Anisotropy of the cyclotron mass in superlattices containing two populated minibands

The cyclotron mass in periodically delta-doped InP was studied, using the temperature dependence of the Shubnikov-de Haas (SdH) effect in tilted magnetic fields. The samples had two populated minibands, E-1 and E-2, both of which contributed with oscillatory components to the SdH spectrum. When the magnetic field is tilted from the direction parallel to the axis of the superlattice, the cyclotron mass associated with E-1 electrons increases, as expected for a quasi-two-dimensional system. In contrast, the cyclotron mass of E-2 electrons decreases. This decrease is due to Bragg reflections of electrons by the superlattice, which lead to shorter orbits when the magnetic field is tilted. It is estimated that in periodically delta-doped semiconductors the cyclotron mass can decrease at most by a factor of three when the magnetic field is rotated by pi /2.