Growth of ZnO ZnSe nanowires

Yuya Sakamoto

Character of ZnO ZnSe Nanowire (NW)

WZ ZnOZB ZnSe

2.8 eV3.2 eV

1.9 eV

Feature

・ Type-II heterojunction・ ZnSe and ZnO have a wide bandgap・ Lattice mismatched combinations

WZ ZnOWZ ZnSe

2.8 eV

3.2 eV1.5 eV

For Photovoltaic devices

Increase surface-to-volume-ratio

Chemical Vapor Deposition (CVD) method

Quartz tube heaterAu on Si substrate ZnO/C or ZnSe

Ar Gas inletAr Gas outlet

0 10 20 30 40 50 600

400

800

1200

Position [cm]

Tem

pera

ture

[]

℃

Two-step CVD method

Au

Si ZnO

Si

First step Second step

ZnSeSi

ZnSe

Si

ZnOSi

ZnO/ZnSe Core/Shell NW

ZnO ZnSe Branch NWSi

Growth conditions of ZnO/ZnSe core/shell NWs

Au

Si

ZnO

Si

ZnSe

Si

Temperature Duration Ar gas flow rateFirst step 600 60 min 125sccm

Second step 590 60 min 235sccm

Source material : ZnO (99.99%) and C(99.9%) with the weight ratio of 1:1 ： ZnSe (99.99%)Thickness of Au film : 10 nm

SEM imageZnO NWs ZnO/ZnSe core/ shell NWs

The average NW diameter : 40 nm → 75 nm

500 nm 500 nm

1 μm 2 μm

EDX spectrum

The diameter correspond to ZnO/ZnSe core/shell NW

0 20 40 60 80 100 120 140 160 180 2000

50100150200250300

Distance [nm]

Inte

nsity

[a. u

.]

1 μm

90 nm120 nm

Photoluminescence Spectrum

ZnO Bandedge (BE) emission : 380 nm = 3.26 eVZnSe BE emission : 460 nm = 2.69 eV

ZnSe Deep Level (DL) emission: 640 nm = 1.93 eV

Laser wavelength : 361.2 nmRoom temperature

Growth conditions of ZnO ZnSe branch NWs

Au

Si

Temperatu Duration Ar gas flow rateFirst step 640 60 min 235sccm

Second step 590 60 min 125sccm

ZnSe

SiZnO

Si

Source material : ZnO (99.99%) and C(99.9%) with the weight ratio of 1:1 ZnSe (99.99%)Thickness of Au film : 10 nm

SEM imageZnSe NWs ZnO ZnSe branch NWs

The average diameter of thin NWs is 29 nm → 33 nm

5 μm 5 μm

1 μm 1 μm

0 50 100 150 200 250 3000

100200300400

Distance [nm]

Inte

nsity

[a. u

.]0 30 60 90 120 150 180

050

100150200

Distance [nm]In

tens

ity [a

. u.]

ZnO ZnSe branch NW data by EDX line profile

2

1 1

2

1 μm

PL

ZnSe BE emission : 442 nm = 2.8 eV

ZnSe DL emission : 640 nm = 1.9 eVZnO BE emission : 380 nm =3.26 eV

Laser wavelength : 361.2 nmRoom temperature

Conclusion

・ Characterize the ZnO/ZnSe core/shell NWs and ZnO ZnSe branch NW by XRD and PL

・ Observe the surface morphology of ZnO/ZnSe core/shell NW, and ZnO ZnSe branch heterostructure NW by SEM

・ Found the conditions for growth ZnO/ZnSe core/shell heterostructure NW, and ZnO ZnSe branch heterostructure NW

Future Work

・ Measure the electrical property by Electron beam induced current

・ Fabricate the single NW device with ZnO ZnSe branch structure NW by electron beam lithography

・ Upgrade the quality of ZnO and ZnSe NWs before growth second material

・ Measure the junction of ZnO and ZnSe by transmission electron microscopy to confirm ZnO NWs are connecting to ZnSe NWs

Acknowledgement

・ I would like to express my deep gratitude to Professor Harry E. Ruda, for his patient guidance and useful critiques of this research work.

・ I would also like to thank Dr. Carlos Fernandes, for his advice and assistance in keeping my progress on schedule.

・ I would also like to thank Dr Souza Christina and Dave Wisnieski for measuring PL spectrum and teaching me how to analyze spectrum.

・ I wish to express my sincere gratitude to all of the concerned people, who help me to finish my all procedure, correct my English, promote my experiments.

Laser reference

330 360 390

0

2000

4000

6000

Inte

nsity

(arb

.uni

t)

Wavelength (nm)

Leaser reference

Analysis

The mean diameter of base : 223 nm

The mean diameter of branch : 52 nm

The diameter of ZnO was also almost 40 nm

ZnSe : June 28

ZnO : July 4

ZnO ZnSe branch NW data by EDX line profile

①

②

②

①

There is the ZnSe ZnO hetero structure NW

My opinion

I measured 20 NWs by ESM and EDX. The compositions of thin NWs were ZnSe

ZnO NWs weren’t grown on ZnSe NWs

ZnO

Au

ZnSe

Before using EDX,I guessed this structure

ZnO

ZnSe

After using EDX, I believe it was happened in the furnace

∆𝐸𝑉+∆𝐸𝑣=¿