Molecular-beam epitaxy growth of device-compatible GaAs on silicon substrates with thin (～80 nm) Si_(1-x)Ge_x step-graded buffer layers for high-κ Ⅲ-Ⅴ metal-oxide-semiconductor field effect transistor applications

摘要

The authors report the fabrication of TaN-HfO_2-GaAs metal-oxide-semiconductor capacitors on silicon substrates. GaAs was grown by migration-enhanced epitaxy (MEE) on Si substrates using an ～80-nm-thick Si_(1-x)Ge_x step-graded buffer layer, which was grown by ultrahigh vacuum chemical vapor deposition. The MEE growth temperatures for GaAs were 375 and 400℃, with GaAs layer thicknesses of 15 and 30 nm. We observed an optimal MEE growth condition at 400℃ using a 30 nm GaAs layer. Growth temperatures in excess of 400℃ resulted in semiconductor surfaces rougher than 1 nm rms, which were unsuitable for the subsequent deposition of a 6.5-nm-thick HfO_2 gate dielectric. A minimum GaAs thickness of 30 nm was necessary to obtain reasonable capacitance-voltage (C-V) characteristics from the GaAs layers grown on Si substrates. To improve the interface properties between HfO_2 and GaAs, a thin 1.5 nm Ge interfacial layer was grown by molecular-beam epitaxy in situ after the GaAs growth. The Ge-passivated GaAs samples were then transferred in air for the subsequent ex situ HfO_2 formation. This Ge interfacial layer in between HfO_2 and GaAs was necessary to avoid relatively flat C-V characteristics that are symptomatic of high interface state densities.