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

TL;DR

This paper demonstrates electrical control over exciton trapping and release in GaN/(Al,Ga)N quantum wells, showing how external biases can modulate exciton density and trap depth, with implications for optoelectronic device tuning.

Contribution

It introduces a method to electrically manipulate exciton trapping in wide GaN/(Al,Ga)N quantum wells using electrostatic traps and external biases, revealing new control mechanisms.

Findings

Negative bias deepens the trap but causes exciton dissociation.

Positive bias releases excitons, restoring free propagation.

Carrier losses increase with negative bias, reducing photoluminescence.

Abstract

A giant built-in electric field in the growth direction makes excitons in wide GaN/(Al, Ga)N quantum wells spatially indirect even in the absence of any external bias. Significant densities of indirect excitons can accumulate in electrostatic traps imprinted in the quantum well plane by a thin metal layer deposited on top of the heterostructure. By jointly measuring spatially-resolved photoluminescence and photo-induced current, we demonstrate that exciton density in the trap can be controlled via an external electric bias, which is capable of altering the trap depth. Application of a negative bias deepens the trapping potential, but does not lead to any additional accumulation of excitons in the trap. This is due to exciton dissociation instigated by the lateral electric field at the electrode edges. The resulting carrier losses are detected as an increased photo-current and reduced photoluminescence intensity. By contrast, application of a positive bias washes out the electrode-induced trapping potential. Thus, excitons get released from the trap and recover free propagation in the plane that we reveal by spatially-resolved photoluminescence.