Friday, February 18, 2011 3:30 pm – 4:30 pm
Room G05, Rekhi Hall
Jeramy D. Zimmerman
Department of Electrical Engineering and Computer Science
University of Michigan
Simple lens systems generally suffer from Petzval field curvature aberrations and focus on a curvedsurface; therefore, complicated lens systems are needed to create the flat focal surface required byconventional semiconductor fabrication techniques. To simplify the optics systems, we are designingimagers with curved imaging surfaces, which reduces other optical aberrations as well as system weight.The adoption of curved focal planes requires the development of new processing techniques and newmaterials for conformal surfaces. This talk will focus on two infrared-sensitive organic semiconductorphotodetector systems developed at the University of Michigan for use on conformal substrates.
Organic photodetectors are efficient (20-80% quantum efficient) in the visible region of the spectrum, butvery few organic materials exist with useful photoresponse beyond λ ≈ 1000 nm. Carbon nanotubes(CNTs) have band gaps that absorb in the λ ≈ 1000 to 2000 nm region, motivating our development of aprocedure to use single-wall CNTs wrapped with conjugated polymers as a photoactive component inphotodetectors. We have demonstrated that excitons on CNTs can be dissociated at CNTC60 interfaces, and have created the first photovoltaic detectors fabricated from bulk CNT films. Detectorspecific detectivities above D*=1010 cm-Hz½/W were demonstrated from λ ≈ 400 to 1400 nm, with peakexternal quantum efficiencies of approximately EQE=2% at λ ≈ 1155 and 1300 nm.
More recently, we demonstrated a new porphyrin tape-based organic semiconductor materials systemwith the highest quantum efficiencies demonstrated to date at peak wavelengths greater than λ ≈ 1000nm. The porphyrin tapes consist of two porphyrin units triply linked to form a rigid tape with variousfunctional groups at the terminus of the tape, notably a pyrene group bonded in either one or twolocations. We have demonstrated quantum efficiencies of up to EQE=4% (D*=9×1011 cm-Hz½/W) at λ ≈1080 nm for a singlybonded pyrene end group and EQE=13% (D*=8×1010 cm-Hz½/W) at λ ≈ 1400 nm fora doubly-bonded pyrene end group.
The presentation will discuss fabrication and analysis of devices and materials and conclude with afuture outlook and other applications for these materials.
- M. S. Arnold, J. D. Zimmerman, C. K. Renshaw, X. Xu, R. R. Lunt, C. M. Austin and S. R. Forrest, Nano Lett.9 (9), 3354-3358 (2009).
- J. D. Zimmerman, V. V. Diev, K. Hanson, R. R. Lunt, E. K. Yu, M. E. Thompson and S. R. Forrest, Adv. Mater.22 (25), 2780-2783 (2010).