Schottky enhancement of contacts to n-GaAs via the exchange mechanism using NiAlxGa1−x as a metallization

Abstract

Based on the thermodynamic/kinetic model of the exchange mechanism, the ternary intermetallic compound NiAl x Ga 1Ϫx ͑where 0Ͻxр1) was identified as a metallization that may be used to fabricate Schottky enhanced contacts to n-GaAs. Experimental phase equilibrium studies of the quaternary Al-Ga-Ni-As system, in conjunction with diffusion data available in the literature, indicated that the phase NiAl x Ga 1Ϫx fulfills the thermodynamic and kinetic requirements necessary for participation in an exchange reaction with GaAs. Contacts to n-GaAs were fabricated by sputter deposition of NiAl x Ga 1Ϫx metallizations, with compositions corresponding to xϭ0.00, 0.25, 0.50, 0.75 and 1.00. These contacts were subjected to rapid thermal processing, and analyzed using cross-sectional high resolution transmission electron microscopy and I-V characterization. Electron microscopy and concomitant electron dispersive spectroscopic analysis indicated that a very thin ͑2.5 nm͒ interfacial region of Al x Ga 1Ϫx As was formed in annealed contacts for which xϾ0.00, in accordance with the exchange mechanism model. Schottky barrier enhancement was also observed in all annealed contacts for which xϾ0.00. The degree of Schottky barrier enhancement was shown to be dependent upon the initial composition of the metallization, again in accordance with the prediction of the exchange mechanism model. Schottky barrier heights as high as 0.96 eV were obtained under the optimum annealing conditions of 400°C for 1 min. However, these experimentally determined Schottky barrier heights were somewhat smaller than the values that were anticipated based upon the exchange mechanism model. Potential reasons for these discrepancies were discussed. Overall, it was demonstrated that the thermodynamic/kinetic model of the exchange mechanism is a powerful tool for identifying metallizations that may be used to enhance the Schottky barriers of contacts to n-GaAs.

Schottky enhancement of contacts to n-(In0.52Al0.48)As using PdAl as a metallization

“…In their measurement of Schottky enhancement to nGaAs using Ni(Al 1-x Ga x ) as the metallizations, Chen et al 6 found that the Schottky enhancement increases with the content of NiAl in the metallizations. But in all the cases, the enhancements are appreciably smaller than those obtained by Palmstrom et al, 24 who made graded layers of (Al 1-x Ga x )As with different values of x using molecular-beam epitaxy (MBE).…”

“…These values are qualitatively similar. Chen et al 6 had offered possible reasons for these discrepancies, such as the effects of substrate-surface conditions, metallization materials, and alloyed-semiconductor thickness on the measured Schottky barrier heights. These reasons may also hold true for the results obtained in the present study.…”

“…The basic idea of this model has been presented previously. [2][3][4][5] Subsequently, Chen et al 6 used a series of pseudobinary alloys of NiAl and NiGa, or Ni(Al 1-x Ga x ), as metallizations to n-GaAs. The mole fractions of NiAl in these alloys were varied from (1 Ϫ x) ϭ 0.25 to 1 at equal composition intervals.…”

Low resistance ohmic contacts to n-GaN and n-AlGaN using NiAl

“…22,23 This is in contrast to the complex reactions of the Ti/Al and other multilayer contacts. Using NiAl should then simplify the metal/semiconductor reactions and lead to more a defined and controlled reaction interface.…”