Study Of Defects In GaAs Research Articles

Theoretical Study of Antistructure Defects in GaAs

Theoretical Study of Antistructure Defects in GaAs

Study of Defects in GaAs by 2D-ACAR Positron Annihilation

We describe the two dimensional angular correlation of positron annihilation radiation (2D-ACAR) method and show that it can be advantageously used to study the electronic structure of defects, in addition to standard positron lifetime and Doppler broadening measurements. Using annihilation fractions determined by lifetime measurements, we separate 2D-ACAR distributions for negatively charged and neutral arsenic vacancies in n-type GaAs. In electron-irradiated semi-insulating GaAs, we present 2D-ACAR results for the negatively charged gallium vacancy and for positron Rydberg states induced by gallium antisites. The 2D-ACAR for delocalized positrons, needed in the separation process, has been obtained from measurements on as-grown semi-insulating GaAs. Our results outline the capabilities of the 2D-ACAR technique when it is applied to the study of defects: the electronic structure in the vacancies are found to be well described by recent molecular dynamics calculations. The method also provides information about atomic relaxations around the vacancy sites, they are in agreement with the calculated relaxations. We conclude that the 2D-ACAR method is a promising tool to investigate defects in semiconductors.

The study of native defects in as-grown GaAs by positron annihilation

A mono-energetic positron beam was applied for a study of native defects in GaAs. From measurements of Doppler broadening profiles and lifetime spectra of positrons, it was found that Ga-vacancies were introduced by Si-doping. On the other hand, for p-type GaAs, interstitial clusters were found to be introduced by Zn-doping. The observed species of defects are in agreement with those expected from the Fermi level.

Surface-acoustic-wave study of defects in GaAs grown by molecular-beam epitaxy at 220 degreesC.

Surface acoustic waves (SAW's) were used to study the influence of defects on the elastic properties of epitaxial films of semiconductors. The object of this study was As-rich GaAs grown by molecular-beam-epitaxy at 220 \ifmmode^\circ\else\textdegree\fi{}C. The SAW velocity on 0.3-wavelength-thick epilayers was 1.2% smaller than on the substrate alone. That velocity difference decreased after loss of some excess As as a result of 350 \ifmmode^\circ\else\textdegree\fi{}C--435 \ifmmode^\circ\else\textdegree\fi{}C anneals. A persistent increase as much as 0.4% of the SAW velocity at low temperatures was observed after illumination; this increase could be quenched by annealing at 120--130 K. This behavior is caused by the metastable transition of EL2-like ${\mathrm{As}}_{\mathrm{Ga}}$ defects and constitutes the direct experimental proof of the illumination-induced large lattice relaxation of this defect. The SAW velocity increase was correlated with the persistent bleaching of EL2-related optical absorption. The spectral dependence of rate of illumination-induced SAW velocity increase was measured.

Study of defects in GaAs by differential thermal analysis

Differential thermal analysis is applied to the measurement of defect total energies in GaAs. First, the technique is used to determine the energy liberated in the recombination of an As vacancy-interstitial pair; the result, in agreement with the theoretical estimate of the energy stored in such defect, allows the demonstration of the validity of the technique as well as its limitations. Then, the technique is used to evaluate the introduction rate of such defects by electron irradiation in a semi-insulating material in which electrical techniques cannot be applied. Finally, a characterization of native defects is attempted; it shows that recombination of native vacancies, with interstitials liberated when the movement of α dislocations takes place, occurs around 450 °C.

Electric and tensoelectric study of radiation defects in GaAs

The electric and tensoelectric properties are studied for GaAs crystals which have been irradiated by electrons (2.3 Mev) at 300/sup 0/K with integrated fluxes of up to 2 x 10/sup 15/ - 1 x 10/sup 19/ cm/sup -2/. On the basis of the electrical neutrality equation, including seven energy levels (E1-E5, H0, H1) of the radiation defects, the specific resistivity rho and the strain sensitivity coefficient ..cap alpha../sub rho/ = d(Znrho)dP are quantitatively analyzed as a function of exposure. The pressure coefficients for the E1-E5 levels with respect to the Gamma/sub c//sup 6/ point are determined to be (approx. = 0, 9.6, 11.0, 11.6, 11.6) x 10/sup -6/ eVbar, respectively, at 300/sup 0/K.i

Photoluminescence Study of Defects in GaAs Formed by Annealing in an H2 Gas Flow

GaAs crystals were annealed in an H2 gas flow and the degraded layer formed on the surface by annealing has been investigated by a photoluminescence measurement. The origin of the defects, in particular an emission at 890 nm, formed by annealing has also been investigated with the aid of the liquid phase epitaxy technique. The degradation of the surface is governed by self-diffusion of As vacancies. The degraded layer depth increases in proportion to the square root of the heating time, whose rate depends on carrier concentrations in the crystals. As the crystals are annealed in an H2 gas flow, new emission band at 890 nm grows drastically. It is concluded that the band is due to electron transitions from a shallow donor to an As vacancy acceptor.