Synthesis of High‐Performance Monolayer Molybdenum Disulfide at Low Temperature

Abstract

The large‐area synthesis of high‐quality MoS2 plays an important role in realizing industrial applications of optoelectronics, nanoelectronics, and flexible devices. However, current techniques for chemical vapor deposition (CVD)‐grown MoS2 require a high synthetic temperature and a transfer process, which limits its utilization in device fabrications. Here, the direct synthesis of high‐quality monolayer MoS2 with the domain size up to 120 µm by metal‐organic CVD (MOCVD) at a temperature of 320 °C is reported. Owing to the low‐substrate temperature, the MOCVD‐grown MoS2 exhibits low impurity doping and nearly unstrained properties on the growth substrate, demonstrating enhanced electronic performance with high electron mobility of 68.3 cm2 V−1 s−1 at room temperature. In addition, by tuning the precursor ratio, a better understanding of the MoS2 growth process via a geometric model of the MoS2 flake shape, is developed, which can provide further guidance for the synthesis of 2D materials.

Toward Low-Temperature Solid-Source Synthesis of Monolayer MoS2

“…In Figure we compare the room-temperature electron mobility data of our films grown at 560 °C with previous reports for other CVD-grown (and MOCVD-grown − ) 1L MoS 2 reported in the literature, ,,,,− ,,,− as a function of the growth temperature. We note that some reports are given as effective mobility ,,− (μ eff from TLM, denoted by squares); others are only available as field-effect mobility ,,,,,− (μ FE , denoted by triangles).…”

“…The effective mobility values from this work (grown at 560 °C for 50 min) are marked in yellow. The field-effect mobility values reported from MOCVD growths (at or below 500 °C for 8 to 30 h) are marked in blue. − For this simple comparison, we benchmark two-probe mobility measurements, although more complex four-probe measurements with a threshold voltage correction can yield more accurate mobility values if current shunt paths through the (invasive) inner voltage probes are avoided . In general, we have found no correlation between carrier mobility and growth temperature, only between growth temperature and MoS 2 crystallite size or substrate adhesion.…”

“…μ eff from this report are marked in yellow. MOCVD data − are μ FE marked in blue, and solid-source CVD data from the literature ,,,,− ,,,− are hollow symbols. Growth times (at maximum process temperature) are also labeled, indicating significantly longer growths reported for MOCVD to attain full coverage 1L MoS 2 .…”

“…Growth times (at maximum process temperature) are also labeled, indicating significantly longer growths reported for MOCVD to attain full coverage 1L MoS 2 . The CVD films in this work were grown at 560 °C for 50 min, while MOCVD films were grown at or below 500 °C for 8 to 30 h, − as labeled. The μ eff from sheet resistance (TLM) measurements tend to be more reliable, while μ FE could be under- or overestimated depending on the V GS -dependence of gated contacts. ,, All mobility data are reported at room temperature.…”

“…Thus, in order to incorporate new materials such as MoS 2 into stacked, heterogeneous integrated circuits that increase the transistor density in the third dimension, their BEOL thermal budget becomes crucial. However, direct monolayer (1L) MoS 2 growths with good electrical properties have typically been obtained using solid-source precursor CVD above 650 °C. ,,− Wafer-scale 1L MoS 2 grown using metal–organic CVD (MOCVD) ,− at or below 500 °C appears within the BEOL temperature budget, but the growth times have been >8 h, which limit throughput, and the average carrier mobilities reported remain lower than the best MoS 2 grown at higher temperatures. Efforts to develop atomic layer deposition of MoS 2 at temperatures as low as 50 °C are also underway, , but the resulting films are amorphous and require post-growth anneals above 800 °C to improve their crystallinity. − …”