Photoinduced mid-infrared intraband light absorption and photoconductivity in Ge/Si quantum dots

Photoinduced absorption and photoconductivity are studied in undoped and low-doped Ge/Si quantum dot structures in mid-infrared spectral range under interband optical excitation. Steady-state absorption and photoconductivity spectra demonstrate distinctive features at photon energy of approximately 300 meV related to hole escape from the bound state of the dot to continuum in Si matrix. Dynamics of photoinduced absorption relaxation is studied under conditions of pulsed laser excitation of nonequilibrium electron-hole pairs. The relaxation of the hole concentration inside the quantum dot is found to be a two-stage process related to spatially direct and indirect recombination. Redistribution of the intensities of these two processes with temperature change from 77 K to 300 K is observed. (C) 2015 Elsevier Ltd. All rights reserved.