In epitaxial lateral overgrowth (ELOG) of III-V semiconductor on nano-trench patterned Si substrates, the most important mechanism is aspect ratio trapping, which uses high aspect ratio nano-trenches to trap threading dislocations (TDs). A model based on the theory of dislocation is proposed to calculate proportion of blocking threading dislocations in ELOG of GaAs or InP on nano-trench patterned Si substrates. The model establishes relationship with the structure of nano-trenches and the proportion of blocking threading dislocations. It is found that, the blocking proportion is determined by thickness of the masks, width of the trenches and direction of the nano-trenches (the angle of opening orientations lies off the [110] direction). The blocking proportion gradually increases until 100% as aspect ratio increases with fixed trench direction; with the same aspect ratio, the blocking proportion firstly decreases from 0° to 45°, and symmetrically increases from 45° to 90°. It is worth noting that the blocking proportion abruptly reduces to 50% when the direction is 45°and the aspect ratio is more than 1; But it does not happen if the aspect ratio is less than or equal to 1. The reported experimental results are well consistent with the model. The model provides a method for optimization of nano-trench patterned substrates for more effectively blocking threading dislocations in III-V semiconductors.
Fresnel zone plate is a classic optical element that however can be used as the core spectral component of micro-spectrometer, which optical path volume can be decreased to 1mm3. After passing through the Fresnel zone plate, monochromatic lights of different wavelengths will expand to spectrum because of their different focal length. We designed eight kinds of linear half zone plates to get different focal lengths and spectral performance. In the process of fabrication, we used the electron beam lithography and inductively coupled plasma (ICP) etching to produce the Fresnel zone plates. Finally, performances of Fresnel zone plates were examined by beam-split experiments. After comparison, the simulation conclusion in reference that the number of bands of Fresnel zone plates will affect the final appearance of the spectrum was verified.
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