OPTICAL INVESTIGATION OF IMPURITY BANDS IN A DELTA-DOPED N-LAYER

The radiative recombination of donor-acceptor pairs in a weakly doped delta n-i-delta p-i semiconductor superlattice is detected in time res olved photoluminescence experiments. At short times t less than or equ al to 1 mu s, a narrow luminescence line of FWHM = 2.6 meV is measured , which can be related to the width of the filled donor impurity band, formed by mutual orbital overlap. For longer times, a Coulomb induced broadening of the spectra up to FWHM = 6.5 meV is observed, accompani ed by a strongly non-exponential decay of the integrated luminescence intensity. The time-dependence of both the spectral width and intensit y is in good agreement with a detailed Monte-Carlo simulation of the d ynamical processes.