Application of sprayed carbon nanotubes to light detectors

Transcription

1 Olive Tree (St. Nicholas Church in Bari) Application of sprayed carbon nanotubes to light detectors Valentini A. (1)(2), Melisi D. (1), Valentini M. (1), Nitti M.A. (2), Biagi P.F. (2) (1) INFN Sezione di Bari, Italy (2) Department of Physics, University of Bari A. Moro, Italy

2 Outline CNTs for photodetection Film characterization Device layout Experimental Set-up I-V results QE measurements Summary

3 CNTs for photodetection Semimetallic behavior Absorbance peak ~ 200nm Artist's impression of a carbon nanotube. Image: Digital Art/Corbis UV-NIR Current density 1 GA/cm 2 (J CNTs ~ 1000 J Cu ) (whitout overheating) GOOD CANDIDATE IN PHOTODETECTION

4 CNT Dispersion MWCNT Powder (purity > 95%, diameter nm, Length 5-15 μm) 1) Drying process Deionized water Isopropanole Acetone 1,2-Dichloroethane (DCE) 3) Centrifugation 6000 rpm for 70 minutes Homogenous dispersion of CNT 2) Sonication of CNT in 100 ml DCE 14 hours at 20Khz

5 SPRAY Process PULSED MODE SUBSTRATE TEMPERATURE Argon pressure Time nozzle ON Time nozzle OFF Distance substrate-nozzle 120 C 2.5*10 4 Pa 40 ms 4 s 5 cm Film thickness depending on shot number

6 Results SPRAY TECHNIQUE - Large area deposition - No degradation of the emission tips - DCE is easily vaporized in ambient condition - DCE has low surface tension (good wettability of CNTs Quartz Silicon Aluminium Stainless steel Good adhesion of CNTs to different substrates

7 CNTs characterization OPTICAL MICROSCOPY MWCNTs film on Stainless Steel (100x) Good uniformity of the film (500x) M, Valentini SIF - Trieste 2013

8 CNTs characterization SCANNING ELECTRON MICROSCOPY

9 CNTs characterization TRANSMISSION ELECTRON MICROSCOPY Good separation of CNTs Confirm of the supplier description of the CNTs

10 CNTs characterization X RAY PHOTOELECTRON SPECTROSCOPY CNTs spray 6 shots CNTs spray 12 shots CNTs spray 24 shots C1s Reduction in the Si/O signals CNTs spray 6 shots CNTs spray 12 shots CNTs spray 24 shots No oxidation of CNTs C1s a.u. O1s Si2s Si2p a.u. Shake-up (π π*) Binding Energy (ev) Binding Energy (ev) C1s (Atomic %) 6 shots 12 shots 24 shots MEAN VALUE ST. DEV Improvement of the film uniformity Atomic % (without SiO 2 ) 6 shots MEAN VALUE ST. DEV. 12 shots MEAN VALUE ST. DEV. 24 shots MEAN VALUE ST. DEV. C1s C1s C1s O1s O1s O1s

11 CNTs characterization X RAY PHOTOELECTRON SPECTROSCOPY Sample 1 CNTs film CNTs film after 2 months Sample 2 CNTs film CNTs film after 4 months C1s C1s a.u. a.u Binding Energy (ev) Binding Energy (ev) NO OXIDATION OF CNTs

12 CNTs characterization OPTICAL ABSORBANCE Absorbance (a. u.) _ Spray_MWCNT _Spray_MWCNT λ (nm) Presence of the absorbance peak in the UV region

13 Device Layout (Step 1) Ti 20 / Pt 100 nm PECVD nitride (60 nm) 300 μm Ω*cm p-type Si Ti 30nm / TiN 50nm/ Ti 20nm / Pt 100nm N+ implant

14 Device Layout (Step 2) CNT ITO

15 Device Layout (Step 3) IBS ITO (Indium Tin Oxide) DEPOSITION ITO Optical absorbance glass nm ITO on glass E g > 3 ev hν (ev) ION SOURCE 2. BEAM NEUTRALIZER 3. TARGET HOLDER

16 I-V experimental Set-up Apply voltage Measure current Light Beam p-type Si AGILENT B1500A THORLABS PM100D Optical power/energy meter S = light source L = focusing lens C = Sample or calibrated photodiode

17 Current-Voltage Characteristics Photocurrent Low dark currents

18 QE measurements QE hc I λe I sam sam (%) = R 100 = η 100 ref I I ref R = I P ref R (A/W) = responsivity ; λ (m)= light wavelength ; I sam (A) = sample current ; I ref (A) = calibrated photodiode current η = calibrated photodiode internal quantum efficiency ; P (W) = radiation power QE (%) Max = 59 %

19 Summary Good adhesion of CNTs on different substrates Very low oxidation of sprayed CNTs Film uniformity enhances with spray number Presence of the absorbance peak in the UV region Contribution of CNTs on the device QE

20 Thanks for your attention