Microstructural Evolution and Electrical Characteristics of Er-germanides Formed on Ge Substrate

Abstract

The microstructural and electrical properties of Er-germanides formed by a solid state reaction between Er and Ge have been investigated at different germanide formation temperatures from 400 to 700°C. Er26Ge23 and Er3Ge4 phases were formed at a germanidation temperature of 400°C, followed by the formation of Er3Ge4 and Er2Ge3 at 500 to 600°C and then ErGe2.16 at 700°C. The sheet resistance gradually decreased with increasing annealing temperature up to 600°C, which could be associated with the phase transformation from Er-rich to Ge-rich Er-germanides. Er-germanides on n-type Ge showed Schottky behavior at low formation temperatures of less than 600°C. Above 600°C they exhibit Ohmic behavior. However, due to strong Fermi level pinning, Er-germanide contact to p-type Ge substrates was demonstrated to be Ohmic regardless of the annealing temperatures. The conversion of Schottky to Ohmic behavior could be attributed to a significant increase in current in the forward and reverse biases caused by the formation of square-shaped microvoids driven by Ge out-diffusion near the interface between germanides and the Ge substrate.