Abstract
When channel materials other than Si are urgently demanded to enhance the performance of complementary metal-oxide-semiconductor (CMOS) beyond 16 nm technology node, Ge has always been considered as one viable contender because of its mobility advantages compared to Si. A high-quality interface between high- dielectrics and Ge as well as a small equivalent oxide thickness (EOT) are necessarily required for future high-performance Ge MOS device. However, it is challenging to achieve a good oxide/Ge interface mainly due to the unfavorable surface properties and native oxides of Ge. This work approaches Ge MOS devices with direct deposition of high-κ dielectrics on Ge under ultra-high-vacuum (UHV), while a high κ value of the gate oxides and a decent oxide/Ge interface quality are maintained without significant Ge inter-diffusion and formation of interfacial layers (ILs). In this dissertation, molecular beam deposited (MBD) high- Y2O¬3 and Ga2O3(Gd2O3) [GGO] have been utilized as the gate dielectrics for Ge MOS devices without using ILs. Comprehensive investigations have been carried out chemically, structurally, and electronically, to study the gate stacks, especially the oxide/Ge interfaces. With appropriate post oxide deposition treatment for the gate stacks with GGO, such as annealing and fluorine incorporation, the Ge MOS devices, i.e., MOS capacitors (MOSCAPs) and MOS field-effect-transistors (MOSFETs), have exhibited very high performance. Excellent capacitance-voltage (C-V) characteristics, a low interfacial density of states (Dit’s) in the range of 1011 cm-2eV-1, and a low gate leakage of less than 10-8 A/cm2 along with a high value (14-16) of the GGO indicate the gate dielectrics and GGO/Ge interface are of high quality and thermally stable. Furthermore, the MOSFETs, with a gate length (Lg) of 1 μm an EOT of ~3.8 nm, have yielded high performance in terms of a high drain current density (Id), a maximum transconductance (gm), and hole mobility (μh) of 496 μA/μm, 178 μS/μm, and 389 cm2/V-s, respectively. When further reducing the oxide thickness, a smaller EOT of ~1.38 nm has been achieved. The device performance has been systematically enhanced in good agreement with the increased oxide capacitance, showing an Id of 800 μA/μm and a gm of 423 μS/μm in a MOSFET with a Lg of 1μm, while the μh remained ~300 cm2/V-s. The excellent GGO scalability and its effective passivation for Ge surface suggest GGO stands a good chance of realizing the applications of Ge-channel pMOS devices for next-generation CMOS technology.