No abstract

The possibility of tuning the resonance frequency and photon lifetime corresponding to Anderson localized resonant modes is investigated using the finite-difference time-domain technique. Experimentally obtained dimensions of molecular beam epitaxy grown self-organized nanowires on silicon have been employed to systematically generate disordered patterns, where multiple-scattering mediated light trapping has been analyzed. The results of our analysis indicate that in spite of the inherent randomness of the scattering medium, it is possible to control the wavelength and strength of the localized modes by varying dimensional features of the nanowires. The localization wavelength in the medium can be tuned toward a higher wavelength by increasing the average diameter of nanowires, whereas cavity quality factors in the order of 105 can be attained by increasing the fill factor of the array. The observed behavior is explained and empirically modeled, and the relation is found to be in good agreement with the predicted localization characteristics for experimentally grown self-assembled nanowires. The results of the analysis indicate that in spite of the absence of periodicity, localization in this medium is related to interference effects resulting from Bragg-like diffractions, which in effect results in the observed systematic variation of localization characteristics as nanowire dimensions are varied.

Light transmission characteristics in a strongly disordered medium of dielectric scatterers, having dimensionalities similar to those of self-organized GaN nanowires, is analyzed employing finite difference time domain analysis technique. While photonic bandgap like transmission gaps have already been reported for several quasi-crystalline and weakly disordered media, the results of this work show that in spite of the lack of any form of quasi-crystallinity, distinct transmission gaps can be attained in a strongly disordered medium of dielectric scatterers. In fact, similar to the case of a two-dimensional photonic crystal, transmission gap of a uniform random medium of GaN nanowires can be tuned from ultra-violet to visible regime of the spectrum by varying diameter and fill-factor of the nanowires. Comparison of transmission characteristics of periodic, weakly disordered, correlated strongly disordered and uniform strongly disordered arrays having nanowires of identical diameters and fill factors suggest that in spite of the dominance of multiple scattering process, the underlying Mie and Bragg processes contribute to the emergence and tunability of transmission gaps in a strongly disordered medium. Without any loss of generality, the findings of this work offer significant design latitude for controlling transmission properties in the strong disorder regime, thereby offering the prospect of designing disorder based novel photonic and optoelectronic devices and systems.

No abstract

No abstract