Electronics and optoelectronic applications of Van Der Waals heterostructures

Two-dimensional (2D) layered materials are emerging candidates for future high-performance electronics and optoelectronics due to their unconventional mechanical, electronic and optoelectronic properties. Furthermore, they can be assembled into van der Waals heterostuctures which display novel properties. The aim of my thesis is to develop a versatile and efficient assembling method to fabricate van der Waals heterostructures with clean interfaces, and to improve the performance of corresponding electronic and optoelectronic devices. To achieve this goal, I have done the following work. First, I developed an interface energy-mediated transfer method to fabricate van der Waals heterostructures. 2D layered materials remained intact after transfer because no harsh reaction or supporting polymer was involved in this method. Few-layer graphene, h-BN, MoS2 and WSe2 were printed on the same PET substrate in a layer-by-layer manner. They acted as gate electrode, dielectric, n-channel and p-channel semiconductors, respectively in the complementary inverter fabricated on flexible substrates. Second, the influence of interfacial properties to the photocurrent generation in MoS2 photo-FETs is studied. By comparing the photocurrent of exposed and h-BN-encapsulated MoS2 photo-FETs, I found that the trapping states from the interfaces between MoS2 and SiO2 is the main reason for prolonged photoresponse. I replaced the common SiO2/Si gating stack with h-BN/FLG and achieved stable and fast photoresponse of MoS2 photo-FETs. The hysteresis of the transistors was eliminated because of the dangling bond-free interfaces. Third, a junction gate field-effect transistor was designed and fabricated on high-performance P-N junction of TMDCs. The quality of P-N junction was improved by doping the intrinsic WSe2 with oxygen plasma. The doping level was high and stable. N-type MoS2 was contacted with FLG electrodes to improve the on-currents.DOCTOR OF PHILOSOPHY (MSE