AVS 60th International Symposium and Exhibition
    Electronic Materials and Processing Monday Sessions
       Session EM-MoA

Paper EM-MoA8
High-Carrier-Mobility p- and n-Type Field Effect Transistors Fabricated on Large-Area Wafer-Scale Ge Film Epitaxially Grown on Si

Monday, October 28, 2013, 4:20 pm, Room 101 B

Session: High-k Gate Oxides for High Mobility Semiconductors II
Presenter: S. Ghosh, University of New Mexico
Authors: S. Ghosh, University of New Mexico
S.M. Han, University of New Mexico
Correspondent: Click to Email
Implementing a unique two-step simple molecular beam epitaxy (MBE) growth technique in our laboratory, we have successfully demonstrated heteroepitaxial growth of high-quality Ge on Si (GoS) that opens up a possibility for many applications, including high-mobility transistors integrated on Si substrates and high-speed, read-only memory using Ge as the channel material. We note that our Ge film covers the entire underlying Si substrate at the wafer scale without mesas or limited-area growth. However, the ultimate test of materials quality is device demonstration on engineered GoS substrates. Herein, we have investigated the characteristics of two such devices: p-MESFETs as well as p- and n-MOSFETs fabricated on GoS substrates. For p-MESFETs, we have measured a low-field peak effective hole mobility of 310 cm2/V-sec and a cut-off frequency of 10 GHz at 200K. In this presentation, we will provide additional details of the device characterization. In addition to MESFETs, we have investigated electrical characteristics of planar p-MOSFETs fabricated on n-type GoS substrates. The defect density in n-type GoS obtained from etch pit density measurements is consistently below 1x106 cm-2. p-MOS capacitors are first fabricated, using Ti/HfO2/GeOxNy/n-Ge gate-stack structure. Angle-resolved X-ray photoelectron spectroscopy is employed to quantify nitrogen content within the GeOxNy layer. The corresponding gate leakage current density is below 10-3 A/cm2 and Dit of 6x1012 cm-2 eV-1 at 300K. After characterizing p-MOSCAPs, we have fabricated p-MOSFETs from n-GoS substrates. In this work, a two-step thermally activated method, instead of ion-implantation, is used to define p+ doped source and drain. The sheet resistivity from Hall measurements supports the presence of p+ regions. Forward and transfer current-voltage characteristics are measured, and the p-MOSFETs built on GoS substrates show a subthreshold slope (SS) of ~100 mV/decade, compared to ~80 mV/decade for the identical p-MOSFETs built on Ge substrates. The effective peak mobility obtained from our optimized p-MOSFETs is 401 cm2/V-sec. This is an 82% increase in the effective carrier mobility in the inversion channel in GoS, compared to the universal effective hole mobility in Si. In summary, a wafer-scale, epitaxial Ge layer on Si is used to fabricate high-hole-mobility p-MESFETs and p-MOSFETs. In this talk, we will further discuss n-MOSFETs fabricated on p-type GoS substrates, exploring the possibility of fabricating high-carrier-mobility CMOS devices from GoS substrates.