1 / 8

Photovoltaic Effect in Ideal Carbon Nanotube Diodes

Photovoltaic Effect in Ideal Carbon Nanotube Diodes. Sung Hwan Kim. Outline. Motivation Formation of ideal p-n junction diodes utilizing the structural purity of CNT Examination of photovoltaic effect Single-walled carbon nanotubes(SWNTs) Photovoltaic Fabrication of Ideal Diode

ludlow
Download Presentation

Photovoltaic Effect in Ideal Carbon Nanotube Diodes

An Image/Link below is provided (as is) to download presentation Download Policy: Content on the Website is provided to you AS IS for your information and personal use and may not be sold / licensed / shared on other websites without getting consent from its author. Content is provided to you AS IS for your information and personal use only. Download presentation by click this link. While downloading, if for some reason you are not able to download a presentation, the publisher may have deleted the file from their server. During download, if you can't get a presentation, the file might be deleted by the publisher.

E N D

Presentation Transcript

  1. Photovoltaic Effect in Ideal Carbon Nanotube Diodes Sung Hwan Kim

  2. Outline • Motivation • Formation of ideal p-n junction diodes utilizing the structural purity of CNT • Examination of photovoltaic effect • Single-walled carbon nanotubes(SWNTs) • Photovoltaic • Fabrication of Ideal Diode • Results – ideal diode • Results – photovoltaics • Summary and Conclusion

  3. SWNT • Structural purity – free from impurities and defects • Reduced carrier scattering • Direct bandgap • Wide range of bandgap to accommodate solar spectrum • EG ≈ 0.8eV/d(nm) • Enhanced optical absorption

  4. Photovoltaic • Figure of Merit • Isc – light-generated current • Voc = kT/q*ln(IL/Io+1) • FF – measures the “squareness” of the I-V curve • η – photon energy to electric power conversion efficiency • Diode equation • ID = Io[exp(qVD/nKT - 1)] • Ideality factor(n) is 1 for ideal diode and approached 2 for materials with defects => larger the n, the lower the power conversion efficiency through reduced Voc

  5. Fabrication of Ideal Diode • Standard lithography and deposition used to form Mo split gates (gate spacing 0.5 μm to 1μm) • Lift-off(Ti, Mo, Pd) to define S/D • SWNTs grown on top of the S/D using Fe catalytic CVD • A large number of devices(~400devices/cm2) need to be fabricated to find a single semiconducting SWNT between S and D

  6. Results – ideal diode • Since physical doping is not possible in SWNTs, split gate is used to create ambipolar device • Electrostatic doping - different bias polarities on the split gate electrostatically couple to form separate regions of electron and hole doping along single SWNT. This is possible via e-h tunneling through Schottky barriers from metal contacts to SWNT. • I-V shown below(VG1= -VG2=+10V) exhibits a fit with n=1.0 => ideal diode!

  7. 1.5μm(0.8eV) cw laser diode coupled to a multimode fiber Photogenerated e-h pairs become separated in the middle of the device where the electric field is the greatest Responsivity = Jsc/Pin = 30mA/W η (max) = 0.2% Small absorption due to small diameter of SWNTs Results – photovoltaics

  8. Summary and Conclusion • Some thoughts: • VGtoo high • Reproducibility • Precise control of diameter of SWNTs • Network of SWNTs + Si solar cell(substrate) • Formation of ideal p-n junction diodes using SWNTs • Under illumination, photovoltaic effect and significant power conversion efficiency observed

More Related