Current Controlled Liquid Phase Epitaxy Research Articles

Growth of 4H-SiC in Current-Controlled Liquid Phase Epitaxy

4H-SiC crystallization from Si-C solution in electric current-controlled liquid phase epitaxy was investigated. The dependence of growth speed on a DC current shows that dissolution/growth is controlled by the electric current without altering temperature gradient in the furnace. Application of an electric current leads to reduction of growth speed with negative polarity and enhancement of growth speed with positive polarity. The variation of the growth speed with a DC current density has been explained by the combination of the effects of electromigration of C solute and Joule heating.

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.

Orientation-dependent epitaxial growth of GaAs by current-controlled liquid phase epitaxy

The orientation dependence of the selective epitaxial growth of Gallium Arsenide (GaAs) has been investigated to achieve a thick epitaxial layer for application to X-ray detectors. Selective epitaxial growth was carried out on patterned GaAs with [0 1 1], [0 1 2], [0 1 0], [0 1 −2], [0 1 −1] and their equivalent seed orientations by current-controlled liquid phase epitaxy (CCLPE). SiO 2 was used as a mask layer to fabricate the various seed orientations on the Si-doped GaAs (1 0 0) substrate and various growth periods and current densities were considered. Solute transport in the solution was enhanced by the electromigration of solute by an applied DC electric current, which caused an incremental growth in vertical and lateral directions in all orientations. The highest vertical thickness of 268 μm in the [0 1 −1] orientation and the largest lateral growth of 318 μm in the [0 1 2] orientation were achieved at 7.5 A cm −2 current density for 6 h. The seed aligned in the [0 1 2] orientation was favorable for high lateral growth of GaAs. The [0 1 1], [0 1 0] and [0 1 −2] seed orientations were suitable for application in a GaAs X-ray detector.

Effect of an applied electric current in epitaxial growth of GaAs layer on patterned GaAs substrate

Selective epitaxial growth of a GaAs layer on SiNx masked Si-doped semi-insulating (100) GaAs substrate was performed by current-controlled liquid-phase epitaxy (CCLPE) in the conventional liquid-phase epitaxy. Experiments were carried out with and without the application of electric current. Surface morphology of (100) facet of the grown layer and the vertical and lateral growth rates were significantly improved under applied electric current. A thick layer of about 330μm was achieved at relatively low growth time of 6h with a current density of 20Acm−2. The epitaxial growth is realized by both electromigration of the solute and supercooling under a constant rate of furnace cooling. The dislocation density of the grown layer was significantly reduced, compared with that of the substrate (4×104cm2).

Studies on the growth mechanism of InGaAs during current controlled liquid phase epitaxy

A theoretical model based on the diffusion and electromigration of the solute atoms has been developed to understand the growth mechanism during current controlled liquid phase epitaxy of InGaAs. In the present study, expressions have been generated using a phase diagram relationship to determine the composition variation of the solute atoms under different growth conditions. Growth rate and thickness of the epitaxial layers have been calculated in the absence and presence of convection and found to vary as a function of applied current density and growth period.

Investigation on the concentration profiles of As during the current-controlled liquid phase epitaxial growth of GaAs

Current-controlled liquid phase epitaxy (CCLPE) is a novel method for growing epitaxial layers with precise control of thickness and composition. In the present study, a theoretical model has been developed to understand the growth kinetics of GaAs based on the diffusion and electromigration of solute atoms. Concentration profiles have been simulated by incorporating Peltier effect and electromigration. The growth rates in the absence and presence of convection due to Peltier effect and electromigration are calculated. The results are discussed in detail.

Current controlled liquid phase epitaxial growth and characterization of InGaAsP

The current controlled liquid phase epitaxy (CCLPE) or electroepitaxy growth technique has been employed for the first time to grow lattice matched In 1 - x Ga x As y P 1 - y quaternary layers with composition in the range of 0 < x < 0.47 on (100) InP substrates at a constant furnace temperature of 650°C. The growth results showed a linear relationship between the growth rate of the epilayer and current density (up to 15 A/cm 2). The growth rate varied from 0.62 μm/min for In 0.53Ga 0.47As to 0.03–0.05 μm/min for quaternary layers corresponding to a wavelength of ≌ 1.3 μm, at a current density of 10 A/cm 2. X-ray diffraction measurements showed good lattice match between the epilayer and the substrate. The experimental data are compared with the derived numerical results based on the existing model.

Diffusion coefficient and differential mobility of As in In for LPE and current controlled LPE

InAs has been grown on undoped InAs substrates by liquid phase epitaxy (LPE) and current controlled LPE (CCLPE) in the temperature range of 570 to 670°C. From the LPE growth rate versus temperature results, the diffusion coefficient of As in In was calculated to be D = 525exp[ -(1.4 × 10 4) T ] cm 2 with an activation energy for diffusion of 1.2 eV (27.8 kcal/mol). CCLPE growth results indicated a linear relationship between the growth rate of InAs and the current density. The differential mobility of As in In was computed as μ = 0.9 × 10 -2 cm 2/ V· s at 620°C.

Characterization of GaAs layers grown on polycrystalline GaAs by LPE and current controlled LPE

It is the purpose of this paper to investigate the suitability and effectiveness of growth of thin GaAs layers on polycrystalline GaAs substrates by liquid phase epitaxy (LPE) and current controlled LPE (CCLPE). During each growth run LPE and CCLPE were used to grow thin GaAs layers on two large-grain polycrystalline GaAs substrates cut from the same wafer and simultaneously placed in the same growth system. The grain boundary was exposed by cleaving the samples perpendicular to the grain boundary. Notnarski contrast, SEM, C-V and Hall measurements were performed in order to determine the surface morphology, discontinuity of epilayer at the grain boundary, epilayer thickness unform-ity, resistivity (in directions parallel and perpendicular to the grain boundary), and dopant concentration. The CCLPE system was carefully designed so that growth would take place only by electrotransport in the absence of convection or Peltier cooling. The results indicate that CCLPE yields layers with improved surface morphology and thickness uniformity as compared to those grown by LPE. In some samples the epilayer was discontinuous at certain grain boundaries. Results are presented on CCLPE growth rate dependence upon grain orientation, current density, and continuity of the epilayer at the grain boundary.

Current controlled liquid phase epitaxial growth of Hgl−xCdxTe

Using the technique of current controlled liquid phase epitaxy we have grown crystalline layers of Hgl-xCdxTe from a Hg-melt. Best results were obtained on (111) oriented substrates. The dominant mechanism of solute transport is electromigration rather than the Peltier effect. Composition (x ≈0.1) and homogeneity across a sample surface (Δ x ≈ 0.03) was determined by the electrolyte electroreflectance method.

Use of current controlled GaAs l.p.e. for optimum doping profiles in l.s.a. diodes

Microwave device quality GaAs, grown by the electric current-controlled liquid-phase epitaxy method, is reported. Ratios of peak current to valley current near the theoretical limit for the corresponding layer doping and thickness are reported, along with high breakdown voltages in unloaded l.s.a. oscillators.

Electric current controlled liquid phase epitaxy of GaAs on N+ and semi-insulating substrates

Electric current controlled liquid phase epitaxy (LPE) of GaAs has been performed on both n+ and semi-insulating substrates. Growth is induced by current flow across the substrate-melt interface. The furnace temperature is held constant during growth so that direct electrical control of the growth process is achieved. The dependence of the growth rate on both the electric current density across the substrate-melt interface and the ambient furnace temperature was determined. Current densities from 5 to 20 A/cm2 were employed and furnace temperatures ranging from 680 to 800°C were used. Sustained steady state growth rates as small as 0.022μm/min and as large as 1.4μm/min were obtained. For a given furnace temperature and current density, the measured growth rates on semi-insulating substrates range from 48% to 77% of the rates obtained on n+ n substrates. The surface morphology of the epitaxial layers is observed to depend on the electric current density employed during growth. Electric current controlled doping modulation was studied in epitaxial layers grown from unintentionally doped melts. The degree of doping modulation achieved is approximately proportional to the change in applied current density. Approximately a 40% increase in the net electron concentration is obtained by changing the current density from 10 to 30 A/cm2 during growth. Preliminary experiments with tin doped epitaxial layers indicate that similar changes in the amount of tin incorporation can be achieved.