We report the design and fabrication of the complete visible range omnidirectional mirror, with a dielectric multilayered structure based on porous silicon (PS). The refractive index profile consisted of Bragg type chirped layers with an increasing thicknesses modulated by a potential envelop function f(x)=Cxk. The omnidirectional photonic band gap (OPBG) was measured from 396 to 805 nm, with more than 95% of the reflectivity, for 8° and 68°. The theoretical simulations based on the transfer matrix method along with a photographic sequence of the sample confirmed the OPBG for higher incident angles. It was enhanced by a factor of 19 as compared to the last reported visible region OPBG by PS dielectric multilayered structure.

The effect of gradually varying refractive index at each interface of a multilayered porous silicon photonic structure is studied experimentally and theoretically. The variation of refractive index at the interface, between any two consecutive layers, is done in small ladder-like steps (increasing/decreasing) and the resulting optical properties are compared with the standard structures with the flat interface and similar optical thickness. The proposed structures are proved to be useful in reducing the stress between the layers of high contrast, resulting in the mechanically more stable structures.

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Abstract-We present the electronic spectrum of a n-type deltadoped quantum well in Si coupled to a p-type delta-doped barrier within the envelope function effective mass approximation. We applied the Thomas-Fermi approximation to derive an analytical expression for the confining potential, and thus, we obtain the electronic structure in a simple manner. We analyzed the electron subband structure varying the distance between the doping planes (l) as well as the impurity density in them (n 2D , p 2D ). We also study the mobility trends through an empirical formula that is based on the electron levels, the electron wave functions and the Fermi level. We find a monotonic decrease in the mobility as the p-type barrier moves away from the n-type well, and optimum parameters, l = 70Å and n 2D = 5 × 10 12 cm −2 and p 2D = 5 × 10 13 cm −2 , for maximum mobility.

Tunability of the optical response of multilayered photonic structures has been compared with sequential (SQ) and superposition (SP) addition of refractive index profile functions. The optical response of the composite multilayered structure, formed after the SP addition of the two Bragg type refractive index profile functions has been studied as a function of percentage overlap and relative shift between the profiles. Apart from the substantial advantage in terms of the reduced physical thickness of the SP composite structures (over the SQ addition), at certain optimum values of relative shift, photonic structures with better quality factor resonant modes or a broader PBG could be designed. Similar analysis has been extended for rugate filters as well. The experimental verification of the optical response, was carried out through multilayered dielectric porous silicon structures fabricated by electrochemical anodization.