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  • 1
    Electronic Resource
    Electronic Resource
    Thermally stable ohmic contacts to n-type GaAs. III. GeInW and NiInW contact metals (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 1974-1982 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: Improvement in thermally stable, low-resistance ohmic contacts to n-type GaAs is reported for GeInW and NiInW contact metals. Coevaporation of In with Ge or In with Ni reduced the contact resistances by a factor of about 2 compared with those of the layered structures. The reduction is believed to be due to a uniform In distribution in the contact metals in the as-deposited state which resulted in an increased area of InxGa1−xAs phases in direct contact with the GaAs substrate. Annealing the coevaporated GeInW contacts for a short time at temperatures between 900 and 980 °C resulted in a mean contact resistance of 0.5 Ω mm. Similar annealing of the coevaporated NiInW contacts at temperatures between 800 and 1000 °C resulted in a contact resistance of 0.3 Ω mm. Additionally, the thermal stability of these ohmic contacts at 400 °C after contact formation, which is required by subsequent integrated circuit process steps, was studied. Although a slight increase in the contact resistances was observed after annealing for 100 h at 400 °C for the GeInW contacts, no change in the contact resistances was observed for the NiInW contacts after annealing for 100 h at 400 °C and for 10 h at 500 °C. This excellent thermal stability of the NiInW contacts is believed to be due to the formation of Ni3In intermetallic compounds which have high melting points. The present study suggests that in order to prepare thermally stable, low-resistance contacts it is desirable to deposit a metal which forms high melting point intermetallic compounds with In and which promotes formation of uniform InxGa1−xAs phases at the metal/GaAs interfaces. Further reduction in the measured contact resistances was achieved by reducing the sheet resistance of the contact metals.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341752
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  • 2
    Electronic Resource
    Electronic Resource
    Interfacial microstructure of tungsten silicide Schottky contacts to n-type GaAs (1988)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 64 (1988), S. 2113-2121 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: To investigate the effects of microstructure of the Schottky characteristics of WSix contacts to n-type GaAs, cross-sectional transmission electron microscopy, x-ray diffraction, and secondary-ion mass spectrometry have been used to study the interfacial and bulk film microstructures. The barrier heights and ideality factors of WSi0.1 and WSi0.6 contacts were obtained by forward current-voltage and capacitance-voltage measurements. These Schottky characteristics were found to be unrelated to the bulk film microstructure, but closely related to the interfacial microstructure at the WSix/GaAs interfaces. Both the WSi0.1/GaAs and WSi0.6/GaAs interface morphologies were observed to be stable and remain smooth during annealing at 800 °C for 10 min, while a rough interface with W protrusions and Ga and As out-diffusion was observed in two-layer W/WSi0.6 contacts. The stability of the WSix interfacial microstructure is suggested to depend on both the chemical stability of the WSix films with GaAs and the intervening oxides between WSix and GaAs. Nontrivial amounts of W and Si were observed to diffuse from the WSi0.1 film into the GaAs substrate during annealing at 800 °C for 10 min. Although these in-diffused impurities in the GaAs substrate do not seem to affect the Schottky characteristics after the 800 °C annealing, they could be a potential problem in long-term stability. Of the three WSix film compositions, the single-layer WSi0.6 films were found to have the least W and Si in-diffusion and thus the best thermal stability.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.341721
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  • 3
    Electronic Resource
    Electronic Resource
    Effects of interfacial microstructure on uniformity and thermal stability of AuNiGe ohmic contact to n-type GaAs (1987)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 62 (1987), S. 582-590 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: As part of the investigation of the use of AuNiGe as the ohmic contact to n-type GaAs at a high integration level, cross-sectional transmission electron microscopy was used to explore the uniformity at the metal/GaAs interface and the thermal stability of the AuNiGe contact after the ohmic contact formation. A close relation between spread of the contact resistance and nonuniformity of the interfacial microstructure of the contact was found. Deposition of 5-nm-thick Ni as the first layer of the AuNiGe ohmic contact significantly reduced the spread of the contact resistance and led to the formation of a uniform interface without large protrusions. The improvement in uniformity of compound distribution and the reduction of interface roughness are believed to be due to a change in the sequence of alloying reactions, compared to those in the contact without a Ni first layer. This suggests an ideal interface structure for a low resistance AuNiGe ohmic contact after alloying to be a uniform two layer structure: a high density of the NiAs(Ge) grains contacting the GaAs substrate, and a homogeneous β-AuGa phase close to the top surface. However, due to the existence of β-AuGa phases with a low melting point of around 375 °C, the thermal stability of the contact at 400 °C is of serious concern. Segregation of the NiAs(Ge) grains was observed after annealing at 400 °C for 10 h, which reduced the contact areas between the NiAs(Ge) grains and GaAs. During subsequent annealing at this temperature for up to 90 h, liquidlike flow of the β-AuGa phase was observed which deteriorated the interface uniformity, causing an increase in contact resistance. A typical contact edge slide distance after contact alloying at 440 °C for 2 min was measured to be 0.2 μm and the longest distance among specimens examined was 0.47 μm. This edge deterioration could limit the use of the AuNiGe contact in GaAs submicron devices.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.339860
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  • 4
    Electronic Resource
    Electronic Resource
    Reactions of Pd on (100) and (110) GaAs surfaces (1985)
    [S.l.] : American Institute of Physics (AIP)
    Journal of Applied Physics 58 (1985), S. 1519-1526 
    Details
    ISSN: 1089-7550
    Source: AIP Digital Archive
    Topics: Physics
    Notes: The reactions of Pd on atomically clean or air-exposed (100) and (110) GaAs surfaces at temperatures between 20 to 500 °C in different ambients were investigated by transmission electron microscopy. Interfacial reactions quite different from previous x-ray results were observed and two new Pd-Ga-As ternary phases were identified for the first time. At lower temperatures (T(approximately-less-than)250 °C) the formation of a ternary phase PdGa∼0.3As∼0.2, which has a hexagonal structure very similar to that of Pd2Ge or Pd2Si with a0=b0=0.672 nm and c0=0.340 nm, was observed. This ternary phase is epitaxially oriented with (12¯0)ternary(parallel)(100)GaAs and [001]ternary(parallel)[011]GaAs on (100) GaAs substrates, and with (11¯0)ternary(parallel)(110)GaAs and [001]ternary(parallel)[11¯0]GaAs on (110) GaAs substrates. At temperatures between 350 and 500 °C only one phase, PdGa, was observed to form in a high vacuum environment, whereas in a forming gas ambient, either a mixture of PdAs2 and another ternary phase PdGa∼0.6As∼0.4 (at 350 °C) or a mixture of PdAs2 and PdGa (at 500 °C) was observed. The ternary phase PdGa∼0.6As∼0.4 is also hexagonal in structure with a0=b0=0.947 nm and c0=0.374 nm. The PdGa phase formed at high temperature is epitaxially oriented on (100) substrates with (110) PdGa(parallel)(100)GaAs and [1¯11]PdGa(parallel)[011]GaAs, but is randomly oriented on (110) substrates. All these observations indicate that the Pd-GaAs reactions at T(approximately-greater-than)350 °C are very sensitive to the ambient conditions but not as sensitive to the GaAs surface cleanliness or substrate orientation. Correlation of these structural observations to ultraviolet and x-ray photoelectron spectroscopy data obtained from the same reacted interfaces are also discussed.
    Type of Medium: Electronic Resource
    URL: http://dx.doi.org/10.1063/1.336085
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