Photocurrent transients in presence of a double impurity in semi-insulating semiconductors

A phenomenological model is developed to study the transient behaviour of the photocurrent due to detrapping of carriers from a double impurity in semi-insulating semiconductors. The model predicts a peak in the transient curve at constant temperature. An Arrhenius plot of t(p) (the time at the peak) yields the second ionization energy of the double impurity The activation energy determined from the photoinduced current transient spectroscopy (PICTS) analysis corresponds to the first ionization energy of the impurity. The model explains the appearance of a negative peak in the PICTS spectrum which was reported by previous authors on a number of semiconductors. Experimental investigation of the current decay curves an MgxZn1-xTe (x = 0.10, 0.14, 0.30) showed that for x = 0.10 the behaviour of the photocurrent decay at different temperatures and the PICTS spectrum can be interpreted in terms of the double impurity model. The ionization energies of the impurity were determined to be 0.082 +/- 0.007 eV and 0.12 to 0.13 eV.