Magnetooscillations of the EHD TA‐Line in Pure Germanium

According to Keldysh and Silin ( l ) , electron-hole droplets (2, 3) (EHD) in a magnetic field have a field dependent oscillating equilibrium density, due to OScillating contributions to the free energy (4). This oscillating density causes intensity oscillations of the EHD luminescence in Ge (5 , 6). In this paper, we for the first time present time dependent measurements of the intensity oscillations of the TA-phonon assisted line at 729 meV . They show characteristic differences compared to the LA-assisted line (709 meV) which was investigated in a previous paper (7). As we can show, these differences are due to the fact that the TA-assisted radiative transition is a forbidden one at the band extrema (8). The experiments were carried out on Ge samples with an impurity concentration of about 1 0 l 2 ~ m ~ . The samples were immersed in liquid helium which was pumped to about 1 .5 K. For ca r r i e r excitation a pulsed GaAs laser was used with a peak power of about 5 W , pulse length of 2 ps, and duty factor of 0.2%. The power density on the sample was about 5 W c m during the pulse. A magnetic field in Faraday configuration could be applied in (100) direction to the samples by means of a superconducting coil (H 6 35 kOe). The detection system consisted of an MDR-2 grating monochromator used here as a narrow band filter for the different EHD lines, and a Ge photodiode (rise time < 1 ps). The signal-to-noise ratio was improved by conventional boxcar technique. The intensity of the LAand TA-line, respectively, may be written in the following way: -2