Mobility Model And Surface Treatments Of(In)GaAs MOS Devices With High-k Gate Dielectric

As Si-based metal-oxide-semiconductor(MOS) device is reaching its physical limits in resent years, III-V compound semiconductors with high intrinsic electron mobility, e.g. In Ga As and Ga As, have attracted more and more attention. However, high intrinsic electron mobility doesn't mean high inversion-channel electron mobility. So it is necessary to analyze the relevant scattering mechanisms and investigate effects of the structural and physical parameters of the device on electron mobility by establishing an inversion-channel electron mobility model for In Ga As n MOSFETs. Also, poor interface quality between the high-k gate dielectric and Ga As caused by the native oxides on Ga As surface needs to be improved. Therefore, this thesis focuses on the two issues.Theorecially, a semi-empirical electron mobility model for Al2O3/Inx Ga1-x As n MOSFETs is established by considering three main scattering mechnisms including body scattering, Coulomb scattering of interface charges and interface-roughness scattering of Al2O3/Inx Ga1-x As interface. The simulated results show that the total electron mobility is mainly limited by the Coulomb scattering of interface charges and the interface-roughness scattering under low and high effective fields respectively. On the basis of the semi-empirical model, the remote Coulomb scattering and the remote interface-roughness scattering mechanisms are further considered in the mobility model and their influences on the inversion-channel electron mobility of In Ga As n MOSFETs with stacked high-k gate dieletric are investigated. The simulated results indicate that the total electron mobility is reduced as the interface-roughness increases, and the remote interface-roughness scattering becomes strongest as the correlation length of the interface approaches the inverse of the thermal de Broglie wavenumber, increasing permittivity of the high k dielectric can improve the remote Coulomb scattering mobility but deteriorate the interface roughness scattering mobility, while the opposite situation appears when the interlayer dielectric constant increases; thicker interlayer and high k layer is favorable for improving the remote interface-roughness scattering mobility and the remote Coulomb scattering mobility, but in order to get low EOT, a thin interlayer and high k layer is needed, thus, a compromise should be found between low EOT and high carrier mobility.Experimentally, effects of NH3- or N2-plasma pretreatment on the electrical characteristics of La YON/Ga As and La ON/Ga As MOS devices are investigated. The experimental results show that NH3-plasma pretreatment can effectively suppress the formation of the native oxides on Ga As surface, thus reducing the interface-state density and improving the electrical properties. Furthermore, the comparison between the samples with La YON and La ON as high k gate dielectric indicates that the sample with La YON as high k gate dielectric has better interfacial and electrical properties. Also, influences of NH3-plasma treatment to Ga As surface or La YON surface or La ON surface on the electrical properties of Ga As MOS device are investigated. It is found that the sample with NH3-plasma treatment to La YON surface exhibits the best capacitance-voltage behavior, lowest gate leakage current density(7.1×10-4 A/cm-2 @Vg = Vfb+1V) and lowest interface state density(3.10×1012 e V-1cm-2 near midgap). The mechanism involved lies in that the NH3-plasma pretreatment to La YON surface can effectively suppress the formation of native oxides on Ga As and repair the lattice damages induced during the La YON deposition.