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Ultrafast dynamics in semiconductors

Tailoring semiconducting materials' properties requires an understanding of their behaviour in equilibrium and after excitation. The key to studying electron and lattice dynamics on picosecond timescales proved to be ultrashort laser pulses.
Ultrafast dynamics in semiconductors
The timescales that govern the redistribution of electrons and the rearrangement of atoms in semiconductors after excitation lie in the range of a few femtoseconds up to several microseconds. Laser pulses can excite and probe electron and lattice dynamics with a time resolution up to 10 000 times shorter than other experimental techniques.

Where recent measurements were available, EU-funded scientists used a new method to investigate the features observed. The method to simulate electrons redistribution in bismuth prepared in extreme physical states by ultrashort, polarised laser pulses was developed within the project ULTRADEX (Ultrafast energy transfer and dissipation in electronically excited materials: calculations from first principles).

As electrons conduct through the semiconductor lattice, vibrations called phonons either help or hinder their motion. Based on first principles, the ULTRADEX method allowed the scientists to calculate how the rate of generation of phonons due to electron-phonon coupling varies with time.

In addition to better calculations of the coupling strength, the scientists followed how the generated phonons population evolved with time due to phonon-phonon interactions. The same method was also employed in the case of photo-excited germanium to explain the results of diffuse X-ray scattering experiments.

The interaction between electrons and phonons in semiconductors can reveal and control important properties, facilitating superconductivity or limiting electron mobility through scattering. ULTRADEX findings should promote further advances in the investigation of ultrafast processes in far greater detail than has been possible hitherto.

Related information


Semiconductor, ultrashort laser pulse, bismuth, electron-phonon coupling, superconductivity
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