Point Defects In GaAs Research Articles

The study of the optical properties of the GaAs with point defects

GaAs is a common material for negative electron affinity photoelectric cathodes. It has a widely application in night vision. It is unavoidable to produce point defects in the process of the GaAs growth. In this article, the first principle method is used to calculate the formation energy and the optical properties of six types familiar point defects in GaAs. Three types of point defects (Ga vacancy defect, As antisite defect and As interstitial defect) are easier to be formed in these six types according to the formation energy calculation. In fact, crystal GaAs is grown in an As-rich environment. The Ga vacancy, As antisite and As interstitial defects are easier to be formed in reality. Hence the theoretical calculation results are in keeping with the experiments. In this article, the optical properties of these three types are compared with that of perfect GaAs. The electron structures are changed as a result of the point defects. Some of the defect levels enter into the band gap and the electron transitions become easier. It makes the optical spectra move to the low-energy region. Additionally, GaAs with Ga vacancy defect and that with As interstitial defect shows similar optical properties. Therefore both of the two types of defects can be considered as the same in the later experiments. The theoretical results in this article provide the basis for experimental study for photoelectric emission of the real GaAs material related to the optical properties and electronic structures.

Ultraviolet Radiation Action onto Nanostructures with Quantum Wells GaAs/AlGaAs

Optical properties modification of semiconductor heterostructure with quantum wells GaAs/AlGaAs by the ultraviolet (UV) radiation was investigated in the range of energy density of 0 – 500 mJ/cm2 . It was shown that photoluminescence signal amplitude decreases with an increase of UV energy density; this dependence revealed threshold nature with the threshold value about 100 mJ/cm2 – in agreement with other results on laser formation of the point defects in GaAs. Reflectivity kinetics of the sample detected at the probe radiation wavelength corresponding to the photoluminescence line center showed an increase of electron-hole recombination rate with growth of UV energy density. Sharp focusing of UV laser radiation led to a plume formation over the sample surface; spectrum of the plume contained neutral gallium atoms doublet at wavelengths of 403 нм and 417 nm

Migration barriers of neutral As di-interstitials in GaAs

The recent discovery of intrinsic di-interstitial stability against the isolated self-interstitial point defects in GaAs has evidenced the importance of such complexes in, for instance, irradiated GaAs. In this paper, we illustrate and discuss diffusion of such complexes in comparison with isolated self-interstitials. In particular, the diffusion barriers of neutral di-interstitials have been calculated in the framework of density functional theory, showing that, in addition to their being stable, di-interstitials can also diffuse rapidly through the lattice, similarly to isolated self-interstitials.

Simulation of silicon diffusion in GaAs

The simulation of coupled diffusion of silicon atoms and point defects in GaAs has been carried out for diffusion at the temperatures of 1000 and 850 °C. The amphoteric behavior of silicon atoms in GaAs has been taken into account in the investigation of high concentration diffusion from silicon layer deposited on GaAs substrate. The calculated dopant profiles agree well with the experimental ones and they confirm the adequacy of the model of silicon diffusion used for simulation. A comparison with the experimental data has enabled this work to obtain the parameters of silicon effective diffusivity and other values describing high concentration silicon diffusion in GaAs.

Ab Initio Studies of the Energy Characteristics and Magnetic Properties of Point Defects in GaAs

The formation energies of intrinsic point defects and solution energies of transition metal impurities in gallium arsenide are determined on the basis of ab initio calculations using the method of a locally self-consistent Green’s function, which is a generalization of the coherent potential approximation. Based on the calculated energies, the conclusion is made that the AsGa antisite defect is the most common intrinsic defect in GaAs. Calculations showed that transition metal impurities, except for Ni, preferentially occupy gallium sites substitutionally. The magnetic moments of impurity atoms are calculated as a function of the chemical environment. It is shown that, in compensated GaAs, Mn atoms tend to form clusters.

Reliability of analytical potentials for point-defect simulation in GaAs

Molecular dynamics with analytical potentials is commonly used to obtain the distributionof defects produced by energetic particles in elemental and compound semiconductors.Collision cascades simulated by model-potential molecular dynamics are used to collectstatistical data on the defect distribution but the local structure in such materials as GaAsis commonly recognized to be unreliable in comparison to tight-binding or abinitio total energy calculations. These two methods, however, are not practical insimulations of collision cascades because of their large computational workload.In this paper, we analyse the properties of the basic point defects in GaAs asobtained by using different model potentials and compare them to recent ab initiocalculations based on the density-functional theory (DFT) in the local-densityapproximation (LDA). The aim of this work is to evaluate how close the model potentialmolecular dynamics predictions are to the benchmark DFT results and whichmodel potential most accurately predicts realistic local structures of point defects.

Excess arsenic and point defects in GaAS grown by molecular beam epitaxy at low temperatures

Defect formation in low temperature molecular beam epitaxy GaAs layers (LT-GaAs) is discussed. The influence of growth conditions (temperature, III/V flux ratio) on internal structure, type, and concentration of electrically and optically active point defects is discussed. The effect of annealing on the formation of arsenic precipitates (clusters) is considered.

Molecular Dynamics Analysis of Diffusion of Point Defects in GaAs

Molecular dynamics simulation was carried out to estimate the diffusion coefficient and the mechanism of diffusion with a constant pressure and temperature algorithm. The following results were obtained: there is little diffusion of a vacancy in solid GaAs, even near the melting point, the diffusion coefficient of an interstitial arsenic atom is larger than that of an interstitial gallium atom, after formation of a dumbbell pair in the [110] direction, an interstitial arsenic atom migrates in the [110] direction, while an interstitial gallium atom migrates in either the [110] or direction, and an interstitial arsenic atom pushes out a substitutional arsenic atom and then diffuses by an interstitialcy mechanism, while an interstitial gallium atom pushes out either a substitutional arsenic or gallium atom. Finally, all of migrating interstitial atoms in solid GaAs switch to interstitial arsenic atoms at the final stage of diffusion. © 2003 The Electrochemical Society. All rights reserved.

Variations in first principles calculated defect energies in GaAs and their effect on practical predictions

There is an abundant literature on calculations of formation and ionization energies of point defects in GaAs. Since most of these energies, especially the formation energies, are difficult to measure, the calculations are primary means of obtaining their values. However, based on the assumptions of the calculations, the reported values differ greatly among the various calculations. In this paper we discuss the sources of errors and their impact on practical predictions valuable in GaAs device fabrication. In particular, we have compared a large set of computed energies and selected the most appropriate values. Then, in the context of GaAs material quality, we investigated the impact of errors in calculation of formation energies on the performance of the GaAs substrate for device fabrication. We find that in spite of the errors inherent in ab initio calculations, it is possible to correctly predict the behaviour of GaAs substrate.

Charged native point defects in GaAs and other III–V compounds

The solubility of both native point defects and dopants in semiconductors is dependent on growth temperature, on crystal stoichiometry and on Fermi level position. At high temperatures III–V compounds contain high concentrations of predominantly charged native point defects. Published titration and density/lattice parameter measurements on GaAs show conclusively that melt-grown crystals contain ∼10 19 cm −3 As-vacancies and As-interstitials at the melting point. The arsenic vacancies form a relatively shallow (∼ E c−0.1 eV) donor state. The concentration of these ionised vacancies at the melting point of GaAs, and under the conditions used for LPE growth from Ga-solution, exceeds the intrinsic electron–hole concentration. Hence, these ionised vacancies control the electro-neutrality of the crystal (and hence the position of the Fermi level) during growth under these conditions. The As vacancy concentration obtained from titration measurements, when inserted into a comprehensive equilibrium thermodynamic description of the system, accurately predicts the observed range of linear dopant solubility obtained for both Groups IV and VI donor dopants. The currently accepted hypothesis that this linear range is determined by a non-equilibrium incorporation process controlled by a Schottky barrier at the crystal/melt interface is therefore unnecessary. It is shown that donor and acceptor dopant incorporation, EL2 formation and annealing behaviour in GaAs can all be fully explained by the thermodynamic model. The differing doping behaviour exhibited by the various other zinc-blende III–V compounds is shown to be related to the differing relative numbers of native point defects on the two sub-lattices.

Fermi-Level Effect, Electric Field Effect, and Diffusion Mechanisms in GaAs Based III-V Compound Semiconductors

ABSTRACTDiffusion mechanisms and point defects in GaAs and related III-V compounds are discussed. An understanding of the As sublattice situation has been arrived at fairly recently and is presently tentative. Understanding of the Ga sublattice situation has become more acceptable in that experimental results are consistently explained by the Fermi-level effect and the As4 pressure effect. On the Ga sublattice, though controversies still exist, some are readily resolved by noting the role of the electric field produced by semiconductor electrical junctions, physical junctions, and surfaces.

Erbium in GaAs: Coupling with native defects

We calculated the total energy of Er point defects in GaAs and of Er defects coupled with native defects in GaAs by the ab initio pseudopotential method. The total-energy calculation indicates that various coupled defects comprising an Er atom and native defects will be formed depending on the growth conditions and the Fermi-level position. By investigating the valence charge distribution, it was found that an Er atom forms a strong bond with an As atom. This chemical feature and the lattice relaxation around the coupled defect are the main factors that stabilize the coupled states. The intra-$4f$-shell luminescence spectrum of Er in GaAs is generally complicated and strongly depends on sample preparation methods and growth conditions. We propose that this tendency is due to the sample-dependent concentration of various defects that form complexes with Er.

Device-relevant point defects in GaAs and InP

Positron annihilation is used to determine the vacancy ionization levels and the atomic structure of acceptors, vacancy-type or ion-type, in GaAs and InP materials. Positron annihilation yields information on the size of the vacancy open volume via the annihilation lifetime in the vacancy τ V, on its charge state via the positron trapping coefficient μ V( T) and the concentration C V via the positron trapping rate K V = μ V C V. It is shown that V(As) and V(Ga) vacancies play a role as compensating centers in semi-insulating (SI) and n-type GaAs. V(As) vacancies absorb near-band edge light and interact with holes or electrons depending on their charge state V(As) +, V(As) 0 or V(As) −. The conversion EL2 to EL2 * generates metastable vacancies which are part of the EL2 * structure.

Ab initio study of oxygen point defects in GaAs, GaN, and AlN.

We have studied oxygen point defects with the plane-wave pseudopotential method in GaAs, GaN, and AlN. The calculations demonstrate a qualitatively different behavior of oxygen impurities in these materials. ${\mathrm{O}}_{\mathrm{As}}$ in GaAs acts as a deep center with an off-center displacement and negative-U behavior, in agreement with the experimental data. ${\mathrm{O}}_{\mathrm{N}}$ in GaN is found to be a shallow donor with a low formation energy, and is suggested to act as a partial source for the unintentional n-type conductivity commonly observed in GaN. O in AlN is also found to easily substitute for N, which is consistent with the experimentally observed large oxygen concentrations in AlN. However, ${\mathrm{O}}_{\mathrm{N}}$ in AlN is shown to be a deep center due to the wide band gap, in contrast with ${\mathrm{O}}_{\mathrm{N}}$ in GaN. Our calculations thus predict that isolated oxygen acts as a DX-type center in ${\mathrm{Al}}_{\mathit{x}}$${\mathrm{Ga}}_{1\mathrm{\ensuremath{-}}\mathit{x}}$N alloys. Results for other oxygen point defect configurations and for the dominant native defects are also presented. \textcopyright{} 1996 The American Physical Society.

Using positron 2D-ACAR as a probe of point defects in GaAs: The As vacancy as a case study

Two-Dimensional Angular Correlation of positron Annihilation Radiation (2D-ACAR) experiments have been performed on n-type GaAs. By combining these results with those from positron lifetime experiments, the momentum distribution of the arsenic vacancy in its neutral (V aAs 0 ) and negative (V As − ) charge states have been extracted. These distributions were all normalized to the respective positron lifetime that characterizes them. The first thing to be noticed is that the momentum distributions of the vacancies, as seen by the positron, are fairly isotropic and structureless. The distribution forV As 0 is more peaked than that ofV As − while the latter is more intense in the large momentum regions of the spectra. From this, it can be inferred that VA. has a smaller open volume thanV As 0 A closer look at the momentum distribution of the vacancies reveals that they are not entirely isotropic, but, in fact, have a bulk-like component. Finally, the experimental results for bulk GaAs andV As − compare well in a qualitative manner with the momentum distributions that result from an ab-initio molecular dynamics calculation.

Using positron 2D-ACAR as a probe of point defects in GaAs: The As vacancy as a case study

Using positron 2D-ACAR as a probe of point defects in GaAs: The As vacancy as a case study

Tight-binding molecular-dynamics study of point defects in GaAs.

Tight-binding molecular-dynamics simulations at 0 K have been performed in order to study the effect of defects (vacancies and antisites) in different states of charge on the electronic and structural properties of GaAs. Relaxations are fully included in the model, and for each defect we calculate the local atomic structure, the volume change upon relaxing, the formation energy (including chemical potential contributions), and the ionization levels. We find Ga vacancies to relax by an amount which is independent of the state of charge, consistent with positron lifetime measurements. Our calculations also predict Ga vacancies to exhibit a negative-U effect, and to assume a triply negative charge state for most values of the electron chemical potential. The relaxation of As vacancies, on the contrary, depends sensitively on the state of charge. The model confirms the two experimentally observed ionization levels for this defect, just below the conduction-band minimum. Likewise, Ga antisites exhibit large relaxations. In fact, in the neutral state, relaxation is so large that it leads to a ``broken-bond'' configuration, in excellent accord with the first-principles calculations of Zhang and Chadi [Phys. Rev. Lett. 64, 1789 (1990)]. This system also exhibits a negative-U effect, for values of the electron chemical potential near midgap. For As antisites, we find only a weak relaxation, independent of the charge. The model predicts the neutral state of the defect to be the ground state for values of the electron chemical potential near and above midgap, which supports the view that the EL2 defect is a neutral As antisite. Upon comparing the formation energies of the various defects we finally find that, for all values of the atomic chemical potentials, antisites are most likely to occur than vacancies.

Lattice defects in ion implanted GaAs

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Impurity effect on the creation of point-defects in GaAs and InP investigated by a slow positron beam

The impurity effect on the creation of point-defects in 60-keV Be+-ion implanted GaAs and InP has been studied by a slow positron beam. Vacancy-type defects introduced by ion implantation were observed in n-type GaAs. For p-type GaAs, however, this was not the case. This can be attributed to the recombination of vacancy-type defects with pre-existing interstitial defects in p-type GaAs. In the case of InP, the vacancy-type defects were created by ion implantation and increased with the implantation dose. However, no significant doping effect was observed in InP.

Thermal equilibrium concentrations of point defects in gallium arsenide

Expressions of the thermal equilibrium concentrations of point defects in GaAs, including the neutral and charged species, are derived. These expressions are explicit functions of well-defined thermodynamic quantities, which in turn yield explicit expressions for the reaction constant K in the usual As 4 pressure power law representation of the point defect thermal equilibrium concentrations. Such power laws have been of little quantitative value in the past, because values for K were not known. In the present derivation, emphases are placed upon the difference between the Gibbs free energies of an As atom in the interior of a GaAs crystal and in an As vapor phase molecule, and the role of the crystal Fermi level. Numerical values of the thermal equilibrium concentrations of the neutral and three negatively charged Ga vacancies (V 0 Ga, V − Ga, V 2− Ga and V 3− Ga), the neutral As vacancies V 0 As and the two neutral antisite de Ga 0 As and As 0 Ga have been obtained. The calculated thermal equilibrium concentration of the anion antisite defect As 0 Ga reaches a peak value of about 1 sx 10 17 cm −3 and is practically temperature independent, in agreement with experimental findings. The thermal equilibrium concentrations of the triply negatively charged Ga vacancy V 3− Ga, C eq v 3− Ga ( n), have been found to exhibit a temperature independence or a negati temperature dependence behavior under strong n-doping conditions. That is, the C eq v 3− Ga ( n) value is either unchanged or increases as the temperature is lowered. This C eq v 3− Ga ( n) property provided explanations to a number of outstanding experimental results, either requiring the interpretation that V 3− Ga has attained its thermal equilibrium concentration at the onset of each experiment, or requiring mechanisms involving point defect nonequilibrium phenomena. The calculated C eq v 3− Ga ( n) values are in agreement with available experimental results.