Topics ACOPhys “Opening Week” Get-together by examples 1.) Organic Optoelectronics 2.) Electronic Structure of Organic Materials 3.) Plastic Solar Cell 4.) Random Matrix Theory and Excitons in Disordered Quantum Wells Planning next steps

Get-together by means of examples: Discussing Quantum Wells and Wires Prof. Gerhard Gobsch, “Applied Physics” Prof. Erich Runge, “Computational Physics” Technical University of Ilmenau, Institute of Physics

Semiconductors : An energy gap separates states of mobile electrons from states of mobile holes in the so-called valence band, which is otherwise occupied by electrons. What happens if electrons and holes meet ? What happens at the interface of two semiconductors ? Energy Position

Light Emitting Diodes (LED) + Semiconductor quantum well lasers... and the hairy details as presented by the world‘s best-known expert The simple view of a theoretical physicist... Energy Position Nobel prize 2000: Kroemer und Alferov

Light Emitting Diodes (LED) + Semiconductor quantum well lasers... and the hairy details as presented by the world‘s best-known expert

The Gallium Nitride Revolution: LEDs and lasers based on InGaN / GaN quantum wells Does the revolution eat its children? ‘‘Long reign the OLED’’

Band gaps of hexagonal nitride compounds

What about Quantum Mechanics ?

almaden/media/image_mirage.html Electrons show wave-like properties, some of them are easily explained and some are a bit harder to get used to... Energy Position What about Quantum Mechanics ?

0 1 eV 2 eV 3 eV 4 eV Infra redUltraviolet CdSe nano spheres covered with ZnSe act as quantum dots 2 nm: Lake Placid Blue5 nm: Maple-Red Orange conf h  2m L E 2 ~ ~ 2 2 Confinement energy... some of them are easily explained...

Excitons Enhanced particle-particle interaction: e-h bound state... some of them are easily explained meV 2-20 nm 1.5 eV E B = 5 meV

Computation of quantum wire excitons

Disorder-free structures, exciton parameters Dispersion of multi-subband QWR excitons low-energy states of 10 7 X 10 7 matrix electron-hole correlation decomposition into valence-band orbitals dispersion relation and exciton mass M X spin-splitting, polarization anisotropy A. Siarkos, E. Runge, PRB 61, (2000)

Spatially resolved spectroscopy K. Matsuda et al., PRL 91, (2003): 30 nm resolution, wavefunction mapping but: Ch. Lienau, E. Runge, Physik Journal, Jan and to be published