Topics ACOPhys “Opening Week”

Get-together by examples

1.) Organic Optoelectronics2.) Electronic Structure of Organic Materials3.) Plastic Solar Cell4.) 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 ?

Ene

rgy

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...

Ene

rgy

Position

Nobel prize 2000: Kroemer und Alferov

http://britneyspears.ac/physics/fplasers/images/dhlaser.jpg

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’’

1.0

00

2.0

3.0

4.0

5.0

6.0

7.0

350300

400500600800

AlN

GaN

InN

InGaN

infra-red

visible

ultra-violet

0.2 0.4 0.6 0.8 1.0x

AlGaN 250

200

band

gap

(eV

)

wav

elen

gth

(nm

)

Band gaps of hexagonal nitride compounds

What about Quantum Mechanics ?

http://www.almaden.ibm.com/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 ...

Ener

gyPosition

What about Quantum Mechanics ?

0 1 eV 2 eV 3 eV 4 eV

Infra red Ultraviolet

CdSe nano spheres covered with ZnSe act as quantum dots

http://www.evidenttech.com/products/core_shell_evidots/overview.php

2 nm

: Lak

e Pl

acid

Blu

e

5 nm

: Map

le-R

ed O

rang

e

confh

2m LE

2~~

2

2

Confinement energy ... some of them are easily explained ...

ExcitonsEnhanced particle-particle interaction: e-h bound state

... some of them are easily explained ...

100 meV

2-20 nm

1.5 eV

EB =5 meV

Computation of quantum wire excitons

Disorder-free structures,exciton parameters Dispersion of multi-subband QWR excitons low-energy states of 107 X 107 matrix electron-hole correlation decomposition into valence-band orbitals dispersion relation and exciton mass MX

spin-splitting, polarization anisotropy

A. Siarkos, E. Runge, PRB 61, 16854 (2000)

Spatially resolved spectroscopyK. Matsuda et al., PRL 91, 177401 (2003): 30 nm resolution, wavefunction mapping

but: Ch. Lienau, E. Runge, Physik Journal, Jan. 2004 and to be published