Scavenging effect on plasma oxidized Gd$_2$O$_3$ grown by high pressure sputtering on Si and InP substrates

Abstract

In this work, we analyze the scavenging effect of titanium gates on metal insulator semiconductor capacitors composed of gadolinium oxide as dielectric material deposited on Si and InP substrates. The Gd$_2$O$_3$ film was grown by high pressure sputtering from a metallic target followed by an in situ plasma oxidation. The thickness of the Ti film was varied between 2.5 and 17 nm and was capped with a Pt layer. For the devices grown on Si, a layer of 5 nm of Ti decreases the capacitance equivalent thickness from 2.3 to 1.9 nm without compromising the leakage current (1e-4 A cm$^{-2}$ at Vgate equal to 1 V). Thinner Ti has little impact on device performance, while 17 nm of Ti produces excessive scavenging. For InP capacitors, the scavenging effect is also observed with a decrease in the capacitance equivalent thickness from 2.5 to 1.9 nm (or an increase in the accumulation capacitance after the annealing from 1.4 to 1.7-1.8 uF cm$^{-2}$). The leakage current density remains under 1e-2 A cm$^{-2}$ at Vgate equal to 1.5 V. For these devices, a severe flatband voltage shift with frequency is observed. This can be explained by a very high interface trap state density (in the order of 1e13-1e14 eV$^{-1}$ cm$^{-2}$).