‐xSr_xCu₂O₆ and La_2‐xPr_xCa_0.5Sr_0.5Cu₂O₆ can be formed for x=0.4‐1.1, 0‐0.5 and 0‐1.5, respectively. A new member of La212 type compounds, La_2‐xAg_xCaCu₂O₆ is also prepared. Their structures are verified by Rietveld structure refinement to belong to the structure type of La212 cuprate oxide with space group I4/mmm. Their electrical properties are investigated. La_1.65Ag_0.35CaCu₂O₆ displays metal‐like behavior and its resistivity decreases with the decrease of temperature from 300K to 4.2K.     

LPE Growth of GaInAsP/InP Heterostructures for 1.3 μm Planar Buried Mesa Lasers

LPE heterostructure growth processes devised to prepare GaInAsP/InP planar buried mesa ridge (PBMR) lasers are described. A combination of supercooling and two-step cooling regimes of LPE was used to grow InGaAsP/InP heterostructures with the active layer flanked by two waveguiding layers. The optical waveguide geometry was optimised to yield minimum threshold current density. Low-temperature (600°C) LPE process was employed to regrow the etched mesa structure. The prepared PBMR laser devices with optical resonator lengths of 250 μm exhibited room temperature threshold current values near 20 mA and T₀ values in the range 60–70K. Optical power-versus-current characteristics were linear up to 25 mW.     

Growth and Characterization of Direct-connecting AlGaAs/GaAs TJS Light Emitting Device on SI GaAs Substrate by LPE

High output power (above 3 mW/facet) AlGaAs/GaAs Transverse-Junction Stripe light emitting diodes have been grown on Semi-Insulating (100) GaAs substrates by Liquid Phase Epitaxy. these light emitting diodes utilize a “Direct-connecting” transverse-junction stripe structure, which can confine the transverse-current and reduce the series resistance. By thinning the thickness of the “effective active-layer” of this structure, a room-temperature pulsed lasing operation is also achieved with a threshold current as low as 35 mA and a peak wavelength around 904 nm. This “Direct-connecting” transverse-Junction Stripe light emitting device with a Metal-Semiconductor Field Effect Transistor on an electrical isolated semi-insulating substrate in the future.     

Defect generation in LPE garnet films during annealing

The defects induced in LPE garnet films during annealing processes near 1300°C were investigated by X-ray topography, etching, scanning electron microscopy and Nomarski interference microscopy. The results show that besides loops and more complicated dislocation configurations point defects play an essential role for the stress relaxation mechanism in the film. The observed coarsening effects on the film surface are due to the high surface free energy of {111} faces on garnets. A consistent explanation of the various experimental observations is given by assuming the creation of oxygen vacancies during annealing.     

Electrical characteristics of GaAs LPE schottky diodes

Structural and electrical properties of IMPATT diodes prepared from homoepitaxial GaAs films grown by liquid phase epitaxy have been investigated with the help of metallography and reverse I–V characteristic derivatives. The structural defects in epitaxial layers have been shown lead to the localization of current in separate regions (microplasmas) which brings up a soft breakdown. A method as been proposed for the observation of microplasmas at large currents.     

A new method of stirring for LPE growth

This paper describes a method of stirring a liquid during crystal growth in which each point on the growth face moves round a circle of radius b. If the face has a radius a and completes n revolutions per second, then the stirring is roughly equivalent to rotating the disc about a single axis at a rate $\text{2πc}{}^2\text{b}{}^2\text{n}\text{a}{}^2$ where c is a constant (c ∽ 2) but the system behaves as if only the liquid up to a distance $\text{(}\text{2v}\text{n}\text{)}{}^{\mathrm{<mtext>1</mtext><mtext>2</mtext>}}$ from the face is stirred. Uniform stirring occurs over the whole face except for an annulus of width 2b at the periphery. The necessary design criteria are discussed and a simple dynamically balanced apparatus and the results obtained with it whilst growing iron garnet films are described.