  Two-dimensional (2D) transition metal dichalcogenides (TMDCs) remain a topic
of immense interest. Specifically, given their low operational switching costs,
they find many niche applications in new computing architectures with the
promise of continued miniaturization. However, challenges lie in Back End of
Line (BEOL) integration temperature and time compliance regarding current
requirements for crystal growth. Additionally, deleterious and time-consuming
transfer processes and multiple steps involved in channel/contact engineering
can cripple device performance. This work demonstrates kinetics-governed
in-situ growth regimes (surface or edge growth from gold) of WSe2 and provides
a mechanistic understanding of these regimes via energetics across various
material interfaces. As a proof-of-concept, field effect transistors (FET) with
an in-situ grown WSe2 channel across Au contacts are fabricated, demonstrating
a 2D semiconductor transistor via a transfer-free method within the 450-600 C
2h-time window requirement BEOL integration. We leverage directional edge
growth to fabricate contacts with robust thickness-dependent Schottky-to-Ohmic
behavior. By transitioning between Au and SiO2 growth substrates in situ, this
work achieves strain-induced subthreshold swing of 140 mV/decade, relatively
high mobility of 107 +- 19 cm2V-1s-1, and robust ON/OFF ratios 10^6 in the
fabricated FETs.
