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1

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Al–Ga interdiffusion, carbon acceptor diffusion, and hole reduction in carbon-doped Al0.4Ga0.6As/GaAs superlattices: The As4 pressure effect (1993)

You, H. M. ; Tan, T. Y. ; Gösele, U. M. ; [et al.]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 74 (1993), S. 2450-2460

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: Al–Ga interdiffusion, carbon acceptor diffusion, and hole reduction were studied in carbon doped Al0.4Ga0.6As/GaAs superlattices (SL) annealed under different ambient As4 pressure conditions in the temperature range of 825 °C–960 °C. The SL were doped with carbon to an initial acceptor concentration of ∼2.9×1019 cm−3. Al–Ga interdiffusion was found to be most prominent under Ga-rich annealing ambient conditions, with interdiffusivity values, DAl–Ga, turned out to be about two orders of magnitude smaller than those predicted by the Fermi-level effect model. Under As-rich ambient conditions, the DAl–Ga values are in approximate agreement with those predicted by the Fermi-level effect model. The hole concentrations in the SL decreased significantly after annealing under As-rich and As-poor ambient conditions, while those after annealing in the Ga-rich ambient were almost totally intact. By analyzing the measured hole concentration profiles, it has been found that both carbon acceptor diffusion and reduction have occurred during annealing. Both the carbon acceptor diffusivity data and the carbon acceptor reduction coefficient data are characterized approximately by a dependence on As4 pressure values to the one-quarter power. These As4 pressure dependencies indicate that carbon diffuses via the interstitialcy or interstitial–substitutional mechanism, while hole reduction is governed by a carbon acceptor precipitation mechanism.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.354682

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Modeling of zinc-indiffusion-induced disordering of GaAs/AlAs superlattices (1993)

Zimmermann, H. ; Gösele, U. ; Tan, T. Y.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 73 (1993), S. 150-157

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: A model for the effect of Zn indiffusion on enhancing the GaAs/AlAs superlattice (SL) disordering process, which combines recently proposed models for Ga self-diffusion and Zn diffusion in GaAs, is presented. Four coupled partial differential equations describing the process were solved numerically. Satisfactory agreement between the simulated results and experimental data available in the literature is obtained. At a given temperature, the used values for the diffusion coefficient and the thermal equilibrium concentration of the responsible point defect species, the doubly positively charged Ga self-interstitials IGa2+, are a consistent splitting of the known Ga self-diffusion coefficient dominated by IGa2+. Quantitatively, the SL disordering enhancement is mainly due to the Fermi-level effect while an IGa2+ supersaturation also makes a small contribution. Because of p-doping by Zn acceptor atoms, the IGa2+ concentration is increased tremendously via the Fermi-level effect. An IGa2+ supersaturation also develops because the IGa2+ generation rate is higher than its removal rate. The enhanced SL disordering process mainly proceeds under the Ga-rich SL composition conditions. The Zn-indiffusion-enhanced Al-Ga interdiffusion coefficient shows an apparent dependence on the Zns− concentration differing slightly from a quadratic relationship.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.353892

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3

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SiO2 precipitate strain relief in Czochralski Si: Self-interstitial emission versus prismatic dislocation loop punching (1992)

Taylor, W. J. ; Gösele, U. ; Tan, T. Y.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 72 (1992), S. 2192-2196

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: Formation of SiO2 precipitates in Czochralski Si is associated with a volume expansion of more than 100%. The needed extra volume for precipitate growth to occur is primarily supplied by emission of Si self-interstitials (I) into the Si matrix, in balance with a compressive growth residual strain. During cooling after the anneal, an additional compressive cooling strain component also develops because of the different thermal expansion coefficients of SiO2 and Si. For precipitates grown to a sufficiently large size, the growth residual strain and/or the cooling strain can be further relieved by punching interstitial type prismatic dislocation loops into the Si matrix. Otherwise, only I emission can occur. Up to now, there have been no quantitatively determined strain values, which constitute in a given experiment a measure of the I emission efficiency on the one hand, and a basis for determining whether prismatic punching can also occur on the other. In this study, we have calculated the strain values and obtained a quantitative criterion for prismatic punching to occur. In the order of ∼10−3–10−2, the growth residual strain component values indicate that I emission has attained an efficiency of relieving the precipitate growth strain by ∼90%–99%. Available experimental data on the precipitate size dependence of prismatic dislocation loop punching have been satisfactorily fitted using the obtained strain values and the punching criterion, indicating that these calculated values are in acceptable accuracy ranges.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.351610

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4

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Disordering in 69GaAs/71GaAs isotope superlattice structures (1992)

Tan, T. Y. ; You, H. M. ; Yu, S. ; [et al.]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 72 (1992), S. 5206-5212

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: Undoped 69GaAs/71GaAs isotope superlattice structures grown by molecular beam epitaxy on n-type GaAs substrates, doped by Si to ∼3×1018 cm−3, have been used to study Ga self-diffusion in GaAs by disordering reactions. In the temperature range of 850–960 °C, the secondary ion mass spectrometry (SIMS) measured Ga self-diffusivity values showed an activation enthalpy of 4 eV, and are larger than previously compiled Ga self-diffusivity and Al-Ga interdiffusivity values obtained under thermal equilibrium and intrinsic conditions, which are characterized by a 6 eV activation enthalpy. Characterizations by SIMS, capacitance-voltage (C-V), and transmission electron microscopy showed that the as-grown superlattice layers were intrinsic which turned into p type with hole concentrations of ∼2×1017 cm−3 after annealing, because the layers contain carbon. Dislocations of a density of ∼106–107 cm−2 were also present. However, the factor responsible for the presently observed larger Ga self-diffusivity values appears to be Si out-diffusion from the substrate, which was determined using C-V measurements. Out-diffusion of Si decreases the electron concentration in the substrate which causes the release of Ga vacancies into the superlattice layers where they become supersaturated. This Ga vacancy supersaturation leads to enhanced Ga self-diffusion in the superlattice layers.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.352002

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5

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Determination of vacancy and self-interstitial contributions to gallium self-diffusion in GaAs (1991)

Tan, T. Y. ; Yu, S. ; Gösele, U.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 70 (1991), S. 4823-4826

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: A quantitative determination of the contributions of the triply negatively charged Ga vacancies (V3−Ga) and of the doubly positively charged Ga self-interstitials (I2+Ga) to the Ga self-diffusion coefficient in GaAs has been carried out. Under thermal equilibrium and intrinsic conditions, the V3−Ga contribution is characterized by an activation enthalpy of 6 eV for As-rich crystals and of 7.52 eV for Ga-rich crystals, while the I2+Ga contribution is characterized by an activation enthalpy of 4.89 eV for As-rich crystals and of 3.37 eV for Ga-rich crystals.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.349048

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6

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Diffusion mechanism of zinc and beryllium in gallium arsenide (1991)

Yu, S. ; Tan, T. Y. ; Gösele, U.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 69 (1991), S. 3547-3565

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: The outstanding features associated with Zn and Be diffusion in GaAs substrates and GaAs/AlGaAs superlattices are explained either quantitatively or semiquantitatively using the kick-out mechanism, in which it is assumed that the doubly positively charged Ga self-interstitial governs Ga self-diffusion. These features include (i) the dependence of the Zn solubility upon the pressures of the As and Zn vapor phases, (ii) the square power-law dependence of the Zn diffusivity on its own background concentrations under Zn isoconcentration diffusion conditions, (iii) the different shapes of the Zn in-diffusion profiles, (iv) the much lower diffusivities of Zn and Be under out-diffusion conditions than under in-diffusion conditions, and (v) the tremendous enhancement effect of Zn in-diffusion on GaAs/AlGaAs superlattice disordering and the undetectable effect of Be under out-diffusion conditions. Some useful quantitative information has been obtained. Strictly on a qualitative basis, we have found that the Longini mechanism is also able to explain the above features (i)–(iv) fairly well. The predicted effects of the Longini mechanism on Ga self-diffusion are, however, contrary to experimental results associated with superlattice disordering.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.348497

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7

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Diffusion mechanism of chromium in GaAs (1991)

Yu, S. ; Tan, T. Y. ; Gösele, U.

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 70 (1991), S. 4827-4836

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: The diffusion of the substitutional Cr atoms (Crs) in GaAs results from the rapid migration of the interstitial atoms (Cri) and their subsequent changeover to occupy Ga sites (or vise versa), a typical substitutional-interstitial-diffusion (SID) process. There are two possible ways for the Cri-Crs changeover to occur: the kick-out mechanism in which Ga self-interstitials are involved, and the dissociative mechanism in which Ga vacancies are involved. The Crs in-diffusion profiles are of characteristic shapes indicating the dominance of the kick-out mechanism, while the Crs out-diffusion profiles are error-function shaped, indicating the dominance of the dissociative mechanism. In this study, an integrated SID mechanism, which takes into account both the kick-out and dissociative mechanisms, is used to analyze Cr diffusion results. Going beyond just qualitative consistency, the Cr in- and out-diffusion features in GaAs are explained on a quantitative basis. It is confirmed that the kick-out mechanism dominates Cr in-diffusion while the dissociative mechanism dominates Cr out-diffusion. Parameters used to fit existing experimental results provided quantitative information on the Ga self-interstitial contribution to the Ga self-diffusion coefficient. The values obtained are consistent with those obtained from a study of Zn diffusion in GaAs, and with available experimentally determined Al-Ga interdiffusion coefficients.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.349049

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Formation of epitaxial CoSi2 films on (001) silicon using Ti-Co alloy and bimetal source materials (1991)

Hsia, S. L. ; Tan, T. Y. ; Smith, P. ; [et al.]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 70 (1991), S. 7579-7587

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: Using coevaporated Ti-Co alloy and sequentially evaporated Ti-Co bimetallic layer source materials, CoSi2 films have been grown on (001) Si. The film resistivity and resistance thermal stability are excellent. The CoSi2 are epitaxial single-crystal films containing antiphase domains in the Ti-Co bimetallic layer cases and are polycrystalline films containing a substantial portion of epitaxial grains in the Ti-Co alloy cases. The epitaxial or substantially epitaxial nature of these CoSi2 films is the reason for the excellence in the film resistivity and resistance thermal stability. We believe that the epitaxial nature of the CoSi2 films results from two roles played by Ti. In the first, Ti served as a getterer for removing the native oxide layer on the Si wafer surfaces, which causes the nucleation of CoSi2 grains with random orientations. In the second, Ti silicides formed in the early stage of the annealing process served as Co diffusion barriers preventing Co2Si and CoSi formation, which would also lead to the formation of randomly oriented CoSi2 grains. Models of the interfacial structure of the epitaxial CoSi2 film and Si substrate have been constructed for [001] and [111] orientations. These models revealed that antiphase boundaries serve the role of relieving the lattice mismatch between the epitaxial CoSi2 film and Si substrate.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.349713

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Resistance and structural stabilities of epitaxial CoSi2 films on (001) Si substrates (1992)

Hsia, S. L. ; Tan, T. Y. ; Smith, P. ; [et al.]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 72 (1992), S. 1864-1873

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: The resistance and structural stabilities of the epitaxial CoSi2 films, grown on (001) Si substrates using sequentially deposited Ti-Co bimetallic layer source materials, have been investigated by further anneals under extended conditions. In contrast to reported polycrystalline silicide film cases, the epitaxial CoSi2 films are very stable under the additional rapid thermal annealing treatment at 1100 °C for times from 10 to 60 s. This means that such CoSi2 films are able to stand the further heat treatment required in the ultralarge-scale integration regime of Si integrated circuit fabrication. The quality of the further annealed films has been actually improved: The film resistivity has decreased to reach a value as low as 10 μΩ cm, and the film structure has become more perfect, e.g., the densities of antiphase domains and film-Si interface facets have been decreased. For technological applications, it is necessary to remove the Ti-Co-Si alloy layer formed concomitantly on top of the as-grown CoSi2 film. This has been accomplished by chemical etching using the standard buffered oxide etch solution. In the present experiment, as-grown epitaxial CoSi2 films with and without the Ti-Co-Si alloy top layers have been both included and the same film resistance and structural stabilities have been observed. Thus, the excellent resistance and structural thermal stabilities of the present CoSi2 films result from the single-crystal nature of the films and not the effect of the top Ti-Co-Si capping layer. Mechanisms responsible for the excellent quality of the epitaxial CoSi2 films, as well as for the unacceptable quality of the polycrystalline silicide films, have been discussed.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.351659

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10

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Distribution mechanism of voids in Si-implanted GaAs (1991)

Chen, Samuel ; Lee, S.-Tong ; Braunstein, G. ; [et al.]

[S.l.] : American Institute of Physics (AIP)

Journal of Applied Physics 70 (1991), S. 656-660

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ISSN: 1089-7550

Source: AIP Digital Archive

Topics: Physics

Notes: Voids, formed by the condensation of an excess of implantation-induced vacancies, have been recently identified as the defect directly responsible for dopant diffusion and electrical activation anomalies in Si-implanted and annealed GaAs and GaAs/AlGaAs superlattice materials. Depending on the implanted dose, voids can be distributed either throughout the implanted region or in two bands. We have examined the origin of this void distribution difference. In the as-implanted sample associated with the latter case, a buried continuous band of amorphous GaAs has formed. GaAs formed by the recrystallization of amorphous GaAs does not contain excess vacancies and therefore cannot form voids. However, on either side of the amorphous layer, the excess vacancies can condense to form the observed banded distribution of voids. In the as-implanted sample associated with the former case, a continuous amorphous GaAs layer did not form, and therefore, upon annealing, voids are seen throughout the implanted region.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.349669

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