Electrical control of excitons in GaN/(Al,Ga)N quantum wells

Due to giant built-in electric fields excitons in wide GaN/(Al,Ga)N quantum wells (QWs) are spatially indirect iven in the abscence of any external electric bias and posess microsecond lifetimes, large dipole moment in growth direction, and tens of microns diffusion lengths [Fedichkin2016]. This make them potentially interesting for excitonic devices, in particular ifthey can be manipulated electrically.We have shown previously that despite strong dipolar repulsion between such excitons significant densities can be achieved in electrostatic traps imprinted in the quantum well plane by a thin metal layer deposited on top of the heterostructure [1].In this work we go further. By jointly measuring spatially-resolved photoluminescence and photo-induced current, we demonstrate that indirect exciton (IX) density in the trap can be controlled electrically by applying a bias between the top metal layer and the n-type GaN substrate. This allows as to alter the trap depth [2]. Negative bias deepens the trapping potential experienced by excitons, but it is not associated with a relevant accumulation of excitons in the trap (5% more excitons compared to the zero-bias density). This effect is attributed to exciton dissociation in the spurious lateral electric field building up in the vicinity of the electrodes. The corresponding carrier losses are detected as a decrease of the photoluminescence intensity in favor of the increased photo-current. By contrast, application of positive bias washes out the electrode-induced in-plane potential. This results in efficient release of the excitons from the trap and the reduction of their density by approximately 40%.The ensemble of the experimental results is understood in terms of the exciton transport model, that accounts for exciton dissociation in the increasingly high in-plane electric field that builds up at the electrode edges. This demonstration of the electrically controlled trapping and release of GaN-hosted IX paves the way toward novel optoelectronic devices. More complex multi-electrode devices, inspired by GaAs-based technology [HighScience2008] but operating up to room temperature, may potentially be be developed, provided the non-radiative losses at the electrode edges can be reduced.