Efficient room-temperature spin-amplified luminescence of an InAs quantum dot tunnel coupled with a thin GaNAs spin filter

Dilute nitride GaNAs has attracted much attention for spin generation owing to its defect-engineered spin filtering at room temperature. Strong, circularly polarized luminescence reflecting the spin-polarized electron states generated by a GaNAs spin filter is needed to realize practical opto-spintronics applications. This study examined the impacts of the GaNAs thickness on the room-temperature spin-polarized luminescence properties of tunnel-coupled InAs quantum dots (QDs) through polarization- and time-resolved photoluminescence in combination with a rate equation analysis. Reducing the GaNAs thickness from 20 to 5 nm increased the QD luminescence intensity by over an order of magnitude at low excitation powers. This increased luminescence was attributed to decreased electron capture in the deep-level defect states of GaNAs, which resulted from fewer defects in thinner GaNAs layers. Furthermore, the reduction in GaNAs thickness decreased the excitation power needed to maximize electron spin polarization of QDs while maintaining a near-maximum value. This efficient spin-amplified luminescence of QDs was achieved through spin-selective capture of QD electrons by defect states under low excitation spin densities. These results demonstrate that using a thin GaNAs spin filter can result in strong QD luminescence and high circular polarization at room temperature and low excitation spin densities. The findings give valuable implications for the development of spin-functional optical devices utilizing a GaNAs spin filter.