CVD Growth of Single-Layer TMD films into Pre-Fabricated Substrate StructuresBrandon Davis, E. Preciado, V. Klee, A. E. Nguyen, I. Liu , D. Barroso, S. Naghibi, I. Liao, G Von Son, D. Martinez-Ta, Ludwig Bartels

University of California, Riverside

I. Motivation

Process FlowV. Substrate Preparation: Suspended Growth

VI. Outlook

Before

Si

Metal

SiO2MoS2

HfO2

After

X S S

G

DChannel

a)

VII. Acknowledgements

Transport shows MoS2photo-response. Design for scalability using photo lithography. Pillar is under cut to prevent continuous metal thin film on the sidewall.

In collaboration with:Volker SorgerMark Bockrath

Exposure

Silicon

SiO2

Photoresist

TMD

Key Spin Coat Resist

PL top off trench

DevelopmentEtch StepCVD Growth

II. Goal

Local Seeding Growth of TMD material exactlywhere needed. At any orientation.

II. Substrate Preparation: Local Seeding

Nucleation of TMD Growth

Photo Mask

Photo ResistCr LayerSiO2Si

Exposure MoS CVD2Develop Cr Wet Etch& Resist Strip

O Plasma Etch& Cr Strip

2

IV. Substrate Preparation: Local Seeding

7 mP

7 mP

b)

c)

a)

2 mP

(Left) Optical micrographs of apatterned SiO2/Si substrate aftergrowth of MoS2 single-layer islands. Ø= 2 μm holes through the substrateoxide seed the formation ofcrystalline-single-layer MoS2 islands.

2 mP (Left) AFM imageof the areahighlighted by awhite frame. AFMconfirmshomogeneoussingle-layerheight.Grain

Boundaries

Photon Energy (eV)

300 400 500 600

Inte

nsity

(a.u

.)In

tens

ity(a

.u.)

Raman Shift (cm-1)

E12g A1g

a)

b)

1.4 1.6 1.8 2.0 2.2

(right) Raman andphotoluminescence(PL) spectroscopy ofthe MoS2 islands onthe sample. (left) PLmapping shows highhomogeneity of thefilm. A bright feature

Suspended Material

at the location of the substrate holecorresponds to suspended material.

CVD Growth

Tube Furnace

High Vacuum

TMD materials can begrown by various CVDmethods.

Depending on the method,the resultant material areisolated highly-crystallineislands randomly orientedon a substrate (tubefurnace) or a homogenous,substrate-scale film(vacuum CVD).

Wafer-Scale: the ONLY Goal?Conventional semiconductor epitaxy suggestswafer-scale growth as the key goal of filmpreparation. The 2D nature of the films,however, may limit the utility of the thisapproach

Vs.D. E. Johnston, et al. “One-volt operation of High-Current Vertical channel Polymer semiconductor Field-Effect Transistors” Nano let, 2012, 12(8), pp 4181-4186

2cm

2cm

Sample Clamp

The sample is createdby using a chromiumhard mask. First, a layerof Chromium must bedeposited onto thesubstrate, the pattern istransferred. usingPhotolithography and awet etch. A dry etch isthen performed. FinallyThe sample has MoS2grown onto them

Trench

10μm

• Photo mapping of suspended vs non suspended growth

• Suspended growth shows a higher intensity PL then the non suspended • The PL of non

suspended is measured at 1.85 eV when suspended.

• The PL of the suspended is measured at 1.82 eV showing a difference

10 µm

Photo mapping over trench

PL over trench

1.76 1.81 1.85 1.89

0

5000

10000

15000

20000

25000

Inte

nsity

(a. u

.)

Photon Energy (eV)

On Silicon Suspended

170 340 510 680

0

500

1000

1500

2000

2500

3000

3500

Inte

nsity

(a. u

.)

Raman Shift (cm-1)

Si

SiO2

Metal

MoS2

I. Suspended Growth: Preliminary Results

Pillared substrates

-600

-400

-200

0

200

400

600

-2 -1 0 1 2

I sd(p

A)

Vsd (V)

light ON

50 µm

d)

abbccd

MoS2

MoSe2

No Substrate Quenching Over Hole

MoSe2 Film grown over hole arrays. The PLmap show that the area over the center ofthe hole has a higher intensity then the areasurrounding the hole.

100 μm

c)