In the study, the scientists observed the extreme rapid motion of electrons in a crystal of gallium arsenide, which was placed in a high electrical field for a short duration of time. For the first time ever, this experiment resulted in a combined, oscillatory movement of the electrons with tremendously high frequency level in addition to their usual drift motion. Gallium arsenide (GaAs) is one of the primary components required in the field of semiconductor optoelectronics. In a normal GaAS crystal, there exist a typical pattern of gallium and arsenic atoms. The gallium atoms electrically positively charged and the arsenic atoms are electrically negatively charged. An electron, when it drifts slowly through the crystal leads to some kind of disorder in the crystal lattice in its vicinity. As electrons carry negative electric charge, they repel similar negatively charged arsenic atoms and attract positively charged gallium atoms. This phenomenon results in certain oscillations of the atoms in the crystal surrounding their position of rest and consequently, phonons, or lattice vibrations are generated. Michael Wörner says,
That is similar to a heavy ball rolling over a mattress...The metal springs of the mattress are squeezed together and relax again.
Through the development of these vibrations, movement of electrons becomes sluggish owing to loss of energy. This decelerating effect is due to the phenomenon of electrical resistance. The physical motion of the electrons through the lattice with a steady velocity forms the starting point of the famous Ohm’s law that deals with electrical resistance. However, the scientists found that if the electrons witness faster acceleration by an exceedingly high electric field that it even surpasses the response time taken by the neighbouring atoms, the outcome is completely different. For this, the researchers used an electrical field of 2 million Volts per meter which was exposed to the crystal for a minute time period of only 0.3 picoseconds (where, 1 picosecond = millionth of a millionth of a second). The movements of the electrons resulting from the high electric field were examined with extremely short light pulses falling in the spectral region of infrared rays. It was noticed that the velocity of the electrons then occasionally changed from high values to low ones. This observation was in stark contrast to the previously observed constant velocity of motion of the electrons under a small electric field. The scientists deduced the fact that the frequency of these variations in velocity are exactly equivalent to the highest attainable frequency with which all atoms can pulsate, which can be termed as the frequency of the called longitudinal optical phonons. Following the experiment, there were mathematical analysis undertaken which supported the observed phenomenon. MBI director Professor Thomas Elsaesser was quoted saying,
The fact that strongly accelerated electrons can excite vibrations of the atoms and that in turn they are decelerated and accelerated by the vibrating atoms is of great importance for the charge transfer in nanostructures... Therefore our results are important for the optimization of transportation characteristics of semiconductor nanostructures.
How far this recent scientific breakthrough on crystal behaviour can indeed be practically applied for miniaturization of electrical products is something that can be experienced only in the years to come.
Source:sciencedaily
