Diamond based photoconductors for deep UV detection

Transcription

1 Diamond based photoconductors for deep UV detection Antonio De Sio Dep.. of Astronomy and Space Science University of Firenze, Italy

2 Italian Collaborators University of Firenze A. De Sio, E. Pace, M. Bruzzi University of Roma Tor Vergata M. Marinelli, E. Milani, M.E. Morgada, G. Pucella, M. Scoccia, A. Tucciarone, G. Verona-Rinati University of Reggio Calabria M. G. Donato, G. Faggio, G. Messina, S. Santangelo INAF Catania S. Scuderi UV diamond detectors for space applications Beaune

3 Ideal XUV detector for space Radiation hardness High sensitivity REQUESTS Very low noise Large area Solar blindness Chemical inertness Beaune

4 Why diamond Diamond is an appealing materials for XUV photon detection. Their main properties are hereafter summarized : E g = 5.5 ev dark current < 1 pa visible rejection (ratio 10-7 ) high XUV sensitivity Highly radiation hard Chemical inertness Mechanically robust High electric charge mobility Low dielectric constant = fast response time = low capacitance Beaune

5 Diamond detectors MSM structure Coplanar geometry hν hν Transverse geometry Beaune

6 CVD Polycrystalline-Diamond Interdigitated electrodes Diamond layer Beaune

7 External quantum efficiency Pott µτ E I f = ( σ E) WD = ( qnµ E) WD = q η hν L EQE = I P f ott hν q = µτ E η L = ηg Beaune

8 Dark current 1,25x ,00x10-14 pcvd Polycrystalline diamond Coplanar configuration Interdigitated Au contacts Current (A) 7,50x ,00x ,50x ,00-2,50x ,00x ,50x ,00x ,25x ,5-2,0-1,5-1,0-0,5 0,0 0,5 1,0 1,5 2,0 2,5 Electric field (V / µm) Beaune

9 Electro-optical optical performance E. Pace et al., Diam. Rel. Mater. (2000) pcvd External quantum efficiency ,1 0,01 1E-3 1E-4 1E-5 1E-6 1E-7 1E-8 E = 2.8 V/µm UV / VIS > Wavelength (nm) Beaune

10 Time response and PPC 3,5x10-12 Photocurrent (Flux=10 8 γ /s) 3,0x ,5x10-12 Photocurrent (A) 2,0x ,5x ,0x ,0x ,0-5,0x Time (s) Beaune

11 Advantages: High High gain in the UV spectral range Very Very high UV/Vis Vis rejection (8-9 9 orders of magnitude!) Low Low cost Drawbacks: Pumping Persistent photoconductivity MemoryMemory effects Slow Slow response time Unreliable devices Beaune

12 Single Crystal Diamonds by CVD Typical growth parameters Gas Gas Mixture H 2 -CH 4, CO 2 -CH 4, etc. Temperature C MW MW power W Pressure mbar Gas Gas flow rate sccm Growth Growth rate 1 µm m / h Substrates (100) (100) HPHT (Element 6, Sumitomo, others) Natural Natural diamond Type Type Ib and Iia Substrates are not removed Beaune

13 Raman and PL Intensity (counts) Wavenumber shift (cm -1 ) Micro Raman 514 nm Ar laser cm 1 Extremely low photoluminescence background FWHM = 1.8 cm 1 (including instrum.. broadening) Homogeneous results all over the sample surface M.G. Donato, G. Faggio, G. Messina, S. Santangelo Dip. Meccanica e Materiali Università di Reggio Calabria - Italy Beaune

14 Single pixel UV detectors CVD single crystal diamond No substrate removal Interdigitated Al contacts (blocking) 20µm m electrode spacing Beaune

15 Dark Current 5,0x ,5x ,0x ,5x10-13 Current (A) 3,0x ,5x ,0x ,5x ,0x ,0x ,0-0,5 0,0 0,5 1,0 1,5 2,0 2,5 3,0 3,5 4,0 4,5 5,0 5,5 Electric Field (V / µ m) Beaune

16 DUV electro-optical optical performance EQE (Electrons/Photon) E Wavelength (nm) Beaune

17 Time response and PPC 2,0x10-12 Photocurrent (A) 1,5x ,0x ,0x , Time (s) Beaune

18 EUV electro-optical optical performance 0, nm Current (pa) 0,6 0,4 0, nm 30.4 nm 0, Wavelength (nm) Beaune

19 EUV electro-optical optical performance SCD nm Current (pa) SCD nm Time (s) Current (pa) Time (s) Beaune

20 EUV: bias voltage effect Photocurrent (pa) nm 30.4 nm Dark current V bias (V) Photocurrent as a function of the applied bias voltage Dark current (triangles) and photo- current at 30.4 nm (circles) and at 58.4 nm (squares) (the dark current was subtracted from the reported photocurrents) An almost complete saturation of the reported photocurrents is observed above 30 V Beaune

21 De Sio et al. Appl. Phys. Lett EQE ( e - / Photon ) 1 0,1 0,01 1E-3 1E-4 Coplanar 1V/um Coplanar 5 V/um Transverse 1V/um Transverse 2V/um Wavelength (nm) Single pixel device Material from LIMHP-CNRS Device built and tested in Firenze Single crystal CVD diamond Free standing Mechanically polished Au electric contacts on both surfaces Beaune

22 Pixel array UV detectors Lift-off photolitographic technique Al Al contacts (blocking) µm interelectrode spacing µm m pitch Beaune

23 Dark Current 4,0x ,8x ,6x ,4x10-15 Current (A) 3,2x ,0x ,8x ,6x ,4x ,2x Electric Field (V / µm) Beaune

24 DUV electro-optical optical performance 0,1 EQE (electons/photons) 0,01 1E Wavelength (nm) Beaune

25 Time response and PPC 3,0x ,5x10-13 Photocurrent (A) 2,0x ,5x ,0x ,0x , Time (s) Beaune

26 Pixel array: cross talk 5 ns laser pulses at 215 nm 0.50 * 0.25 Pixel n.1 Pixel n.1 Pixel n.1 Photocurrent (a.u.) Pixel n.2 Pixel n.3 * Pixel n.2 Pixel n.3 * Pixel n.2 Pixel n t (ns) Beaune

27 Conclusion Single crystal diamond based UV single pixel devices have been realised and characterised Single crystal diamond based UV pixels array devices have been realised and characterised Low dark current values High XUV sensitivity was observed Good time response No persistent photoconductivity No pumping effects Negligible cross-talk Beaune