Thermoelectric studies of electronic properties of ferromagnetic GaMnAs layers

Thermoelectric power, electrical conductivity, and high field Hall effect were studied over a broad temperature range in ferromagnetic Ga(1-x)Mn(x)As epitaxial layers (0.015 70 K) the thermoelectric power in GaMnAs linearly increases with increasing temperature. That indicates the presence of a degenerate hole gas with the Fermi energy EF=220+-25 meV, nearly independent of Mn content (for 0.02<x<0.05). At lower temperatures GaMnAs layers with metallic-type conductivity show an additional contribution to the thermoelectric power with the maximum close to the Curie temperature. The layers exhibiting insulating electrical properties show 1/T-type increase of thermoelectric power at low temperatures.