Studying Photocurrents in α-Sn/Ge QW By Terahertz Time-Resolved Spectroscopy

Generation of a terahertz radiation in $\alpha$-Sn / Ge quantum wells by ultrashort laser pulses is studied. Existence of the $\alpha$-Sn at room temperature is shown by Raman spectroscopy. Cardinal differences were found in the parameters of THz pulses generated in samples with quantum wells widths of 4 nm, 6 nm sign and in nanostructures with quantum wells widths of 8.5 nm, 10 nm. The observed changes in the polarization dependences of the electric field of the THz radiation generated in $\alpha$-Sn/Ge nanostructures with changes in the width of quantum well going from 6 nm to 8.5 nm are associated with the transition from a normal band structure to an inverted one in these nanostructures.