LOW RESISTANCE OHMIC CONTACTS TO N+-GAAS WITH REFRACTORY METAL SIDEWALL DIFFUSION BARRIER

Modern device concepts strongly depend on reliable and well-controlled electrical contacts through which one has to communicate with the interior of the device from the outside world. In particular, micron and submicron size III-V devices can be fully exploited only with adequate ohmic contacts. In addition to a wide variety of device and circuit applications, good quality ohmic contacts are required for investigating the physical and electrical properties of bulk materials and related III-V heterostructures. Consequently, much attention has been recently devoted to the development of new techniques for improving the properties of ohmic contacts to III-V materials, such us gallium arsenide (GaAs). This paper presents a comparative analysis of the parameters of non-alloyed Pd/Ge/Ta/Cu and alloyed Ge/Au/Ni/Ta/Au ohmic contacts to n + -GaAs, both with planar as well planar and sidewall diffusion barriers based on Ta films formed by magnetron sputtering. It has been found that use of sidewall diffusion barriers reduces the value of specific contact resistance of ohmic contacts of both types and improves the thermal stability of the edge morphology of the contact pad in the case of alloyed Ge/Au/Ni/Ta/Au ohmic contacts. The effects observed for the samples with effective diffusion barrier are explained by limiting diffusion, as well as limiting the interaction of Au or Cu atoms with underlying metallization layers and with gallium arsenide, taking place along the sidewall surfaces of the ohmic contact.