COST Action MP0805 Meeting, Istanbul, April 12-13, 2010

1. COST Action MP0805 Meeting, Istanbul, April 12-13, 2010 University of Nottingham, UK Effects 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, Universitádi Roma “La Sapienza” Piazzale Aldo Moro 2, Roma, Italy cDepartment of Electronic and Electrical Engineering, University of Sheffield, Sheffield, UK

2. COST Action MP0805 Meeting, Istanbul, April 12-13, 2010 University of Nottingham, UK Outline • Introduction • Motivation • Description of samples • Experimental Techniques • 2. Results and Discussion • 3. Conclusion • 4. Acknowledgement

3. 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. • 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)]

4. COST Action MP0805 Meeting, Istanbul, April 12-13, 2010 University of Nottingham, UK Introduction • 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

5. COST Action MP0805 Meeting, Istanbul, April 12-13, 2010 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.

6. COST Action MP0805 Meeting, Istanbul, April 12-13, 2010 University of Nottingham, UK Description of samples used in this study Growth temperature : 500 0C, Growth rate: 1μm per hour, Nitrogen Contents: 0.4% to 0.8% Samples are hydrogenated by a ion beam irradiation from a Kaufman source with a dose dH = 1.3 × 1019 ions/cm2 at 300 0C Schottky Contacts Ti/Au 1 μm GaAsN layer (Si: 3 ×1016 cm-3) ~ 0.1 μm buffer layer (Highly doped Si: 2 ×1018 cm-3) n+ GaAs Substrate Ge/Au/Ni/Au Ohmic Contacts

7. COST Action MP0805 Meeting, Istanbul, April 12-13, 2010 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)

8. COST Action MP0805 Meeting, Istanbul, April 12-13, 2010 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) Capacitance Transients at Different Temperatures Temperatures 0 t1 t2 C(t1) - C(t2)

9. 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.

10. 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.

11. COST Action MP0805 Meeting, Istanbul, April 12-13, 2010 University of Nottingham, UK Arrhenius Plots • Emission Rates are plotted versus inverse of temperature to calculate the thermal activation energies of the traps. N=0% N=0.4%

12. COST Action MP0805 Meeting, Istanbul, April 12-13, 2010 University of Nottingham, UK Arrhenius Plots • Emission Rates are plotted versus inverse of temperature to calculate the thermal activation energies of the traps. N=0% N=0.8%

13. COST Action MP0805 Meeting, Istanbul, April 12-13, 2010 University of Nottingham, UK Trap parameters calculated from Laplace DLTS data

14. COST Action MP0805 Meeting, Istanbul, April 12-13, 2010 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.

15. COST Action MP0805 Meeting, Istanbul, April 12-13, 2010 University of Nottingham, UK Acknowledgements • M. Shafi, R.H. Mari, D. Taylor, A. B. Khatab • University of Nottingham, UK • Polimeni • Universitádi Roma “La Sapienza” Piazzale Aldo Moro 2, Roma, Italy • Mark. Hopkinson • University of Sheffield, Sheffield, UK UK Funding Agency

16. COST Action MP0805 Meeting, Istanbul, April 12-13, 2010 University of Nottingham, UK Thank you very much for your attention