David J. Keeble

Spin-dependent Shockley-read recombination of electrons and holes in indirect-band-gap semiconductor p-n junction diodes

Abstract This paper presents a new model for spin-dependent recombination and generation processes based on the electrical detection of magnetic resonance in semiconductor p - n junction diodes. Based on a modified Shockley-Read recombination statistics, this model differs from those models previously proposed in that the spin-dependent enhancement of free-carrier capture processes can occur directly at a paramagnetic deep defect without the need for other defects nearby. This model incorporates singlet-triplet mechanisms of existing models, but is shown to be consistent with new experimental results which indicate the absence of any adjacent trapping centers.

Electrically detected magnetic resonance of a transition metal related recombination center in Si p–n diodes

A hyperfine structure has been observed by electrically detected magnetic resonance from a Si p–n diode. From the hyperfine splitting, and the natural abundance of the interacting I=1/2 nuclear species, the recombination center is found to be consistent with a platinum complex.

Annealing of low-temperature GaAs studied using a variable energy positron beam

The annihilation characteristics of monoenergetic positrons implanted in a molecular beam epitaxy layer of low‐temperature (LT) GaAs annealed at temperatures from 300 to 600 °C were measured. A gallium vacancy concentration of approximately 3×1017 cm−3 is inferred for the as‐grown material. The S parameter increased significantly upon anneal to 500 °C. The dominant positron traps in samples annealed at and below 400 °C are distinct from those acting for samples annealed to 500 or 600 °C. The change in S parameter for the 600 °C annealed sample compared to the GaAs substrate, SLT,600=1.047Ssub, is consistent with divacancies or larger open volume defects.

Electron paramagnetic resonance of Mn4+ in PbTiO3

The electron paramagnetic resonance spectrum of Mn4+ in single-crystal lead titanate has been studied at 9.8 and 33.8 GHz. An axial sextet with gperpendicular to eff=3.7742(1) to g/sub ///eff approximately=2.00 was measured at 9.8 GHz and with gperpendicular to eff=2.7048(15) at 33.8 GHz; a second sextet was observed at high field at 9.8 GHz. The spectr um was fitted using spin .Hamiltonian parameters S=3/2, I=5/2, g/sub ///=1.99, gperpendicular to =1.987, A/sub ///=79.46*10-4 cm-1. Aperpendicular to =71.05*10-4 cm-1 and mod D mod =0.3166 cm-1. The electronic spin value and the magnitude of the hyperfine constant, mod A mod =73.9 cm-1, confirm the Mn4+ assignment. A superposition model analysis using available b2(R) functions for 3d3 configuration ions in oxide hosts was unable to reproduce the observed axial crystal field magnitude, mod D mod .

Electron Paramagnetic Resonance Studies of Impurity Defects in PbTiO3

Electron paramagnetic resonance studies of metal ion impurities in the perovskite titan ate PbTiO3 are presented. Results for Pt+3, Mn+4, and Cu+2 are given, and near-neighbor superhyper fine structure (shfs) splittings for the first Pb shell are reported for these ions at low temperature. The relation between the shfs and the local structure of the ion is discussed.

Positron annihilation studies of vacancy related defects in ceramic and thin film Pb(Zr,Ti)O3 materials

Abstract Preliminary positron annihilation studies of ceramic and thin film Pb(Zr,Ti)O3 (PZT) materials have been completed. The aim of this work was to examine the effects of processing conditions on vacancy related defects. Positron lifetime measurements on bulk PLZT plates showed an increase in positron trapping to a defect state with increasing grain size consistent with trapping to lead vacancy related defects formed through lead oxide loss during processing. Variable energy positron beam measurements were completed on bulk PLZT plates, sol-gel PZT thin films and laser ablated PLZT thin films. Films processed in a reduced oxygen atmosphere were found to give a higher S-parameter, due to an increase in concentration of neutral or negatively charged vacancy type defects, compared with material processed in an oxidizing ambient.

Vacancy related defects in thin film Pb(ZrTi)O{sub 3} materials

Positron annihilation techniques have been applied to characterize vacancy-related defects in ferroelectric thin film structures. Variable energy positron beam measurements were carried out on doped and undoped Pb(ZrTi)O{sub 3} (PZT) samples subjected to different post-deposition cool down and anneal conditions. The PZT was deposited by sol-gel with either with platinum or RuO{sub 2} electrodes, or by laser ablation with La{sub 0.5}Sr{sub 0.5}CoO{sub 3} electrodes. The RuO{sub 2} and La{sub 0.5}Sr{sub 0.5}CoO{sub 3} electrode samples showed a smaller S-parameter compared to those deposited with Pt electrodes consistent with an improved PZT layer quality. For laser ablated samples cooled in a reducing ambient an increase in S-parameter for both the PZT and La{sub 0.5}Sr{sub 0.5}CoO{sub 3} layers was observed indicating an increase in neutral or negatively charged open-volume defects.

Positron annihilation studies of defects in molecular beam epitaxy grown III–V layers

Abstract A summary of recent positron annihilation experiments on molecular beam epitaxy (MBE) grown III–V layers is presented. Variable energy positron beam measurements on Al0.32Ga0.68As undoped and Si-doped have been completed. Positron trapping at an open volume defect in Al0.32Ga0.68As:Si for temperatures from 300 to 25 K in the dark was observed. The positron trap was lost after 1.3 eV illumination at 25 K. These results indicate an open volume defect is associated with the local structure of the deep donor state of the DX center. Stability of MBE GaAs to thermal annealing was investigated over the temperature range 230–700°C. Proximity wafer furnace anneals in flowing argon were used. Samples grown above 450°C were shown to be stable but for samples below this temperature an anneal-induced vacancy-related defect was produced for anneals between 400 and 500°C. The nature of the defect was shown to be different for materials grown at 350 and 230°C. Activation energies of 2.5-2.3 eV were obtained from isochronal anneal experiments for samples grown at 350 and 230°C, respectively.

Variable energy positron beam characterization of defects in As-grown and annealed low temperature grown GaAs

Variable energy positron annihilation measurements on as-grown and annealed GaAs grown by molecular beam epitaxy at temperatures between 230 and 350°C have been performed. Samples were subjected to either isochronal anneals to temperatures in the range 300 to 600°C or rapid thermal anneals to 700, 800, and 900°C. A significant increase in the S-parameter was observed for all samples annealed to temperatures greater than 400°C. The positron annihilation characteristics of the defect produced upon annealing are consistent with divacancies or larger vacancy clusters. The concentration of as-grown and anneal generated defects is found to decrease with increasing growth temperature.

Electrically-detected magnetic resonance near the p-doped/n-doped interface of Si junction diodes

Hyperfine structure has been observed in the electrically-detected magnetic resonance signal from a silicon p-n junction diode. By comparing the g value, hyperfine parameters, and bandgap energy level with known species having suitable abundances of isotopes with I = ½, the center is tentatively assigned as a platinum moiety, of presently undetermined structure. The observation indicates the usefulness of EDMR in the study of defects in ultrasmall Si devices, and raises certain questions regarding the current theories of spin-dependent recombination.