Long-living shallow donor excited states of GaP:Te

Abstract

Long-living shallow donor excited states in semiconductors existing forseveral miliseconds have been observed. Te-donors in GaP have been ionized by means of phonon assisted tunneling in the electric field of pulsed far-infrared laser radiation. The measurements have been carried out in the temperature range of 20-90 K using radiation of wavelength between 35 and 280 mm and intensities up to 1 MW/cm2. The photocunductive signal caused by ionization in response to the laser pulse shows in addition to a fast component (of the order 100 ns) a second component rising after the exciting pulse has ceased and afterwards decaying exponentially. This decay has a strongly temperature dependent time constant varying from microseconds to several miliseconds. It is shown that this complex temporal structure of the signal is caused by a storage of carriers in the valley-orbit split 1s(E) Te shallow donor state. Furthermore it has been proved by the observation of far-infrared to mid-infrared up-conversion that the final step of recombination is achieved by radiative transitions.