Scattering involving LO phonons in tunneling to the 2D electron system of a delta layer

Tunneling to both one and two or three subbands of the 2D electron system of a delta-doped layer is observed in Al/δ-GaAs structures. The energy positions of 2D subbands in one sample are varied due to the diamagnetic shift or persistent tunneling photoconductivity. The change of the sign of a step in tunneling conductivity is observed at the threshold of the emission of an LO phonon when a successive subband is involved in tunneling. An increase in conductivity (positive step) is observed for inelastic intrasubband electron-phonon scattering. A decrease in conductivity (negative step) is observed when the ordinary processes of inelastic tunneling are supplemented by intersubband transitions of electrons that have tunneled in 2D electron systems with the emission of an LO phonon.