Y. Shiraishi et al., INFLUENCE OF METAL N-INAS/INTERLAYER/N-GAAS STRUCTURE ON NONALLOYED OHMIC CONTACT RESISTANCE/, Journal of applied physics, 76(9), 1994, pp. 5099-5110
We have investigated in detail the influence of interlayer structures
on nonalloyed ohmic contact resistance (p(c)), in terms of the crystal
line defects and the potential barrier at the interlayer/GaAs interfac
e. The interlayer structures are a graded-band-gap InAs/GaAs strained-
layer superlattice (graded SLS), a graded-band-gap InGaAs, and convent
ional SLSs without graded band gaps. A two-layer transmission line mod
el indicates that the barrier resistance in the interlayer highly depe
nds on the interlayer structure: less than or equal to 5X10(-8) Omega
cm(2) for the graded SLS and graded InGaAs interlayers and 10(-5)-10(-
6) Omega cm(2) for the conventional SLS interlayers. To explain the la
rge dependence of the interlayer structure, first, the density and dis
tribution of the misfit dislocations and stacking faults caused by the
large lattice mismatch between InAs and GaAs have been investigated i
n detail by high-resolution transmission electron microscopy. In the g
raded SLS and conventional SLS interlayers, the influence of the high-
density depletion regions spread near the crystalline defects is found
to be negligible because of the high doping concentrations (similar t
o 10(19) cm(-3)) in the interlayers. Second, the potential barrier at
the interlayer/GaAs interface has been investigated by simulating the
barrier resistance. The potential barrier profile is calculated self-c
onsistently with Poisson's equation and the Schrodinger equation. Tunn
eling current through the barrier is analyzed using the Wentzel-Kramer
s-Brillouin approximation or the numerical wave solution to the Schrod
inger equation. The graded SLS interlayer has the effectively smooth c
onduction band profile without the barriers, which is similar to that
of the graded InGaAs interlayer, because of its short period SLS. In t
he conventional SLS interlayers, the reasonable barrier heights of 0.1
4-0.26 eV obtained by this simulation indicates that these barriers ar
e the dominant factor which increases the contact resistances. For the
low-resistance nonalloyed ohmic contact, therefore, a smooth conducti
on band profile without band discontinuity is more predominant than th
e reduction in the crystalline defect density.