Impurities In GaAs Research Articles

Manganese-oxygen impurities in GaAs

Manganese-oxygen impurities in GaAs

Local mode sideband IR absorption and second harmonic intensity calculation for various isolated impurities in GaAs

We have calculated the intensity and shape of the local mode sidebands and the second harmonic intensity for various isolated impurities in GaAs. To calculate the absorption we have considered the second order dipole moment in the harmonic approximation. The absorption depends on the values of the impurity charge and polarizability, on the corresponding quantities for the nearest neighbours of each impurity and on a charge migration factor. The latter accounts for charge variations during the motion. Although these quantities vary from impurity to impurity, the results are presented in a general form valid also for other impurities. The point group symmetry properties are used in order to give a physical meaning to the results. The effects on the dynamical properties from the mass defect and the local changes in the force constant are also taken into account.

Infrared absorption of various isolated impurities in GaAs

We have calculated the infrared absorption at the local mode frequency for various isolated impurities such as B, Al, Mg, Si, C, and P in GaAs. To calculate the local mode frequency we take into account the effects from impurity mass defect and local force constant shifts and use the symmetry properties of the lattice. To calculate the absorption we consider contributions to the dipole moment from impurity and nearest neighbour charges and from charge migration effects. We suggest a physical model which accounts for impurity and nearest neighbour charges and polarizabilities.

Infrared absorption of various isolated impurities in GaAs

The structural, vibrational and microwave dielectric properties of double perovskite ceramics Ba2Zn1−xCaxWO6(x=0−0.4) were investigated. The samples were sintered at different temperatures in the range 1300–1400 °C for 4 h. The grown samples were characterized by means of X–ray diffraction, Raman spectroscopy, scanning electron microscopy and energy dispersive X–ray spectroscopy analysis. Microwave dielectric properties of the samples were measured using the TE01δ resonance mode of the cylindrical pellets. The relative permittivity (εr), calculated using Clausius–Mossotti equation is found to be comparable with the experimental results. Our analysis shows that the tolerance factor (t) as well as the temperature coefficient of resonant frequency (τf) of these perovskites decreases with the increase in Ca content. The value of τf is zero for the samples with x = 0.3 and 0.4.

A study of deep levels in GaAs by capacitance spectroscopy

We show how the DLTS capacitance spectroscopy technique can be used to detect small amounts of deep level impurities in GaAs p-n junctions. The DLTS spectra associated with Cu, Fe, Cr, 0, and two unidentified but commonly occurring deep levels in GaAs are shown. The LPE distribution coefficients are obtained for Cu, Fe, and Cr. The carrier capture cross sections for six levels are measured and give evidence for capture by multiphonon emission.

The localized vibrations of charged and uncharged impurities in GaAs and GaP

Beryllium-doped GaAs grown by the liquid phase epitaxial technique shows an infrared absorption line due to the localized vibrations of 9BeGa at 482 cm-1. This is discussed in relation to vibrations of 9BeGa in GaP and boron in GaAs and GaP.

Force-Constant Changes due to Impurities in GaAs and GaP

The theory of localized modes due to Dawber and Elliott has been extended to include force-constant changes near the impurity site. This has been used to evaluate the force-constant changes due to impurities in GaAs and GaP. Calculations have been made by assuming a band model for the density of phonon states of the host crystals. The results are compared to a calculation of force-constant changes of these impurities in a molecular model. It is observed that the band model is more suitable than the molecular model for calculating the force-constant changes. It is pointed out that the present theory is inadequate for treating very light impurities.

Influence of surface band bending on the incorporation of impurities in semiconductors: Te in GaAs

A portion of the 1000°C solid solubility isotherm for Te in GaAs was determined by liquid-phase epitaxial growth of layers doped with radioactive 129 m Te. The Te concentration in the solid was varied from 2 × 10 17 to 4 × 10 19 atoms/cm 3 and was found to depend linearly on the Te atom fraction in the liquid phase. For a linear dependence, a distribution coefficient of 0·35 may be assigned to Te at 1000°C. For extrinsic conditions and dilute liquid solutions, present models for the incorporation of fully ionized impurities, which do not include surface band bending, lead to a square-root dependence of the impurity concentration in the solid on the impurity concentration in the liquid phase. Treatment of the liquid-solid interface as a metal-semiconductor Schottky barrier gives an electron concentration at the semiconductor surface which is independent of the impurity concentration in the solid, and results in a linear relationship between the concentration in the solid and liquid phase. Existing results for other impurities in GaAs and GaP suggest that it is necessary to consider surface band bending in the interpretation of other impurity III-V semiconductor systems.

Surface Raman scattering by the localized mode of phosphorus impurities in GaAs

We have observed Raman scattering from the localized mode of phosphorus impurities in GaAs, using the 4800 Å line of an argon ion laser in reflection from a sample surface.

Mobility Effects Due to Dilute Multilevel Impurities in GaAs

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Electroreflectance of impurities in GaAs: manganese, silicon and cadmium : E. W. Williams, Solid St. Commun.7 (1969), p. 541

Electroreflectance of impurities in GaAs: manganese, silicon and cadmium : E. W. Williams, Solid St. Commun.7 (1969), p. 541

Electroabsorption by Substitutional Copper Impurities in GaAs

Previously, Hall effect and other thermal activation measurements have suggested that a copper atom substituted on a gallium site in GaAs is a double acceptor with its first ionization level at 0.145 eV and its second between 0.44 and 0.49 eV above the valence band. Also, previous photoluminescence measurements have revealed broad lines attributable to copper at the Stokes-shifted positions 0.155 eV and between 0.49 and 0.53 eV. Using an electroabsorption technique, we have studied the spectrum of substitutional copper in GaAs. We find an absorption line associated with a level at 0.463 eV above the valence band for temperatures of 103° and 300°K. We conclude from the selection rules that the wavefunction associated with this level transforms as the Γ6 representation of the double group Td. Except for a weaker additional absorption line (which we do not yet understand) occurring at 0.454 eV in a single p-type sample, we were able to find no other lines. These results supplement earlier work on the 0.145 eV state. We propose a simple model which we feel describes the substitutional copper impurity and apply it to our measurements on the 0.463 eV state and our earlier work on the 0.145 eV state. While this model is not adequate for a first-principles calculation, it does provide a framework in which to understand and discuss our results.

Electroreflectance of impurities in GaAs: Manganese, silicon and cadmium

Manganese impurities in GaAs can be seen in electroreflectance at 300°K. The electroreflectance peak due to manganese is at 1.36 eV for the heaviest doping used (1 × 10 18 holes/cm 3). Hydrogenic cadmium and silicon acceptors were observed and there is some evidence for hydrogenic silicon donors.

Local-Mode Absorption and Defects in Compensated Silicon-Doped Gallium Arsenide

Silicon is known to be an amphoteric impurity in GaAs. A large number of ir absorption bands have been previously reported for Si-doped GaAs which has been compensated by Li or Cu diffusion. These bands, which are at frequencies above the pure GaAs single-phonon spectrum, have been attributed to localized vibration modes of defects. The present experimental study extends previous work to show that all the observed bands (frequencies given in parentheses) are explicable in terms of the presence of the following defects: SiGa (384 cm−1), SiAs (399 cm−1) SiGa-LiGa (374, 379, 405, 470, 480, 487 cm−1), SiGa-CuGa (374, 376, 399 cm−1), and SiGa-SiAs. (367, 393, 464 cm−1). These assignments appears to be consistent with results obtained by varying the Si concentration and by different thermal treatments.

GaAsInSb graded-gap heterojunction

The interface-alloy technique has been used to produce heterojunctions between GaAs and InSb. X-ray and Kossel line patterns show that, despite the relatively large 14 percent lattice mismatch between the semiconductors, these heterojunctions are single-crystal. Photocurrent and I–V measurements are explained by a model for the heterojunction band structure in which the salient feature is a region of the order of 60 Å long which has a linearly-graded energy gap joining the GaAs to the InSb. In addition, interface states ‘fix’ the location of the GaAs bands at the heterojunction interface such that, at room temperature, the conduction band extrapolates to a value approximately 0.93 eV above the Fermi level. The photocurrent occurs via hot carriers generated in the graded-gap region which traverse this region (with a mean free path of approx. 20 Å) to the heterojunction barrier maximum. As predicted by the model, incident monochromatic radiation of energy smaller than the GaAs bandgap produces a photocurrent which varies exponentially with photon energy as I 0 exp[ C( hν − E g )], where C is a positive parameter which decreases for increasing reverse bias on the heterojunction, and I 0 is the extrapolated response at the GaAs bandgap, which is independent of applied bias. The forward current of units fabricated with n-type GaAs varies as exp( qV ηkT ) , and, except at lower temperatures where tunneling becomes important, the values of η as a function of the GaAs impurity doping concentration can be explained in terms of the increase in the heterojunction barrier height with voltage, since part of the depletion layer potential is across the graded-gap region. Similarly, the voltage dependence of the reverse current is quantitatively explained by this model. The results of the C–V measurements are consistent with the I–V and photocurrent measurements evaluated in terms of the graded-gap heterojunction model.

SOME EFFECTS OF Zn DIFFUSION ON Mn-DOPED GaAs

Radiotracer techniques have been used to show that Zn diffusion into an originally uniformly Mn-doped GaAs wafer produces marked changes in the Mn concentration profile, resulting in a large minimum behind and a small minimum ahead of the Zn diffusion front. A model which assumes that Mn is an amphoteric impurity in GaAs is proposed to explain these changes.

Gaussian impurity bands in GaAs

It is shown that the density of states function for acceptor and donor impurities in GaAs is described by a Gaussian distribution function. Values of the Gaussian half-width determined from an analysis of optical absorption data are in excellent quantitative agreement with values given by the Kane formula.

Edge emission involving manganese impurities in GaAs at 4.2°K

Recombination radiation in manganese doped GaAs at 4.2°K shows a set of lines, separated by the longitudinal optical phonon energy (0.036 eV). This is interpreted to be of the same recombination mechanism involved in the edge emission of such polar crystals as ZnS and CdS. Relative line intensities approximately follow a Poisson distribution in accordance with Hopfield's theory.