Manipulating the Band Bending of InGaN/GaN Quantum Dots in Nanowires by Surface Passivation

Abstract

InGaN/GaN quantum dots (QD) in nanowires exhibit excellent optical properties and are promising candidates for nanoscale optoelectronic devices. However, a large amount of surface states would cause low quantum efficiency more severely than bulk materials, through not only nonradiative recombination centers but also upward band bending. Therefore, it is necessary to control the band bending effect in order to improve the quantum efficiency of QDs. In this work, quantitative measurements are carried out by ultraviolet photoelectron spectroscopy (UPS) to describe the band bending effect in InGaN/GaN QD in nanowires coated with three different dielectric layers including SiN x , Al2O3, and SiO2. Furthermore, their passivation mechanisms are investigated by photoluminescence (PL), time-resolved PL. Contrary to SiO2 passivation, the SiN x and Al2O3 passivation nanowires demonstrate notable improvements in emission intensity. Most essentially, all experimental findings are consilience with the physical model that the deposition of dielectric layers effectively alter the surface states of nanowires resulting a weakening or strengthen in band bending near the surface. Our systematic studies on passivation of nanowires can provide strategies for optimizing the performance of nanowire-based optoelectronic applications.

Enhanced Radiative Efficiency in GaN Nanowires Grown on Sputtered TiNx: Effects of Surface Electric Fields

“…Since the nonradiative decay is mediated by the field ionization of excitons, the radial electric fields should be eliminated or at least reduced. This task can be achieved by either reducing unintentional doping or, perhaps more practically, by a suitable surface passivation. − On the contrary, the growth of a thin shell with a larger band gap [e.g., made of (Al,Ga)­N] is generally inadequate to cancel the surface electric fields. We stress that the mechanism described in this work is not restricted to GaN NWs, but applies to nano- and microstructures in general.…”

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

“…The modification of the surface electronic properties caused by the grafting of phosphonic acids should also impact the EQE of GaN. In particular, the decrease of internal electric fields [56][57][58][59][60][61] and the passivation of surface states [14,[62][63][64][65][66][67] could both enhance the radiative recombination of excitons. This issue is further evaluated here by examining the PL intensity of the coated GaN samples.…”

Fast Response GaAs Photodetector Based on Constructing Electron Transmission Channel

“…For NW photodetectors, photo-generated electrons are usually trapped by the surface states, which leads to low responsivity. In order to improve the properties of photodetectors, many efforts have been carried out to eliminate the surface states [13][14][15][16]. These include applying sulfur passivation to remove surface states through saturating dangling bonds in GaAs NWs, which effectively reduces the dark current of the corresponding device.…”