Ohmic Pd/Zn/Au/LaB6/Au contacts on p-type In0.53Ga0.47As: Electrical and metallurgical properties

Abstract

The development of a shallow and low-resistive contact on moderately doped (p≈5×1018 cm−3) In0.53Ga0.47As is demonstrated. By reducing the layer thicknesses of a conventional Pd/Zn/Pd/Au scheme to a minimum and coupling this system to an outer Au layer via an amorphous LaB6 diffusion barrier, contact resistivities ⩽1×10−6 Ω cm2 were achieved only slightly exceeding that of the conventional scheme (2–4×10−7 Ω cm2). The contact reaction depth, however, could be reduced from several hundred to well below 100 nm, since the LaB6 barrier effectively prevents the outer Au layer from reaction with the semiconductor during contact formation. The influence of Zn content on electrical and metallurgical properties has been studied by varying it over orders of magnitude using both implantation and evaporation as a means of introducing Zn into the metallization. Implanted contacts with low Zn content annealed at 375 °C exhibit a reaction depth as low as 55 nm with the Zn diffusion depth practically coinciding with the reaction depth. If Zn is evaporated, the reaction depth is enhanced and the Zn diffusion depth exceeds the reaction depth noticeably. Secondary ion mass spectrometry demonstrated the onset of ohmic behavior to be correlated with the buildup of high interfacial Zn concentrations suggesting that these contacts conform to the standard model of interfacial doping. Simultaneously a solution phase emerges, reported here first, namely (Pd,Au)12(Ga,In)5As2 based on hexagonal Pd12Ga5As2 as revealed by cross-sectional transmission electron microscopy and x-ray diffraction analysis. Contacts with evaporated Zn exhibit stable resistivity during thermal stressing at 400 °C for 24 h. The stability loss for longer times is correlated with the appearance of (Au,Pd)9In4, a solution phase based on cubic Au9In4, evolving from indiffused Au and replacing increasingly the low-resistive (Pd,Au)12(Ga,In)5As2/p+-In0.53Ga0.47As junction areas.