This document discusses the growth and characterization of 2D transition metal dichalcogenides (TMDs) using molecular beam epitaxy (MBE) and the demonstration of room-temperature negative differential resistance (NDR) in TMD heterostructures. Specifically, it shows the first ever MBE growth of MoTe2 and MoSe2 films on sapphire substrates, as characterized through techniques like RHEED, XRD, XPS, TEM, Raman, and electrical measurements. It also demonstrates NDR in dual-gated MoS2/hBN/WSe2 heterostructures, fabricated using dry transfer and etching of exfoliated flakes, indicating potential for new quantum devices using van der Waals

1. MBE Growth and Characterization of 2D TMDs &
Room-Temperature NDR in 2D Heterostructures
Anupam Roy, Hema C. P. Movva, Amritesh Rai, Emanuel Tutuc, and Sanjay K. Banerjee
Microelectronics Research Center, Department of Electrical and Computer Engineering, The University of Texas at Austin, Austin, TX, USA
A.1 MBE of TMDs: Motivation
 Large area growth of 2D Transition Metal
Dichalcogenides (TMDs) typically done using
CVD, MBE growth relatively unexplored
 ‘MBE’ a proven method for growing high purity
single crystal thin films and heterostructures
 We demonstrate growth of MoSe2 and the first
ever growth of MoTe2 using MBE on sapphire
substrates
 This work was supported by NRI SWAN and NSF NNCI
A.2 Large Area Growth
MoTe2
A.4 RHEED and XRD Patterns
A.3 XPS Analysis
A.5 TEM and EDX Analysis A.6 Raman and PL
A.7 Electrical Characterization
B.1 2D Heterostructures: Motivation
 The availability of diverse band-structures within the 2D material
family, coupled with their atomically thin nature and absence of
dangling bonds, can be used to realize van der Waals
heterostructures with varying band-alignments, and abrupt pristine
interfaces, capable of showing interesting quantum phenomena
 We demonstrate room-temperature negative differential resistance
(NDR) in dual-gated heterostructures of molybdenum disulfide
(MoS2)/hexagonal boron nitride (hBN)/tungsten diselenide (WSe2)
B.2 Device Schematic
B.3 Device Fabrication B.4 Layer Characterization
B.5 NDR vs. Bias and Temperature B.6 Band Alignments
Publications
 Roy, Anupam, et al. "Structural and Electrical Properties of MoTe2 and MoSe2
Grown by Molecular Beam Epitaxy." ACS applied materials & interfaces 8.11
(2016): 7396-7402.
 Movva, Hema C. P., et al. “Room Temperature Gate-tunable Negative
Differential Resistance in MoS2/hBN/WSe2 Heterostructures.” Device Research
Conference (DRC) 2016, accepted.
Acknowledgements
MoSe2
 RHEED shows
streaky features
after growth
indicative of
layered film
growth with
atomically flat
surfaces
 XRD shows
peaks
characteristic
of the 2H
polytypes
After MoSe2 Growth
MoTe2 MoSe2
Sapphire-Before Growth
MoTe2
MoSe2
 HR-XTEM (a) and
plan-view TEM (b)
images of MoTe2
show its layered
structure and
hexagonal lattice
 EDX area spectrum
(c) and EDX line
spectrum (d) of
MoTe2 shows
signals from
constituent
elements
 Plan-view TEM
image (e) and EDX
area spectrum (f)
of MoSe2 shows its
hexagonal lattice
and constituent
elements
 Raman
spectra of
MBE
grown
films
match well
with the
spectra of
exfoliated
few-layer
flakes
 PL
spectrum
of MoSe2
shows the
expected
peak at ~
1.55 eV  Temperature dependent electrical
measurements reveal 2D Mott VRH transport
MoTe2 MoSe2
 MoS2
shows n-
type
conduction
 WSe2
shows p-
type
conduction
 Individual flakes
obtained via
exfoliation onto
SiO2 substrates
 Heterostructure
made using dry
transfer of
flakes, metal
deposition and
etching
Sapphire-Before Growth
After MoTe2 Growth