Fermi level position in GaMnAs - a thermoelectric study

Thermoelectric power was studied in the temperature range 100 less than or equal to T less than or equal to 300 K in 0.3-1 mum thick ferromagnetic Ga1 -xMnxAs epitaxial layers (0.015 less than or equal to x less than or equal to 0.06) in order to determine Fermi energy E-F, and carrier concentration p. For 0.015 less than or equal to x less than or equal to 0.05, at T = 273 K we find E-F = 275 +/- 50 meV and p = (2.5 +/- 0.5) x 10(20) cm(-3) (appr oximately Mn content independent). For x = 0.06, the Fermi energy decreases by about 100 meV with the corresponding reduction of hole concentration to p = 1.2 x 10(20) cm(-3). At T = 120 K, these parameters vary between E-F = 380 meV and p = 3.5 x 10(20) cm(-3) for x = 0.015 to E-F = 110 meV and p = 5 x 10(19) cm(-3) for x = 0.06.