LEC Technique Research Articles

The temperature dependence of electron and magneto transport properties in Te-doped InSb

Resistivity, magnetoresistivity and Hall effect measurements in n-type Te-doped InSb grown by the LEC technique were carried out as a function of temperature (14–350 K) and magnetic field (0–1.35 T). The measurement results are analyzed using the conventional and quantitative mobility spectrum analysis methods. It is found that the impurity levels arising from LEC technique and intentionally dopants have a strong influence on both the electron and magneto transport properties. The temperature dependence of the magnetoresistivity coefficient shows an overall increase by representing two minima as the temperature decreases. These minima are associated with two types of impurities. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

Conductivity, Hall and magnetoresistance effect measurements on SI GaAs and InP

The conductivity, Hall effect and magnetoresistance quantities in semi-insulating undoped GaAs and Fe-doped GaAs and InP grown by the LEC technique have been measured in the temperature range 300–420 K. It is shown that mixed conductivity is present in all samples. The experimental data were analyzed using a two-band model including electron and hole transport. A good fit has been obtained self-consistently to both conductivity and mobility. The single-band parameters have been extracted from the measured data in the studied temperature range. From ln (|RH, 0| T3/2) and σ vs T−1 plots, activation energies of 0.77 and 0.65 eV have also been observed for GaAs and InP, respectively. (© 2004 WILEY-VCH Verlag GmbH & Co. KGaA, Weinheim)

PREPARATION AND CHARACTERISATION OF Ti/BaTiO3/InP MIS STRUCTURES

Indium Phosphide (InP) is one of the most promising materials for high-speed electronic and optoelectronic devices. In the present investigation n-type InP substrates of <111> orientation grown by LEC technique in our laboratory were used to study the surface state densities. The wafer was polished with HBr:K 2 Cr 2 O 7: H 2 O (BCA) polishing solution and decreased with organic solvents. Au:Ge was used has a back ohmic contact and the wafer was annealed at 623K for 5 min. under nitrogen ambient. Barium Titanante ( BaTiO 3), a dielectric material was used as an insulator to fabricate InP -MIS structures. BaTiO 3 thin film has been deposited on InP substrates by sol-gel technique through organic precursor route. Titanium metal contact was made on the BaTiO 3 to obtain MIS structure. Compositional analysis of the BaTiO 3 thin film on InP substrates has been carried out using XPS and EDX. By the Capacitance Voltage measurements a minimum surface state density ( N ss) value as low as 4.5 × 1010 cm -2 eV -1 has been obtained for Ti/BaTiO 3/ InP MIS structures which is comparatively less than that of other deposited insulators.

Dislocations and 90°-twins in LEC-grown InP crystals

The results of dislocation density and 90°-twins investigations in 〈1 1 1〉-oriented InP crystals grown by the LEC technique with two different axial temperature gradients, d T/d z=260 and 100 K/cm, are reported. Estimation of the maximum diameters ( D max) of dislocation-free crystals, which can be grown with a given d T/d z, is made. It is discovered that 90°-twin formation for a given d T/d z takes place in a narrow range of crystal diameters ( D T), and D T≈ D max for both d T/d z=260 and 100 K/cm. By the selective etching of the crystal axial section, crystallization front shape in the 90°-twin region is revealed. It is discovered that 90°-twin formation coincides with the morphological signs of a change from crystal dislocation-free growth mechanism to a dislocation growth mechanism. A possible mechanism of influence of the dislocations on twin formation in the framework of the theory of the crystals lateral growth from the melt is discussed.

Response of semi-insulating GaAs detectors to low energy protons

The performance of semi-insulating GaAs detectors, grown with the LEC technique, has been studied by irradiating the Schottky diodes with 2 and 2.4 MeV monoenergetic protons in a pencil beam with sub-millimeter width (70 or 600 μm). The beam was moved across the surface of the front (Schottky) contact, in order to investigate the uniformity of the detection characteristics over the sensitive area of the diodes, and to study the electric field behavior around the Schottky contact. For each scanning position, a pulse-height spectrum was measured. Then, the charge collected and the energy resolution were obtained as a function of the irradiation position both on the contact and outside it. The data show that • the best spectroscopic response occurs for the beam with 70 μm width, • when the beam is incident onto the contact, the energy resolution is between 1% and 5%, and the variation of the charge collected, for different irradiation position, is less than 30%, • when the beam is incident onto the border of the contact (substrate is irradiated), the spectrum is degraded and no clear peak is present, • collection of charge still occurs at distances up to about 500 μm from the border of the Schottky contact (for a pixel size of 200 μm), or up to about 200 μm (for a pixel diameter of 3 mm), • saturation of the curve collected charge vs. reverse bias voltage occurs at about 100 V for both 2 MeV (range=32 μm) and 2.4 MeV protons (range=41 μm).

気液界面及び液液界面における表面張力流の相互作用の可視化計測

Marangoni convection, driven by an interfacial instability due to a surface tension gradient, has become a large problem in the crystal growth on the ground or in a micro gravity environment. To suppress and control the convection is important for the material processing. Especially in the crystal growth by LEC or EFZ technique, in which the melt is encapsulated with an immiscible medium, Marangoni convection may occur on the liquid-liquid interface and on the gas-liquid free surface. In the present paper, experiments were carried out with a two immiscible liquids layer both in a open-boat system and in an enclosed system. Flow in a cavity subject to a horizontal temperature gradient was observed. An interactive flow near the interface was measured by using a simple Ply technique. The measured flow field seemed to agree enough with the numerical prediction.

Growth of semi-insulating InP with uniform axial Fe doping by a double-crucible LEC technique

The level of an Fe-doped InP melt in a growth crucible is kept constant throughout a Czochralski growth experiment by replenishing it with undoped melt from a second crucible. 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. As a result the ingot obtained exhibits axial Fe concentration much more uniform than in standard LEC crystals. This growth method can increase the yield of semi-insulating InP wafers as it prevents the accumulation of iron and the formation of precipitates in the last to freeze part of the crystal.

Characterization of microdefects in GaAs crystals with high-resolution X-ray diffractometry

The aim of the present work was to correlate the electric characteristics of Te-doped gallium arsenide grown by LEC technique with the defect contents of the samples. Measurements for GaAs samples, doped with Si, Ge and Ge+Te as well as undoped ones, grown by various methods (HB, VGF and LEC), were also performed. In order to characterize the defects High Resolution X-Ray Diffractometry was used. Measurements of diffuse scattering intensity maps around the reciprocal lattice points and plane wave reflection topography were employed. For most cases in the range of free-electron concentrations between 1·1017 cm−3 and 6·1018 cm−3 (as well as for SI samples) the isointensity contours in the maps exhibit generally the same character. For higher doping level the intensity of X-ray diffuse scattering increases and it can be further increased by the annealing which causes a decrease of free-electron concentration. An analysis of the reciprocal-space maps is presented. Several types of defects should be considered in order to describe isointensity contours.

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

AbstractA 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.

Electrical characteristics of 100 MeV 28Si implanted LEC grown GaAs〈100〉

Undoped semi-insulating gallium arsenide single crystals were grown in pBN crucible using LEC technique. 28Si implantation at various fluences was carried out using 100 MeV 28Si ion. Implanted samples were characterised using four probe and Hall measurements. In-situ resistance measurements were carried out for samples implanted with various fluences. The electrical characterisation results of 100 MeV 28Si implanted GaAs samples show an increase in mobility 5774 cm 2/V.s (3800 cm 2/V.s) and a decrease in sheet resistivity of the order of 2 × 10 2 Ω/q . The increase in mobility at 300 K may be due to better electrical homogeneity in the implanted layer, than in the virgin substrate. The implanted samples ( 100 MeV 1.5 × 10 13cm −2 ) were annealed at different temperatures in the range of 200–400°C and characterised using Hall measurements at different temperatures (300–380 K). The implantation profile of the two buried layers by 100 MeV 1 × 10 12cm −2 and 80 MeV 1 × 10 12cm −2 for 28Si ion were observed and analysed using Scanning Electron Microscopy.

Photoluminescence investigations on liquid encapsulated czochralski grown gallium arsenide

The growth aspects of 50 mm diameter gallium arsenide single crystals using LEC technique are presented. Defect investigations are made using photoluminescence studies. Photoluminescence studies on the wafers reveal the presence of the EL2 level, the presence of transition metal impurity copper which cannot be eliminated by surface treatments, and the presence of carbon. Photoluminescence scans are also obtained at room temperature to study the uniformity. The presence of carbon is also revealed by FTIR measurements.

Thermal cycling, DLTS, and PEC studies on LEC gallium arsenide

AbstractThis paper discusses the growth of gallium arsenide single crystals using the LEC technique. The Semi‐insulating gallium arsenide was studied. The defect investigations were made by DLTS and etching studies. The variation of deep level concentration along the wafer was estimated using DLTS. The fabrication and efficiency of the PEC Solar cells are also reported.

Optical and electrical characterization ofn- andp-type Fe-doped InP

N-andp-type Fe doped InP crystals were grown by the LEC technique by co-doping with Zn and Te, respectively. The incorporation of these dopants is examined by chemical, electrical and optical analysis. The electronic transport properties of the InP: Fe, Zn crystal are investigated by a comparison of Hall effect measurements and theoretical calculations indicating a partial compensation of the Zn atoms by a deep donor.

Anomalous behaviour of dopants in GaAs during growth process

The concentration dependence of effective distribution coefficients for electrically active and isoelectronic impurities in GaAs have been studied. GaAs single crystals were grown in and by the LEC technique.

X-ray characterization of defect structure in LEC GaAs crystals

Semi-insulating (SI) GaAs crystals grown by LEC technique contain as the trade mark of this method at present level of technology complicated network of defects frequently called cellular structure. Structure and properties of this feature being in the mainstream of interest of GaAs investigations still should be considered as far from being fully understood. We report here features of images recorded by means of X-ray diffraction, electron microscopy and after photoetching obtained for an As-rich, undoped, semi-insulating GaAs crystals grown by LEC technique. For the formation of cellular network instead of simplified dislocation only based structure we postulate that As precipitates, impurities and dislocations could from image constituting the real cellular structure.

Annealing of Undoped InP and the Evaluation by Photoluminescence

Undoped single crystals grown by the LEC technique have been annealed at temperatures between 520°–820°C for 5h and their electrical properties and the photoluminescence spectra have been evaluated. It was found that the carrier concentration can be decreased up to by annealing at 620°C and the photoluminescence spectra are largely changed by annealing. When the annealing temperature is increased to higher than 720°C, the free exciton peak appears very prominently and many peaks appear at the longer wavelength region between 900 and 980 nm.

Czochralski crystal growth in the system PtMnxSb2−x

Abstract Czochralski growth of the system PtMn x Sb 2− x was investigated to explore its magnetic semiconducting potential. Using the LEC technique, PtSb 2 single crystals, p-type with ~ 10 18 carriers cm -3 , were obtained from BN crucibles; doping with Te exhibited a k (eff) of about one and produced n-type material. Melts of a composition PtMnSb crystallized as PtMnSb in single crystal form. Melt compositions of PtMn 0.25 Sb 1.75 resulted in the formation of PtSb 2 and with continuing growth in the appearance of several different phases, suggesting the likely absence of congruently melting compositions with x

Modelling of the growth of GaAs by the LEC technique: II. Thermal stress distribution and influence of interface shape

Results are presented for the thermal stress distribution which produces dislocations in GaAs crystals grown by the LEC method. Stresses have been computed by finite-element methods from the temperature solutions recently obtained by Crowley, Stern and Hurle (see preceding paper) using radiative heat transfer methods. Various cone angles, melt-solid interface shapes and stages of growth have been modelled for a range of heat-loss conditions into the encapsulant. The results show that the stresses are strongly dependent on interface shape and heat loss, and the dependence varies with both cone angle and the stage of crystal development. Experimentally observed interface shapes are generally not those which lead to a minimisation of thermal stress.

Modelling of the growth of GaAs by the LEC technique: I. Thermal distribution in the crystal

A model for the simulation for the thermal distribution during crystal growth by the LEC process is described. Full account is taken of the radiation optics of the enclosure and the view factor matrix is calculated for growth of the conical section of the crystal, as well as for the cylindrical portion. The model is used to compute the temperature distribution in 3 inch diameter GaAs crystals for differing values of cone angle, interface shape and rate of heat transfer to the encapsulant. The results are used in the companion paper (G.O. Meduoye, K.E. Evans and D.J. Bacon) to calculate the stress distribution in the simulated crystals.

A new model for the calculation of dislocation formation in semiconductor melt growth by taking into account the dynamics of plastic deformation

A new model is presented for the calculation of the dislocation density of semiconductor crystals as a function of the thermal boundary conditions during growth. This model is based upon the basic equations of plastic deformation to describe the movement and multiplication of dislocations according to Alexander and Haasen instead of using the unrealistic concept of a critical resolved shear stress (CRSS). It takes into consideration the non-linear behaviour of the deformation process, e.g. the dependence of the multiplication of dislocations on stress and the dependence of the strain rate on the actual dislocation density, the stress and the temperature. This dynamic model also includes the temporal variation of parameters during the growth process and can, for example, be used to calculate the dislocation density as a function of the growth rate. In the last section of this paper the model is applied to the growth of InP crystals by the LEC technique. A quantitative agreement is obtained for the results of the numerical modeling and real crystal growth for different boundary conditions.