Effect of threading dislocation density and dielectric layer on temperature-dependent electrical characteristics of high-hole-mobility metal semiconductor field effect transistors fabricated from wafer-scale epitaxially grown p-type germanium on silicon substrates

Abstract

We report the electrical characteristics of Schottky contacts and high-hole-mobility, enhancement-mode, p-channel metal semiconductor field effect transistors (MESFETs) fabricated on Ge epitaxially grown on Si substrates. The Ge film covers the entire underlying Si substrate at the wafer scale without mesas or limited-area growth. The device performance is characterized primarily as a function of threading dislocation density in the epitaxial Ge film (2 × 107, 5 × 107, 7 × 107, and 2 × 108 cm−2) and dielectric layers (SiO2, Al2O3, and HfO2) inserted between gate metal and Ge. The thin dielectric layers (∼1.3 nm) are used to unpin the Fermi level. The device performance improves with decreasing threading dislocation density and the use of HfO2. The hole mobility in the Ge film with 2 × 107 cm−2 dislocation density, obtained from Hall measurements, is 1020 cm2/V-s. Capacitance-voltage measurements on Schottky contacts provide the energy-dependent interfacial trap density of 6 × 1011 cm−2 eV−1, while current-voltage measurements provide an ON/OFF current ratio of 250. Based on the current-voltage characteristics of p-MESFETs, we have obtained an external transconductance of 7 mS/mm and low-field, effective hole-mobility of 307 cm2/V-s under 0.1 MV/cm at room temperature. The cut-off frequency of MESFETs is 10 GHz at 200 K and 2 GHz at 300 K. These results compare well with other reported transistor performance.