III-V channel MOS devices with atomic-layer-deposited high-k gate dielectrics : interface and carrier transport studies

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Shahrjerdi, Davood, 1980-

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The performance scaling of metal-oxide-semiconductor field-effect-transistors (MOSFETs) has been historically achieved through shrinking the gate length of transistors for over four decades. Addressing the current challenges with CMOS scaling, the 2005 edition of International Technology Roadmap for Semiconductors has predicted the need for so-called technology boosters involving new materials for the gate dielectric and the channel as well as innovative structures. Theoretical studies suggest that the incorporation of high-mobility channel materials such as germanium and III-Vs could outperform bulk Si technology in terms of switching characteristics. Hence, this has recently led to tremendous research activity to explore the prospects of III-V materials for CMOS applications. Nevertheless, technological challenges such as formation of highquality interface between gate dielectric and III-V channel have hindered the demonstration of enhancement-mode III-V MOSFETs. Hence, tremendous effort has been devoted to study the exact origin of Fermi level pinning at the oxide/III-V interface. On the other hand, the advent of high-k materials has opened up the possibility of exploring new channel materials, for which it is challenging to achieve high-quality interface analogous to that of SiO2 on Si. Lately, III-Vs have been extensively explored in order to find compatible gate dielectrics which can unpin the Fermi level at the interface. Amongst various schemes, atomic layer deposition of high-k dielectrics offers some unique advantages such as reduction of GaAs interfacial oxides upon high-k deposition through an appropriate choice of precursor chemistry. The chief focus of this dissertation is to develop a simple wet clean process prior to high-k deposition, suitable for III-V substrates. The impact of various chemical treatments of GaAs substrates on the properties of high-k/GaAs interface was studied through extensive material and electrical characterization methods. The suitability of the ALD-grown high-k gate dielectrics on GaAs for MOSFET fabrication was explored. Charge trapping was found to result in significant errors in mobility extraction in high-k GaAs interface, where the role of high-k is not well understood. Hence, pulsed I-V and QV measurements and galvanomagnetic effects were utilized in order to directly measure the inversion charge in the channel without being affected by the charge traps as much as possible. It was also found that the material studies on GaAs substrates can be readily extended to other III-V channels, such as InGaAs.