Mathematical Challenges of Quantum Transport in Nano-Optoelectronic Systems - Abstract
Calarco, Raffaella
In recent years III-nitride based nanowires (NWs) have attracted a lot of interest because of their potential applications for nanoelectronic devices. The growth of Nitride nanowires by MBE occurs on various substrates under N-rich conditions without using a liquid-phase catalyst. We addressed the optimization [1, 2] of the crystalline and optical quality of GaN and InN. The growth of GaN NWs on bare Si(111) is characterized by a long nucleation period [3-5], which results in a broad distribution of the nanowire sizes. The investigation of the electrical properties of GaN NWs showed that the band-to-band photoelectric effect varies by orders of magnitude as a function of the nanowire diameter [6]. Photovoltage Spectroscopy and Spectral Photoconductivity (SPC) measurements have been carried out to analyze the near band-edge absorption in GaN nanowires [7]. A strong diameter dependence of the band absorption tail was found by SPC measurements. The band-edge tailoring and its wire-diameter dependence can be explained by the Franz-Keldysh effect induced by the electric field at the wire surface. In InN NWs a highly conductive surface accumulation was observed [8]. We performed also Raman characterization on nanowire ensemble in comparison with single nanowire measurements [9, 10]. The ensemble spectra of GaN NWs did not reveal a deviation from the selection rules for the wurtzite structure, in contrast in the single wire spectra, only A1(TO) was observed, which intensity is almost suppressed if the laser polarization was perpendicular to the nanowire axis. These results indicate that the penetration of the laser light and the Raman scattering in isolated GaN nanowires thinner than 100 nm is governed by size effects.
This is a joint work with T. Stoica, E. Sutter, P. Sutter, E.O. Schäfer-Nolte, T. Schäpers, Michel Marso, Hans L¨th, A. Cavallini, L. Polenta, T. Schumann, T. Gotschke, F. Limbach, D. Gr¨tzmacher.
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