Liquid Phase Epitaxial Growth Research Articles

Selective epitaxial growth of GaAs by current controlled liquid phase epitaxy

Selective epitaxial growth of Te-doped GaAs on circularly patterned GaAs (100) substrate was investigated by liquid phase epitaxy (LPE) and current controlled liquid phase epitaxy (CCLPE). SiNx was used as a mask layer to fabricate circular windows on the substrate and the effect of various growth periods and current densities on the growth morphology were investigated. A truncated pyramid like structure with a vertical thickness of 337μm and a lateral thickness of 268μm was achieved on the circularly patterned substrate at 6h growth with an applied current density of 20Acm−2. The vertical growth was increased almost one order and lateral growth was increased up to nine times compared to standard LPE growth. The growth step density was higher at window walls and it caused relatively higher growth compared to its centre. The surface morphology and selective epitaxial growth were greatly improved by an applied DC electric current. The dislocation density of the grown epilayer was significantly reduced when compared with that of the substrate. Solute transport in the solution was enhanced by the electromigration of solute by an electric current, which enhanced growth in vertical and lateral directions.

Growth of GaAs/AlxGa1−xAs layers by LPE method and their characterization by SIMS

Growth of thin layers of compound semiconductors such as GaAs and Alx Ga1−x As was obtained by Liquid Phase Epitaxy (LPE) at 838–828 ° C in thickness range of 0.1–4.3 μm which was estimated by Scanning Electron Microscopy (SEM). By Secondary Ion Mass Spectroscopy (SIMS) measurements, type of impurity atoms and their density and uniformity with respect to thickness were measured. In this way we are sure that variation of impurity atoms such as Si, Te, Sn and Ge indicates that epilayers were formed uniformly and it demonstrated that the LPE growth was a suitable way to obtain a good quality of epitaxy layers. Amount of composition parameter x in the compound semiconductor AlxGa1−xAs was measured which varies from 0.13 to 0.4. In-depth profiles of SIMS indicated that Al atom can be replaced by Ga atom in the GaAs crystalline structure.

Characterization and optical properties of ZnS nanorods branched out from ZnS film on Zn foil

AbstractComplex nanomaterial‐film‐metal substrate architectures, which are composed of ZnS nanorods, island‐like ZnS film and Zn foil, have been formed via a simple vapor deposition route. The growth of the complex nanostructures is initiated by the preferred formation of ZnS film, and ZnS nanorods branches out from ZnS film flows a liquid‐phase epitaxial growth mode. The ZnS nanorod is switched to an angle, which may be attributed to the sudden change of vapor pressure and temperature reduction by the end of vapor deposition process. The room‐temperature photoluminescence spectrum shows that complex ZnS nanostructures have a strong blue emission band centered at about 423 nm and a weak broad green emission band centered at about 515 nm. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Transport of nitrogen atoms during liquid phase epitaxial growth of InAsN and GaAsN

We have used a one-dimensional diffusion model to investigate the transport of nitrogen during a liquid phase epitaxial growth of InAsN layers from Bi and In solvents and GaAsN layers from Ga solvent. The concentration profile of nitrogen near the growing interface has been obtained for the materials for different melt supercooling and cooling rates. Experimental results on the growth of InAsN layers from Bi solutions using the optimum growth parameters suggested by the study are shown.

The Application of Simulation and Optimization in the Growth of High-Purity Silicon Thin Film on Low-Purity Silicon Substrate by Liquid Phase Epitaxial

This paper describe a method in the growth of high-purity Si thin film on low-purity silicon substrate by liquid phase epitaxial (LPE) growth, in order to eliminate the effect of melt substrate on the matrix, we simulate the matrix temperature effect on the epitaxial substrate temperature choice and the growth of thin film thickness with the growth time, then we carried out experiment according to the simulation result. Through the analyses experimental results, we found that on the low-purity silicon substrate can grow very good high-purity silicon thin film by liquid phase epitaxial (LPE) growth and thickness with growth time have little difference between the simulation. So we come to the conclusion: The growth of high-purity Si thin film on low-purity silicon substrate by liquid phase epitaxial (LPE) growth is a good way to make solar cell material; through the numerical simulation, we can effectively reduce the test energy consumption and test repeat times, which provide a good theoretical basis for the experiment successfully conduct.

KY 0.58Gd 0.22Lu 0.17Tm 0.03(WO 4) 2 buried rib waveguide lasers

CW mirrorless laser operation at 1840 nm at room temperature was observed in buried rib waveguides of KY 0.58Gd 0.22Lu 0.17Tm 0.03(WO 4) 2 fabricated by structuring KY(WO 4) substrates by Ar-ion milling and subsequent liquid phase epitaxial growth of the active layer on these substrates. Laser efficiency and laser threshold seems to change with the width of the channels fabricated.

Epitaxial Growth of NaGd0.935Yb0.065(WO4)2 Layers on Lattice Matched Tetragonal Double Tungstate Substrates for Ultrafast Thin Disk Lasers

Liquid-phase epitaxial growth of Yb 3+ doped NaGd(WO 4 ) 2 crystalline layers has been obtained on Y modified NaGd(WO 4 ) 2 Czochralski grown single crystal substrates. It is shown that the lattice parameter of the layer and substrate can be equalized by proper selection of the Yb and Y compositions. The epitaxial layers obtained are highly transparent, with thicknesses in the range 10―70 μm, and with crystallographic quality close to that of the used substrates. The spectroscopic properties of Yb 3+ in the layer are anisotropic and similar to those of Yb-doped NaGd(WO 4 ) 2 single crystals. The layers are envisaged as optical gain media for the design of ultrafast modelocked thin disk lasers.

Strained single-crystal GOI (Ge on Insulator) arrays by rapid-melting growth from Si (1 1 1) micro-seeds

Liquid-phase epitaxial growth of Ge islands on insulator (GOI) using Ni-imprint-induced Si (1 1 1) micro-crystal seeds (∼1 μm ϕ) is proposed. As a result, single-crystalline GOI (1 1 1) structures with large area (∼10 μm ϕ) are realized. The transmission electron microscopy observations reveal no dislocation or stacking fault in the laterally grown regions. Moreover, the Raman measurements show that the tensile strain (∼0.2%) which enhances the carrier mobility is induced in the growth regions. This new method can be employed to realize the multi-functional SiGe large scale integrated circuits.

Low-temperature LPE growth and characterization of InGaAsN thick layers

Abstract This work demonstrates the possibility for low-temperature Liquid-Phase Epitaxy (LPE) growth of lattice matched to GaAs substrate dilute nitride InGaAsN layers with good crystalline quality and high Hall electron mobility. X-ray microanalysis and X-ray diffraction methods have been used to determine the composition and crystalline quality of the grown InGaAsN layers. Surface roughness is examined by atomic force microscopy. N-related local vibration modes are observed by Raman scattering. The Hall electron mobility and free carrier concentration have been measured in the temperature range 80-300K by conventional Van der Pauw method.

Mirrorless buried waveguide laser in monoclinic double tungstates fabricated by a novel combination of ion milling and liquid phase epitaxy

Buried channel waveguides were fabricated by liquid phase epitaxial growth of a lattice-matched KY(0.58)Gd(0.22)Lu(0.17)Tm(0.03)(WO4)2 film on a microstructured KY(WO4)2 substrate. Channels were transferred to the substrates by standard photolithography and Ar-ion milling. The bottom and sidewalls of the milled channels were smooth enough (rms roughness = 70 nm and 20 nm, respectively) to favour the epitaxial growth of the active layer without defects at the boundary of substrate/epitaxial layer. The refractive index contrast was sufficient to enable light confinement and guided modes with low scattering losses were observed at wavelengths between 1440 nm and 1640 nm. CW laser operation at 1840 nm at room temperature was observed with feedback provided only by Fresnel reflection at the end faces, with slope efficiencies of 4% and 9% for TE and TM polarizations, respectively.

Low bandgap GaInAsSbP pentanary thermophotovoltaic diodes

The liquid phase epitaxial growth of pentanary GaInAsSbP lattice matched onto InAs substrates is reported for use in narrow bandgap thermophotovoltaic cells. The epitaxial layers were characterised and exhibited bright photoluminescence up to room temperature. Prototype thermophotovoltaic cells were fabricated, which were sensitive in the mid-infrared spectral range having cut-off wavelengths in the range 4.0–4.5 μm at room temperature.

Narrow gap III–V materials for infrared photodiodes and thermophotovoltaic cells

The paper describes liquid phase epitaxial growth and characterization of the GaSb- and InAs-related materials for the photodiodes and thermophotovoltaic applications. It was shown that doping of the melt with holmium results in obtaining the high purity GaInAsSb and InAs layers. The passivation with the 1 M Na 2S aqueous solution makes it possible to prepare flat growth surfaces of GaSb(1 0 0) and InAs(1 0 0) substrates after annealing. A reproducible technique has been developed for fabrication of the high-efficiency GaInAsSb/GaAlAsSb and InAs/InAsSbP photodiodes with the long-wavelength photosensitivity edge of 2.4 and 3.8 μm, respectively. Room temperature detectivity in the spectral peak reaches D∗ = (0.8–1.0) × 10 11 W −1 cm Hz 1/2 for the GaInAsSb/GaAlAsSb photodiodes and D∗ = (3.0–5.0) × 10 9 W −1 cm Hz 1/2 for the InAs/InAsSbP devices. We have adapted the technology for thermophotovoltaic cells operating at an emitter temperature of 1000–1700 °C.

A thermodynamic analysis of native point defect and dopant solubilities in zinc-blende III–V semiconductors

A thermodynamic model is used to analyze available experimental data relevant to point defects in the binary zinc-blende III–V compounds (Ga,In)-(P,As,Sb). The important point defects and their complexes in each of the materials are identified and included in the model. Essentially all of the available experimental data on dopant solubility, crystal density, and lattice parameter of melt and solution grown crystals and epilayers are reproduced by the model. It extends an earlier study [Hurle, J. Appl. Phys. 85, 6957 (1999)] devoted solely to GaAs. Values for the enthalpy and entropy of formation of both native and dopant related point defects are obtained by fitting to experimental data. In undoped material, vacancies, and interstitials on the Group V sublattice dominate in the vicinity of the melting point (MP) in both the phosphides and arsenides, whereas, in the antimonides, vacancies on both sublattices dominate. The calculated concentrations of the native point defects are used to construct the solidus curves of all the compounds. The charged native point defect concentrations at the MP in four of the six materials are significantly higher than their intrinsic carrier concentrations. Thus the usually assumed high temperature “intrinsic” electroneutrality condition for undoped material (n=p) is not valid for these materials. In GaSb, the GaSb antisite defect appears to be grown-in from the melt. This contrasts with the AsGa defect in GaAs for which the concentration grown-in at the MP is negligibly small. Compensation of donor-doped material by donor-Group III vacancy complexes is shown to exist in all the compounds except InP where Group VI doped crystals are uncompensated and in InSb where there is a lack of experimental data. The annealing effects in n+ GaAs, including lattice superdilation, which were shown in the earlier paper to be due to Group III vacancy undersaturation during cooling, are found to be present also in GaSb and InAs. Results for native point defects are compared with reported “first principles” calculations for GaAs. It is seen that, while there is some accord with experimental findings for low temperature molecular beam epitaxial (MBE) growth, they fail totally to predict the behavior under high temperature growth conditions. The analysis of data on liquid phase epitaxy (LPE) growth of GaAs from Bi solution in the earlier paper has been re-calculated in the light of experimental data that showed that the model used in that paper to represent the Ga–As–Bi phase equilibria was inadequate. An improved model reveals that Ga vacancies exert a greater effect in controlling the extent of the linear range of donor dopant solubility than previously predicted. It has also led to a re-evaluation of the equilibrium EL2 and Ga vacancy concentrations in GaAs during MBE growth under As-rich conditions at low temperatures (∼500 K). The amended model predicts that the very high concentrations of EL2 and of Ga vacancies observed experimentally are near equilibrium values. The predicted increase in the equilibrium concentrations of these defects at low temperatures results from coulombic attraction between the two defects. At temperatures somewhat lower than 500 K the rate of increase becomes catastrophic.

Crystal growth and characterization of epitaxial layers of laser and nonlinear optical materials for thin-disk and waveguide laser applications

This paper summarizes the main results we obtained in our laboratories in relation with crystalline layers obtained by Liquid Phase Epitaxial growth of lanthanide doped KLu(WO 4) 2 and Nb:RbTiOPO 4 grown on KLu(WO 4) 2 and RbTiOPO 4 substrates, respectively. Macroscopic defect free epitaxial layers were grown and characterized in terms of their compositional homogeneity, structural stress in the layer/substrate interface and laser and waveguiding performances.

ZnO nanorods on ZnO seed layer derived by sol–gel process

Well-aligned ZnO nanorods are obtained by a liquid phase epitaxial growth on the indium-doped tin oxide glass deposited with a ZnO thin film as the seed layer, which is prepared by combining a sol–gel process and a spin coating technique. The effects of water content in the sol and heat treatment temperature on the properties of the ZnO thin film are investigated. Relationship among the seed layer, the growing time, the growing temperature, the concentration of Zn2+ in the solution, the anions in the solution and the resulting ZnO nanorods are discussed in detail. X-ray diffraction analysis and scanning electronic microscopy are employed to characterize the structural and morphological properties of the resulting ZnO nanorods. Results indicate that the ZnO nanorods with a preferred orientation show a single crystal with a wurtzite structure in the direction of [0001], the diameter of the ZnO nanorods seems to depend on the size of the seed grain, while the length of the ZnO nanorods is determined by the growing time and the growing temperature.

Liquid-phase epitaxial growth of Ge island on insulator using Ni-imprint-induced Si crystal as seed

Liquid-phase epitaxial growth (LPE) of Ge islands on insulator (GOI) using Ni-imprint-induced Si (111) crystal seeds (~ 1 μmϕ) is investigated. By optimizing cap and bottom SiO 2 layer thickness, single-crystalline GOI (111) structures (~ 10 μmϕ) are realized. The Raman peaks due to Ge–Ge bonds of the growth regions reveal that the full width at half maximum (FWHM) is equal to that of single-crystalline Ge bulk wafers (3.2 cm − 1 ). This result demonstrates the very high crystal quality of the growth regions.

Study of the metastable region in the growth of GaN using the Na flux method

It was revealed that the metastable region, in which liquid phase epitaxy (LPE) of GaN single crystals proceeds without the generation of polycrystals, expands with growth temperature in the Na flux method. The metastable region appears when LPE growth proceeds at temperatures above 1073 K, although generation of polycrystals inevitably occurs on a crucible at temperatures less than 1073 K. The highest growth rate of 14 μm/h in a small experimental setup was achieved at a temperature of 1163 K with a nitrogen pressure of 5.5 MPa due to complete suppression of the growth of polycrystals on a crucible, even though the supersaturation at this condition reached a fairly high level. Also, an LPE crystal with a flat surface could easily be obtained under high-temperature conditions.

Properties of gallium- and aluminum-doped bulk ZnO obtained from single-crystals grown by liquid phase epitaxy

Bulk properties of gallium (Ga)- and aluminum (Al)-doped zinc oxide (ZnO) were studied using bulky single-crystalline thick films grown by liquid phase epitaxy (LPE). The highest possible dopant concentration was 1×10 19 cm –3 for LPE growth at around 800 °C. The electron concentration was nearly same to the Ga and Al concentrations. The donor binding energy decreased to nearly zero with an increase in dopant concentration, and electron mobility of the sample with relatively high dopant concentration (1×10 19 cm –3) was more than 60 cm 2 V –1 s –1 at room temperature. The LPE technique is a potential solution for the production of ZnO for optical applications because the well-defined excitonic luminescence could be seen from the LPE-grown-doped single-crystals.

A phase-field/Monte-Carlo model describing organic crystal growth from solution

In this paper work we present a phase-field/Monte-Carlo hybrid algorithm for the simulation of solutal growth of organic crystals. The algorithm is subsequently used for an investigation of diffusion effects on the growth mechanisms. This method combines a two-scale phase-field model of the liquid phase epitaxial growth and a Monte-Carlo algorithm of the 2D nucleation and thus is faster than previous purely Monte Carlo simulations of crystal growth. The inclusion of supersaturation and diffusion in the method allows the study of crystal growth under various growth conditions. Parameters used in the hybrid algorithm are bound to the energetic parameters of crystal faces, which can be estimated from a detailed study of the actual crystal structure based on a connected nets analysis, which allows the prediction of the shape and morphology of real crystals. The study of the diffusion effect is carried out based on an example of a hydroquinone crystal, which grows from the water solution at various supersaturations. The dependencies of the growth rate and the nucleation rate on the supersaturation indicate the change of the growth mechanism from spiral growth to 2D nucleation. The difference in the growth rate for various faces is in agreement with the crystal morphologies derived from the attachment energy method and observed experimentally. The main result of the simulation is the evaluation of engineering limits for choosing appropriate external process conditions.

UV emission on a Si substrate: Optical and structural properties of γ‐CuCl on Si grown using liquid phase epitaxy techniques

AbstractConsiderable research is being carried out in the area of wide band gap semiconductor materials for light emission in the 300–400 nm spectral range. Current materials being used for such devices are typically based on II–VI and III‐nitride compounds and variants thereof. However, one of the major obstacles to the successful fabrication of III‐N devices is lattice mismatch‐induced high dislocation densities for epitaxially grown layers on non‐native substrates. γ‐CuCl is a direct bandgap material and an ionic wide bandgap I–VII semiconductor with a room temperature free exciton binding energy of ∼190 meV (compared to ∼25 meV and ∼60 meV for GaN and ZnO, respectively) and has a band gap of 3.4 eV (λ ∼ 366 nm). The lattice constant of γ‐CuCl (0.541 nm) is closely matched to that of Si (0.543 nm). This could, in principle, lead to the development of optoelectronic systems based on CuCl grown on Si. Research towards this end has successfully yielded polycrystalline γ‐CuCl on Si(100) and Si(111) using vacuum‐based deposition techniques [1]. We report on developments towards achieving single crystal growth of CuCl from solution via Liquid Phase Epitaxy (LPE) based techniques. Work is being carried out using alkali halide flux compounds to depress the liquidus temperature of the CuCl below its solid phase wurtzite‐zincblende transition temperature (407 °C [2]) for solution based epitaxy on Si substrates. Initial results show that the resulting KCl flux‐driven deposition of CuCl onto the Si substrate has yielded superior photoluminescence (PL) and X‐ray excited optical luminescence (XEOL) behavior relative to comparitively observed spectra for GaN or polycrystalline CuCl. This enhancement is believed to be caused by an interaction between the KCl and CuCl material subsequent to the deposition process, perhaps involving a reduction in Cl vacancy distributions in CuCl. This paper presents a detailed discussion of a CuCl LPE growth system as well as the characterization of deposited materials using X‐ray diffraction (XRD), room temperature and low temperature PL, and XEOL. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)