= 아 래 =
1. 일 시 : 2012. 5. 15 (화), 16:00 ~
2. 장 소 : 응용공학동 1층 영상강의실
3. 연 사 : 조문호 교수 (연세대학교 신소재공학과)
4. 제 목 : Giant Electro-Optical Susceptibility Mediated by Strong Photoconductive Gain in Ge Nanocrystals
Large spectral modulation in the photon-to-electron conversion near the absorption band-edge of a semiconductor by an applied electrical field is prerequisite for the development of electro-optical modulators in the photonic circuitry. This electro-absorption effect in Group IV semiconductors is, however, inherently weak and this poses the technological challenges to their electro-photonic integration into the Si photonic circuitry. Here we report unprecedentedly large electro-absorption susceptibility at the direct band-edge of intrinsic Ge nanowire (NW) photodetectors, which is strongly diameter-dependent. We provide evidence that the large spectral shift at the 1.55 μm wavelength, enhanced up to 20 times larger than Ge bulk crystals, is attributed to the internal Franz-Keldysh (F-K) effect across the NW surface field of ~105 V/cm, mediated by the strong photoconductive gain. This classical size-effect operating at the nanometer scale in one-dimensional semiconductors, which has not been explored earlier, is universal, regardless of the choice of materials, and thus suggests general implications for their electro-photonic integration.