ABSTRACT
For addressing electron spin coherence, the quantum dot sample was studied
by Faraday rotation spectroscopy. The pump beam was circularly polar-
ized and directed along the heterostructure growth direction. Since it was
resonant with the ground state, it may inject an electron and a hole into
the conduction and valence band ground states of the quantum dots. These
carriers will have well defined spin orientations due to the optical selection
rules. For example, for σ+ (σ−)-excitation the electron have a spin projection, Sz = −1/2 (Sz = +1/2), along z, while the total angular momentum of the hole (being the sum of the orbital moment and the spin moment
coupled due to the spin-orbit interaction) are Jz = +3/2 (Jz = −3/2). Injection of such an electron-hole combination will of course only be possible
if it is allowed by the Pauli principle, since there is already an electron in
the quantum dot due to the doping: The spin orientation of this residual
electron has to be opposite to the one of the optically injected electron in
order to allow for optical excitation.
