Metal-agglomeration-suppressed growth of MoS and MoSe films with small sulfur and selenium molecules for high mobility field effect transistor applications.

This work reports a breakthrough technique for achieving high quality and uniform molybdenum dichalcogenide (MoX2 where X = S, Se) films on large-area wafers via metal-agglomeration-suppressed growth (MASG) with small chalcogen (X-) molecules at growth temperatures (TG) of 600 °C or lower. In order to grow MoS2 films suitable for field effect transistors (FETs), S-molecules should be pre-deposited on Mo films at 60 °C prior to heating the substrate up to TG. The pre-deposited S-molecules successfully suppressed the agglomeration of Mo during sulfurization and prevented the formation of protruding islands in the resultant sulfide films. The small X-molecules supplied from a thermal cracker reacted with Mo-precursor film to form MoX2. The film quality strongly depends on the temperatures of cracking and reservoir zones, as well as TG. The MoS2 film grown at 570 °C showed a thickness variation of less than 3.3% on a 6 inch-wafer. The mobility and on/off current ratio of 6.1 nm-MoS2 FET at TG = 570 °C were 59.8 cm2 V-1 s-1 and 105, respectively. The most significant advantages of the MASG method proposed in this work are its expandability to various metal dichalcogenides on larger substrates as well as a lower TG enabled by using reactive small molecules supplied from a cracker, for which temperature is independently controlled.