Mw. Cole et al., PT TI/GE/PD OHMIC CONTACTS TO GAAS - A STRUCTURAL, CHEMICAL, AND ELECTRICAL INVESTIGATION/, Journal of vacuum science & technology. A. Vacuum, surfaces, and films, 12(4), 1994, pp. 1904-1909
Citations number
13
Categorie Soggetti
Physics, Applied","Materials Science, Coatings & Films
Interface morphology, phase composition, and elemental diffusion of Pt
/Ti/Ge/Pd ohmic contacts to both n+- and p+-GaAs have been investigate
d as a function of annealing temperature. Structural and chemical resu
lts were correlated with specific contact resistances (rho(c)) measure
d for each thermal treatment in an attempt to determine how the indiff
usion of contact metal and the out-diffusion of Ga and As affect speci
fic contact resistance, and how effective Ti is as a diffusion barrier
. Annealing at 450-degrees-C yielded the lowest rho(c), approximately
6.4 X 10(-7) OMEGA CM2 . The interface was observed to be smooth and a
brupt, and there was little As out-diffusion and Pt indiffusion. Two i
nterface phases were detected; a primary phase, PdGe, and a secondary,
Ga rich Pd-Ga-As ternary phase. The presence of this ternary phase is
believed to be critical to contact formation on n-type GaAs. The Ti a
nd Pt layers remained pristine. Annealing at 550-degrees-C resulted in
a slightly higher p(c), approximately 2.1 X 10(-6) OMEGA Cm2. There w
as significant elemental diffusion within the contact metal and minor
diffusion into the GaAs substrate. The interface possessed limited are
as of spiking with uniform composition. Annealing at 600-degrees-C pro
ved to have a detrimental effect on the rho(c), approximately 10(-4) O
MEGA CM2. This electrical degradation was accompanied by strong chemic
al intermixing between the contact and substrate, resulting in a conti
nuous nonplanar interface with deep multiphase protrusions, and the Ti
layer no longer was effective as a diffusion barrier.