Dresden 2017 – wissenschaftliches Programm
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DS: Fachverband Dünne Schichten
DS 48: Oxide Semiconductors (jointly with HL)
DS 48.5: Vortrag
Freitag, 24. März 2017, 10:45–11:00, POT 51
Excitons at SrTiO3 and ZnO interfaces in ellipsometry spectra — •Stefan Zollner1, C. Rodriguez1, N. Samarasingha1, J. Moya1, N. Fernando1, P. Ponath2, K. Kormondy2, A.A. Demkov2, and S. Chattopadhyay3 — 1New Mexico State University, Las Cruces, NM, USA — 2University of Texas, Austin, TX, USA — 3Indian Institute of Technology, Indore, India
Excitonic features in optical spectra of semiconductors and insulators have been studied for many years. In an epitaxial layer on a substrate with a different band gap, the wave functions of electron and hole are strongly modified. In a type-I quantum well, consisting of a narrow-gap semiconductor grown on a large-gap substrate, both electron and hole are confined, which leads to an increase in the dipole overlap matrix element. Therefore, the dominant absorption peak at 4.2 eV is larger in a 20 nm thick SrTiO3 layer on LaAlO3 than in bulk SrTiO3. (The band gap of LaAlO3 is larger than that of SrTiO3.) On the other hand, in a staggered type-II quantum well, either the electron is confined, or the hole, but not both. Therefore, the overlap dipole matrix element (and the excitonic absorption) is strongly reduced, because one quasiparticle resides in the quantum well and the other in the substrate. If a SrTiO3 layer is grown on Si or Ge, the valence band maximum occurs in the substrate, while the conduction band offset is very small. Therefore, the exciton wave function is delocalized, which reduces the dipole overlap matrix element. The real and imaginary part of thin SrTiO3 layers on Si or Ge are much smaller than in the bulk and decrease monotonically with decreasing thickness.