Photo-induced transient thermoelectric effect in MnTe

Resistivity, Hall effect, and pulsed laser-induced 'transient thermoelectri c effect (TTE)' measurements have been carried out for semiconductor MnTe p olycrystals in the temperature range of 4.5-350 K. The resistivity is reduc ed appreciably in the antiferromagnetic (AF) phase that is due to a suppres sion of the magnetic scattering. The conduction carriers are electrons in t he AF phase but holes in the paramagnetic phase. We have observed TTE decay processes with characteristic relaxation times tau (1) and tau (2) that ha ve been attributed to electron-hole pair recombination via ionized donors a s capture centers. Both relaxation times decrease abruptly near the Neel te mperature, reflecting the magnetic ordering of the system. From the fast re laxation time tau (1), the capture cross sectional area sigma (1) is evalua ted in the AF phase. This behavior is interpreted based on an extended casc ade model. (C) 2001 Published by Elsevier Science Ltd.