The inherent ability of plasmonic bowtie nanoapertures (NAs) to localize the electromagnetic field at a subwavelength scale will be exploited to engineer the H removal process in dilute nitrides at the nanometer level. Dilute nitride semiconductor alloys (e.g. GaAsN with a small percentage of nitrogen) are characterized by peculiar optoelectronic properties and, most importantly, by an even more peculiar response to hydrogen incorporation. In this class of materials, it is indeed possible to tune post-growth the alloy bandgap energy by a controlled incorporation of hydrogen atoms. The formation of N-H complexes neutralizes all the effects N has on the host matrix, among which is the strong narrowing of bandgap energy. In this work, bowtie NAs resonant to the N-H complex dissociation energy have to be numerically modeled by finite element method simulations, realized by a lithographic approach, and characterized by scanning probe microscopy and resonant scattering spectroscopies. The conditions to get the maximum field enhancement at a specific position below the metal/semiconductor interface, namely at the dilute nitride quantum well position, were identified, demonstrating the ability to achieve a plasmon-assisted spatially selective hydrogen removal in a GaAsN/GaAs quantum well sample. Hydrogen removal through bowtie NAs turns out to be way more efficient (approximately two orders of magnitude) than through the plain surface, thus indicating that bandgap engineering through plasmonic nanostructures can be optimized for future efficient realization of site-controlled single-photon emitters and for their deterministic integration in plasmonic devices.
Bowtie-shaped plasmonic nanoapertures (NAs) could open a new pathway to the efficient in-plane bandgap engineering of hydrogenated dilute nitrides by spatially selective H removal. Bowtie NAs resonant to the N-H complex dissociation energy (wavelength ~ 700 nm) could help us avoid complicated optical setups for the fabrication of QDs, like avoiding the use of focused ion milling, and then characterization steps by scanning probe microscopy and resonant scattering spectroscopies. The conditions to get the maximum field enhancement at a specific position below the metal/semiconductor interface (namely, at the center of the dilute nitride quantum well, QW) have already been identified, and we will demonstrate the achievement of plasmon-assisted spatially selective hydrogen removal in a fully hydrogenated GaAsN/GaAs QW sample. Hydrogen removal through bowtie NAs turns will be few orders of magnitude more efficient than through the plain surface of the sample. Ordered arrays of identical Al bowtie NAs will be fabricated by e-beam lithography, followed by a single lift-off step. In spite of its simplicity, this method can be employed to shape a wide range of complex nanostructure designs with good resolution and reproducibility, without involving aggressive etching processes, or damaging focused ion milling steps. In addition, the roughness of the metal film, which has been shown to affect strongly the plasmon resonance condition, can be controlled by varying the process parameters and be kept at very low level.
This technique of bandgap engineering through plasmonic nanostructures represents a versatile and powerful tool to control the optoelectronic properties of dilute nitride in a spatially controlled way. In particular, this study will be the first, pivotal step towards the realization of deterministically coupled optically active semiconductor-plasmonic integrated components, which is of great interest for the practical implementation of quantum information and communication protocols [1]. Indeed, this ability to locally manipulate the bandgap energy of hydrogenated dilute nitrides via plasmonic NAs can lead to the realization of spatially controlled quantum dots (QDs), which can be directly coupled with the plasmonic nanostructures used to fabricate them. Ideally, it might even be possible to purposely design doubly resonant plasmonic structures [62], with one resonance centered at 700 nm ¿to have efficient H removal to create the QD¿ and another resonance peaked at ~900 nm ¿to boost and control the emission properties of the fabricated nanostructures.
References:
1. Lyamkina A., Schraml K., Regler A., et al. Monolithically integrated single quantum dots coupled to bowtie nanoantennas. Optics express 2016, 24, 28936¿28944.
2. Chou Chau Y.-F., Chou Chao C.-T., Rao J.-Y., et al. Tunable Optical Performances on a Periodic Array of Plasmonic Bow-tie Nanoantennas with Hollow Cavities. Nanoscale Research Letters 2016, 11, 411.