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- ItemSurface acoustic wave modulation of single photon emission from GaN/InGaN nanowire quantum dots(Bristol : IOP Publ., 2018) Lazić, S.; Chernysheva, E.; Hernández-Mínguez, A.; Santos, P.V.; van der Meulen, H.P.On-chip quantum information processing requires controllable quantum light sources that can be operated on-demand at high-speeds and with the possibility of in-situ control of the photon emission wavelength and its optical polarization properties. Here, we report on the dynamic control of the optical emission from core-shell GaN/InGaN nanowire (NW) heterostructures using radio frequency surface acoustic waves (SAWs). The SAWs are excited on the surface of a piezoelectric lithium niobate crystal equipped with a SAW delay line onto which the NWs were mechanically transferred. Luminescent quantum dot (QD)-like exciton localization centers induced by compositional fluctuations within the InGaN nanoshell were identified using stroboscopic micro-photoluminescence (micro-PL) spectroscopy. They exhibit narrow and almost fully linearly polarized emission lines in the micro-PL spectra and a pronounced anti-bunching signature of single photon emission in the photon correlation experiments. When the nanowire is perturbed by the propagating SAW, the embedded QD is periodically strained and its excitonic transitions are modulated by the acousto-mechanical coupling, giving rise to a spectral fine-tuning within a ~1.5 meV bandwidth at the acoustic frequency of ~330 MHz. This outcome can be further combined with spectral detection filtering for temporal control of the emitted photons. The effect of the SAW piezoelectric field on the QD charge population and on the optical polarization degree is also observed. The advantage of the acousto-optoelectric over other control schemes is that it allows in-situ manipulation of the optical emission properties over a wide frequency range (up to GHz frequencies).
- ItemWavefunction of polariton condensates in a tunable acoustic lattice(Bristol : IOP, 2012) Cerda-Méndez, E.A.; Krizhanovskii, D.N.; Biermann, K.; Hey, R.; Skolnick, M.S.; Santos, P.V.We study the spatial coherence of polariton condensates subjected to coherent modulation by a one-dimensional tunable acoustic potential.We use an interferometric technique to measure the amplitude and phase of the macroscopic condensate wavefunction. By increasing the acoustic modulation amplitude, we track the transition from the extended wavefunction of the unperturbed condensate to a regime where the wavefunction is spatially modulated and then to a fully confined regime, where independent condensates form at the minima of the potential with negligible particle tunneling between adjacent sites.
- ItemAdvances in group-III-nitride photodetectors(Sharjah [u.a.] : Bentham Open, 2010) Rivera, C.; Pereiro, J.; Navarro, A.; Muñoz, E.; Brandt, O.; Grahn, H.T.Group-III nitrides are considered to be a strategic technology for the development of ultraviolet photodetectors due to their remarkable properties in terms of spectral selectivity, radiation hardness, and noise. The potential advantages of these materials were initially obscured by their large density of intrinsic defects. The advances were thus associated in general with improvements in material quality. Although technology still also needs improvement, efforts are being intensified in the fabrication of advanced structures for photodetector applications. In particular, this review discusses the recent progress in group-III-nitride photodetectors, emphasizing the work reported on quantum-well-based photodetectors, the use of novel structures exploiting the effect of piezoelectric polarization-induced fields, and polarization-sensitive photodetectors. Furthermore, some ideas can be generalized to other material systems such as ZnO and their related compounds, which exhibit the same crystal structure as group-III nitrides. © Rivera et al.; Licensee Bentham Open.