Liquid Phase Epitaxy Films Research Articles

液相エピタキシ法におけるYBa<SUB>2</SUB>Cu<SUB>3</SUB>O<SUB>7−δ</SUB>膜の高品質化

We have investigated the in-plane homogeneity of the large LPE (liquid phase epitaxy) crystals in microstructure and the growth mode in order to clarify the growth mechanism. The growth rate distribution dependence on the crystal rotation was observed in 20×20 mm2 LPE films. In the YBa2Cu3O7−δ system the higher rotation rate caused a larger growth rate distribution. It was considered that the distribution of both the growth interface temperature and the solute diffusion boundary layer thickness was existed. In this paper, we have focused the effect of the heat flux from the bottom of the crucible (hot region) during the LPE growth. Investigation of the growth rate distribution in the NdBa2Cu3OX(NdBCO) system was effective in order to confirm the influence of the heat flux, since the influence was negligible for the LPE growth in the NdBCO system. The higher rotation rate in the NdBCO system caused a smaller growth rate distribution. These phenomena could be explained by the difference in the crystal rotation effect on the growth interface temperature.

Structure investigation on Hg1−xCdxTe liquid phase epitaxial films grown by the meltetch technique

Hg1−xCdxTe films were grown by a modified meltetch liquid phase epitaxial (LPE) technique which includes both substrate and epilayer etchback steps. The crystal quality of epilayer has been investigated by means of transmission electron microscopy, scanning electron microscopy, and double crystal x-ray diffraction. It has been found that adequate meltetch of the substrate at the beginning of LPE provides a fresh and flat surface for epitaxial growth, while epilayer meltetch at the end of LPE may prevent spurious melt sticking.

The magnetic field dependence of R0A products in n-on-p homojunctions and p-on-n heterojunctions from Hg0.78Cd0.22Te liquid phase epitaxy films

The analysis of R0A products as a function of magnetic field in n-on-p diodes using a simple diffusion current model has previously been shown to yield both Jep/Jtotal ratio (the relative contribution of the p-side diffusion current) and μep (the minority carrier, electron mobility). In this paper, we report the good agreement between the experimental and theoretical dependence of μep on the hole concentration over a wide range between 1 x 1016 and 4 x 1017 cm−3 in n-on-p homojunction diodes fabricated on undoped p-type Hg0.78Cd0.22Te liquid phase epitaxial (LPE) films. The averaged Jep/Jtotal ratio varied between 68 and 90% with the hole concentration. These Jep/Jtotal ratios indicate that other leakage current mechanisms than the p-side diffusion current were not negligible. Also, for the first time, comparative measurements were made on p+/n heterojunction diodes consisting of As-doped Hg0.07Cd0.30Te and In-doped Hg0.78Cd0.22Te LPE layers. Unlike a typical change in R0A products by a factor of 2–3 in n-on-p homojunction diodes, the R0A products in p+/n heterojunction diodes at 7 kG were typically only 2–3% higher than that at the zero field. The typical Jep/Jtotal ratio in p+/n heterojunction diodes was about 3–4 %, which confirms the general belief that the p+ cap layer, due to the high doping and a larger bandgap, contributes very little to the total leakage current.

Influence of the liquid phase epitaxial growth conditions on composition profile for Hg1-xCdxTe film

In this paper, the expressions for the effective segregation coefficient and composition depth profile of Hg1-xCdxTe liquid phase epitaxial (LPE) film are presented and compared with the experimental data. The expressions are derived based on the associated solution model and the phase diagram theory of Hg1-xCdxTe. The results show that supercooling, cooling rate, liquid composition, and nonequilibrium Hg pressure over the solution will result in the changes of average composition and composition-depth profile of the grown film. Adequate Hg loss, slow cooling rate, and proper prescription of liquid composition can improve the uniformity of longitudinal composition of Hg1-xCdxTe LPE film.

The minority carrier lifetime in doped and undoped p-type Hg0.78Cd0.22Te liquid phase epitaxy films

This paper will describe: (1) the first comparative study of recombination mechanisms between doped and undoped p-type Hg1-xCdxTe liquid phase epitaxy films with an x value of about 0.22, and (2) the first determination of τA7i/τA1i ratio by lifetime’s dependence on both carrier concentration and temperature. The doped films were either copper- or gold-doped with the carrier concentration ranging from 2 x 1015 to 1.5 x 1017 cm-3, and the lifetime varied from 2 μs to 8 ns. The undoped (Hg-vacancy) films had a carrier concentration range between 3 x 1015 and 8 x 1016 cm-3, and the lifetime changed from 150 to 3 ns. It was found that for the same carrier concentration, the doped films had lifetimes several times longer than those of the undoped films, limited mostly by Auger 7 and radiative recombination processes. The ineffectiveness of Shockley-Read-Hall (SRH) recombination process in the doped films was also demonstrated in lifetime vs temperature curves. The important ratio of intrinsic Auger 7 lifetime to intrinsic Auger 1 lifetime, τA7i/τA1i, was determined to be about 20 from fitting both concentration and temperature curves. The reduction of minority carrier lifetime in undoped films can be explained by an effective SRH recombination center associated with the Hg vacancy. Indeed, a donor-like SRH recombination center located at midgap (Ev+60 meV) with a capture cross section for minority carriers much larger than that for majority carriers was deduced from fitting lifetime vs temperature curves of undoped films.

Reducing the optical absorption of LPE garnet films at a wavelength of around 1000 nm

This paper concerns the reduction of optical absorption loss L of Bi-substituted rare-earth iron garnet films at a wavelength of around 1000 nm for use as a 45/spl deg/ Faraday rotator of an optical isolator. First, a single crystal of Nd/sub 1.21/Gd/sub 1.74/Sc/sub 2.07/Ga/sub 2.98/O/sub 12/, with a lattice constant of 1.2619 nm, was grown by the Czochralski method. Using this crystal as a substrate, Nd/sub 1.69/Bi/sub 1.31/Fe/sub 5/O/sub 12/ film was grown by the LPE (Liquid Phase Epitaxial) method. The resultant LPE film showed a reduced optical absorption at around 1000 nm, because its optical absorption peak at around 900 nm due to the Fe/sup 3+/ crystal field transition from /sup 8/A/sub 1g/ to /sup 4/T/sub 1g/ shifted toward short wavelengths. In addition, the LPE film's Faraday rotation coefficient increased, since Nd, as Bi does, contributes negatively to the Faraday rotation. The value of L for the LPE film was found to be 2.6 dB at a wavelength of 980 nm, and 1.0 dB at 1017 nm.

Photorefractive damage in LiNbO3 thin-film optical waveguides grown by liquid phase epitaxy

Photorefractive damage in LiNbO3 thin film optical waveguides grown by liquid phase epitaxy (LPE) was evaluated by the in-plane scattering method at the irradiation wavelength of 514 nm. We were particularly interested in comparing films grown from a Li2O–B2O3 flux and a Li2O–V2O5 flux, and investigating the effect of Mg and Fe doping. Two powerful tools were used for data analysis: the Glass model and the ray model, which estimates the refractive index change. The LPE film grown from the Li2O–B2O3 flux showed a much higher resistance to photorefractive damage than the LPE film grown from the Li2O–V2O5 flux. The photorefractive effect was suppressed by Mg doping and enhanced by Fe doping as in the bulk crystal. The refractive index change in the 0.7 mol % Mg-doped LPE film grown from the Li2O–B2O3 flux was small enough (10−5 at most) to induce no beam fanning. Conventional Ti-indiffused, H+-exchanged, and annealed H+-exchanged waveguides were used as reference samples.

The majority carrier mobility of n-type and p-type Hg0.78Cd0.22Te liquid phase epitaxial films at 77 K

The dependence of majority carrier mobility on carrier concentration at 77 K in Hg0.78Cd0.22Te has been studied by Hall measurements on about 190 n-type and 360 p-type liquid phase epitaxial films. The n-type films were indium doped with the carrier concentration varying from 1×1014 to 2×1016 cm−3. The measured electron mobility changed from 2×105 to 8×104 cm2/V s. The p-type films were undoped (Hg vacancy) with the carrier concentration varying from 2×1015 to 3×1017 cm−3. The measured hole mobility changed from 600 to 200 cm2/V s. By comparing calculated mobility curves with the experimental data, we found that the major scattering mechanisms for electron mobility in n-type materials were polar optical phonon, ionized impurity, and alloy disorder scatterings. These three scattering mechanisms also dominate the hole mobility in p-type materials at 77 K. It was also found that a model with Hg vacancy as doubly ionized shallow acceptors fitted very well the hole mobility versus carrier concentration data.

On the flux growth and some properties of superconducting YBa2Cu3O7-ϰ single crystals and LPE films

DTA and crystal growth experiments were applied in order to determine the primary crystallization field of YBa2Cu3O7-ϰ in BaO-CuOx-YO1.5 flux melts for crystal growth and liquid phase epitaxy (LPE). Simultaneous thermogravimetric (TG) and DTA experiments prove an essential reduction of CuO to Cu2O during heating; the complete reduction of Cu2+ occurs at 1026°C. In the presence of alkaline earth oxides CaO, SrO, and BaO a decreasing temperature for Cu2+ reduction and melting is found. Reduced oxygen partial pressure results in a higher Cu+ concentration and in lower crystallization temperatures as well as lower eutectic ones. Crystal growth experiments under isothermic conditions at about 900°C have been carried out, where the supersaturation is produced by an increasing oxygen partial pressure. X-ray diffraction, electron microanalytic, polarization microscopic, and magnetic measurements prove the LPE growth of twinned c-YBa2Cu3O7-ϰ films on (001) LaGaO3 substrates and of twinned a,b films on (110) NdGaO3 substrates. Relatively smooth films with planar defects and thicknesses of 5-10 μm were grown by this vertical LPE technique.

Etch pit study of dislocation formation in Hg1−xCdxTe during array hybridization and its effect on device performance

The relationship between hybridization force, dislocation (etch pit) density, and device performance has been investigated for devices fabricated from Hg1−xCdxTe liquid phase epitaxy (LPE) material. Coldwelded indium column interconnects are the predominant method used to mechanically and electrically attach mosaic arrays to silicon multiplexers. The mismatch in thermal expansion between the Hg1−xCdxTe photodiode arrays and silicon multiplexers stresses the interconnects when the arrays are cooled to their operating temperature (typically 40–120 K) which can lead to failures. Increased hybridization force improves the mechanical stability of the interconnects but can introduce dislocations in the Hg1−xCdxTe. Dislocations have been reported to degrade the performance of some device structures. The dislocation density in the LPE film after growth was ≊8×105/cm2. We have found no significant change in dislocation density at hybridization forces up to ≊3.9×107 N/m2. At forces on the order of 5.9×107 N/m2 (≊10% of the Vickers hardness), the dislocation density in the films increased to 90×105/cm2 in the areas where the indium columns were. The diffusion limited performance of the test structures at 120 K was not significantly degraded by the increased dislocation density. At 80 K, however, where the devices were modeled to be generation–recombination limited, there was an increase in dark current with increased dislocation density. The structures used in the study were fabricated from LPE Hg1−xCdxTe grown on a CdTe substrate. Implantation of boron into the p-type material through a ZnS passivation layer was used to form junctions. A zero-bias junction resistance of 1000 to 7000 Ω cm2 was typical for the test structures which had a cutoff wavelength of 4.7 μm at 120 K.

Deep levels in n-type HgCdTe

Deep levels in both bulk and LPE (liquid phase epitaxy) n-type Hg0.685Cd0.315Te have been studied by deep level transient spectroscopy (DLTS) between 78 and 170 K using metal-insulator-semiconductor (MIS) capacitors. One major acceptor-like electron trap was observed in the depletion region of the semiconductor with an energy level at Ec-85 meV, or Ec-0.3Eg. The electron capture cross section was found to be independent of the temperature and has an average value of 1X10-16 cm2. The ratio of the trap concentration (Nt) to the shallow donor concentration (Nd) in both the bulk material and the LPE film was found to be close to 1. A general expression allowing numerical calculation of the capacitance transient due to the thermal ionization of traps in MIS capacitors with any value of Nt/Nd is also given.

Investigation of growth conditions for the liquid phase epitaxy of hexaferrite films using a Bi 2O 3-BaO-B 2O 3 flux

Conditions favoring the liquid phase epitaxy (LPE) growth of barium hexaferrite films have been investigated using the Bi 2O 3-BaO-B 2O 3 flux system. The barium hexaferrite-saturated solutions based on this flux system exhibit relatively large degrees of supercooling (up to 65°C). However, the BaFe 12O 19 phase field occupies a limited region of the BaO/Fe 2O 3/Bi 2O 3 pseudo ternary phase diagram. LPE films of pure barium hexaferrite and aluminum-substituted hexaferrite were successfully grown on Sr(Ga, Mg, Zr) 12O 19 substrates using this flux system. Microstructural evaluation of the films by X-ray topography and optical microscopy indicates that smooth, uncracked barium hexaferrite films can be grown on strontium hexagallate substrates from selected compositions in the BaO/Fe 2O 3/Bi 2O 3 ternary system under conditions which minimize lattice mismatch between film and substrate.

Growth Parameter Optimization and Tb3+ Sensitization of Ce3+ Activated Y 3Al5 O 12 Phosphor

Cerium activated has been grown by liquid phase epitaxy (LPE) from a flux. Cathodoluminescence measurements of show an internal efficiency of 6.5% at the film composition and optimal growth conditions. Numerous lanthanide ions were studied in a series of LPE film growths to evaluate each as a sensitizer of Ce3+emisson in hosts. Tb3+ additions increased the cathodoluminescence by 70% to yield an internal efficiency of 11%. The conditions of LPE growth which provide maximum performance in and in are discussed. Consideration is given to reagent purity of the solute and flux components. The luminescence of was analyzed by photoluminescence and time‐resolved cathodoluminescence. The energy transfer from Tb3+ to Ce3+ in the host crystal was demonstrated by both techniques.

The Faraday rotation of bismuth- and thulium-substituted yttrium iron garnet

The substitution of bismuth in the dodecahedral site of rare-earth garnet films is known to enhance the Faraday rotation by orders of magnitude. The effect of the bismuth ion on the iron sublattice that produces this enhancement is not known, and experimental evidence suggests that the rare-earth ion is not a significant contributor to the Faraday rotation. As the Faraday rotation probes the orbital angular momentum states of the garnet film, Tm3+-substituted yttrium iron garnet (YIG) films were investigated because of the large orbital contribution to the angular momentum and the crystal-field effect of the Tm ion. The temperature dependence of the Faraday rotation in Tm:YIG did not show any significant variations other than the bismuth enhancement. The major contribution to the Faraday rotation comes from the tetrahedral symmetry site, which is evaluated from the fit of the experimental data to a simple sublattice model. The temperature dependence of the Faraday rotation is presented between 4 and 300 K at wavelengths of 546, 578, and 633 nm. The liquid-phase epitaxial films have a composition of Y2.4−xTmxBi0.6Fe5−yGayO12, where x=1.2, y=0; x=1.9, y=1.3; and x=2.4, y=1.3. The Faraday rotation passes through a compensation point in the Ga-doped samples, and the Faraday rotation is shown to be independent of the Tm concentration.

Electrical properties of antimony-doped p-type Hg0.78Cd0.22Te liquid-phase-epitaxy films

Abstract Hall measurements have been performed on antimony-doped p-type Hg0.78Cd0.22Te LPE (Liquid-Phase-Epitaxy) films between 20 and 150 K. The ionization energy of isolated shallow acceptors was estimated to be about 11 meV. From the analysis of the Hall coefficient and the hole mobility data, we found that compensation in the films is not enough to explain the typically low hole mobility at low temperatures.

Optical operation of a magnetic bubble

A magnetic bubble domain is generated on liquid-phase epitaxial (LPE) garnet film by focusing laser light. It is possible to write with only a few milliwatts light power on a thin film with a low anisotropy field. Because the Bi-containing LPE films used have a high Faraday rotation angle, a written bit or bubble can be read out with a high contrast ratio. Because of its low coercivity, the bubble moves along the temperature gradient to the region heated by the light beam and is then stabilized at a corner of a square formed on the film by etching or ion-implantation. Erasure is possible selectively or all together by increasing the bias field. These optical operations of a magnetic bubble are discussed in connection with the material parameters.

Liquid Phase Epitaxial Growth of Thick Magneto-Optic Garnet Films

Growth and characterization of thick liquid phase epitaxial films of magneto-optic garnets are reviewed. In preparing thick epitaxial garnet films, it is important to make full use of the merits of epitaxial growth, and to minimize the drawbacks due to "bulk-like" behavior during thick film growth, such as morphological changes followed by flux inclusion. The primary phase region of the garnet should be checked carefully prior to epitaxial growth. A guiding principle concerning control over the level of substitution of Bi <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3+</sup> is reviewed. Thick epitaxial films of Bi-substituted garnets show superior magneto-optic properties, enabling practical use in optical isolators at a wavelength of 1.3 μm. Further efforts are necessary to reduce the optical absorption at 0.8 μm.

Inhomogeneity model for anomalous Hall effects in n-type Hg0.8Cd0.2Te liquid-phase-epitaxy films

Anomalous Hall effects, i.e., peaks in the temperature dependence of the Hall coefficient and Hall mobility, have been observed in liquid-phase-epitaxy (LPE) Hg0.8 Cd0.2Te films. After establishing that surface effects are not the cause of the anomalies and that our LPE films are indeed n type, we propose an inhomogeneity model with a network of extended p-type inclusions in an n-type matrix. Good fits to the experimental data have been obtained by computer simulation based on this model.

Effects of spacer layer elastic properties on metallic thin film edge-induced stress gradients in bubble memory devices

It is well-known that metallization edge-induced stresses can change the uniaxial magnetic anisotropy of a liquid phase epitaxial (LPE) garnet film near the metallization edge. We have investigated this magnetostrictive interaction of patterned metallic films with ion-implanted LPE films by using several different spacer layers such as polyimide, SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> , Si <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">3</inf> N <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">4</inf> , and combinations of polyimide and SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> beneath a Cr-Cu-Cr conductor pattern. It is concluded that the stress eliminating capability of a spacer depends on the hardness parameter <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K = \frac{E_{s}(1-\nu\min{f}\max{2})}{E_{f}(1-\nu\min{s}\max{2})}</tex> where <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E_{s} , E_{f}</tex> are Young's moduli and <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">\nu_{s}, \nu_{f}</tex> are Poisson's ratios for the spacer and metallic film, respectively. The polyimide spacer with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">E_{s} &lt; 10^{11}</tex> dyn/cm <sup xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</sup> and with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K \leq 0.1</tex> transmits an order of magnitude of smaller stress than a SiO <inf xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">2</inf> spacer with <tex xmlns:mml="http://www.w3.org/1998/Math/MathML" xmlns:xlink="http://www.w3.org/1999/xlink">K \geq 1</tex> with the stress being more uniformly distributed across the spacer.

New bubble garnet films with orthorhombic magnetic anisotropy and high mobility: (YBi)3(FeGa)5O12 and (YTmBi)3(FeGa)5O12/(110)GGG

New orthorhombic magnetic anisotropy garnet liquid phase epitaxial films with high mobility and low coercivity, (YBi)3(FeGa)5O12 and (YTmBi)3(FeGa)5O12/(110)GGG, have been successfully obtained. There are no hard bubbles, and wall states are either S = 0, 1, or −1. For 2 μm bubble material (YBi)3(FeGa)5O12/(110)GGG, mobility is μw = 85 m/s Oe and saturation velocity is Vs ≃130 m/s. For 6 μm bubble material (YTmBi)3(FeGa)5O12/(110)GGG, μw = 23 m/s Oe and Vs ≃130 m/s are observed. Vs ≃130 m/s for 2 μm bubble material assures bubble transfer at more than 10 MHz in a current access dual conductor device and utilization of the material for a magneto-optic readout head. Orthorhombic anisotropy for these materials is mostly growth induced. Growth-induced perpendicular anisotropies are not observed for eight other garnet systems on the (110)-GGG. Growth-induced orthorhombic anisotropy energy for Bi containing garnets is discussed using Gyorgy’s phenomenological parameters, A and B, compared with growth-induced anisotropy for (111)-oriented garnet films. A unique behavior of Y3+ in Bi containing garnets supports perpendicular anisotropy for orthorhombic anisotropy materials.