COST Action MP0805 Meeting, Istanbul, April 12-13, 2010 University of Nottingham, UK Effects of Hydrogen Irradiation on Deep Levels in MBE Grown Dilute

COST Action MP0805 Meeting, Istanbul, April

12-13, 2010University of Nottingham, UKEffects of Hydrogen Irradiation on Deep Levels in

MBE Grown Dilute GaAsN

M. Shafia, R.H. Maria, A. B. Khataba, M. Heninia , A. Polimenib, M.Hopkinsonc

aSchool of Physics and Astronomy, University of Nottingham, NG7 2RD Nottingham, UK

bDepartment of Physics and INFM, Universitá di Roma “La Sapienza” Piazzale Aldo Moro 2, Roma, Italy

c Department of Electronic and Electrical Engineering, University of Sheffield, Sheffield, UK

University of Nottingham, UK

Outline

1. Introduction • Motivation

• Description of samples

• Experimental Techniques

2. Results and Discussion

3. Conclusion

4. Acknowledgement


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Introduction

• Dilute nitride alloys are attracting a considerable deal of attention due to their remarkable properties and potential applications.


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Applications

• Solar cells [Appl. Phys. Lett. 74, 729 (1999)]

• Long wavelength lasers [IEEE Photonics Tech. Lett.,4, 597(2002)]

• Terahertz emitters [GDR-E-2008 THz Workshop, 25.-26.09.2008, Paris, France]

• Optical Amplifiers [IEEE J. Quantum Electron. 27, 1426 (1991)]

• Temperature-insensitive semiconductor band gap [Appl. Phys. Lett. 77, 3021 (2000)]


Introduction


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•Deep levels defects can play an important role in the optical and electronic properties of materials and devices

• Deep level defects are also responsible for the degradation of the optical and electronic properties of materials and devices

• Hydrogen irradiation produces remarkable effects on the electronic properties of dilute nitride alloys. Since hydrogen atom has a high chemical reactivity, it makes bonding with other lattice atoms and neutralise the dangling bonds. This has the effect of eliminating non-radiative recombination centres including shallow and deep levels from the bandgap of the semiconductor materials

It is therefore very valuable to have some knowledge of these defect levels in order to improve the quality and properties of semiconductor materials and devices


Motivation

Interest

•To study defects levels in dilute GaAsN epitaxial layers with different N concentration (from 0.4% to 0.8%) grown by Molecular Beam Epitaxy

•To investigate the effects of hydrogen Irradiation on these levels.


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Description of samples used in this study

n+ GaAs Substrate

~ 0.1 μm buffer layer (Highly doped Si: 2 ×1018 cm-3)

1 μm GaAsN layer (Si: 3 ×1016 cm-3)

Schottky Contacts Ti/Au

Growth temperature : 500 0C,

Growth rate: 1μm per hour,

Nitrogen Contents: 0.4% to 0.8%

Ge/Au/Ni/AuOhmic Contacts


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Samples are hydrogenated by a ion beam irradiation

from a Kaufman source with a dose

dH = 1.3 × 1019 ions/cm2 at 300 0C


Techniques: Deep Level Transient Spectroscopy

Ref. Photovoltaic Energy Conversion, Conference Record of the 2006 IEEE 4th World Conference, 2, 1763 (2006)


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Techniques: Deep Level Transient Spectroscopy

Cap

acita

nce

Tra

nsie

nts

at

Diff

eren

t Tem

pera

ture

s

Tem

pera

ture

s

Ref. Photovoltaic Energy Conversion, Conference Record of the 2006 IEEE 4th World Conference, 2, 1763 (2006)

0 t1 t2 C(t1) - C(t2)


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DLTS & Laplace DLTS Scans

Experimental parameters

used are;Pulse width (tp): 1msec,

Reverse Bias: -4V

Bias height (VP): -0.5V

Rate Window = 50Hz.


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0 50 100 150 200 250 300 350 400 450 500

0

4

8

12 Control Sample GaAs GaAsN (N=0.4 %) Hydrogenated GaAsN

Stan

dard

DLT

S Am

plitu

de (

arb.

uni

ts)

Temprature( K)

A1

A2 A

3

A4

A5

A6

A7

E1

AH1

AH2

÷ 3


DLTS & Laplace DLTS Scans

Experimental parameters

used are;Pulse width (tp): 1msec,

Reverse Bias: -4V

Bias height (VP): -0.5V

Rate Window = 50Hz.


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0 50 100 150 200 250 300 350 400 450 500

0

3

6

9

12

15

18

21

24

BH1

Control Sample GaAs GaAsN (N= 0.8%) Hydrogenated GaAsN

Sta

ndar

d D

LTS

Am

plitu

de (

arb.

uni

ts)

Temperature (K)

E1

B1

B2

B3

B4

BH1

BH4

BH3

BH2

BH2

BH3

BH4

10 100 1000 10000

Lapl

ace

DLT

S S

igna

l (ar

b. U

nits

)

Emission Rates (s-1)

@ 330K


Arrhenius Plots

• Emission Rates are plotted versus inverse of temperature to calculate the thermal activation energies of the traps.


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2 4 6 8 10 12 20 25 3010-4

10-3

10-2

10-1

E1

AH2

AH1

A7

A6

A5

A4

A3

A2

A1

Log

(en/T

2 )

1000/T (K-1)

N=0%N=0.4%


Arrhenius Plots

• Emission Rates are plotted versus inverse of temperature to calculate the thermal activation energies of the traps.


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3 4 5 7.2 7.6 8.0

1E-3

0.01

0.1

Log

(en/T

2)

1000/T (K-1)

E1

BH4

BH3

BH2

BH1

B4

B2

B3

B1

N=0%N=0.8%


Trap parameters calculated from Laplace DLTS data


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Sample Nitrogen

(%) Trap

Activation Energy (eV)

Cross-section σn(∞) (cm2)

Concentration (cm-3) Control(GaAs) 0 𝐸1 𝐸𝑐 − 0.76 5.1 × 10−16 2.85 × 1015

Vn667 (GaAsN) 0.4 𝐴1 𝐸𝑐 − 0.036 2.1 × 10−19 4.0 × 1015 𝐴2 𝐸𝑐 − 0.13 6.9 × 10−18 3.2 × 1014 𝐴3 𝐸𝑐 − 0.28 1.8 × 10−18 3.5 × 1014 𝐴4 𝐸𝑐 − 0.35 1.2 × 10−17 4.4 × 1015 𝐴5 𝐸𝑐 − 0.43 4.0 × 10−17 3.0 × 1014 𝐴6 𝐸𝑐 − 0.51 3.8 × 10−17 4.1 × 1014 𝐴7 𝐸𝑐 − 0.81 5.7 × 10−17 1.5 × 1015 Vn667_Hydrogenated 𝐴𝐻1 𝐸𝑐 − 0.53 2.9 × 10−17 1.2 × 1016 𝐴𝐻2 𝐸𝑐 − 0.82 4.0 × 10−16 5.13 × 1014

Vn669 (GaAsN) 0.8

𝐵1 𝐸𝑐 − 0.34 8.6 × 10−18 6.3 × 1014 𝐵2 𝐸𝑐 − 0.38 1.6 × 10−17 1.2 × 1016 𝐵3 𝐸𝑐 − 0.44 1.8 × 10−17 2.3 × 1015 𝐵4 𝐸𝑐 − 0.63 4.9 × 10−17 1.9 × 1015

Vn669_Hydrogenated

𝐵𝐻1 𝐸𝑐 − 0.37 3.0 × 10−17 3.5 × 1015 𝐵𝐻2 𝐸𝑐 − 0.61 2.7 × 10−17 7.6 × 1015 𝐵𝐻3 𝐸𝑐 − 0.58 3.8 × 10−17 7.6 × 1015 𝐵𝐻4 𝐸𝑐 − 0.82 5.3 × 10−16 9.8 × 1014


Conclusions

We have used DLTS to investigate the effect of hydrogen irradiation on the electrically active defects present in MBE grown dilute GaAs1-xNx (x= 0.4% to 0.8%).

• Hydrogen irradiation annihilate some of the electrically active electron traps detected by the DLTS measurements in as-grown GaAs1-xNx (x= 0.4% to 0.8%) samples.

•EL2-like electron trap which was present in the control sample (N=0%) and in the sample containing N=0.4% is also found in hydrogenated sample.


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M. Shafi, R.H. Mari, D. Taylor, A. B. Khatab University of Nottingham, UK

A.PolimeniUniversitá di Roma “La Sapienza” Piazzale Aldo Moro 2, Roma, Italy

Mark. HopkinsonUniversity of Sheffield, Sheffield, UK

UK Funding Agency


Acknowledgements


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Thank you very much for your attention


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Documents

COST Action MP0805 Meeting, Istanbul, April 12-13, 2010 University of Nottingham, UK Effects of Hydrogen Irradiation on Deep Levels in MBE Grown Dilute