Liquid Encapsulated Czochralski Method Research Articles

EL2 Out-Diffusion in Thermally Annealed Liquid-Encapsulated Czochralski GaAs

The annealing behavior of the native defect EL2 in GaAs grown by the liquid-encapsulated Czochralski (LEC) method has been investigated by means of deep-level transient spectroscopy (DLTS). After annealing in vacuum, the EL2 out-diffusion profiles were strongly dependent on the annealing temperature and time. Applying the three-step model for EL2 out-diffusion, the activation energy of the diffusion for an arsenic vacancy (VAs) was estimated to be about 3-4 eV.

X-Ray Topographic Investigation of Cellular Structure and its Relation to another Defects in Various Types of GaAs Single-Crystals

The defect patterns in GaAs crystal grown using liquid encapsulated Czochralski and gradient freeze methods with various types of doping were characterized using complementary X-ray topographic methods. It was found that the structure occurring in the 1ow doped crystal is developed independently from the actual surface. The occurrence of the structure is connected with significant 1attice deformation, and some results point that significant stress can influence its formation. The high doping prevents formation of the structure, but at higher doping the phenomenon of cellular growth can occur due to instabilities of the surface. The present results point that defect pattern in GaAs crystals is more affected by the type of doping than by the choice of the method.

Influence of Boron in Semi-insulating GaAs Crystals on Their Electrical Activation by Si-Ion Implantation

The influence of boron on the activation of silicon ions implanted in semi-insulating GaAs crystals grown by liquid encapsulated Czochralski (LEC) method from As-rich melt was investigated using crystals with the same carbon concentration and the same deep donor (EL2) concentration. The resistivity of the crystal was not affected by the boron concentration. The sheet resistivity of the implanted layer, however, became higher with increase of the boron concentration. An analysis of the electrical properties of the implanted layer suggested that the occupation rate of the implanted silicon at As site (SiAs), which decides the acceptor level, increased with the boron concentration. The dependence of this occupation rate was influenced by the annealing temperature for activation in the region of low boron concentration under 15×1016 cm-3.

ZnGeP2 grown by the liquid encapsulated Czochralski method

The growth of ZnGeP2 by the liquid encapsulated Czochralski method is reported for the first time herein. Large boules of ZnGeP2, with diameters up to 40 mm and weights up to 400 gm were grown by Czochralski pulling from B2O3 encapsulated melts under high pressure (20 atm Ar) using axial gradients ≤120 °C/cm. Boules pulled at ≤4 mm/h exhibited large (50×20×15 mm3) monocrystalline grains of α-phase ZnGeP2 with room temperature electrical properties of p-type conduction, carrier concentrations ranging from 1012 to 1016 cm−3, and mobilities of 20 cm2/V s or less. Optical samples exhibited broad IR transmission (0.7 to 12.5 μm), second harmonic generation at 4.7 μm with 7.2% conversion efficiency, a broad subband gap photoluminescence signature, and near band-edge absorption similar to that observed in Bridgman-grown ZnGeP2.

Hydrostatic-Pressure Deep Level Transient Spectroscopy Study of the Heteroantisite Antimony Level in GaAs

We present some preliminary results of the first hydrostatic-pressure study of the electronic level related to the Sb-heteroantisite defect in GaAs. We studied two kinds of n-type GaAs samples doped with antimony: bulk samples grown by liquid encapsulated Czochralski method and thin layers grown by metalorganic chemical vapour deposition technique. We found strongly nonlinear pressure dependence of the activation energy of the emission rate for the level. Moreover, the results obtained for the bulk material were fairly different from those obtained for thin metalorganic chemical vapour deposition layers. The possible explanation of this difference is presented.

Quantitative characterization of residual strains in gallium phosphide (100) wafers

Residual strains in thin GaP (100) wafers, sliced from crystalline ingot grown by the liquid-encapsulated Czochralski method, have been first characterized by measuring strain-induced birefringence. The absolute values of the residual strain components ‖Sr−St ‖, ‖Syy−Szz ‖, and 2‖Syz ‖ are quantitatively characterized. It is found that their two-dimensional distribution maps exhibit fourfold symmetry and that most of wafers exhibit U- or M-shape distributions along diametric directions, but some wafers with a low level of strains exhibit distorted-shape distributions. The maximum strain value attains to the order of 10−4 and the corresponding stress is about 7.5×106 N/m2.

Damage coefficient associated with free exciton lifetime in GaAs irradiated with neutrons and electrons

The lifetime τ of the free exciton at T=17 K in irradiated GaAs has been determined by the reflectance of layers grown by metalorganic chemical vapor deposition and of semi-insulating samples grown by the liquid-encapsulated Czochralski method. The samples had been irradiated with 1 MeV and thermal neutrons, and with 7 MeV and white electrons up to 7 MeV. The linear increase of τ −1 as a function of the fluence is explained by a simple kinetics model, which applies especially well to the epitaxial layers. The damage coefficient kτ associated with this lifetime has been measured. For the defects created by all types of radiation, the radius associated with the cross section for the capture of excitons is three to ten times the radius of the free exciton. The exciton transition energy is found to decrease as its reflectance structure is broadened.

Near Infrared Photoacoustic Spectra of Deep Levels in GaAs Grown by Liquid Encapsulated Czochralski Method

Piezoelectric photoacoustic measurements on semi-insulating (SI) and n-type GaAs were carried out at 90 K. A distinctive peak at 0.92 eV and a hump near 1.2 eV have been observed for the SI samples. By comparing with the optical absorption and the electron photoionization cross section spectra, it is considered that these features are due to the electron transition involving deep EL2 defect levels. The present experimental results show that the PA spectroscopic technique is a novel and a useful tool to characterize the deep levels in semiconductors.

Constant Temperature LEC Growth of Uniform Composition InGaAs Bulk Crystals through Continuous Supply of GaAs

ABSTRACTA 45 mm long In0.05 Ga0.95 As ternary bulk crystal with an extremely uniform composition has succeeded to be grown at a constant temperature by the liquid encapsulated Czochralski (LEC) method with a continuous supply of only GaAs to the pseudobinary InAs-GaAs growth melt. A double crucible which has both growth and source melt zones has been developed to improve the controllability of die supply of GaAs to the melt. These zones are separated by a cylindrical wall with a slit through which source elements are continuously supplied from die source melt zone to the growth melt zone. These results demonstrate mat large and uniform InGaAs bulk crystals can be grown using the constant temperature LEC method with a double crucible and with a continuous supply of only GaAs.

Rapid thermal annealing effects on InP grown by the LEC method

InP crystals, grown by the liquid-encapsulated Czochralski method, were prepared by rapid thermal annealing and were investigated by photoluminescence spectroscopy as a function of annealing time. In the photoluminescence spectra of as-grown samples, the 1.414 eV acceptor-bound peak and the 1.378 eV free-to-acceptor peak dominated. A shift toward higher energy was observed at high excitation intensity for the 1.375 eV peak of the donor-to-acceptor emission of InP. The dominant transition centred at the 1.378 eV peak can be ascribed to zinc impurities in the starting material. Changes in the excitation intensity and the sample temperature resulted in the identification of zinc-related free-to-acceptor transitions where the zinc ionization energy was calculated to be 46 meV. Analysis of the temperature-dependent data yield an activation energy of 47 meV.

Growth of low dislocation density InP single crystals by the phosphorus vapor controlled LEC method

The growth of 3-in S-doped and Fe-doped and 2-in Sn-doped InP single crystals with reduced axial temperature gradients using the phosphorus vapor controlled liquid encapsulation Czochralski (PC-LEC) method is discussed. It is shown that, in the case of S-doped crystals, the dislocation-free area of the crystal is increased using the PC-LEC method, compared to that of crystals grown using the conventional LEC method. It is also shown that 3-in Fe-doped InP could be grown with a dislocation density lower than 10/sup 4/ cm/sup -2/. The average EPD was lower than 5*10/sup 3/ cm/sup -2/ in 2-in Sn-doped InP. The photoluminescence intensity of PC-LEC crystals was much higher than that of conventional LEC crystals in the case of Sn-doped InP. >

InP single crystal growth with controlled supercooling during the early stage by a modified LEC method

A new liquid encapsulated Czochralski (LEC) technique for InP single crystal growth has been developed. In order to restrain the generation of twin bondaries from the shoulder of InP crystal by the LEC method, at the beginning of InP crystal growth, we tried to produce growth toward the lateral direction until reaching a 2-inch diameter without forming a cone angle ( θ = 90°) by controlling the optimum supercooling of the InP melt. As a result, it was found that although isotropic growth could restrain the twin boundary, anisotropic growth was likely to generate a twin boundary at the completion of lateral growth. After isotropic growth, InP single, crystals were obtained reproducibly. That is, ten single crystal ingots of InP were obtained by this method. Furthermore, the etch pit density (EPD) of InP water with a 2-inch diameter was less than 2000 cm -2, except at the edge of the water, by Zn doping ((3.0-4.0) X 10 18 cm -3).

Anomalous photoluminescence and raman scattering behavior in heavily Mg+ ion-implanted InP

Mg+ ions were implanted into highly pure InP grown by the liquid encapsulated Czochralski (LEC) method in which the Mg concentration [Mg] was varied between 1×1015 cm−3 and 3×1020 cm–3. Two annealing methods were used: furnace annealing (FA) up to 740° C and flash lamp annealing (rapid thermal annealing, RTA) up to 900° C. For characterization, photoluminescence (PL) spectra were measured between 2K and room temperature together with Raman scattering measurements at room temperature. An emission designated by g, which was attributed to a novel energy state of an isolated acceptor, was found to be produced for a rather low value of [Mg]. In addition, a broad emission denoted by [g−g], which was ascribed to acceptor-acceptor pairs, was observed below bound exciton emissions for moderate values of [Mg]. These features were quite similar to those previously observed in acceptor-doped GaAs when the background concentration of donors is extremely low. Two additional novel emissions located far below the band-to-acceptor emission were also obtained, and each showed a remarkable energy shift towards lower energy with increasing [Mg]. The binding energies of these emissions were estimated from the temperature dependence of PL spectra and the results suggest that they are complex-type radiative recombination centers, presumably donor-acceptor-type centers. A strong broad emission centered near the band-to-acceptor emission was observed for [Mg]=3×1020 cm−3. This observation indicates a formation of a new material between In, P and Mg, which was also attested by the appearance of a new TO-like Raman signal for [Mg] greater than 1×1019 cm−3. A substantial difference of PL and Raman spectra was revealed for the two annealing methods, suggesting that the annealing behaviour of ion-implanted InP should be investigated more extensively in order to establish reliable annealing procedures.

Deep levels in Si- and Be-coimplanted GaAs

Deep levels and electrical properties in Si- and Be-coimplanted semi-insulating GaAs, grown by liquid-encapsulated Czochralski methods, were investigated. The Si implantation with a dose of 8×1012 ions cm−2 and energy of 65 keV was performed into GaAs already implanted with a Be dose of 2×1012 cm−2 and 90 keV for the purpose of an abrupt implant profile in a deeper region. During the Be coimplantation, an electron deep level at 0.62 eV below the conduction band and a hole deep level at 0.68 eV above the valence band were newly observed. In the Be-implanted region of ion-implanted GaAs, the deep levels Ec − 0.62 eV and Ev + 0.68 eV dominate, but are not found in the bulk. From this work, it is suggested that the Ec − 0.62 eV trap could be the defect due to the implantation damage and that the Ev + 0.68 eV trap could be the Be complex related to a Si dose during the implantation.

Photoluminescence from InP heavily ion-implanted with Mg+

Abstract Ion-implantation of magnesium into extremely pure InP grown by the liquid-encapsulated Czochralski method was carried out with magnesium concentrations [Mg] ranging from 1 × 1015 to 3 × 1020 cm−3 with a maximum energy of 400 keV. Low temperature photoluminescence and Raman scattering measurements were performed on these samples. A new state of excitions bound to what was presumed to be a new type of acceptor g and an emission attributed to acceptor-acceptor pairs [g-g] were found below the bound exciton emission series. Two novel emissions located far below the band-to-acceptor emissions were also observed, and these showed remarkable energy shifts towards the lower energy side with increasing [Mg]. With heavily implanted samples, a strong broad emission of a new type was observed in the vicinity of the band-to-acceptor emissions.

Comparison of deep centers in semi-insulating liquid-encapsulated Czochralski and vertical-gradient freeze GaAs

Three-inch, semi-insulating (SI) GaAs, grown by the vertical gradient freeze (VGF) technique, has been studied by IR absorption, temperature-dependent dark current and Hall-effect, thermally stimulated current (TSC), and photoinduced current transient spectroscopy and has been compared with undoped, SI GaAs, both As-rich and Ga-rich, grown by the high-pressure liquid-encapsulated Czochralski method. The results clearly indicate that (1) the VGF GaAs contains less EL2, which suggests a less As-rich crystal stoichiometry; (2) in some VGF samples activation energies of 0.43 or 0.46 eV are deduced from temperature-dependent carrier concentration or resistivity measurements, respectively, and (3) VGF samples often show a thermal quenching behavior in the TSC peak T5. There is evidence to suggest that the 0.43 eV center is related to VAs, and T5 to VGa.

Neutron transmutation doping of GaP: optical studies

An unambiguous proof for successful neutron transmutation doping (NTD) of GaP is presented on the basis of optically detected magnetic resonance (ODMR). GaP:S samples grown by the liquid encapsulated Czochralski method were irradiated with thermal neutrons and subsequently annealed at 800°C. In the ODMR experiments the transmuted Ge substitutional on Ga sites was detected. The NTD process was also found to create deep acceptors, the nature of which will be tentatively discussed.

Neutron Transmutation Doped GaP: Optically Detected Magnetic Resonance Studies

The first direct proof for successful neutron transmutation doping (NTD) of GaP is presented on the basis of optically detected magnetic resonance . (ODMR). GaP:S samples grown by the liquid encapsulated Czochralski method were irradiated with thermal neutrons and subsequently annealed at 800° C. In the ODMR experiments the transmuted Ge substitutional on Ga sites was detected. The NTD process was also found to create deep acceptors, the nature of which will be tentatively discussed.

Lattice spacing measurements around dislocations in an undoped GaAs crystal grown by the liquid-encapsulated Czochralski method

Abstract The lattice spacing in a cellular structure of an undoped liquid-encapsulated Czochralski GaAs crystal has been measured by synchrotron X-ray topography with a (+n, −n, +n) triple-crystal system. Distinguishable lattice spacing variations were observed in dislocation-related regions. One region, neighbouring to the cell walls, shows a small lattice spacing compared with the average value. Another region, where dislocations intersect with the crystal surface inside the cell, shows a large lattice spacing. The lattice spacing variation depends on the dislocation features.

Composition dependence of lattice spacing for low dislocation density undoped liquid encapsulated Czochralski GaAs crystals

Crystals with varied composition were pulled by the As-partial-pressure controlled liquid encapsulated Czochralski method. The dislocation density was found to be as low as 2×103 cm−2 at the cores of the crystals. Lattice spacing (d) was measured with a precision of Δd/d ∼ 5.9 × 10−6 using synchrotron radiation. For a variation of 7×10−5 in the As-atom fraction in the crystals, the lattice spacing varied by less than 1×10−5 Å.