Epitaxy Of Large Area And High Quality MoS₂ Films

In the quest of higher device density and higher performance in modern electronic systems,the dimensions of device has to decrease.The electrical performance of the silicon-based bulk semiconductors degrades substantially when the thickness below 4nm,causing problems such as high power consumption.MoS₂ with atomic-thin body thickness can maintain good electrical performance even below 1 nm,has shown great potential in next-generation electronics,especially for low power devices and flexible electronics.To achieve the practical applications of MoS₂,the production of high quality materials shows significance.This thesis mainly focused on the growth of large-area high quality MoS₂ films,which consists of the following three aspects:1.Epitaxial growth of 4 in.wafer-scale highly-oriented monolayer MoS₂ with large domain sizes.4 in.monolayer MoS₂ films grew in a special designed multisource chemical vapor deposition(CVD)system.The achieved film is composed of highly oriented domains,and the average domain size can exceed 180?m.The wafer-scale Raman and photoluminescence line scans results reveal the excellent uniformity of the achieved films.The very straight grain boundary in our films is a nearly perfect 4|4E type structure.2.Electrical performance of the 4 in.monolayer MoS₂ films.We transferred the achieved films on the Si O₂/Si substrate and fabricated filed-effect-transistors.The average device mobility can achieve 70 cm² V^-1 s^-1,and a high on/off ratio of 10⁹ is obtained.Furthermore,we fabricated logic circuits and the logic function can be successfully achieved.We also transferred the 4 in.films on flexible substrate and fabricated high density device arrays,these flexible devices also show high electrical performance.We then demonstrated 5-stage ring oscillators on flexible substrate and achieved the high oscillation frequency of 13.12 MHz at V_dd=15 V.3.The epitaxial growth of large-area bilayer MoS₂ continuous films.We achieved the bilayer MoS₂ continuous films through a two-stage CVD method,the continuous area can be several centimeters.The achieved films show high crystallinity,and the domain size in first layer is larger than 100?m and in second layer is about 10?m.We use the aberration-corrected scanning-transmission electron microscope(STEM)to study the stacking orders and film continuity of our bilayer MoS₂ sample.There are two stacking orders in our bilayer sample,AA stacking(2L-AA)and AB stacking(2L-AB),and this two different stacking domains can coalesce together without disconnect gap,demonstrating good continuity of our films.This bilayer films shows excellent electrical performance,the on-current density can achieve 360?A/?m and the average mobility can achieve 110 cm² V^-1 s^-1,suggesting a good application prospect.