Growth of Very Large MoS2 Single Crystals Using Out-Diffusion Transport and Their Use in Field Effect Transistors

Monolayer molybdenum disulfide (MoS
₂
) is an attractive 2D material with a wide range of potential applications in the field of electronics and optoelectronics. To obtain the best performance, it is very necessary to grow large area single crystals of MoS
₂
(single domain) to avoid the effects of grain boundaries, but is exceptionally challenging to do this. Here, we report a novel method which we call out-diffusion vapor transport to grow large area single crystal monolayer MoS
₂
using an otherwise conventional chemical vapor deposition system. In this method, microchannels were created on the boat to significantly limit the region where MoOx vapor can react with S vapor to form crystals. This growth method resulted in triangular monolayer MoS
₂
single crystals up to ~640 μm on a side grown on an oxidized silicon substrate, the largest crystals reported to date. Most of these crystals were multilayer at the center. This common feature has been identified in the literature as partially reduced transition metal oxide nucleates a second layer. We also achieved fully monolayer MoS
₂
single crystals up to ~450 μm on a side, the largest demonstrated without the MoOx. Fabricated field effect transistors (FET) using MoS
₂
monolayer crystal as the active layer demonstrate a conventional n-type behavior, room-temperature mobility up to 45.5 cm
²
V
^-1
s
^-1
and a maximum ON-Current (ION)/OFF-current (IOFF) ratio of 1.8 × 10
⁷
. Raman and Photoluminescence results indicate that the as-grown large area monolayer crystals have high crystalline quality and uniformity with minimal defects, a finding that is consistent with the high electron mobility. This research work provides a superior technique to grow large-area high-quality single-crystal monolayer MoS
₂
without resorting to exotic equipment or techniques.