All solid-state 2D tunnel FET

2D materials are highly promising for tunnel FETs with low subthreshold swing and high drive current because the shorter tunnel distance and strong gate controllability can be expected from the van der Waals gap distance and the atomically sharp heterointerface formed independently of lattice matching. However, the common problem for 2D-2D TFETs is the lack of highly doped 2D materials with the high process stability as the sources. In this study, we have found that
$p^{+}$
-WSe
2
doped by charge transfer from a WO
x
surface oxide layer can be stabilized by transferring it onto a
$h$
-BN substrate. Using this
$p^{+}$
-WSe
2
as a source, we fabricate all-solid-state 2D-2D heterostructure TFETs with an Al
2
O
3
top gate insulator, i.e., type-III
$p^{+}$
-WSe
2
/WSe
2
. The band-to-band tunneling and negative differential resistance trends are clearly demonstrated at low temperatures. This work suggests that high doped 2D crystal of the charge transfer type is an excellent choice as sources for TFETs.