The optimal structural parameters for an antireflective structure in high resistive float zone silicon are deduced for a rectangular and a hexagonal structure. For this the dependence of the effective index from the filling factor was calculated for both grating types. The structures were manufactured by the Bosch-process. The required structural parameters for a continuous profile require an adaption of the fabrication process. Challenges are the depth and the slight positive slope of the structures. Starting point for the realization of the antireflective structures was the manufacturing of deep binary gratings. A rectangular structure and a hexagonal structure with period 50 mum and depth 500 mum were realized. Measurements with a THz time domain spectroscopy setup show an increase of the electric field amplitude of 15.2% for the rectangular grating and 21.76% for the hexagonal grating. The spectral analysis shows that the bandwidth of the hexagonal grating reaches from 0.1 to 2 THz.

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The requirements for a broadband antireflective structure in the THz spectral region are derived. Optimized structural parameters for a surface-relief grating adapted to the spectrum of an intended THz pulse are deduced. The effect of a structure fabricated into Topas((R)) by a single-point diamond-turning process is demonstrated.

Terahertz radiation was measured from InN and compared to p-InAs excited by femtosecond optical pulses at 1060 and 800 nm. At 800 nm, atomically smooth InN with low background electron concentration exhibit higher THz emission than the highly effective material p-InAs. The higher THz emission efficiency of InN is caused by the absences of any intervalley scattering, which in the case of InAs increases the effective mass of the photo generated electrons and, thus, reduces the Dember field, which is responsible for THz emission. Consequently, InN is a promising material for THz emission; however, further improvement of the material quality (surface roughness and carrier concentration) is needed