InGaN/GaN quantum dots as optical probes for the electric field at the GaN/electrolyte interface

Abstract

We investigated the electric-field dependence of the photoluminescence-emission properties of InGaN/GaN quantum dot multilayers in contact with an electrolyte. Controlled variations of the surface potential were achieved by the application of external electric fields using the electrolytic Schottky contact and by variation of the solution's pH value. Prior to characterization, a selective electrochemical passivation process was required to suppress leakage currents. The quantum dot luminescence is strongly affected by surface potential variations, i.e., it increases exponentially with cathodic bias and acidic pH values. The results cannot be explained by a modification of intra-dot polarization induced electric fields via the quantum confined Stark effect but are attributed to the suppression/enhancement of non-radiative recombination processes, i.e., mainly hole transfer into the electrolyte. The results establish a link between the photoluminescence intensity and the magnitude of electric fields at the semiconductor/electrolyte interface.

External Control of GaN Band Bending Using Phosphonate Self-Assembled Monolayers

“…Such a perturbation modifies the electrostatic potential landscape within the semiconductor, likely with sizable consequences on carrier transport and recombination. In the case of GaN, the surface band bending has been reported to strongly depend on the adsorption of H + and OH – radicals, a phenomenon used to develop highly sensitive nitride-based pH sensors. , Interestingly, even the sole physisorption of molecular acceptors or a direct contact with electrolytes of different ionic strengths is sufficient to alter the internal GaN electrostatic potential. This long-range electrochemical perturbation, propagating well below the GaN surface, is exploited in nitride-based bio and chemosensors.…”

External control of GaN band bending using phosphonate self-assembled monolayers

“…Such a perturbation modifies the electrostatic potential landscape within the semiconductor, likely with sizeable consequences on carrier transport and recombination. In the case of GaN, the surface band bending has been reported to strongly depend on the adsorption of H + and OH − radicals [2], a phenomenom used to develop highly sensitive nitride-based pH sensors [3,4]. Interestingly, even the sole physisorption of molecular acceptors [5] or a direct contact with electrolytes of different ionic strength [6] is sufficient to alter the internal GaN electrostatic potential.…”