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. Shafi a, R.H. Mari a, A. B. Khatab a, M. Henini a, A. Polimeni b, M.Hopkinson c a School of Physics and Astronomy, University of Nottingham, NG7 2RD Nottingham, UK b Department of Physics and INFM, Universit á di Roma “La Sapienza” Piazzale Aldo Moro 2, Roma, Italy c Department of Electronic and Electrical Engineering, University of Sheffield, Sheffield, UK

2. 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

3. 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)]

4. 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

5. 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

6. University of Nottingham, UK Description of samples used in this study n + GaAs Substrate ~ 0.1 μm buffer layer (Highly doped Si: 2 ×10 18 cm -3 ) 1 μm GaAsN layer (Si: 3 ×10 16 cm -3 ) Schottky Contacts Ti/Au Growth temperature : 500 0 C, Growth rate: 1μm per hour, Nitrogen Contents: 0.4% to 0.8% Ge/Au/Ni/Au Ohmic 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 d H = 1.3 × 10 19 ions/cm 2 at 300 0 C

7. 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

8. University of Nottingham, UK Techniques: Deep Level Transient Spectroscopy Capacitance Transients at Different Temperatures Temperatures Ref. Photovoltaic Energy Conversion, Conference Record of the 2006 IEEE 4th World Conference, 2, 1763 (2006) 0 t 1 t 2 C(t 1 ) - C(t 2 ) COST Action MP0805 Meeting, Istanbul, April 12-13, 2010

9. University of Nottingham, UK DLTS & Laplace DLTS Scans Experimental parameters used are; Pulse width (tp): 1msec, Reverse Bias: -4V Bias height (V P ): -0.5V Rate Window = 50Hz. COST Action MP0805 Meeting, Istanbul, April 12-13, 2010

10. University of Nottingham, UK DLTS & Laplace DLTS Scans Experimental parameters used are; Pulse width (tp): 1msec, Reverse Bias: -4V Bias height (V P ): -0.5V Rate Window = 50Hz. COST Action MP0805 Meeting, Istanbul, April 12-13, 2010

11. 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 N=0% N=0.4%

12. 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 N=0% N=0.8%

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

14. 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 GaAs 1-x N x (x= 0.4% to 0.8%). Hydrogen irradiation annihilate some of the electrically active electron traps detected by the DLTS measurements in as-grown GaAs 1-x N x (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

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

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