Photo-induced transient thermoelectric effect in MnTe

Resistivity, Hall effect, and pulsed laser-induced ‘transient thermoelectric effect (TTE)’ measurements have been carried out for semiconductor MnTe polycrystals in the temperature range of 4.5–350 K. The resistivity is reduced appreciably in the antiferromagnetic (AF) phase that is due to a suppression of the magnetic scattering. The conduction carriers are electrons in the AF phase but holes in the paramagnetic phase. We have observed TTE decay processes with characteristic relaxation times τ1 and τ2 that have been attributed to electron–hole pair recombination via ionized donors as capture centers. Both relaxation times decrease abruptly near the Néel temperature, reflecting the magnetic ordering of the system. From the fast relaxation time τ1, the capture cross sectional area σ1 is evaluated in the AF phase. This behavior is interpreted based on an extended cascade model.