UV VIS OPTOELECTRONICS WITH OXIDESADRIAN HIERRO, ELIAS MUÑOZ

UV‐VIS OPTOELECTRONICS WITH OXIDES

INSTITUTE OF SYSTEMS BASED ON OPTOELECTRONICS AND MICROTECHNOLOGYELECTRONICS ENGINEERING DEPT.

UNIVERSIDAD POLITECNICA DE MADRID (UPM), MADRID, SPAINUNIVERSIDAD POLITECNICA DE MADRID (UPM), MADRID, SPAIN

A. Nakamura and J. TemmyoResearch Institute of Electronics Shizuoka University HamamatsuResearch Institute of Electronics,   Shizuoka University, Hamamatsu

JOINT JST‐MINECO PROJECT,    SU‐UPM collaboration

From “Wide bandgap semiconductors”, Springer 2007.K. Takahashi,  A. Yoshikawa, A. Sandhu,  editors.  162 Committee JSPS

ZnO

Why ZnCdMgO?ZnO Easy to grow with with different plane orientations High exciton binding energy 60 meV;  Excitonic effects at RT ZnO high quality substrates already available for homoepitaxy A variety of nanostructures/shapes easily grown Reactive surfaces and prone to get –OH groups Reactive surfaces and prone to get –OH groups

ZnCdO→ ZnO→ Zn1‐xMgxO Potentially , bandgap control from  (VIS) 2.2 eV to (UV)   8 eV As an example, from present work, ZnMgO keep WZ structure up 

to Mg 50% (4.4 eV) g ( )

DIFFICULTIES‐to reach high Mg/Cd m fractions while keeping WZ S (NPS)to reach high Mg/Cd m fractions while keeping WZ S (NPS)‐to obtain reliable and robust p‐type doping

CAN ZnCdMgO NANOSTRUCTURES HELP TO‐CAN ZnCdMgO NANOSTRUCTURES HELP TO CIRCUNVENT SUCH PROBLEMS?

outline• RPE‐MOCVD growth reactor at SU

• ZnCdO nanowires grown on a Sapphire paternned substrate:search for high Cd content

• Acceptors in undoped ZnMgO

• Typical p‐doping results in ZnMgO layers

A t i N d d Z M O• Acceptors in N‐doped ZnMgO

• MQW ZnCdO/p‐type SiC green LEDMQW nCdO/p type SiC green

• Summary/reflections

Zn(Mg,Cd)O:N by RPE‐MOCVD

Plasma spectrum in situRF13 56MHRemote plasma Heater 10KHz

A. Nakamura, J. Temmyo, Shizuoka U.

OH O2 plasma/ H2 carrier

Plasma spectrum in situRF13.56MHz

Oxygen/HydrogenNitrogen

O

H

y (a

rb. u

nits

)

OH

substrate

MeCp2Mg(EtCp2Mg)

susceptor

O2 plasma/ N2 carrier

O2

N2

N2

N2

NOInte

nsityDEZn

DMCd

H2/N2

MBP/RPGrowth conditions:Pressure: 0.1TorrTemp: 300-600oC

200 300 400 500 600 700 800

Wavelength (nm)

Hi hl ilib i th

2 2

exhaust

p

Highly non-equilibrium growth:- radical energy enhances decomposition and doping- WZ type ZnO alloys become available

66

STRUCTURAL and OPTICAL PROPERTIES of  ZnCdONANOCOLUMNS

‐ PL+HRXRD*+microEDX+HRTEM* of ZnCdO nanocolumns‐ Cd%: x=0, 0.14, 0.27 and 0.45!!‐Length 1‐4 m

SEM

*HRTEM/EDX collaboration with V.Muñoz, U.Valencia, SP

 As‐grown

RT

‐Length  1‐4 m‐Diameter  100‐200 nmHRTEM

V.Muñoz, U.Valencia, SP

ZnO

14% Cd

27% Cd

 Annealed

y (a

.u)

45% Cd

PL

PL

Inte

nsity

0.8

1.0

0.8

1.0

Con%

) Zn

Annealed nanowire

1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2 3.4

Energy (eV)

micro‐EDX

0.2

0.4

0.6

0.2

0.4

0.6

centration (atcent

ratio

n (a

t

Cd

1. Emission demonstrated down to 2.02 eV2. Only wurtzite phase observed even for

45% Cd, no phase separation!

0.0 0.1 0.2 0.3 0.4 0.5

0.0

0.1 0.2

0.0NanowireSurface

t %)

Con

c

Nanowire Tip

Width (m) Lenght (m) Results accepted for publication in Appl.Phys.Lett.

3. State of the art ZnCdO nanocolumns!

CHARACTERIZATION of  ZnMgO (MOCVD) LAYERS (SU)

0.9

1.0

d

<1120>

RBS determination of stoichiometry and quality*

1017

m-3) 5.6%Mg

DARKC‐V profiles

0.7

0.8

0.9

aliz

ed y

ield

Nd-N

a) (cm

9.5%Mg 14.5%Mg 18.0%Mg

0.5

0.6

Zn MgO

Nor

ma

a-plane MgZnO 0 15 0 30 0 45 0 60

1016

n=(N

-2.0 -1.5 -1.0 -0.5 0.0 0.5 1.0 1.5 2.00.4

O

Theta (º)

MgZnO

*Collaboration with A. Redondo, ITN, Portugal

0.15 0.30 0.45 0.60Depth (m)

Zn1-xMgxO1 O rich behavior of samples

DLOS + Lighted CV profiling EC

Mg(%)

n=(Nd-Na)(cm-3)

Ev+280 meV(cm-3)

Ev+580 meV(cm-3)

1. O‐rich behavior of samples2.Growth plane (a‐plane or c‐plane)does not affect Mg incorporation3 ZnMgO is highly compensated

E

Ev+580 meV

Ev+280 meVVZn (-/2-) *VZn (0/-) *

5.6 8.02x1016 1.08x1017 1.66x1016

9.5 1.98x1016 3.44x1017 1.54x1016

14.5 1.47x1016 8.62x1017 2.27x1016

18 0 1 27 1016 1 01 1018 5 23 1016

3. ZnMgO is highly compensateddue to two acceptor levels related

to VZn4. Can use ZnMgO samples toEV

* A.F. Kohan et al. Phys.Rev.B 61, 15019 (2000)

18.0 1.27x1016 1.01x1018 5.23x1016 4. Can use ZnMgO samples toachieve p‐type doping

Same VZn related acceptors also found in MBE ZnMgOlayers from JM Chauveau, CNRS‐CRHEA, FR

Typical p‐doping resultsA. Nakamura, J. Temmyo, Shizuoka U.

n-typep-type

MgZnO:(N,In,Cu) co-doping

n-typep-type

g ( , , ) p gshowed p-type- N solubility enhanced by codoping

(N) acceptor activated- (N)O acceptor activated

against expectation:- n-type conductivity for N, Cun type conductivity for N, Cu- Conductivity-type change for N, Inwas occurred under RTA activation.

ref: morphology change after RTA200nm 200nm

As grown RTA 800oC

9

S. Mohanta, et al. J. Appl. Phys 110 (2011) 013524.

*Implanted profile (SRIM) Crystal recovery (RBS)

N‐implantation in MOCVD ZnMgO LAYERSOptical emission (PL)

3000

3500

4000

As implanted+500 ºC (10')

s)

RBS/C 2 MeV He+

=140º, Q=5 C

0.30

0.35

0.40

on Å

150 keV N 10º

Implanted profile (SRIM) Crystal recovery (RBS)

.)

MgxZn

1-xO (as grown)(b)

x=15%x=9%

Optical emission (PL)

1500

2000

2500+500 C (10 )

+700 ºC (10') +900 ºC (10') Random

Yie

ld (c

ount

s

O

Zn

0 10

0.15

0.20

0.25 Zn+O

OVac

anci

es /

io

Zn

nsity

(a.u x=5%

x=0%

400 600 800 1000 1200 1400 16000

500

1000

YAl

0 100 200 300 400 5000.00

0.05

0.10

Depth (nm)

V

(b)

PL

inte

n

(c) MgxZn1-xO:N (+RTA 900ºC)

Energy (keV)Depth (nm)*Collaboration with A. Redondo, ITN, Portugal

CV profiling using Schottky diodes3.3 3.4 3.5 3.6

Photon energy (eV)1E18

5 % Mg 9 % Mg

Implanted + RTAm-3)

As implanted

p f g g y

1. N implantation at 150 keV

1E17

Implanted + RTA

Nd-

Na (

cm 2. Implanted films are highly n‐type3. Best crystal recovery found at 900°C (strong Alout‐diffusion from substrate at higher T).

h l l d l d f l

0.138 0.207 0.276 0.3451E16

as-grown

W (m)

1 KHz

4. Thermal annealing reduces Xtal damage, films areless n‐type, BUT no direct observation of p‐typebehavior ; defects overcome N‐related acceptors

MQW ZnCdO/ZnO/p‐SiC VIS  LED

b. u

nit)

room temprerature

Mesa: 200m

FWHM: 690 meV

Layers grown at Shizuoka U. 5 QW ZnCdO (20% Cd)

ensi

ty (a

rb

80mA70 A

Mesa: 200m

EL

inte 70mA

60mA40mA20mA

1.5 2.0 2.5 3.0 3.5Photon energy (eV)

10-2

10-1 Rectify ratio: 107 @4V

unit)1. RT CW Emission at

2 55 V ( i h

5

10-4

10-3

10 2

ity (A

/cm

2 )

nsity

, L (a

rb. 2.55eV (agreement with

PL from ZnCdO/ZnOQW)

10-7

10-6

10-5

urre

nt d

ens

grat

ed E

L in

te2. First demonstration of ZnCdO MQW LED in literature!!....green

-4 -3 -2 -1 0 1 2 3 410-9

10-8C

Voltage (V)

0 20 40 60 80 100Inte

g

In jec tion cu rren t, I (m A )

Results published in IEEE Photon.Tech.Lett.2011

ggap!

• Single-phase wurtzite nanowires of ZnCdO with Cd up to

SUMMARYSingle-phase wurtzite nanowires of ZnCdO, with Cd up to50%, have been demonstrated by RPE- MOCVD (C-planeon sapphire)

• Single phase wurtzite QW and thick layers of ZnMgO with• Single-phase wurtzite QW and thick layers of ZnMgO withMg up to 55% have been demonstrated by MBE

B th th t h l i it f f lib i• Both growth technologies grow quite far from equlibriumand Zinc vacancies are promoted

• Proper growth coditions and substrates seem to allowsingle phase WZ ZnMgCdO alloys for UV and VIS optoelectronics

• In N doped MgZnO alloys (MOCVD) and in N:ZnO (MBE) a shallow acceptor has been detected that seems to

d t th N V l di t d bcorrespond to the NO‐VZn complex predicted bycomputer simulations and that may play a key role in obtaining robust p-type doping

the future of ZnMgCdO alloys for optoelectronics still open….

Besides SU‐ UPM joint efforts, ….collaboration with other groups

1. Centre de Recherche sur l'Hétéro‐Epitaxie et ses Applications‐CNRS (France)Prof. Jean‐Michel Chauveau

Samples grown by MBE: ZnMgO with very high Mg contents and nonpolarSamples grown by MBE: ZnMgO with very high Mg contents, and nonpolar ZnMgO/ZnO MQW structures; ZnO with low residual concentrations 

‐6 invited/oral presentations, ‐3 papers, ‐1 visit to UPM in 01/20132 Instituto Tecnológico e Nuclear (ITN Portugal) Dr Andres Redondo2. Instituto Tecnológico e Nuclear (ITN, Portugal), Dr. Andres Redondo

Analysis of ZnMgO by RBS,  N‐implantation on ZnMgO; analysis of residual H in ZnO‐2 invited presentations, ‐2 papers

3. Ohio State University (EEUU),   Prof. Steve RingelDLTS/DLOS, CV, analysis of ZnMgO and ZnO

‐1 oral presentation, ‐1 paper, ‐ OSU‐UPM Agreement on research ongoingp , p p , g g g‐Visits to UPM in 10/2011 and 05/2012

4. Univ. Valencia (Spain),  Prof. Vicente Muñoz‐SanjoseHRTEM and micro‐EDX of ZnCdO and ZnMgO samples grown by spray‐pyrolisisHRTEM and micro‐EDX of ZnCdO, and ZnMgO samples grown by spray‐pyrolisis

‐1 oral presentation, ‐2 papers‐1 Joined MINECO‐funded project (TEC2011‐28076‐C02‐01)5 University of Montpellier II (France) Prof Pierre Lefebvre5. University of Montpellier II  (France), Prof. Pierre LefebvreTime resolved micro‐photoluminescence, student exchange