Electrical characteristics of gadolinium gallium oxide/gallium oxide insulators on GaAs and lno.53Gao.47As in metal-oxide-semiconductor field effect transistors - admittance and subthreshold characteristics

摘要

The admittances and subthreshold characteristics of capacitors and MOSFETs on buried In_xGa_1-xAs channel wafers with a dielectric stack of Gd_0.25Ga_0.i5O_0.6/Ga_2O_3 deposited on GaAs and Ino.53Gao.47As are reported. Both the GaAs and InGaAs interface samples show admittance characteristics indicative of the presence of defect states within the oxide, in agreement with previously reported data from the same oxides on n~+ substrates. The interface state model is applied to the admittance data to extract an apparent interface state density (D_it) that includes interface and oxide states. The D_it profiles are very different and have pronounced effects on the device performance. The device subthreshold swings (SS) at low source-drain voltages are also used to extract an apparent D_it. A simple method is used to estimate the Fermi-level position within the bandgap (E_t) at threshold, and the resulting D_it{E_t) are found to be in good agreement with the admittance data. The importance of proper interpretation of SS and D_it in general and in GaAs interface devices in particular is emphasized. A model that accounts for the logarithmic sweep rate dependence of the extracted D_it due to the presence of oxide states is reported and used to estimate their density from SS measurements. The implications of the band parameters of an oxide with defect states within it for the comparison of different oxides on the same substrate and the issues around the comparison of results in general are discussed.