Dislocation density in InxGa1–xAs films grown on GaAs substrates with intermediate buffer layer InGaAsP of variable composition

In_xGa_1–xAs films with x = 0.03 and 0.05 were grown from an In Ga As P liquid phase. Because of high value of distribution coefficient of P we have heterojunction GaAs In_yGa_1–yP_zAs_1–x–In_xGa_1–xAs. The influence of Phosphorus atom fraction (X_p) in liquid phase on dislocation density in the top In_xGa_1–xAs layer was studied. It was found that dislocation density (N_d) as a function of X_p is a curve with some minima. The minima of N_d for substrates of (111) A and (111) B orientations are observed in the different intervals of X_p axis. — The width of N_d minimum is decreased if the substrate is misoriented from the (111) plane. — It was supposed that the clusters exist in the liquid phase. On the basis of this assumption one can explain the influence of substrate position over or under the melt on the film perfection. The diameter of these clusters is estimated to be about 500 Å.     

Optical properties of Ga1–xInxAs LPE-layers and p-n structures

The multiple layer structure nGaAs(n Ga_1–xIn_xAs) p Ga_1–xIn_xAs (0 ≦ × ≦ 0.18) was realized by liquid phase epitaxy from In–Ga–As-melts on (111)-oriented GaAs substrates. The InAs-content of the mixed crystal layers was found to be dominating for crystal perfection and growth rate. The cathodoluminescence spectra of p-and n-type Ga_1–xIn_xAs and spectral distribution of the electroluminescence from pn-junctions were measured at T = 77 K and 300 K. The external quantum efficiency wa found to have a maximum for diodes with x ≈ ≈ 0.006. This is caused by the decrease of the optical absorption with increasing x and increasing dislocation density on the other hand.     

Germanium Incorporation in Ga1–xInxAs LPE Layers and GaAs Bulk Crystals

Atomic absorption spectroscopy (AAS) is used to determine the Ge concentration in Ga_1–xIn_xAs and GaAs. The orientation dependence of Ge incorporation in (111)A-and (111)B oriented samples has been studied. The distribution coefficients for both the orientations were determined to be k_Ge^(111)A = 2.6 · 10⁻² and k_Ge^(111B = 1.4 · 10⁻² for Ga_1–xIn_xAs with 0 ≦ x ≦ 0.13. The differences between the two orientations are explained with the aid of the band bending model. Doping gradients in thick epitaxial layers and along crystal length of polycristalline TGS-grown GaAs ingots have been investigated too. In Ga_1–xIn_xAs layers any Ge concentration gradient couldn't be observed, but in TGS compact crystals Ge concentration increases with crystal length because the melt composition changes significantly during solidification. The results are compared with those of electrical measurements.     

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).     

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.     

A study of phase equilibria and heterojunctions in Ga–In–As–Sb quaternary system

The phase diagram of the Ga–In–As–Sb quaternary system has been determined experimentally and also has been treated on the base of thermodynamic calculations. The liquidus data were obtained by DTA and solidus data were determined using electron microprobe analysis on LPE-layers of Ga_xIn_1–xAs_ySb_1–y on GaSb and InAs substrates. Isolattice-parameter heterostructures prepared on these substrates were free of mismatch dislocations and suitable for application to light-emitting diodes and semiconductor lasers.     

Ga and In incorporation rates in Ga1−xInxAs growth by chemical beam epitaxy

GaAs, InAs and Ga_1?xIn_xAs layers were grown by chemical beam epitaxy (CBE) using triethylgallium, trimethylindium and tertiarybutylarsine as precursors for Ga, In and As, respectively. The growth rate during the homoepitaxial growth of GaAs and InAs, deduced from the frequency of reflection high-energy electron diffraction intensity oscillations, was used to calibrate the incorporation rates for the III elements. The In content of the Ga_1?xIn_xAs layers was measured by Rutherford backscattering spectrometry and compared with the value predicted from the above calibration data; while the measured In mole fraction is close to the predicted value for the samples grown for low In to Ga flux ratios (x<0.2), the In incorporation is enhanced for larger values of this ratio. The results obtained on layers grown at different substrate temperatures show that In mole fraction is almost constant at growth temperatures in the range 400–500 °C, but a strong dependence on the substrate temperature has been found outside this range. The above results, not observed for samples grown by solid source molecular beam epitaxy, indicate that some interaction between Ga and In precursors at the sample surface could take place during the growth by CBE.     

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.     

X-ray diffraction studies of interdiffusion in InAs—GaAs powder blends

Interdiffusion in the pseudobinary system In_xGa_1−xAs is investigated by means of X-ray diffractometry of annealed powder blends. The interpretation of the experimental results by means both of the concentric spheres and concentric cubes model yields for In_0.43Ga_0.57As an activation energy of (5.39 ± 0.11) eV. This value shows that the diffusion mechanism could be a vacancy one as in the pure compounds. According to the lower atomic radius the Ga atoms within the temperature interval of 550–625 °C diffuse more easily than the In atoms.     

Preparation of Al?Ga?P?As heterostructures

The present paper reports on the results of an investigation of crystallization of multilayer structures with a narrow-gap semiconductor surrounded by two wide-gap ones in the Al-Ga-P-As system on GaAs and GaP substrates. Influence of the lattice parameters' difference on the value of thermal stress in structures with a composition gradient was determined by the bend of structures separated from the substrate. It has been proved that with the P concentration in solid solutions being less than 1% heterojunctions with less tensions than in the Al–Ga–As system are available. A new method of obtaining Al_xGa_1–xP_yAs_1–y solid solutions with the concentration of P proportional to that of Al has been worked out on the basis of which multilayer heterolight-emitting structures have been prepared.     

Epitaxial low-temperature growth of In<Subscript>0.5</Subscript>Ga<Subscript>0.5</Subscript>As films on GaAs(100) and GaAs(111)<Emphasis Type="Italic">A</Emphasis> substrates using a metamorphic buffer

A complex investigation of epitaxial In_0.5Ga_0.5As films grown on GaAs substrates with crystallographic orientations of (100) and (111)A in the standard high- and low-temperature modes has been performed. The parameters of the GaAs substrate and In_0.5Ga_0.5As film were matched using the technology of step-graded metamorphic buffer. The electrical and structural characteristics of the grown samples have been studied by the van der Pauw method, atomic force microscopy, scanning electron microscopy, and transmission/ scanning electron microscopy. The surface morphology is found to correlate with the sample growth temperature and doping with silicon. It is revealed that doping of low-temperature In_0.5Ga_0.5As layers with silicon significantly reduces both the surface roughness and highly improves the structural quality. Pores 50–100 nm in size are found in the low-temperature samples.     

LPE Growth of Ga1 – xInxSb Multi-grading Layers

Electronegativity difference approach (ENDA) has been successfully employed to obtain good prediction of the In atomic fraction, energy bandgap and lattice constant of the Ga_{1 – x}In_xSb/Ga_{1 – y}In_ySb/GaSb system. Nearly lattice-matched GalnSb epilayers with In atomic fraction of 0.42 have been obtained by the liquid phase epitaxy. The cut-off wavelength was 2.2 μm at room temperature.     

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.     

AlxGa1−xAs LPE growth

Al_xGa_1−xAs LPE growth was studied within the temperature range of 930–900°C with Al concentrations in solutions from 0.04 to 2.4 at.%. AlAs concentration in layers has been shown to grow with the cooling rate increase of solution. Interface and volume nucleation parameter dependence of K_i and K_v and formation time t_f on Al concentration in Ga solution have been found. Addition of Al to Ga solution increases critical values of As supersaturation (supercooling) and, as a result, increase in thickness of Al_xGa_1−xAs layers compared with GaAs layers have been determined in spite of As concentration lowering in Ga solution.     

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.     

Die Konzentrationsabhängigkeit des Brechungsindex von Ga(PAs)- und (GaIn)P-Mischkristallen

In the two systems of mixed crystals Ga_xPAs_1–x and Ga_xIn_1–xP the refraction index — using the wavelength of the green Hg line (λ = 5461 Å) — is determined ellipsometrically in dependence on the mole fraction x. The nonlinearity parameter c_n of this dependence is compared with that estimated theoretically by the use of PENNS model.     

Growth of Heterostructures Based on InAs–AlxGa1–xSb

It is reported on the liquid phase epitaxial (LPE) growth of heterostructures on the base of InAs–Al_xGa_1–xSb. The paper includes the investigation of epitaxial layers of Al_xGa_1–xSb alloys on InAs substrates and results of experiments for the determination of optimum growth regimes.     

Phase Equilibrium of the Ga–Al–Sb system

Employing the method of liquid-phase epitaxy (LPE) solid-solutions of Ga_1–xAl_xAl_xSb (0 ≦ x ≦ 0.8) have been obtained. The dependence of Sb solubility on Al concentration in the liquid phase at 403°C, 452°C, 500°C has been established. The dependence of AlSb concentration in the solid phase on the composition of the liquid phase has been investigated at 452°C. Using the chemical constants equilibrium method, the phase equilibrium of the Ga–Al–Sb system in the region of liquid phase composition near the Ga-rich corner of the phase diagram has been calculated. The comparison of experimental and calculated data for the liquid and solid phases shows their agreement within the limits of experimental error.     

Thermodynamic Calculation of the Alloy Composition of GaxIn1−xAs Grown in the Trichloride System Using Solid Sources

The dependence of the Ga_xIn_1−xAs alloy composition as a function of the experimental input variables is calculated for a growth system using AsCl₃ and solid GaAs and InAs sources. The results are similar to those earlier obtained for growth in the hydride system. Additional AsCl₃ introduced downstream the source regions shifts the alloy composition towards higher GaAs content.     

Growth of InxGa1−xN quantum dots by nitridation of nano-alloyed droplet method using MOCVD

In_xGa_1−xN quantum dots (QDs) were grown on GaN/sapphire (0 0 0 1) substrates by employing nitridation of nano-alloyed droplet (NNAD) method using metal-organic chemical vapor deposition (MOCVD). In+Ga alloy droplets were initially formed by flowing the precursors TMIn and TMGa. Density of the In+Ga alloy droplets was increased with increasing precursors flow rate; however, the droplet size was scarcely changed in the range of about 100–200 nm. Two cases of In_xGa_1−xN QDs growth were investigated by varying the nitridation time and the growth temperature. It was observed that the In_xGa_1−xN QDs size can be easily changed by controlling the nitridation process at the temperature between 680 and 700 °C for the time of 5–30 min. Self-assembled In_xGa_1−xN QDs were successfully grown by employing NNAD method.