Growth mechanisms in GaAs-VPE at low deposition temperature

The VPE growth of GaAs in the system GaAs AsCl₃ with either H₂ or He as the Carrier gas was studied in the range of low deposition temperatures. Down to about 670 °C the growth in the H₂-system is limited by the kinetics of chlorine desorption by molecular hydrogen. The increase in growth rate at lower temperatures results from the onset of GaCl₃-desorption (disproportionation mechanism). The addition of NH₃ to the vapour phase enhances this effect. Below about 700 °C the growth rate in the GaAs AsCl₃ H₂ NH₃ system becomes comparable to that in the GaAs AsCl₃ He-system, where the GaCl₃ desorption mechanism is the only possible growth mechanism.     

Ein eindimensionales Modell zur Beschreibung von Transporteigenschaften in offenen Systemen

A simple one-dimensional model is dealt with describing the material transport by means of linear gas flow and diffusion. In the GaAs AsCl₃ H₂ system the dependence of the partial pressure on the x-coordinate is calculated, and the role of the temperature gradient near the growing interface is discussed in view of the constitutional supercooling of the gas phase.     

Free Enthalpy of Ternary Alloy Superlattice

Increments due to superlattice structure are formulated for the free enthalpy and some other thermodynamic entities as functions of composition, geometry parameters and temperature. Physical contents of the general expressions, derived for simple (quasi-regular) pseudobinary solutions, are illustrated by numerical data valid for the In_xGa_1–xAs/GaAs system. It is suggested that the free enthalpy of superlattice, is, at least at higher temperatures, largely dominated by the configuration entropy term. Corrections due to nonideality appear to be quite sizeable for the selected ternary alloy.     

A multi-wafer growth technique for GaAs vapor phase epitaxy using the AsCl3-Ga-N2 system with a horizontal reactor

A multi-wafer growth technique for vapor phase epitaxial GaAs has been developed using the open-tube AsCl₃-Ga-N₂ system with a conventional horizontal reactor. Use of this technique allows to process 4 wafers in a run with each wafer being 6 cm². The uniformities of growth rate, carrier concentration, and Hall mobility with wafer-to-wafer are typically ∽±3%, ∽±4%, and ∽±3%, respectively, and are shown to be sufficient for demanding microwave device applications.     

Das quaternäre Schmelzdiagramm Ga?As-P Sn

The pseudoternary cut Sn GaAs GaP of the quarternary system Ga As P Sn has been investigated in a temperature range from 860 to 1200°C. The calculation based on Vieland's method by use of Darken's quadratic formalism. A comparision between the solvents tin and gallium shows a higher solubility in tin for the mixed crystal Ga_xPAs_1−x and a stronger variation of the composition along the growth direction.     

Effect of Ampoule Rotation on Growth of InGaAs Ternary Bulk Crystals from Solution

In_xGa_1-xAs (x = 0.045) ternary bulk crystals were grown on GaAs seeds from an In–Ga–As solution by the temperature-difference method modified to rotate a growth ampoule. The effect of ampoule rotation on the profiles of the composition and the growth rate were investigated. The In compositional profiles were uniform irrespective of the ampoule rotation. On the other hand, the growth rate at the center of the crystal increased from 40 μm/h at 0 rpm to 55 μm/h at 100 rpm. The profile of growth rate changed from concave to convex toward the seed due to the ampoule rotation. Flow patterns and compositional profiles in the solution were simulated by solving four equations: Navier-Stokes, continuity, energy, and solute diffusion. The ampoule rotation enhanced the transportation of As component from the GaAs feed toward the seed at the central region in the solution. This led to the increase of the growth rate.     

Dislocation density in heteroepitaxial indium arsenide layers

In As layers have been grown by CVD on (111)B-oriented GaAs substrates. The dislocation density (N_D) distribution through the layer thickness has been studied. N_D is dependent on the mole fraction of AsCl₃ in the gaseous phase and, consequently, on the current carriers concentration. This results in the supposition that the decreasing of N_D in the layers after a “critical” thickness is due to the “pinning” of dislocations at impurity atoms which form stronger bonds with the host In or As atoms than the bond In–As, an effect which is known for bulk GaAs and InP crystals.     

Zum Wachstum von AIIIBV-Halbleitern aus nichtstöchiometrischen Schmelzen (II) Dotierung von GaAs und Ga1−xAlxAs mit Zink

Doping of GaAs and Ga_1−xAl_xAs with Zn in the LPE process was studied by a radioanalytical method. It is found that Zn diffuses from the Ga-(Al)-As-Zn-solution into the n-GaAs substrate before epitaxial growth starts. This “pre-diffusion” and the following diffusion of Zn out of the epitaxial layer into the substrate results in three regions with distinct Zn-graduation in the vicinity of the pn-junction. There are no striking differences for GaAs/GaAs and Ga_1−xAl_xAs/GaAs structures. The Zn concentration in GaAs epitaxial layers decreases exponentially from the substrate up to the layer surface. From this profile the temperature dependence of the Zn segregation coefficient is calculated. At 900°C a value k_eff = 5,2 · 10⁻² is found. The doping profile in Ga_1−xAl/As layers is more complex. It is influenced by the changings of temperature during the growth of the layer and by the nonuniform Aldistribution over the layer thickness.     

Experimental Determination and Thermodynamic Calcultions of the Relationship between Vapour Phase Composition and Mixed Crystal Composition in the Ga-HCI-PH3-AsH3-(NH3)-H2 System

The relationship between the composition of GaAs_1–xP_x layers and the composition of the vapour phase has been investigated experimentally and theoretically. Using KIRWAN'S equilibrium constants excellent agreement between calculated and experimental data is obtained over the whole composition range. Different models and parameters for the calculation of the soild solution activity coefficients result in only small differences for the calculated alloy composition so that no decision can be made from the experiments for one model to be preferred. Increasing addition of NH₃ to the vapour phase up to concentrations exceeding those of the crystal forming gases by an order of magnitude has no influence on the alloy composition, although the nitrogen concentration in the layers increases as deduced from the shift of the wavelength of the maximum photoluminescence intensity.     

Investigation of GaAs—InyGa1−yPzAs1−z–InxGa1−x-As grading heterojunctions formation

The initial stages of growth of GaAs–InGaAsP_var–In_xGa_1−xAs heterostructures (x = 0.1 and 0.17) were investigated for the equilibrium-cooling method of LPE growth. Similar investigations were carried out for GaAs–InGaAsP_var–In_0.05Ga_0.95As heterocompositions, but for the step-cooling technique. The scheme of growing of In_0.17Ga_0.83As films of GaAs substrates with several intermediate buffler InGaAsP_var layers is represented. These heterostructures were shown to have less than 10⁶ cm⁻² dislocation density on the overall area of the film (> 2 cm²).     

The Extrapolation Method in the Electron Probe Microanalysis

From the energy dependance of the k-ratio measured for the SbL_α and BiL_α-lines in the alloy system Bi_1–xSb_x the k-ratio at the critical energy E_c is determined by extrapolation. The stopping power correction is discussed for the system investigated here on the basis of the known composition of the specimens. The mean ionization potentials J for Sb and Bi are estimated from the experiments.     

Vapour epitaxial growth and characterization of InAs1-xPx

The vapour growth of InAs_1-xP_x layers has been carried out by the hydride process. The phosphorus rich part of the system (0.7 ? x ? 1) was especially investigated. Heteroepitaxial deposits of InAs_1-xP_x and InP have been performed on substrates such as InAs, GaAs and GaP. A systematic study of the influence of the substrate orientation on the quality of the layer has been carried out by growth on hemispherical substrates. Preferential planes have been pointed out: (100) and (111) A for InAs, (111) for GaAs and GaP. The band gap variation as a function of the composition has been determined by photoluminescence at 4.2 °K and X-ray diffraction measurements. It fits the equation: E_G(x) eV = 0.425 + 0.722 x + 0.273 x² at 4.2 °K.     

Effect of electrical field on growth of gallium arsenide layers from vapour phase

The effect of electrical fields on the growth rate and morphology of gallium arsenide layers in the GaAs AsCl₃ H₂ system is investigated. The fields both parallel and perpendicular to the substrate surface are used. It is found that application of the parallel field results n increase of growth rate of (111)A face but does not change that of 2° (001). The morphology of layers grown in such a field is better than that grown without any. The application of perpendicular field results in decrease of growth rate for both crystallographic orientations, the layer morphology worthening. In both cases the effect is greater when the substrate has a negative potential. Possible mechanisms of the field influence on the growth rates of gallium arsenide layers are discussed such as: supersaturation decrease because of nucleation in vapour phase and the change in the rates of surface processes.     

Metamorphic growth of tensile strained GaInP on GaAs substrate

Optical and structural properties of tensile strained graded Ga_xIn_1−xP buffers grown on GaAs substrate have been studied by photoluminescence, X-ray diffraction, atomic force microscopy, and scanning electron microscopy measurements. The Ga composition in the graded buffer layers was varied from x=0.51 (lattice matched to GaAs) to x=0.66 (1% lattice mismatch to GaAs). The optimal growth temperature for the graded buffer layer was found to be about 80–100 °C lower than that for the lattice matched GaInP growth. The photoluminescence intensity and surface smoothness of the Ga_0.66In_0.34P layer grown on top of the graded buffer were strongly enhanced by temperature optimization. The relaxation of tensile GaInP was found to be highly anisotropic. A 1.5 μm thick graded buffer led to a 92% average relaxation and a room temperature photoluminescence peak wavelength of 596 nm.     

Gas etching of GaAs monocrystalline substrates in the presence of Ga- and In sources

A special case of gas etching of GaAs substrates in the process of VPE in the presence of (Ga + In) source was investigated. The dependence of the etching rate on the source and the substrate temperature, and the AsCl₃ content in the gas flow was studied.     

Structural changes in molten (GaxIn1−x)As: Sound velocity measurements

Ultrasonic velocities, ν_s, in molten (Ga_xIn_1−x)As pseudo-binary alloys covering the whole composition range have been measured in detail in the temperature range from the liquidus temperature to 1280 °C under the saturated vapour pressure. The isotherm of ν_s shows a smooth increase from InAs to GaAs. Around the liquidus point, the temperature coefficient of the sound velocity is very small for the InAs and InAs-rich alloy. The results indicate that the sp³ resonance bonding reminiscent of the crystalline state gradually disappears with increasing temperature especially in the InAs-rich alloy.     

Optische Eigenschaften von Wismut–Antimon-Aufdampfschichten

The change in position and in magnitude of absorption peaks due to interband transitions E_i (i = 1, 2, 3) for Bi_xSb_1–x evaporated layers have been studied for different compositions in the range 0 ≦ (1 − x) ≦ 0.30 in the visible part of the spectrum. It has been founded nonlinear shiftings for all absorption peaks in function of layer composition. The joint density of states due to transition E₂ is more sensitive as the two other transitions with modification of alloy composition.     

Influence of the graduated composition region on the properties of GaInAs epitaxial layers grown on GaAs substrates

The electrical properties of Ga_1-xIn_xAs layers (0 < x < 0.3) are investigated. The layers are grown on <111> oriented GaAs substrates. A transition layer is grown with an increasing indium content to decrease the mismatch of the lattice parameters of the substrate and the final layer. A special many-section crucible is used. In dependence on composition the decrease both of mobility and carrier concentration with the increase of compensation is observed. These facts are connected with the introducing of additional acceptors without donor concentration changes.     

Electron-beam microprobe analysis of epitaxial GaxIn1−xP solid solutions

Ga_xIn_1–xP epitaxial layers were investigated by means of a scanning electron microscope X-ray microanalyser. The conditions for quantitative X-ray microprobe analysis are discussed. The growth of Ga_xIn_1–xP layers is possible on GaP substrates with x > 0,8 and on GaAs with 0,3 < x < 0,6. For the deposition of layers with 0,5 < x < 0,8 two substrate materials are possible: GaAs_1–xP_x or Ga_xIn_1–xP with suitable compositions. These materials must be epitaxially deposited by step by step layer growth or by vapour phase epitaxy, respectively.