Optical spin-filtering effect in charged InAs/GaAs quantum dots

Abstract

We present time resolved photoluminescence results using nonresonant polarized light which show that the electron spin-flip time is much longer than the recombination time for an ensemble of p-doped InAs/GaAs quantum dots. Under continuous wave excitation the degree of optical polarization of the ground state is found to be around 10%. However, the excited state polarization is twice this value. We attribute this effect to Pauli blocking of the injected spin population captured into the dots and show that the effect persists up to room temperature. For resonant excitation, values are nearly doubled in accordance with increased spin injection efficiency.

Power-dependent spin amplification in (In, Ga)As/GaAs quantum well via Pauli blocking by tunnel-coupled quantum dot ensembles

“…[11][12][13][14] Enhanced electron spin polarization was observed at excited states (ESs) of QDs by spin blocking from ground states (GSs). 11,[15][16][17] Although extensively studied, these previous works mainly focused on the localized spin states of the QDs. Wider application of this spin amplification effect can be found by tunnel-coupling QDs with quasi-two-dimensional (2D) mobile carriers/excitons in QWs.…”

“…This feature is characteristic of the spindependent intra-level carrier relaxation, i.e., the spin blockade effect. 11,[15][16][17] Since holes in QWs experience stronger spin-orbit interaction and mixing of heavy-light hole sub-valence bands, 10,21-23 their spins are easily randomized, which leaves electron spins better preserved to determine the PL helicity of the QW and QDs. By increasing P exc to 14.2 W/cm 2 -see Figure 1(b), the CPD of the QW and QD ES2 increased to $60%.…”

Resolving Zeeman splitting in quantum dot ensembles

“…A low excitation level was used throughout, sufficient to suppress emission from excited states, which can significantly alter the QD ensemble photoluminescence (PL) polarization spectrum. 6,7 QDs subjected to low power, unpolarized excitation, and a magnetic field in the growth direction will exhibit polarized exciton emission lines split by an energy D Z due to the Zeeman effect. These lines are distinguished by their opposing circular polarization (CP), resulting from their spin orientation.…”

“…The real QD ensemble deviates from true Gaussian form on the high energy side of the PL peak. This is attributed to the nonuniform distribution of QD sizes, 7,8 in particular, the presence of sub-populations of smaller dots. 7,9 Nevertheless, the low energy Gaussian-like region observed is typical of QD ensembles, allowing such a treatment to be applied to a wide range of samples.…”

“…This is attributed to the nonuniform distribution of QD sizes, 7,8 in particular, the presence of sub-populations of smaller dots. 7,9 Nevertheless, the low energy Gaussian-like region observed is typical of QD ensembles, allowing such a treatment to be applied to a wide range of samples. The QD excited states, which become apparent at higher laser power, 7 do not contribute significantly to this spectrum due to the low level excitation used.…”