RESUMEN
The development of a controllable, selective, and repeatable etch process is crucial for controlling the layer thickness and patterning of two-dimensional (2D) materials. However, the atomically thin dimensions and high structural similarity of different 2D materials make it difficult to adapt conventional thin-film etch processes. In this work, we propose a selective, damage-free atomic layer etch (ALE) that enables layer-by-layer removal of monolayer WSe2 without altering the physical, optical, and electronic properties of the underlying layers. The etch uses a top-down approach where the topmost layer is oxidized in a self-limited manner and then removed using a selective etch. Using a comprehensive set of material, optical, and electrical characterization, we show that the quality of our ALE processed layers is comparable to that of pristine layers of similar thickness. The ALE processed WSe2 layers preserve their bright photoluminescence characteristics and possess high room-temperature hole mobilities of 515 cm2/V·s, essential for fabricating high-performance 2D devices. Further, using graphene as a testbed, we demonstrate the fabrication of ultra-clean 2D devices using a sacrificial monolayer WSe2 layer to protect the channel during processing, which is etched in the final process step in a technique we call sacrificial WSe2 with ALE processing (SWAP). The graphene transistors made using the SWAP technique demonstrate high room-temperature field-effect mobilities, up to 200,000 cm2/V·s, better than previously reported unencapsulated graphene devices.
RESUMEN
Tungsten diselenide (WSe2) has received significant attention because it shows the pristine ambipolar property arising from the Fermi level located near the midgap and can be converted to uni-polar form. In this study, we observe the formation of tungsten oxide (WOx) on the WSe2 surface after oxygen plasma treatment and show that the p-type WOx dopes WSe2. In our devices that underwent plasma treatment, it was interesting to find a strong correlation between the changes in the work function of WSe2 and a gold electrode, and the channel and contact resistances. The channel resistance changes very sensitively at a rate of 64 meV per dec with the increase in the WSe2 channel work function, which is close to the thermal limit; this indicates the defect-free oxidized WSe2 channel. The carrier transport in the oxidized WSe2 FET is shown to change to a high performance p-type device with greatly reduced channel and contact resistances with the increase in the plasma oxidation time.