Berlin researchers have demonstrated a novel spectroscopic technique in which electrons in semiconductors can be described best as a cloud with a size of few nanometers (a nanometer is one billionth of a meter). This size is determined by the interaction of the electron with the vibrations of the crystal lattice.
The semiconductor electronics is based on the generation, control and amplification of electrical currents in devices like the transistor. Carrying the electrical current are freely moving electrons, which move at high speed through the crystal lattice of the semiconductor. They lose some of their kinetic energy by displacing the atoms in the crystal lattice vibrations.
Contacts and sources:
The semiconductor electronics is based on the generation, control and amplification of electrical currents in devices like the transistor. Carrying the electrical current are freely moving electrons, which move at high speed through the crystal lattice of the semiconductor. They lose some of their kinetic energy by displacing the atoms in the crystal lattice vibrations.
In semiconductors such as gallium arsenide, the positively and negatively charged ions are deflected and the crystal lattice oscillate with an extremely short period of 100 fs (1 fs = 10 -15 against each s = 1 billionth of a millionth of a second). In the microcosm of the electrons and ions, the vibrational motion is quantized. This may mean that the energy of this vibration only an integer multiple of a vibrational quantum, a so-called phonon be. In the interaction of an electron with the crystal lattice, the so-called electron-phonon interaction, in the form of individual packets of energy quanta are transferred.
As Berlin researchers report in the latest edition of the journal Physical Review Letters, the current depends on the strength of the electron-phonon interaction that is sensitive to the size of the electron, on the spatial extent of its charge cloud.
As Berlin researchers report in the latest edition of the journal Physical Review Letters, the current depends on the strength of the electron-phonon interaction that is sensitive to the size of the electron, on the spatial extent of its charge cloud.
Experiments in the time range of the phonon oscillation period show that for a reduced expansion of the electron cloud occurs up to a 50-fold enhanced interaction. This allows the movement of electrons and ions are coupled to each other so much that the individual movements no longer recognizable. Electron and phonon form a new quasiparticle, a polaron.
To make this phenomenon visible, the researchers used gallium arsenide and gallium aluminum arsenide nanostructures, in which the energies of the electron and ion movement were adapted to each other.The coupling of the movement was made visible with a new optical method. The system is supported by several ultra-short light pulses excited in the infrared and the light emitted by the moving charges field is measured in real time.
To make this phenomenon visible, the researchers used gallium arsenide and gallium aluminum arsenide nanostructures, in which the energies of the electron and ion movement were adapted to each other.The coupling of the movement was made visible with a new optical method. The system is supported by several ultra-short light pulses excited in the infrared and the light emitted by the moving charges field is measured in real time.
The measurements yield the so-called two-dimensional non-linear spectra (Fig.), which appear separately in coupled optical transitions, which can be derived from the coupling strength between electrons and phonons. From the analysis of data results in the expansion of the electron charge cloud, the only 3-4 nanometers (one nanometer = 10 -9 m = 1 billionth of a meter) is. In addition, the new method proves for the first time the strong influence of electron-phonon coupling on the optical spectra of the semiconductor. This offers interesting perspectives for the development of optoelectronic devices with tailored optical and electrical properties.
Measured two-dimensional spectrum. Without the interaction of the electron with the crystal vibrations in the range shown there is no signal.
Fig: MBI
Klaus Reimann,
Michael Woerner,
Thomas Elsaesser,
0 comments:
Post a Comment