Investigation of MOS Interfaces with Atomic-Layer-Deposited High-k Gate Dielectrics on III-V Semiconductors

The purpose of this research work was to investigate the surface passivation methods and metal gate/high-k dielectric gate stacks for metal-oxide-semiconductor devices (MOS) on III-V compound semiconductor materials -- (i) GaAs for future high-speed low-power logic devices and (ii) AlGaN/GaN heterostructure for future high-speed high-power devices. GaAs is a candidate material for high-mobility channel in a NMOS transistor to extend the CMOS scaling up to and beyond the 16-nm technology node. AlGaN/GaN heterostructure is useful in a MOS-high electron mobility transistor (MOS-HEMT) device for providing a high current-carrying two dimensional electron gas (2DEG) channel.;The interaction of GaAs surface with atomic layer deposition of high- k dielectrics was investigated to gain fundamental insights into the chemical properties of GaAs surface oxides and high-k/GaAs interface. Electrical characterization of devices was performed to understand the impact of high-k/GaAs interface on MOS device characteristics in order to form a suitable metal/high-k/GaAs gatestack for future high-speed logic and power devices. Reduction of native oxides on GaAs was found to occur during atomic layer deposition (ALD) of high-k dielectrics- HfO2 and Al2O3/HfO 2 nanolaminates on GaAs. Reaction between ALD metal precursor and native oxides on GaAs was identified to be the cause for consumption of native oxides. It was established that the ALD growth temperature has a strong impact on this phenomenon. During post-dielectric annealing the residual arsenic oxides at the interface decomposed leading to an increase in the interfacial gallium oxides. Presence of gallium oxide, Ga2O3 was identified as a cause for observed frequency dispersion in MOS capacitance-voltage curves indicative of a high interface state density.;The chemical properties of the AlGaN/GaN heterostructure surface prepared by wet chemical treatment using HCl/HF and NH4OH solutions were investigated and compared. Both HCl and NH4OH solutions were effective in etching the native oxide layer and reducing the surface carbon content; HCl treatment being slightly more effective. Atomic layer deposition of Al 2O3 on AlGaN/GaN surface revealed a reduction of surface gallium oxides due to the reaction between metal precursor and Ga2O 3. This oxide reduction provides an in-situ ALD surface cleaning action and provides a passivation effect useful for suppressing surface states. The interface and electrical properties of Al2O3 and SiO 2 grown by ALD on HCl-treated AlGaN/GaN surface were investigated. An upward band bending in the semiconductor was observed; Al2O 3 resulting in a greater band bending at the interface than SiO2. SiO2 based device yielded a more positive threshold voltage than Al2O 3 suggesting the potential use of a thin SiO2 interface passivation layer to achieve enhancement mode operation. Energy band alignment of ALD dielectrics- SiO2, HfO2, HfAlO and Al2O 3 on GaN was determined using x-ray photoelectron spectroscopy. Fundamental chemical properties of the AlGaN/GaN heterostructure surfaces, interaction of the AlGaN/GaN surfaces with atomic layer deposition of dielectrics and electrical properties of AlGaN/GaN based MOS devices were studied and are the key to improving the device performance of MOS-HEMT transistors for high-power applications.