Complexes In GaAs Research Articles

Gallium vacancy --- shallows donor complexes in n-GaAs doped with elements of group VI Te or S (R e v i e w)

The results of studies of Ga vacancy --- shallow donor (Te or S atom substituting As atom in the lattice site closest to the vacancy VGa) complexes by methods of photoluminescence under resonant polarized excitation and piezospectroscopy are considered. An analysis of the experimental data in the classical dipole approximation shows that the symmetry of the complexes is lower than the trigonal one and their optical properties are explained in the model of a monoclinic defect with a symmetry plane of the \011\ type, in which the initial trigonal axis and the axis of the optical dipole lie. The reason for the lowering of the symmetry of the initially trigonal center is the distortions arising from the Jahn-Teller effect. A microscopic model is proposed that relates the behavior peculiarities of the optical properties of the VGaTeAs complex under uniaxial deformations and temperature changes with the structure of the electronic levels and the change in the charge state of the complex. The differences in this behavior observed for the VGaTeAs complex are analyzed and possible reasons for their appearance are discussed. Keywords: vacancy complexes in GaAs, Jahn-Teller effect, photoluminescence under resonant excitation, piezospectroscopy.

27a-N-12 GaAs中のErと複合欠陥

27a-N-12 GaAs中のErと複合欠陥

Symmetry and structure of carbon-nitrogen complexes in gallium arsenide from infrared spectroscopy and first-principles calculations

Molecular-like carbon-nitrogen complexes in GaAs are investigated both experimentally and theoretically. Two characteristic high-frequency stretching modes at 1973 and 2060 cm−1, detected by Fourier transform infrared absorption (FTIR) spectroscopy, appear in carbon- and nitrogen-implanted and annealed layers. From isotopic substitution, it is deduced that the chemical composition of the underlying complexes is CN2 and C2N, respectively. Piezospectroscopic FTIR measurements reveal that both centers have tetragonal symmetry. For density functional theory (DFT) calculations, linear entities are substituted for the As anion, with the axis oriented along the 〈1 0 0〉 direction, in accordance with the experimentally ascertained symmetry. The DFT calculations support the stability of linear N-C-N and C-C-N complexes in the GaAs host crystal in the charge states ranging from + 3 to –3. The valence bonds of the complexes are analyzed using molecular-like orbitals from DFT. It turns out that internal bonds and bonds to the lattice are essentially independent of the charge state. The calculated vibrational mode frequencies are close to the experimental values and reproduce precisely the isotopic mass splitting from FTIR experiments. Finally, the formation energies show that under thermodynamic equilibrium CN2 is more stable than C2N.

Vibrational signature of the Si–N defect in Si-doped GaN xAs 1− x

Using first principles density functional theory in a supercell approach, we calculate the full spectrum of localized vibration modes associated with the Si–N defect complex in GaAs. Two recently proposed structures are investigated in detail: (a) substitutional Si on a Ga site with substitutional N on an adjacent As site [ (Si Ga–N As) q , where q is the charge state of the defect complex], and (b) Si and N atoms forming a split-interstitial defect on an As site [ (Si–N) q As]. All the localized mode frequencies for both defect structures are calculated in the relevant charge states. We have also calculated the formation energy of the (Si Ga–N As) q defect as a function of Si–N separation, finding that the configuration with the Si on a second-nearest-neighbor Ga site is more favorable in the positive charge state than the configuration with the Si on a nearest-neighbor Ga site to the N atom.

Quantum Dots for Future Nanophotonic Devices: Lateral Ordering, Position, and Number Control

After the general aspects of InAs/InP (100) quantum dots (QDs) regarding the formation of QDs versus quantum dashes, wavelength tuning from telecom to mid-infrared region, and device applications, we discuss our recent progress on the lateral ordering, position, and number control of QDs. Single-layer and stacked linear InAs QD arrays are formed by self-organized anisotropic strain engineering of an InAs/InGaAsP superlattice template on InP (100) with emission wavelength at room temperature in the important 1.55-?m telecom wavelength region. Guided and directed self-organized anisotropic strain engineering is demonstrated on shallow- and deep-patterned GaAs (311)B for the formation of complex InGaAs QD arrays and absolute QD position control. The lateral position, distribution, and number control of InAs QDs, down to a single QD, are demonstrated on truncated InP (100) pyramids by selective-area growth with sharp emission at 1.55 ?m. Submicrometer-scale active-passive integration is established by the lateral regrowth of InP around the pyramids for planarization. Such control over QD formation is the key to future quantum functional nanophotonic devices and integrated circuits operating at the single- and multiple-electron and photon level with controlled interactions.

Ultrafast pulsed-laser dissociation of Mn–H complexes in GaAs

We demonstrate direct writing of ferromagnetism in hydrogenated Ga0.96Mn0.04As using femtosecond laser pulses. Tight beam focusing results in the local dissociation of Mn–H defect complexes with sub-500 nm resolution and no detected surface damage. Dot, line, and Hall-bar patterns were drawn in the hydrogenated films by translating the sample during laser irradiation. Magnetotransport measurements on the Hall-bar patterns reveal recovery of hole-mediated ferromagnetism with a Curie temperature of 50 K while magnetic anisotropy is similar to prehydrogenated Ga0.96Mn0.04As. Interruption of the laser beam during writing leads to the formation of a paramagnetic gap with controllable conductance separating two ferromagnetic line segments. These features, along with the laser tunability of magnetic and electrical properties in the activated regions, represent a planar approach to defining all-semiconductor spintronic structures for device applications.

Lateral Ordering, Position, and Number Control of Self-Organized Quantum Dots: The Key to Future Functional Nanophotonic Devices

Lateral ordering, position, and number control of self-organized epitaxial semiconductor quantum dots (QDs) are demonstrated. Straight linear InAs QD arrays are formed by self- organized anisotropic strain engineering of an InGaAsP/InP (10 0) superlattice template in chemical beam epitaxy. The QD emission wavelength at room temperature is tuned into the important 1.55 mum telecom wavelength region through the insertion of ultrathin GaAs interlayers. Guided self-organized anisotropic strain engineering is demonstrated on shallow- and deep-patterned GaAs (3 1 1)B substrates by molecular beam epitaxy for the formation of complex InGaAs QD arrays. Lateral positioning and number control of InAs QDs, down to a single QD, are demonstrated on truncated InP (100) pyramids by selective-area metal-organic vapor phase epitaxy. Sharp emission around 1.55 mum is observed well above liquid nitrogen temperatures. The regrowth of a passive waveguide structure establishes submicrometer-scale active- passive integration. The demonstrated control over QD formation is the key to future functional nanophotonic devices and paves the way toward the ultimates of photonic-integrated circuits operating at the single and multiple electron and photon level with control of the quantum mechanical and electromagnetic interactions.

Theory of Mn–H co-doping for GaAs and related magnetic semiconductors

GaAs has recently received attention due to the potential use of Mn-doped material in spintronics applications. Mn Ga both magnetically and electrically dopes the material, and, in order to increase the control over the materials properties, selective passivation by hydrogen has been suggested. However, some debate exists over the location of H in Mn Ga–H complexes. We have examined the energetics, structure and vibrational modes of Mn Ga–H complexes in GaAs. In addition, we have examined the properties of Mn–H complexes in InP, where the vibrational modes have been detected, and GaN, which is also of interest for spintronics applications and exhibits enhanced magnetisation subsequent to hydrogenation. For GaAs and InP, H lies at the bond-centre, whereas in GaN H anti-bonds to N. In all cases Mn is electrically passivated by H, but retains the high spin ground state required for magnetic material.

Thermally induced carbon–oxygen complexes in GaAs

AbstractIn LEC‐grown oxygen‐containing GaAs, a vibrational absorption line is observed at 2059.6 cm–1 for T = 7 K after long‐time annealing at (700 ± 100) °C. This line is due to the stretching mode of a 12C–16O complex, since the line due to the isotopically shifted 13C–16O mode is observed at 2003.8 cm–1. Several other 12C–16O stretching modes found in this frequency region are assigned to C–O complexes with different environments. The formation of C–O complexes around 700 °C becomes possible as a result of the mobility of oxygen atoms. After the same annealing procedure, two vibrational lines are measured at 1828.2 and 1891.4 cm–1 for T = 7 K and assigned to the stretching modes of an 11B–16O (10B–16O) complex. (© 2005 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Structure and vibrational properties ofN−H2complexes in GaAs:N

Considerable attention has been focused on GaAs:N since it was discovered that the addition of nitrogen to gallium arsenide leads to a surprisingly large reduction in its band gap and changes in its electronic properties. Equally surprising was the discovery that subsequent hydrogenation largely negates these effects, generating a material whose properties are similar to those of GaAs. Infrared studies of the hydrogenated defect indicate that it contains two hydrogen atoms. Despite the efforts that have been made to understand these effects, there is to date no satisfactory model for the structure of the pertinent nitrogen-dihydrogen defect. We have investigated theoretically several possible models for this defect and suggest that a strong candidate is a nitrogen-dihydrogen complex of ${C}_{1h}$ symmetry in which the two hydrogens are in specific inequivalent locations. Ab initio calculations using CRYSTAL2003 predict that this structure is indeed metastable, and while some issues remain unresolved, the relative magnitudes of the resulting force constants are consistent with those required in mass-and-spring models to fit experimental vibrational data.

Evidence of a sulfur-boron-hydrogen complex in GaAs grown by the liquid encapsulation Czochralski technique

In LEC-grown GaAs:S, two vibrational absorption lines are measured at 2382.2 and $2392.8\phantom{\rule{0.3em}{0ex}}{\mathrm{cm}}^{\ensuremath{-}1}$ $(T=7\phantom{\rule{0.3em}{0ex}}\mathrm{K})$ and assigned to $^{11}\mathrm{B}\ensuremath{-}\mathrm{H}$ and $^{10}\mathrm{B}\ensuremath{-}\mathrm{H}$ stretching modes. Uniaxial stress experiments reveal that the symmetry of the responsible complex is ${C}_{s}$. Bond strength considerations suggest that this complex is a ${\mathrm{S}}_{\mathrm{As}}\ensuremath{-}{\mathrm{B}}_{\mathrm{Ga}}$ pair passivated by hydrogen bonded to boron. The constituents of this $\mathrm{S}\ensuremath{-}\mathrm{B}\ensuremath{-}\mathrm{H}$ complex are located within a {110} plane.

The nitrogen–hydrogen–vacancy complex in GaAs

AbstractThe local vibrational mode absorption lines at 3079.2 and 983.3 cm−1, measured in semi‐insulating LEC‐grown GaAs, are due to the stretching and wagging mode of one hydrogen bonded to a light impurity atom. The investigation of GaAs grown without boric oxide encapsulant delivers arguments that this impurity atom is nitrogen in the nitrogen‐vacancy (NAs–VGa) defect, which is responsible for the vibrational quadruplet line at 638 cm−1. (© 2004 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)

Optically active erbium–oxygen complexes in GaAs

Density functional modeling of Er and Er–O complexes in GaAs show that Er impurities at the Ga site are not efficient channels for exciton recombination, but decorative O atoms play crucial roles in inhibiting Er precipitation and in creating the necessary conditions for electron-hole capture. Among the defects studied, the ErGaOAs and ErGa(OAs)2 models have the symmetry and carrier trap location close to the defect responsible for the strong 1.54 μm photoluminescence band in Er, O codoped GaAs.

Imaging of the (Mn 2+3d 5 + hole) complex in GaAs by cross-sectional scanning tunneling microscopy

We present results on the direct spatial mapping of the wave function of a hole bound to a Mn acceptor in GaAs. To investigate individual Mn dopants at the atomic scale in both ionized and neutral configurations, we used a room temperature cross-sectional scanning tunneling microscope. We found that in the neutral configuration manganese manifests itself as an anisotropic cross-like feature. We attribute this feature to a hole, weakly bound to the Mn ion forming the (Mn 2+3d 5 + hole) complex.

Vibrational modes of a di-hydrogen complex in GaAs

Two vibrational absorption lines at 3015.5 and 3092.8cm−1, observed in liquid encapsulation Czochralski-grown GaAs, are investigated and are assigned to hydrogen stretching modes. The intensities of both lines measured in different samples are strictly correlated. Samples containing both hydrogen and deuterium show six additional lines, which are related to those. Two of them are located close to them and four lie in the region of the deuterium stretching modes. This result indicates that a di-hydrogen complex HA–X–HB is responsible for the lines, where the two hydrogen are bonded on inequivalent positions A and B to an atom X. The four values r=ω(H)/ω(D)≈1.34 of the stretching modes show that X must be a light impurity atom, probably oxygen. Illumination with light hν>0.75eV at T<90K results in a decrease of the intensity of the eight lines and the simultaneous appearance of eight new lines. This effect is due to the capture of photogenerated holes by the HA–X–HB complex.

Analysis of the emission band of V GaTeAs complexes in n-GaAs under uniaxial pressure

For approximating the insignificant deviation of the axes of radiating optical dipoles of VGaTeAs complexes in GaAs from one of the 〈111〉 directions, the shape of the structureless photoluminescence band of these defects at a pressure of 10 kbar along the [111] axis is analyzed. For separating split components of this band, which belong to centers with different orientations, a procedure is developed which uses the laws of the piezospectroscopic behavior of anisotropic centers. According to this procedure, spectral measurements are carried out when the electric vector of the optical wave is either parallel or normal to the pressure axis. The model suggested for analysis is verified. It is determined that the splitting of the energies of the centers with different orientations at a pressure of 10 kbar is approximately equal to 38 meV. In this case, the relative fraction of the rotator that describes the polarization properties of light emitted by an individual complex in a classical dipole approximation is equal to 0.15. This fact is indicative of the comparability of the roles of spin-orbit and Jahn-Teller interactions in the formation of the emitting state of the complex.

Thermal transport of charge and polarization of 1.2-eV luminescence broad band in uniaxially strained n-GaAs:Te

The effect of temperature on the pressure-induced polarization of the photoluminescence broad band related to VGaTeAs complexes in GaAs:Te is analyzed. It is shown that, within a certain temperature range, the pressure-induced difference in the activation energy of thermal emission of holes for dissimilarly oriented complexes leads to an abrupt increase in the integral polarization of radiation caused by recombination of free electrons with holes localized at these complexes compared to polarization at lower temperatures. In the samples subjected to 10-kbar pressure applied along the [111] axis, the described behavior of polarization was observed in the temperature range from 140 to 190 K. The results obtained validate the previously suggested model of a set of defects that give rise to the luminescence band under study. Fitting results of calculations to experimental data enabled us to correct the values of a number of the parameters of defects and to estimate a pressure-induced change in the activation energy of the thermal emission of holes from the defects with different orientation.

Charge Transfer at the Mn Acceptor Level in GaN

MBE-grown GaN : Mn layers with Mn doping concentrations around 1020 cm−3 were investigated by photoconductivity measurements. From electron spin resonance (ESR), Mn is known to be mostly present in the neutral Mn3+ or Mn2+ + h+ state, which leads to a reassignment of the known optical absorption features to charge transfer from Mn3+, either by direct photoionization at about 1.8 eV or by a photothermal ionization process via an excited state (Mn3+)* at 1.42 V higher internal energy than the Mn3+ ground state. It is proposed that the Mn3+/Mn2+ acceptor level is located about 1.8 eV above the valence band edge of GaN so that the nature of the acceptor wavefunction is very different from an effective-mass-like state such as the Mn2+ + h+ complex in GaAs : Mn. According to these experimental results, the realization of carrier-mediated ferromagnetism becomes rather unlikely in not co-doped GaN : Mn.

Nitrogen–hydrogen complexes in GaAs and GaAs1–xNx alloys

AbstractWe investigate the atomic structure of various N–H complexes in GaAs and GaAs1–xNx alloys through first‐principles pseudopotential calculations within the local‐density‐functional approximation. For GaAs with low H concentrations, we suggest that nitrogen forms a N–H(BC) complex, where H is positioned at a bond‐center site between a substitutional N and one of the neighboring Ga atoms. For very high H concentrations, an optically inactive N–H2*(BC‐ABN) complex, which corresponds to a configuration of H2* in the vicinity of N, is suggested to be an energetically favorable structure. These atomic models explain many experimental features observed in GaAs and GaAs1–xNx alloys, which contain both N and H.

Stability and electronic structure of hydrogen–nitrogen complexes in GaAs

We investigate the stability and electronic properties of defects formed by a substitutional nitrogen in GaAs (NAs) plus interstitial hydrogen atoms using first-principles total-energy calculations. We find the formation of strong NAs–H bond when a single H atom is incorporated in the lowest-energy bond centered (BC) position. This defect induces an electrically active level in the GaAs band gap. When two H atoms are incorporated, we find the stable NAs–H2* complex as the lowest-energy configuration, with one H atom at the BC position and the second H atom at an antibonding position. The electronic structure of this complex shows the passivation of the gap level restoring the GaAs band gap.