Dynamics and electronic transitions at impurity complexes in semiconductors

Local structure, stability and electronic properties of impurity complexes in semiconductors can be studied on an atomic scale by perturbed angular correlation spectroscopy (PAC). Here the complexes are identified by their characteristic electric field gradients. In this contribution the main emphasis is given to dynamical behaviour caused by electronic transitions or locally restricted kinetics. Details of the electronic transitions will be demonstrated on close acceptor-donor pairs in silicon formed by In/Cd acceptors and P, As or Sb donors, respectively. Based on a general PAC theory for fluctuating hyperfine interactions between Cd probe atoms and their surrounding charge distributions transition rates in the range between 106 and 1010 s-1 are derived. Besides the energy level of the complex capture and/or emission cross sections in the framework of Shockley-Hall-Read statistics are also deduced. The locally restricted kinetics of hydrogen and deuterium atoms trapped at an acceptor will be demonstrated on close Cd-H and Cd-D pairs in silicon. Here the PAC time spectra reveal clear evidence of a thermally activated motion of hydrogen or deuterium about the cadmium. The present results favour an interpretation in terms of a thermally activated tunneling process. (orig.)