Incorporation of group V elements in Gaxin1−xAsyP1−y grown by gas source molecular beam epitaxy

A simple growth model has been successfully developed for the determination of the As to P incorporation ratio, i.e., mole fraction y, in growing Ga_xIn_1−xAs_yP_1−y quaternary alloys by gas source molecular beam epitaxy. The model covers the whole composition range with only two fitting parameters, k_In and k_Ga, whose physical meanings are the product of As to P desorption time constant ratio and incorporation rate constant ratio for InAs_yP_1−y and GaAs_yP_1−y, respectively. The best fitting values of k_In and k_Ga from our experimental results are 28 and 3, respectively, at a growth temperature of 480°C. The temperature dependency of the parameters were also studied. The activation energies of k_In and k_Ga are +30 and −330 meV, respectively. The significant differences between the parameters may be due to the different bond energies of binary alloys.     

Spinodal Decomposition of GaxIn1?xAsyP1?yQuaternary Alloys

Using X-ray structural analysis, scanning electron microscopy, atomic force microscopy, and photoluminescent spectroscopy, it is shown that it is possible to obtain a small-scale domain structure on the surface of liquid-phase epitaxial heterostructures. The domain structure emerges as a result of spinodal decomposition of the Ga _x In_{1 − x} As _y P_{1 − y} quaternary alloy due to immiscibility of its components and relaxation of its lattice parameter to surrounding layers.     

Solid solution InxGa1−x AsySbzP1−y−z : A new material for infrared optoelectronics. I. Thermodynamic analysis of the conditions for obtaining solid solutions, isoperiodic to InAs and GaSb substrates, by liquid-phase epitaxy

The diagrams of melt-solid solution (fusibility curves) and solid solution (I)-solid solution (II) (surfaces of spinodal decomposition of solid solutions) phase equilibria in the five-component system In-Ga-As-Sb-P (the solid solutions are isoperiodic to the GaSb and InAs substrates) are calculated. The concentration ranges of the isovalent substitution solid solutions In_xGa_1−x As_ySb_zP_1−y−z , which are accessible for synthesis by liquid-phase epitaxy, are calculated. Fiz. Tekh. Poluprovodn. 31, 410–415 (April 1997)     

GaInAsSb/GaSb heterostructures grown in the spinodal decay region by liquid-phase epitaxy from Sb-enriched solution-melts

Nearly isoperiodic solitary Ga_1−x In_xAs_ySb_1−y /GaSb heterostructures, in which the composition of the solid solution should be found inside the region of spinodal decay (x⩽0.4), were grown by liquid-phase epitaxy from solution-melts enriched with antimony. On the basis of the results of a study of structural and luminescence properties of Ga_1−x In_xAs_ySb_1−y /GaSb heterostructures we have determined the main conditions ensuring reproducible growth of epitaxial layers, homogeneous in the composition of their solid solutions in the region where the existence of processes of spinodal and binodal decay have been theoretically predicted. It is shown that the magnitude and sign of the deformation which the layer undergoes during growth and also the thickness of the layer are the main factors influencing the properties of the growing GaInAsSb solid solutions in the spinodal-decay zone. Fiz. Tekh. Poluprovodn. 33, 1134–1136 (September 1999)     

Growth of quaternary InP-based materials by LP-MOVPE using TBA and TBP in N2 ambient

We have investigated the growth of quaternary In_1−xGa_xAs_yP_1−y/InP materials using TBA and TBP in a N₂ ambient. This process improves significantly the uniformity of In_1−xGa_xAs/InP QWs whereas it does not improve the quaternary Q(1.3)/InP uniformity compared to the conventional process utilizing AsH₃ and PH₃ in H₂. The effect on the x and y uniformity for different combinations of the group-V precursors TBA, TBP, PH₃, and AsH₃ with the carrier gases H₂ and N₂ is evaluated. Advantages with the TBA/TBP/N₂ process are discussed.     

Bandgap and lattice constant of GaInAsP as a function of alloy composition

Published data for the composition dependence of the room-temperature bandgap (E_g) and lattice constant (a_o) in the pseudobinary Ga_yIn_1-yAs, Ga_yIn_1-yP, GaAs_xP_l-x, and InAs_xP_l-x systems have been used to derive the following equations for the quaternary Ga_yIn_l-yAs_x P_l-x, alloys: $$\begin{gathered} a_o ({\AA}) = 5.87 + 0.18x - 0.42y + 0.02xy \hfill \\ E_g (eV) = 1.35 - x + 1.4y - 0.33xy - (0.758 - 0.28x)y(1 - y) \hfill \\ - (0.101 + 0.109y) x(1 - x). \hfill \\ \end{gathered} $$ Available experimental data are in excellent agreement with these equations.     

Composition and parameters of domains resulting from spinodal decomposition of quaternary alloys in epitaxial GaInP/Ga x In1 ? x As y P1 ? y /GaInP/GaAs(001) heterostructures

Structural and optical properties of two- and three-layer epitaxial heterostructures containing GaInP/Ga _x In_{1 − x} As _y P_{1 − y} quaternary alloy layers were studied. Domain formation due to spinodal decomposition of the quaternary alloy was detected in three-layer heterostructures. As a result, an additional long-wavelength band appears in the photoluminescence spectra, and an additional doublet of the line appears in X-ray diffraction patterns of the (006) line. The domain composition was determined on the basis of Vegard’s law and the Kouphal equation. Original Russian Text ? E.P. Domashevskaya, N.N. Gordienko, N.A. Rumyantseva, B.L. Agapov, P.V. Seredin, L.A. Bityutskaya, I.N. Arsent’ev, L.S. Vavilova, I.S. Tarasov, 2008, published in Fizika i Tekhnika Poluprovodnikov, 2008, Vol. 42, No. 9, pp. 1086–1093.     

Phase separation, effects of biaxial strain, and ordered phase formations in cubic nitride alloys

The thermodynamics as well as the energetics and the structural properties of cubic group-III nitrides alloys have been investigated by combining first-principles total energy calculations and cluster expansion methods. In particular results are shown for the ternary In_xGa_1−xN and the quaternary Al_xGa_yIn_1−x−yN alloys. Phase separation is predicted to occur at growth temperatures, for both fully relaxed alloys. A remarkable influence of an external biaxial strain on the phase separation, with the formation of ordered phase structures has been found for the InGaN alloy. These findings are used to clarify the origin of the light emission process in InGaN-based optoelectronic devices. Results are shown for the composition dependence of the lattice constant and of the energy gap in quaternary Al_xGa_yIn_1−x−yN alloys.     

Group-V composition control for InGaAsP grown by gas source molecular beam epitaxy

Based on our kinetics models for gas source molecular beam epitaxy of mixed group-V ternary materials, the group-V composition control in In_yGa_1−yAs_1−xP_x epilayers has been studied. The P or As composition in In_yGa_1−yAs_1−xP_x (lattice matched to InP or GaAs) can be obtained from a simple equation for substrate temperatures below 500°C. This has been verified by a series of experimental results.     

Crystallophysical properties of the In1 ? yGayAs1 ? xNx/GaAs heterostructures

Some properties of the In_{1 − y} Ga _y As_{1 − x} N _x unordered alloys and physical prerequisites of their use in science and technology are considered. The results of studying the intermolecular interaction in the systems under study and the features of their application to the In_{1 − y} Ga _y As_{1 − x} N _x /GaAs functional hetero-structures are presented.     

Engineering phase formation thermo-chemistry for crystal growth of homogeneous ternary and quaternary III–V compound semiconductors from melts

Based on intrinsic alloy phase formation chemistry and thermodynamics, a novel and unique way of producing compositionally homogeneous multi-component (binary, ternary, quaternary) semiconductor materials is presented. A free energy minimization computer program licensed from AEA Technology Engineering Software, Inc., has been employed to study the composition of the solidifying phases from Ga-In-As-Sb melts at different temperatures and with various liquid compositions. The solid phases have been identified (theoretically and experimentally) to be either ternary compounds of Ga_1−xIn_xAs_ySb_1−y depending on the melt temperature and composition. By engineering the thermochemistry of preferential phase formation in the Ga-In-As-Sb melt, compositionally uniform, single phase, crack free, large polycrystalline Ga_1−xIn_xSb and Ga_1−xIn_xAs have been grown.     

Gas-Source molecular beam epitaxy and characterization of inGaAs/lnGaAsP quantum well structures on InP

In this paper, we report the effect of using a group-V residual source evacuation (RSE) time on the interfaces of InGaAs/lnGaAsP quantum wells (QWs) grown by gas-source molecular beam epitaxy. High-resolution x-ray rocking curve and low-temperature photoluminescence (PL) were used to characterize the material quality. By optimizing the RSE time, a PL line width at 15K as narrow as 6.6 meV is observed from a 2 nm wide single QW, which is as good as or better than what has been reported for this material system. Very sharp and distinct satellite peaks as well as Pendellosung fringes are observed in the x-ray rocking curves of In_xGa_1−xAs/InxGa_1−xAS_yP_1−y multiple QWs, indicating good crystalline quality, lateral uniformity, and vertical periodicity. Theoretical considerations of the PL linewidths of In_xGa_1−xAs/InxGa_1−xAS_yP_1−y single QWs show that for QW structures grown with the optimized RSE time, the PL linewidth is mainly due to alloy scattering, whereas the contribution from interface roughness is small, indicating a good interface control.     

Efficient 2.0–2.6 μm wavelength photoluminescence from narrow bandgap InAsP/InGaAs double heterostructures grown on InP substrates

Photoluminescence spectra and efficiency have been measured for several strained InAs_yP_1−yIn_xGa_1−xAs (0.28 < y ≤ 0.62; 0.66 ≤ x ≤ 0.83) double heterostructures grown by vapor phase epitaxy on InP substrates with graded InAsP buffer layers. Luminescence peak positions between the wavelengths of 1.99 and 2.57 (μm at a temperature of 295K are consistent with bandgap luminescence from the In_xGa_1−xAs active regions. Despite a high density of dislocations in the buffer layers, internal radiative recombination efficiencies of from 25 to 50% for the structures are found at 295K.     

Characterization of AlxInyGa1−x−yN quaternary alloys grown on sapphire substrates by molecular-beam epitaxy

High-resolution X-ray diffraction (HR-XRD) with rocking curve, atomic force microscopy (AFM) and photoluminescence (PL) spectroscopy have been performed on high-quality quaternary Al_xIn_yGa_1−x−yN thin films at room temperature. The Al_xIn_yGa_1−x−yN films were grown on c-plane (0 0 0 1) sapphire substrates with AlN as buffer layers using a molecular beam epitaxy (MBE) technique with aluminum (Al) mole fractions x ranging from 0.0 to 0.2 and constant indium (In) mole fraction y=0.1. HR-XRD measurements confirmed the high crystalline quality of these alloys without any phase separation. The X-ray rocking curve of Al_xIn_yGa_1−x−yN films typically shows full widths at half maximum (FWHM) intensity between 14.4 and 28.8 arcmin. AFM measurements revealed a two-dimensional (2D) growth mode with a smooth surface morphology of quaternary epilayers. PL spectra exhibited both an enhancement of the integrated intensity and an increasing blueshift with increased Al content with reference to the ternary sample In_0.1Ga_0.90N. Both effects arise from Al-enhanced exciton localization. PL was used to determine the behavior of the energy band gap of the quaternary films, which was found to increase with increasing Al composition from 0.05 to 0.2. This trend is expected since the incorporation of Al increases the energy band gap of ternary In_0.1Ga_0.90N (3.004 eV). We have also investigated the bowing parameter for the variation of energy band gaps and found it to be very sensitive on the Al composition. A value of b=10.4 has been obtained for our quaternary Al_xIn_yGa_1−x−yN alloys.     

Band-edge photoluminescence of heavily doped InxGa1−x As1−y Py(λ=1.2 µm)

Band-edge photoluminescence spectra of heavily donor-doped samples of In_xGa_1−x As_1−y P_y (x=0.77, y=0.53) were investigated in the temperature range (77–300) K. A theory of luminescence that takes into account fluctuations in the band-edge potentials due to nonuniform distribution of impurities is used to calculate temperature dependences of the positions and half-widths of peaks in these spectra. Good agreement is obtained between experimental and calculated curves. For heavily doped In_xGa_1−x As_1−y P_y samples with either p-or n-type conductivity, the peak energy of the band-edge PL is observed to shift towards lower frequencies at low temperatures. This shift is accompanied by broadening of the spectra and a decrease in the photoluminescence intensity compared to the analogous parameters for the spectra of undoped material. Possible mechanisms for radiative recombination are analyzed. Fiz. Tekh. Poluprovodn. 33, 907–912 (August 1999)     

A novel pseudomorphic (GaAs1−xSbx-InyGa1−yAs)/GaAs bilayer-quantum-well structure lattice-matched to GaAs for long-wavelength optoelectronics

Two types of quantum well (QW) structures grown lattice matched on (100) GaAs have been studied. The first type of structure consists of pseudomorphic GaAs_xSb_1-x/GaAs (x≤0.3) SQWs which show emission wavelengths longer than those reported for pseudomorphic In_yGa_1−yAs/GaAs QWs. However, the attractive emission wavelength of 1.3 μm has not been achieved. To reach this goal, a novel type of bilayer QW (BQW) has been grown consisting of a stack of two adjacent pseudomorphic layers of GaAs_xSb_1−x and In Ga_1-y As embedded between GaAs confinement layers. In this BQW, a type-II heterojunction is formed between GaAs_xSb_1−x and In_yGa_1−yAs, resulting in a spatially indirect radiative recombination of electrons and holes at emission wavelengths longer than those achieved in the GaAs_xSb_1−x/GaAs and Ii_yGa_1−yAs/GaAs SQWs. The longest 300K emission wavelength observed so far was 1.332 μm.     

Calculation of energy band gaps in quaternary iii/v alloys

The dielectric theory of electronegativity is applied to the calculation of the compositional dependence of the energy band gap for quaternary III/V alloys of type A_l-xB_xC_1-yD_y and A_1-x-yB_xC_yD. The departure from linearity of E_G versus x and y is taken to be the sum of two terms, the intrinsic or virtual crystal term and the extrinsic term due to effects of aperiodicity which for one type of alloy may occur on both sublattices. Rather than simply treating the quaternary as an average of the bounding ternary systems, as has been common in the past, the intrinsic departure from linearity is calculated by assuming E_h,i,C, and D_av to vary linearly with x and y. The result is a smaller intrinsic deviation from linearity and a much better fit to existing data in the system Ga_1-xIn_xAs_1-y P_y. The calculation is also applied to three systems where no data exist but which are of great interest because of their potential application for the fabrication of lattice matched tandem solar cells: Ga_l-xA1_xAs_l-ySb_y. Ga_1-x-yA1_xIn_yAs, and GaAs_1-x-yP_xSb_y.     

Long-wavelength photodiodes based on Ga1−x InxAsySb1−y wit composition near the miscibility boundary

The possibility of using liquid-phase epitaxy to obtain Ga_1−x In_xAs_ySb_1−y solid solutions isoperiodic with GaSb near the miscibility boundary is investigated. The effect of crystallographic orientation of the substrate on the composition of the solid solutions grown in this way is examined, and the indium concentration is observed to grow from 0.215 to 0.238 in the Ga_1−x In_xAs_ySb_1−y solid phase in the series of substrate orientations (100), (111)A, (111)B. A change in the composition of the solid solution leads to a shift of the long-wavelength edge of the spectral distribution of the photosensitivity. The use of a GaSb (111)B substrate made it possible, without lowering the epitaxy temperature, to increase the indium content in the solid phase to 23.8% and to create long-wavelength photodiodes with spectral photosensitivity threshold λ _th=2.55 μm. The primary characteristics of such photodiodes are described, along with aspects of their fabrication. The proposed fabrication technique shows potential for building optoelectronic devices (lasers, LED’s, photodiodes) based on Ga_1−x In_xAs_ySb_1−y solid solutions with red boundary as high as 2.7 μm. Fiz. Tekh. Poluprovodn. 33, 249–253 (February 1999)     

Fundamental absorption edge of semiconductor alloys with the direct-gap energy-band structure

A procedure convenient for practical application to the calculations of the fundamental absorption spectra of semiconductor alloys with the direct-gap energy-band structure is developed. The procedure is based on the knowledge of the fundamental absorption spectra of binary constituents of the alloy, takes into account the nonparabolic structure of the conduction band, and involves only one adjustable parameter that characterizes the inhomogeneous broadening of the spectra. The procedure is tested by the examples of the best-studied and practically most important Al _x Ga_{1 − x} As alloys, the (Al _x Ga_{1 − x} )_0.5In_0.5P alloys isostructural to GaAs, and the Ga _x In_{1 − x} As alloys isostructural to InP. The procedure can be used in the case of other III–V and II–VI compounds. The results make it possible to calculate the intrinsic luminescence spectra of the alloys.