Identification of recombination centers in wide-band-gap crystals and related nanostructures from spin-dependent tunneling afterglow

The centers involved in the spin-dependent recombination in KCl: AgCl insulator-semiconductor wide-band-gap crystal structures, bulk ZnO crystals, and quantum dots based on ZnO nanocrystals have been identified by detecting electron paramagnetic resonance from tunneling afterglow. Long tunneling after-glow has been excited by short-term UV irradiation of the sample at liquid-helium temperatures. The observed magnetic quenching of the afterglow at low temperatures results from the Boltzmann polarization of spins of recombination centers. The revealed giant increase in the afterglow intensity is induced by the reorientation of spins of these centers at electron paramagnetic resonance. A new technique for recording the spectra at a high frequency of 94 GHz has been developed and used with the aim of increasing the sensitivity and spectral resolution. This technique has made it possible to separate electron and hole centers in the KCl: AgCl structures and to demonstrate that ZnO: Al quantum dots contain two types of deep acceptors.