Speaker
Description
The results of pump-probe experiments devoted to investigation of relaxation of bound electrons in elemental semiconductors will be presented. The radiation of free electron lasers was used to excite the donor and measure the relaxation times. Several donors were investigated to uunderstand the common features as well as difference originated from different chemical nature of particular donor. The uniaxial stress was used to modify the multivalley donor states. The typical relaxation times of bound electrons while emitting acoustical phonons in silicon were measured to be in the range of hundreds or tens of picoseconds. The optical phonon assisted relaxation yields picosecond times. The applied stress allowed to suppess the relaxation rates in the case of the resonances with intervalley phonons. In the case of donors in germanium the typical relaxation times are in the subnanosecond or nanosecond range. The binding energy of group-V donors in germanium is less than optical phonons (10-14 meV) thus the intervalley phonons which could influence the relaxation are of TA type. The stress application to germanium crystal results in increase of lifetimes for some donor states. For the case of Ge:As the pump-probe experiments allow to determine lifetime for 1s split off state. The latter result helps to suppose the possible inversion in the system under optical pumping.
Summary
The results of pump-probe experiments devoted to investigation of relaxation of bound electrons in elemental semiconductors will be presented. The radiation of free electron lasers was used to excite the donor and measure the relaxation times. Several donors were investigated to uunderstand the common features as well as difference originated from different chemical nature of particular donor. The uniaxial stress was used to modify the multivalley donor states.
