cost action mp0805 meeting, istanbul, april 12-13, 2010
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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
COST Action MP0805 Meeting, Istanbul, April
12-13, 2010
University of Nottingham, UK
Introduction
• Dilute nitride alloys are attracting a considerable deal of attention due to their remarkable properties and potential applications.
COST Action MP0805 Meeting, Istanbul, April
12-13, 2010
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)]
University of Nottingham, UK
Introduction
COST Action MP0805 Meeting, Istanbul, April
12-13, 2010
•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
University of Nottingham, UK
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.
COST Action MP0805 Meeting, Istanbul, April
12-13, 2010
University of Nottingham, UK
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
COST Action MP0805 Meeting, Istanbul, April
12-13, 2010
Samples are hydrogenated by a ion beam irradiation
from a Kaufman source with a dose
dH = 1.3 × 1019 ions/cm2 at 300 0C
University of Nottingham, UK
Techniques: Deep Level Transient Spectroscopy
Ref. Photovoltaic Energy Conversion, Conference Record of the 2006 IEEE 4th World Conference, 2, 1763 (2006)
COST Action MP0805 Meeting, Istanbul, April
12-13, 2010
University of Nottingham, UK
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)
COST Action MP0805 Meeting, Istanbul, April
12-13, 2010
University of Nottingham, UK
DLTS & Laplace DLTS Scans
Experimental parameters
used are;Pulse width (tp): 1msec,
Reverse Bias: -4V
Bias height (VP): -0.5V
Rate Window = 50Hz.
COST Action MP0805 Meeting, Istanbul, April
12-13, 2010
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
University of Nottingham, UK
DLTS & Laplace DLTS Scans
Experimental parameters
used are;Pulse width (tp): 1msec,
Reverse Bias: -4V
Bias height (VP): -0.5V
Rate Window = 50Hz.
COST Action MP0805 Meeting, Istanbul, April
12-13, 2010
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
University of Nottingham, UK
Arrhenius Plots
• Emission Rates are plotted versus inverse of temperature to calculate the thermal activation energies of the traps.
COST Action MP0805 Meeting, Istanbul, April
12-13, 2010
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%
University of Nottingham, UK
Arrhenius Plots
• Emission Rates are plotted versus inverse of temperature to calculate the thermal activation energies of the traps.
COST Action MP0805 Meeting, Istanbul, April
12-13, 2010
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%
University of Nottingham, UK
Trap parameters calculated from Laplace DLTS data
COST Action MP0805 Meeting, Istanbul, April
12-13, 2010
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
University of Nottingham, UK
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.
COST Action MP0805 Meeting, Istanbul, April
12-13, 2010
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
University of Nottingham, UK
Acknowledgements
COST Action MP0805 Meeting, Istanbul, April
12-13, 2010
University of Nottingham, UK
Thank you very much for your attention
COST Action MP0805 Meeting, Istanbul, April
12-13, 2010
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