The effect of second subband occupation on the thermopower of a high mobility GaAs-Al0.33Ga0.67As heterojunction

Abstract
By the use of persistent photoconductivity and magnetic depopulation the authors have investigated the effect on the thermopower S of sweeping the Fermi energy EF through the bottom of the second electric subband in a 2D electron gas. The data were taken in the 4He temperature range where phonon drag is expected to dominate. For a given electron density, the absolute magnitude of S increases when EF moves into the second subband. At high magnetic fields and low temperatures a strong negative peak appears in S when EF coincides with the bottom of the second subband; this peak is of opposite sign to that which has been predicted to occur in the diffusion thermopower.