Liquid Phase Epitaxial Growth Research Articles

Liquid phase epitaxy of KTiOPO 4 on KTi 1− xGe xOPO 4 substrates

We have studied the liquid phase epitaxy growth of KTiOPO 4 on several faces of KTi 1− x Ge x OPO 4 substrates as a function of the crystal face, growth time and level of substitution of Ge by Ti in the substrate. The best quality films were on the {1 0 0} and {2 0 1} faces. Only slight growth steps were observed on these faces in some experiments. The lowest quality of the films was on the {1 1 0} and {0 1 1} faces and the typical defects were hillocks. The worst quality of epitaxial growth was on the {1 0 1} face and pyramidal growth was detected in all cases. There was not observed diffusion of the Ge from the substrates to the film and the maximal change in refractive indices between substrate and film was of the order of 0.01.

Liquid phase epitaxy growth of langasite film for resonators and oscillators

We report the growth of crystalline langasite (LGS) films using the liquid phase epitaxy technique. Utilizing a eutectic PbO : Bi 2O 3 flux system we have demonstrated that epitaxial LGS films can be grown on a spinel substrate. The films were characterized by optical and electron microscopes and X-ray diffraction. Detailed analysis revealed that the crystalline langasite films grow epitaxially along the c-direction (in hexagonal setting) which is parallel to the (1 1 1) orientation of the cubic spinel substrate.

Liquid-phase epitaxial growth of Bi-2212 films using an infrared image furnace

We report on the liquid-phase epitaxial growth of the single-crystalline Bi2Sr2CaCu2Ox (Bi-2212) films. As in the case of the travelling solvent floating zone method, the Bi-2212 films are grown from a liquid phase by sweeping a heating zone. A specific point is that the liquid phase takes the form of a two-dimensional layer between two MgO substrates, which yields the excellent epitaxial growth. The films display a multigrain structure, and the maximum grain size is typically 1 mm in the in-plane directions and a few microns in thickness. The zero resistance state is attained at 86 K. From the x-ray rocking curves of the films and substrates, we infer that the mosaic structures in substrates degrade the crystallinity of the films. In the x-ray pole figure experiment we observe the misorientation angle of 12° between Bi-2212 [100] and MgO [100] directions as a major epitaxial state.

Ga 0.97Mn 0.03As epitaxial layers grown from Ga–Mn–As–Bi solutions by liquid-phase epitaxy

The liquid phase epitaxial growth of Ga 0.97Mn 0.03As from Ga–Mn–As and Ga–Mn–As–Bi solutions were investigated. The addition of 10 at.% of Bi to the Ga–Mn–As solution increases the growth rate of the grown epilayers nearly 4.4 times than in the case of Ga 0.97Mn 0.03As layers from Bi solution. Above 9 at.% of Bi in Ga solution, the problems associated with the edge growth were almost eliminated.

General theory of multi-phase melt crystallization

A new approach is presented which has wide-ranging application for the modeling and understanding of both open multi-phase crystallization from the melt while the temperature is decreasing, and isothermal crystallization from solution while solvent is evaporating. The results are widely applicable. Examples are given which relate to laboratory situations such as the liquid-phase epitaxial growth of complex III–V alloys and also to crystallization processes in oceans or sea water.

Specific features of the liquid-phase epitaxial growth of SiC epilayers in vacuum

4H-SiC epilayers were grown by a liquid-phase epitaxy in vacuum. It was found that the seed layer with steps characteristic of liquid-phase epitaxy should be preliminary deposited on the substrate. It is demonstrated that growth in a vacuum leads to a decrease in the concentration of uncompensated carriers Nd–Na to the level of 2×1016 cm−3.

Initial growth mechanism of Yba2Cu3Oycrystal on MgO substrate by liquid-phase epitaxy

Initial growth features of Yba2Cu3Oy (YBCO) crystal on an MgO substrate by a liquid-phase epitaxy (LPE) process were investigated and compared with homoepitaxial growth on a YBCO substrate. The partial dissolution of the seed grains in the initial stage of the LPE growth was influenced by the crystallinity of in-plane alignment of the seed grains, which could be explained by the preferential dissolution and growth mechanism. Concurrently, the slope angle of the growth grain varied with growth time. The opposite tendency of the slope angle change between the hetero- and the homoepitaxial growth was observed and could be explained by considering the difference in the step-advancing rates on each interface. It could be understood that the formation of entrapped liquid inclusions was the combination phenomena of both the small step-advancing rate of YBCO crystal on the MgO surface and the roughening of the MgO surface due to the partial dissolution of MgO to the solution.

ORDERED VERSUS DISORDERED InGaP LAYERS GROWN BY LIQUID PHASE EPITAXY

We make a comparative study of the optical and structural characteristics of two InxGa1-xP(x≈0.5 ) films nearly lattice matched to GaAs, (here referred to as disordered type 1 sample (S1) and ordered type 2 sample (S2)). The films were grown by liquid phase epitaxy (LPE). Photoluminescence (PL) measurements were performed in a wide temperature and exciting power density range for different polarization of the emitted radiation along the [110] and [1-10] directions. Observations suggest that the InxGa1-xP layer in sample 1 is disordered, as commonly obtained in LPE growth, while in sample 2 at least a partially spontaneously ordered layer was obtained. Moreover, the energy position of the 20 K PL peak is close to the predicted band gap energy for the InGaP 2 material ordered in the CuPt phase. [1].

Microstructural studies of YBCO films grown on MgO substrate with Y–Ba–Fe–O seeds by liquid phase epitaxy

Y–Ba–Fe–O (YBFO) thin films deposited by laser ablation were firstly used as seeds for liquid phase epitaxial (LPE) growth of YBCO films on MgO substrates. The film microstructure was characterized by transmission electron microscopy. Before the LPE growth of YBCO thick films, the YBFO seed films are very uniform with a fcc structure but not a typical 123 structure. The interface is usually flat between the YBFO film and MgO substrate. After the LPE growth of YBCO film, however, it was found that the YBFO seed layer was dramatically changed to be a layer with Ba–Cu–O and Cu–O mixture. The flat interface between the seed layer and the substrate was also changed to be very rough, indicating a chemical reaction occurred in the seed layer area during the YBCO LPE growth. The interfaces between the YBCO thick films and the seed layers keep flat and a high quality YBCO film can be still grown.

Optimization of seed film for fabrication of Y123 LPE film on metal substrate with MgO buffer layer

Study of liquid phase epitaxy (LPE) process has been developed. The LPE growth is affected by the seed film quality. To investigate the influence of the seed film quality on the LPE growth, we prepared several different kinds of seed films by pulsed laser deposition method, and dipped those samples into MgO-saturated Ba–Cu–O solution. It was found that the larger grain size and the in-plane alignment of seed crystals were desirable. In addition, the partially MgO substituted Y123 seed films improved the reproducibility of the LPE growth from MgO-saturated solution.

Growth mechanism of RE-Ba–Cu–O film on MgO substrate by liquid phase epitaxy

Hetero-epitaxial growth of YBa 2Cu 3O y (YBCO) crystals on MgO substrates has been investigated by comparing with the homo-epitaxial growth on a YBCO substrate, in order to clarify the initial growth mechanism of the liquid phase epitaxy (LPE). It was found that the slope angle of the growth grain varied with growing in the initial stage of the LPE growth. In the case of the homo-epitaxial growth, the slope angle decreased with growing the crystal. On the other hand, the slope angle increased with growing the crystal in the hetero-epitaxial growth. These phenomena could be explained by considering the difference in step-advancing rates between on the hetero- and homo-epitaxial interfaces. It was found that the hetero-epitaxial interface strongly affected the quality of the LPE film. The guideline for the high quality LPE film by the hetero-epitaxial growth could be obtained.

Characterization of YBa 2Cu 3O 7− δ films grown on NiO buffer layer by liquid-phase epitaxy process

By means of a liquid-phase epitaxy (LPE) process, superconducting YBa 2Cu 3O 7− δ (YBCO) thick film is grown on a biaxially textured NiO buffer layer which is pulsed-laser deposited on a (0 0 1) surface of SrTiO 3 single crystal. Employment of BaF 2-added Ba–Cu–O flux is found to be effective for LPE-YBCO growth because the growth temperature of YBCO is drastically lowered down to 900–920°C compared to the case of usually used simple Ba–Cu–O flux. This strongly suggests that the low-temperature LPE growth of YBCO on a NiO/Ni substrate is hopeful process for coated-conductor production. Superconductivity transition temperature ( T c) of the LPE-YBCO film is measured to be 91 K for onset and 87 K for a zero-resistance state.

Investigations on the growth and morphology of TiO 2 in the TiO 2–Na 2B 4O 7 system with and without impurities using a new LPE method

Liquid phase epitaxy (LPE) growth mechanisms and the effects of impurities were investigated using a new method. It was demonstrated that the Volmer–Weber mechanism operates on (0 0 1), a K face according to the Hartman–Perdok theory, whereas the Frank–van der Merve mechanism operates on (1 1 0), an F face, and on (1 1 1), an S face. It was also confirmed that tri-valent cations with ionic radii close to Ti 4+ ions transform the character of the (1 1 1) face from an S face to a K face, producing a greatly accelerated growth rate in the c-axis direction, whereas the same impure ions reduce the growth rate on the (1 1 0) face. This difference is well represented in the change of the surface morphologies of the respective faces. The observed morphological changes are interpreted on the assumption that oxygen ions around Ti 4+ ions are destabilized by the adsorption of tri-valent cations, leading to breaking the PBC in the (1 1 1) face.

Physics and technology of mid–infrared light emitting diodes

There is increasing interest in mid–infrared (mid–IR) light emitting diodes which operate in the 2–5 μm spectral region. Efficient LEDs operating at the characteristic absorption wavelengths of target gases, such as CH 4 , CO 2 and CO, have great potential for the next generation of optical gas sensors. The fundamental difficulties associated with realizing suitable mid–IR LEDs at different wavelengths, with high continuous wave (CW) output power at room temperature, relate principally to quantum efficiency and optical extraction of the light. Each of these will be briefly considered. Some of the different device designs and techniques used for the suppression of non–radiative Auger recombination and the reduction of Shockley–Read–Hall centres are discussed. Liquid phase epitaxy (LPE) continues to hold a strong position in mid–IR LED technology and many of the best LEDs currently available have been fabricated using this technique. In this respect, the LPE growth of associated InAs(Sb)–based epitaxial structures and their purification is briefly reported. An overview of the ‘state of the art’ is also given with respect to the application of mid–IR LEDs in practical gas sensors.

YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// thick films grown on textured metal substrates by liquid-phase epitaxy process

Towards high-current wire application of high-temperature superconductors, YBa/sub 2/Cu/sub 3/O/sub 7-/spl delta// (YBCO) thick films are grown by means of a liquid-phase epitaxy (LPE) process on a [001] surface of NiO single crystal and laser-sputtered NiO buffer layer deposited on a [001] surface of SrTiO/sub 3/ single crystal. NiO buffer layers can be rapidly formed on textured Ni tape by the recently developed surface-oxidation-epitaxy (SOE) technique which is expected to be a low-cost production method of long metal substrates with highly-textured oxide buffer layer. LPE growth on SOE-buffered textured Ni tapes are also attempted. Moreover, we successfully prepared /spl sim/0.1 m-long LPE-YBCO tapes on {120} Ag-0.1 wt.% Cu alloy tape by using a specially designed LPE furnace equipped with a reel-to-reel attachment. BaF/sub 2/-added BaO-CuO flux is used in this work, in which the growth temperature of YBCO is drastically lowered from the usually used value of /spl sim/1000/spl deg/C down to 900-930/spl deg/C. While current transport performances of these LPE-YBCO films are still insufficient for high-current wire application, the present results show the high potential of this LPE process for long-length coated-conductor production.

Liquid phase epitaxial growth of 3C-SiC films deposited on Si

In this paper, we present a novel method to grow 3C-SiC crystal in a liquid-phase epitaxy-like manner, but without any substantial substrate. The starting material to be used in this method is the 3C-SiC-thin film deposited on Si substrate in a gas-phase heteroepitaxial technology. The free 3C-SiC film which remained of the molten Si substrate epitaxially grows up from the Si solution saturated by SiC in a highly purified graphite crucible heated by an inductive heater. XRD, XPS and Raman spectroscopy were used to characterize the samples. The only one peak with full width at half maximum (FWHM) of 0.2 at 2θ=35.65° in XRD is attributed to the diffraction of (111) planes in 3C-SiC. The energy difference between C1s and Si2p binding energy in XPS data is 183.2 eV, which is well consistent with the result published before for single crystal 3C-SiC. Although the only sharp and strongest peak at 796.6 cm −1 in the Raman spectrum also confirms the crystal structure, the additional broadened weak peak at 523.6 cm −1 may imply the existence of some lattice defects related to nitrogen unintentionally introduced in the growth process.

Influence of LPE growth conditions on the electroluminescence properties of InP/InGaAs(P) infrared emitting diodes

Liquid phase epitaxial growth of InP/InGaAs(P) infrared emitting diodes was studied systematically. Small area surface emitting LED chips were prepared to cover completely the 1100–1700 nm wavelength ranges. Nine different diodes were fabricated with optimal spacing of the peak emission wavelengths in order to have sufficient overlapping of their spectra. Efficient LEDs with narrow spectra have been realised by careful selection of the layer structure and growth conditions. Thick active layers with constant composition and abrupt interfaces have been grown for each emission wavelength. The long wavelength diodes (1275–1675 nm) were grown with additional quaternary layer(s) to prevent the melt-back of the active layer by InP melt. Low growth temperature (590°C) was used to prepare the LED structures. In the spectral range of 1250–1520 nm higher growth temperatures (625–645°C) were necessary to improve the device parameters. Such phenomena confirm the existence of the miscibility gap in the InGaAsP quaternary crystal system. Quaternary layers grown in the middle of the immiscibile region showed non-uniform composition and ragged interfaces at the upper heterojunction.

LPE growth of RE123 crystals from NiO saturated solution

We tried to apply NiO materials as a buffer layer for LPE (Liquid Phase Epitaxy) coated conductors with Ni substrate. We confirmed that NiO could suppress the reaction between NiO/Ni substrate and solution saturated with NiO. On the other hand, NiO addition to the solution decreased the peritectic temperature of the Y123 and increased the crystallization temperature of the Ba-Cu-Ni-O compound. This makes it difficult to grow the Y123 crystal from the NiO saturated solution. Instead of Y123, we selected Sm123 which has a higher peritectic temperature than Y123, and confirmed that Sm123 could be grown stably from the NiO saturated solution not only on MgO substrate but also Ni substrate. Because of its low T/sub c/ value of Sm123 grown from the NiO saturated solution, the (Y,Yb)123 layer was epitaxially grown as the superconductive layer on it from the solution without NiO.

MgO飽和LPEプロセスを用いた二重構造希土類系高温超電導線材の作製

In our study, we have developed coated conductors using the LPE (Liquid Phase Epitaxy) method. We found that MgO saturated solution can prevent the Metal solution reaction. It is also found that double LPE structured films on MgO crystals exhibit the Tc value of 90 K. We succeeded in producing a film consisting of YBa2Cu3Oy/YBa2(Cu, Mg)3Oy by LPE growth on MgO buffer/Hastelloy. However, 1st LPE layer was unstable during the second LPE growth. Therefore, we discussed the thermodynamics about the LPE layer growth, and realized that the lower growth temperature is advantageous for the second LPE. Finally, we succeeded in producing the double LPE layer structure without meltback of the 1st layer.

Observation of anisotropic initial growth nucleation in liquid phase epitaxy of InP

Liquid-phase epitaxial growth of InP was performed at constant growth temperature by the temperature difference method under controlled vapor pressure on InP substrates. Growth temperature was kept constant from 550°C to 280°C. The as-grown surface morphology was investigated by Nomarski interference optical microscope and electron microscope. The anisotropic initial growth nuclei are investigated on {0 0 1},{1 1 1}A,B and {1 1 0} oriented InP substrates. This anisotropic behavior is discussed in view of the anisotropy of lateral growth rate due to the preferential surface migration and sticking at specific kinks and steps on the surface.