H-induced dangling bonds in H-isoelectronic-impurity complexes formed in GaAs1-yNy alloys

Complexes formed by H and the isoelectronic impurity N in GaAs1-yNy alloys have been widely investigated because the significant effects of N on the GaAs properties and their passivation by H represent a unique tool for a defect engineering of semiconductors. However, available results still present a quite puzzling picture. Both the N-H2* and C2v complexes proposed by theory were challenged indeed by experimental results. In the present Letter, we disclose a double-faced behavior of a H atom interacting with an isoelectronic impurity: while H, on one side, binds to N and induces the formation of dangling bonds (DB) on its Ga neighbors, on the other side, it saturates these DBs, thus permitting the formation of multiple-H complexes. This peculiar H behavior fully explains the experimental findings and likely represents a general feature of H-isoelectronic-impurity interactions.     

Spectral image cathodoluminescence,photoluminescence and Raman study of GaAs layers grown on Si substrates

GaAs layers grown on Si substrates by the conformal method were investigated by means of Raman, photoluminescence and cathodoluminescence spectroscopies. The combination of these optical techniques allows a better knowledge of the properties of these layers, with special emphasis on the stress distribution and the incorporation of dopants. In particular, samples intentionally doped, with alternate doped and undoped fringes, have been analyzed. The effective incorporation of Si atoms in the GaAs structure to produce n-type layers and the formation of Si complexes are determined by Raman and cathodoluminescence data. The lateral quasi-periodic stress distribution, typically observed in these layers, is shown to affect the Si incorporation.     

Structure and passivation effects of mono- and dihydrogen complexes in GaAsyN(1-y) alloys

In GaAsyN(1-y), the presence of a few percent of N induces a large reduction of the GaAs band gap that vanishes upon hydrogenation. In the present Letter, the energetics of N-H complexes and their effects on the band structure of the GaAs0.97N0.03 alloy have been investigated by first-principles density functional methods. We find that monohydrogen N-H+ and dihydrogen N-H* 2 complexes are formed depending on doping. Moreover, only N-H* 2 complexes account for the neutralization of nitrogen effects. A model is proposed that clarifies the passivation mechanism of nitrogen by H.     

Structural and electronic properties of mixed Au/Te/n-GaAs structures

The structural and electronic properties of the intermixed interfaces of layered Au/Te/n-GaAs structures were investigated by the combined application of¹²⁹I Mössbauer spectroscopy (in the decay of^129mTe), X-ray diffraction, Raman spectroscopy and electrical measurements. The transition from Schottky-type to ohmic contact by high fluence pulsed laser irradiation was examined and compared to rapid time furnace heat treatment. Distinctly different ohmic contact formation mechanisms have been observed. Whereas for furnace alloying the formation of a crystalline (graded As doped) Ga₂Te₃ interface layer is crucial, strong evidence is adduced that the ohmic character of high-fluence laser mixed structures is correlated to the formation of a high density of defect complexes in the GaAs top layer.     

Kinetics of an exciton-trion system in shallow GaAs/AlGaAs quantum wells

The formation of three-particle charged exciton complexes (trions) in shallow GaAs/AlGaAs quantum wells in the temperature range 1.7–15 K has been investigated by luminescence spectroscopy and resonant light scattering. The effect of the photon energy and the intensity of additional above-barrier illumination on the trion formation kinetics has been analyzed. It is established that, upon intrawell excitation, illumination leads to the formation of trions when the light photon energy corresponds to the regions of effective formation of trions in the photoluminescence excitation spectra. It is shown that, with an increase in the illumination level, the trion concentration first increases and then reaches a plateau since the quantum well acquires an electric charge whose field equalizes the electron and hole capture rates.     

Defects in H implanted GaAs studied by ion-beam and low-energy positron techniques

Ion-beam and low-energy positron-beam techniques have been used to study damage and implanted ion distributions and their annealing behavior in semi-insulating GaAs after the room temperature implantation of 3 × 10¹⁵−1 × 10¹⁷ 60 keV H⁺ cm^-2. The redistribution of the implanted H during annealing was observed to be connected to the migration of implantation-induced defect-complexes. A huge increase in the displaced atom concentration in the region of the H concentration was observed after annealings. A monovacancy overlayer, dissociation of H-vacancy complexes, and formation of stable vacancy-H agglomerates were observed in the different parts of the slowing-down region of the implanted H.     

Transmission electron microscopy study of defects in Sn-doped GaAs films grown by molecular beam epitaxy

Films of GaAs, heavily doped with Sn, which have been grown by molecular-beam epitaxy are found to contain single-crystal Sn particles situated in the nearsurface region of the epilayer GaAs. The morphology and chemical composition of the particles have been examined by using cross-section transmission electron microscopy combined with energy-dispersive x-ray spectroscopy. Different growth conditions were used to study the Sn-particle formation and high-resolution transmission electron microscopy was used to investigate microstructures. The observations are discussed in terms of several models previously proposed for these phenomena.     

Divacancy complexes induced by Cu diffusion in Zn-doped GaAs

Positron annihilation spectroscopy was applied to investigate the nature and thermal behavior of defects induced by Cu diffusion in Zn-doped p-type GaAs crystals. Cu atoms were intentionally introduced in the GaAs lattice through thermally activated diffusion from a thin Cu capping layer at 1100 °C under defined arsenic vapor pressure. During isochronal annealing of the obtained Cu-diffused GaAs in the temperature range of 450?850 K, vacancy clusters were found to form, grow and finally disappear. We found that annealing at 650 K triggers the formation of divacancies, whereas further increasing in the annealing temperature up to 750 K leads to the formation of divacancy-copper complexes. The observations suggest that the formation of these vacancy-like defects in GaAs is related to the out-diffusion of Cu. Two kinds of acceptors are detected with a concentration of about 10¹⁶ ? 10¹⁷ cm^?3, negative ions and arsenic vacancy copper complexes. Transmission electron microscopy showed the presence of voids and Cu precipitates which are not observed by positron measurements. The positron binding energy to shallow traps is estimated using the positron trapping model. Coincidence Doppler broadening spectroscopy showed the presence of Cu in the immediate vicinity of the detected vacancies. Theoretical calculations suggested that the detected defect is V _Ga V _As-2Cu_Ga.     

Formation of Dislocations in the Process of Impurity Diffusion in GaAs

Russian Physics Journal - A study of the formation of dislocations in the process of impurity diffusion in GaAs has been carried out. The formation of dislocations in GaAs diffusion layers doped...     

Formation of Cu nanoparticles in GaAs using MeV ion implantation followed by thermal annealing

Analytical electron microscopy, high-resolution X-ray diffraction and combined Rutherford backscattering spectrometry and channeling experiments have been used to investigate the radiation damage and the effect of post-implantation annealing on the microstructure of GaAs(100) single crystals implanted with 1.00 MeV Cu⁺ ions to a dose of ≈ 3×10¹⁶ cm^-2 at room temperature. The experiments reveal the formation of a thick and continuous amorphous layer in the as-implanted state. Annealing up to 600 °C for 60 min does not result in the complete recovery of the lattice order. The residual disorder in GaAs has been found to be mostly microtwins and stacking fault bundles. The redistribution of implanted atoms during annealing results in the formation of nano-sized Cu particles in the GaAs matrix. The X-ray diffraction result shows a cube-on-cube orientation of the Cu particles with the GaAs lattice. The depth distribution and size of the Cu particles have been determined from the experimental data. A tentative explanation for these results is presented. Received: 15 February 1999 / Accepted: 18 February 1999 / Published online: 28 April 1999     

INVESTIGATION OF DEFECTS IN Ge-DOPED GaAs CRYSTAL GROWN IN A MAGNETIC FIELD

Ge-doped GaAs single crystals have been grown by liquid-encapsulated Czochralski method in absence and presence of a magnetic field of 4000Gauss. By means of high op-tical efficiency photoluminescence, spectra of the grown crystals at room temperature were obtained, which consist of two emission bands A and B at 1.39-1.42eV and 0.97-1.05eV, respectively. Comparing the photoluminescence mappings with microphotographs of etched wafers, Hall effect results and electron probe microanalyses of the n- and p-type crystals with different Ge concentrations, we considered that the emission bands A and B originate from Ge-related acceptor and donor complexes, respectively. The complexes were formed during crystal growth, mainly due to temperature fluctuations in molten Ge-doped GaAs. The concentrations and homogeneities of the defects can be improved by the application of a magnetic field during crystal growth to suppress the temperature fluctuation.     

Impurity vibrations of copper defect complexes in gallium arsenide crystals

Dynamical properties of several copper defect complexes in GaAs are studied. The complexes studied include models for the C and F centers recently investigated experimentally by Gross, Safarov, Sedov, and Marushchak. It is shown that these models are capable of giving rise to resonance modes whose frequencies agree with the positions of peaks in the optical spectra of these defect complexes, when reasonable changes in the force constants coupling the substitutional copper impurities to the host crystal are included in the dynamical models. In addition the vibronic and infrared absorption spectra of these complexes have been calculated.     

Heterostructures with InGaAs/GaAs quantum dots doped by transition elements. Part I: Photoluminescence properties

The optical properties of InGaAs/GaAs quantum dot heterostructures that are doped by manganese and chromium during growth by Metal-organic vapor phase epitaxy have been studied. Surface topography photoluminescence spectra measurements have demonstrated the possibility of controlling the spectral characteristics of the structure by varying quantum well growth conditions and sizes in the presence of impurity atoms. Research results are explained by the peculiarities of InAs nanoclusters formation on the GaAs surface in the presence of Mn and Cr atoms.     

Study of radiation-induced damage to type III–V semiconductor compounds irradiated with γ quanta and protons using positron annihilation spectroscopy

The effect of proton and ?? radiation on characteristics of the spectra for the angular distribution of annihilation photons (ADAP) have been studied in the case of positron annihilation in GaAs and GaP single crystals. Relative variations in defect accumulation and annealing under irradiation and subsequent isochronous annealing of the samples have been studied using variations in the basic parameters of the ADAP spectra. In both cases (GaAs and GaP), the variations in the ADAP spectral parameters as functions of the annealing temperature have a steplike character, which is interpreted as the formation of a certain type of defects with different annealing activation energies.     

Structure of heteroepitaxial GaAs on Si

The current interest in GaAs grown on nonpolar substrates such as Si has been stimulated by the potential technological advantages of this system. Although the two major obstacles impeding the progress of heteroepitaxial growth of GaAs on Si (100) substrates, the large lattice mismatch and the formation of antiphase boundaries, have recently been overcome, the understanding of the microstructural growth process is still not satisfactory. We are presenting new x-ray scattering results which indicate that thin GaAs films are compressed in the film plane at room temperature, while thicker films are under tensil stress, the cross-over region being at about 1000Å. In addition, we show that the GaAs lattice is translationally incommensurate with the Si substrate and that the in-plane [001] axes are misaligned by 3–5°. Thermal expansion measurements of the out-of-plane lattice parameters of the film and substrate indicate that the GaAs in-plane thermal expansion follows from the anharmonicity of the substrate.     

α-P/GaAs(100)界面的光电子能谱研究

本文采用X射线光电子能谱、紫外光电子能谱和低能电子衍射对室温下P在GaAs(100)表面上的生长进行了研究。结果表明,在生长初期P是成团吸附的,随着淀积量的增加而生长成α-P薄膜,该薄膜的价带结构与等离子体淀积的α-P:H薄膜的价带结构相似。在界面处有约一单层的P与衬底表面的Ga成键。α-P覆盖层使GaAs表面势垒下降约0.2eV。 关键词：     

Modulation of the resonant Rayleigh light scattering spectrum of GaAs/AlGaAs structures with quantum wells under above-barrier illumination

It is found that additional illumination by photons with energies above the band gap width in barrier layers leads to a strong (up to 40% in depth at the values of the illumination power used in this work) modulation of the light intensity elastically scattered upon resonant excitation of exciton states in quantum wells of GaAs/AlGaAs structures. Evidently, the effect observed is associated with the redistribution of oscillator strengths of exciton transitions due to the formation of three-particle exciton complexes (trions). These complexes arise through preferred capture of nonequilibrium like charge carriers (in our case, holes).     

Interface <Emphasis Type="Italic">D</Emphasis><Superscript>−</Superscript> complexes in a two-dimensional electron system

The excitation spectrum of a two-dimensional electron system in high-quality AlGaAs/GaAs quantum wells has been studied by Raman scattering. New Raman lines due to the excitation of interface D ⁻ complexes in which two electrons localized in a quantum well are coupled to a charged impurity at the quantum well interface have been identified. The ground state of the interface D ⁻ complexes has been found to change in the transverse magnetic field from spin-singlet to spin-triplet, similar to a change in the ground state of the system of two electrons localized in a harmonic potential.     

Interface D − complexes in a two-dimensional electron system

The excitation spectrum of a two-dimensional electron system in high-quality AlGaAs/GaAs quantum wells has been studied by Raman scattering. New Raman lines due to the excitation of interface D ^? complexes in which two electrons localized in a quantum well are coupled to a charged impurity at the quantum well interface have been identified. The ground state of the interface D ^? complexes has been found to change in the transverse magnetic field from spin-singlet to spin-triplet, similar to a change in the ground state of the system of two electrons localized in a harmonic potential.

     

Intrinsic defects in GaAs and InGaAs through hybrid functional calculations

Vacancies, antisites, and dangling bonds in GaAs and In_0.5Ga_0.5As are studied through hybrid density functionals. The As antisite is found to have a low formation energy in As-rich conditions and defect levels at mid-gap in correspondence of experimental defect densities at the GaAs/oxide and InGaAs/oxide interfaces. In n-type GaAs, the Ga vacancy also shows defect levels in agreement with measured defect densities and competitive formation energies. For both GaAs and InGaAs, the As dangling bonds are located near the valence band maximum. The Ga dangling bond in GaAs is found just below the conduction band-edge in correspondence of experimentally observed states, whereas its defect level is resonant with the conduction band in InGaAs.