Ohmic contacts on p-In0.53Ga0.47As prepared by Zn implantation into Pd-based metallizations

Abstract

A new technique is presented for the fabrication of low-resistivity Ohmic contacts on p-In0.53Ga0.47As doped below 1×1019 cm−3 consisting of dopant implantation into the contact metal and subsequent rapid thermal annealing. Zn-implanted and annealed Pd/Au/Pt/Au, Pd/LaB6/Au, and Pd/Ge contacts exhibit drastically lowerer contact resistivity in comparison to corresponding systems prepared without implantation. A resistivity decrease by approximately one and a half orders of magnitude is observed in cases of Pd/Au/Pt/Au and Pd/LaB6/Au contacts. The lowest value is found for Pd/Au/Pt/Au on p-In0.53Ga0.47As doped to 4×1018 cm−3 with 1×10−6 Ω cm2, whereas 1–2×10−5 Ω cm2 is obtained for Pd/Ge contacts on p-In0.53Ga0.47As doped to 7×1018 cm−3. The elemental redistribution and the interface morphology of annealed contacts have been studied with backside secondary ion mass spectroscopy and cross-sectional transmission electron microscopy. No contact penetration and a planar interface are found in the case of Pd/Ge, whereas significant penetration of contact components into the semiconductor and nonplanarity of the interface are observed in Pd/Au/Pt/Au and Pd/LaB6/Au contacts. In contacts annealed at conditions for minimal resistivity the penetration depth is 200 and 105 nm, respectively. Implanted Zn is redistributed toward the contact interface during thermal processing. Thus the resistivity lowering is attributed to enhanced p-doping by Zn, which diffused from the contact into the underlying semiconductor. Residual implantation damage is discussed as the essential cause of the comparably high resistivity of implanted and annealed Pd/Ge contacts.