Towards High Performance Two Dimensional Transistors: Doping, Contacts, and Gate Dielectri

Recently two dimensional (2D) materials have trigged intensive research interest duo to their unique electrical, optical, mechanical properties. Semiconducting 2D crystal, such as transition metal dichalcogenides (TMDs) and black phosphorous (BP) are considered as promising candidates for ultra-scaled transistors due to their variable bandgaps and mobilities as well as their immunity to short-channel-effect (SCE).;This thesis focuses on the a few challenges of achieving high performance 2D semiconductor field-effect-transistors (FETs), such as doping technique, contact resistance, and gate dielectric. In the first part of the thesis, a chloride doping technique is proposed to produce n type doping in TMDs such as MoS2 and WS2. The contact resistance of doped MoS 2 and WS2 are more than 10 times smaller than that of undoped devices. Furthermore the channel lengths of MoS2 FETs are scaled down to 10 nm with scaled gate oxide of 2.5 nm EOT. As a result, high performance few-layer MoS2 short channel transistors have been demonstrated with drain current of 520 muA/mum.;Next, a bilayer of 1.6 nm MOCVD BN and 1.3 nm ALD Al2O 3 is successfully demonstrated as the passivation layer as well as the gate dielectric on BP FETs. The degradation of BP has been successfully suppressed by the passivation of BN/Al2O3. Meanwhile, record high drain current of 940 muA/mum is achieved on BP top gate FETs by engineering the BP-metal contacts. The role of BN tunneling barrier at BP-metal contact is also investigated. By using an asymmetric tunneling contact structure, the reverse drain leakage current has been reduced significantly.;Finally, electrically tunable bandgap has been achieved on black phosphorus double gate devices by applying an external displacement filed. This unique material property provides a new route to design and fabricate novel electronic and photonic devices based on 2D materials.