Optical spin injection and detection in submonolayer InAs/GaAs nanostructures

Recently, InAs/GaAs nanostructures assembled by cyclic, alternating deposition of submonolayer (SML) InAs and monolayer GaAs using Molecular Beam Epitaxy (MBE) has been gaining interest for their novel and highly tunable optoelectronic properties. Furthermore, it has recently been revealed that a growth transition during SML growth leads to two types of nanostructures: 2D islands and 3D structures. Although the highly tunable properties of SML nanostructures make them strong candidates for spintronics applications, investigations on the spin properties of SML nanostructures are lacking. In this study, the spin properties of SML nanostructures are investigated using optical spin injection and detection measurements. Spins are injected into the SML nanostructures using the optical selection rules in GaAs for Circularly Polarized Light (CPL) excitation, whereas spin state in the SML is detected by measuring the right (σ+) and left (σ- ) CPL intensity components of the luminescence. The degree of CPL is estimated by quantity P = I(σ+ ) - I(σ- )/I(σ+ ) + I(σ- ), where I(σ± ) is the luminescence intensity for the σ± component. The quantity P is directly related to the spin state in the SML. Our experiments have yielded a relatively high P = 6% for the 3D SML nanostructures, whereas a relatively low P = 1% for the 2D SML nanostructures. The difference may be attributed to the higher carrier confinement for 3D SML resulting in preservation of spin state and thus resulting to a higher P. These results reveal fundamental differences in the spin dynamics of 2D and 3D SML nanostructures.