대면적 고품질 이황화 몰리브덴 성장 및 광센서 응용 연구

Abstract

Transition metal dichalcogenides (TMDs) are well-known layered materials with sizable bandgap, which can be changed from bulk to layered forms (indirect to direct transitions) to yield unique physical properties. So, these could be employed in future semiconducting devices as a supplement to silicon-based technology. Among the TMDs, in particular, molybdenum disulfide (MoS2) has attracted much research interest due to its interesting electronic and optical properties of high mobility, photo responsibility and flexibility and so on. Various approaches have been developed to obtain electronics-grade layered MoS2, such as exfoliation from bulk material, chemical vapor deposition (CVD), atomic layer deposition and metal-organic CVD. In particular, CVD is attractive for low-cost and scaled-up production. However, MoS2 grown by CVD usually forms triangular flakes with low surface coverage and random size, orientation and position. For their fabrication and eventual application in electronic devices, it is highly desirable to grow continuous and large-scale MoS2 thin films with control over the location, size, and shape of its features. In addition, the optical and electrical properties are significantly degraded when defect and grain boundary are formed in continuous film. In this work, we tried to grow continuous MoS2 film by increasing temperature because it is known that growth or nucleation rate is strongly dependent on surface dominant reaction mechanism at the normal growth temperature of MoS2 about 700 ˚C. With increasing the temperature of 800 ˚C, we succeeded to grow continuous MoS2 films. In here, we found that nucleation is significantly dependent on growth temperature while domain size is not affected by growth temperature. Although we got the continuous MoS2 films, we found that a lot of grain boundaries formed in continuous MoS2 films. So, optical and electrical properties of continuous MoS2 films which is grown at 800 ˚C is significantly degraded compared to single domain triangular shape. So, we tried to use Na catalyst which is known to reduce activation energy for lateral growth. With the use of Na catalyst, the single domain size of MoS2 is 6 times increased at the same growth condition, compared to that grown without Na catalyst. In addition, the grain size is increased with increasing temperature. This result indicated that high activation energy of lateral growth is the key to growth large coutinous MoS2 films without defect such as grain boundary. With fabrication of FET with MoS2 film grown with Na catalyst, the mobility is 6 times increased compared to continuous MoS2 film grown without Na catalyst. In addition, we found the optical and gas response of TFT sensor based on MoS2 film grown with Na catalyst. These results demonstrate a promising path towards the growth of high quality continuous layered MoS2 film without grain boundaries.