We demonstrate highly directional etching in silicon 100 nm in diameter with an aspect ratio of 160 with no spiking on the pore walls using magnetic-field-assisted anodization. The relationship between the surface geometry of a silicon electrode and its highly directional etching properties have been investigated. Specifically, we show that the pore shape and pore wall orientation are not determined by the surface pattern but by the etching mechanisms specific to the magnetic-field-assisted anodization. These etching mechanisms enable highly directional and high aspect ratio etching at diameters below 100 nm in scale.

We propose a new design concept and a fabrication process for three-dimensional (3D) silicon photonic crystals on a 100 nm scale that does not require any alignment processes. The elemental technique used in this process is two directional electrochemical etching processes at a particular magnetic field. First, we have performed photonic band calculation and estimated device parameters to obtain the maximum photonic band gap in the visible range centered at around 800 nm. Next, we have experimentally observed the formation of a two-dimensional periodic pore with a diameter of 80 nm and an aspect ratio above 80 on an n þ (100) silicon substrate. Finally, we have fabricated 3D microstructures by two directional etching processes. A clear directionality for the pore formation was observed in two directions, showing the possibility of projecting the patterns formed on the slope to the side of the wafer. These fundamental etching processes can be applied to the fabrication of 3D photonic crystals in the visible range without any alignment processes.

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a b s t r a c tA silicon three-dimensional photonic crystal (3DPC) structure has been fabricated using a self-aligned, two-directional electrochemical etching method. The spectral component of the photoluminescence (PL) for silicon nanocrystals deposited on the 3DPC structures increase at 750 nm and slightly decrease at 800 nm. Time-resolved PL measurements reveal that the radiative recombination lifetime of the silicon nanocrystals on 3DPC structures decreases at 750 nm and increases at 800 nm compared to those on a silicon substrate without 3DPC structures. We conclude that the spontaneous emission control of silicon nanocrystals has been observed using the 3DPC structures.

Abstract:We propose a new design of nanocrystalline silicon optical devices which are based on control of electromagnetic fields, electronic states, as well as the phonon dispersion of size-controlled silicon quantum dots. IntroductionSince optical gain was first reported for nanocrystalline silicon in 2000 by Pavesi et al [1], operation of silicon-based lasers have continuously been studied. Stimulated emission was reported in 2004 for a nanostructured silicon pn junction diode using current injection [2], and a silicon Raman laser has been demonstrated with pulsed optical pumping [3]. A continuous wave silicon Raman laser have also been reported recently [4].Silicon based laser operation is expected as a key technology in realizing opto-electronic integrated circuits which circumvent the problem of interconnect bottleneck in the state-of-the-art ULSI technology. However, in the present state, silicon based lasers operate only under very high excitation conditions [2-4], making it difficult to incorporate them into the CMOS circuits in which ultra low power consumptions are required.In this paper, we propose a completely different approach to realize silicon based laser operation at submicron scale using 3-dimensional photonic crystal structures combined with nanocrystalline silicon quantum dots. First, the 3-dimensional photonic crystal structures are introduced to increase the stimulated emission probability caused by the standing wave at the photonic band edge, thereby resulting in a significant increase in the external quantum efficiency. Second, nanocrystalline silicon quantum dots are used for constructing an active layer which emits light in the visible band due to the quantum confinement effect. As for the excitation mechanism, current injection is absolutely required for any practical applications. However, there has so far been no report on optical gain from nanocrystalline silicon under current injection although high efficiency band-edge electrolumminescence has already been reported for silicon light emitting diodes. One of the reasons is that current injection into nanocrystalline silicon causes a significant decrease in the internal quantum efficiency due to the interfacial oxide layer. To circumvent this problem we propose a new high energy electron emission approach which is unique to a nanocrystalline silicon dot array structure [5].