Ohmic contact metallization on p-type indium phosphide

Abstract

For the first time, a defect-assisted ohmic contact on p-InP is demonstrated. it is known that an ohmic contact with a low contact resistivity is difficult to achieve on p-InP due to the surface Fermi level pinning effect (-O.9 eV above valence band maximum). The commonly used Au-based contacts (such as Au:Zn and Au:Be contacts) on p-InP employ the principle of creating a heavily doped surface layer during annealing to achieve ohmic behavior with contact resistivities of -5xlO-' to 3xlO@f2- CM2 . However, the strong reactions between Au and InP result in deep penetration of Au into the InP layer. This deep penetration is not desirable for most device application In this study, I report a new approach to form shallow contacts on p-InP by utilizing defects in InP to enhance the tunneling current across the barrier, thus resulting in ohmic contact behavior. It is found that an ohmic behavior of pure Pd contact on pInP can be obtained if appropriate types of defects are present in the InP layer. A contact resistivities comparable to those of Au-based contacts, determined by the Cox and Strack structure, can be obtained for a pure Pd contact on p-InP (hole concentration -3xlOl' cm-'). The defects can be identified to be related with phosphorus vacancies by photoluminescence(PL) technique. A model of defect-assisted tunneling ohmic contact is proposed to account for the good ohmic behavior. A novel approach to fabricate ohmic contacts of lower contact resistivities on p-InP is also proposed.