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Blazed gratings are widely used in optical detection devices with the unique property of concentration of light energy to a desired diffraction order. However, traditional substrates for fabricating blazed gratings are easily damaged with the wear and tear in long-term usage under harsh conditions. Here, we propose the fabrication of blazed gratings on sapphire with high mechanical stability by femtosecond laser lithography combined with subsequent reactive ion etching (RIE). Various sapphire blazed gratings with periods from 2 μm to 10 μm and heights from 260 nm to 2 μm were realized to concentrate light energy (wavelengths of 405 nm, 532 nm and 633 nm) to different diffraction orders (1st, 2nd, and 3rd). The results provide great insights for the construction of micro-optical devices that have potential applications under harsh conditions. [ABSTRACT FROM AUTHOR]

In this paper, we carried out an analysis of the breakdown characterization method by the investigation on off-state leakage currents and breakdown curves. For conventional breakdown, seven kinds of breakdown curves are summarized and it is found that only two of them can be shown by the conventional three-terminal breakdown characterization method reasonably. For the other five kinds of breakdown curves, the value of the gate leakage current is larger than that of the drain leakage current for a certain drain-bias range. Besides, the source leakage current cannot represent the buffer leakage current, and the values and signs of them are different. These problems contradict the conventional characterization method, indicating that the conventional method should be modified to characterize the breakdown mechanisms correctly. The similar problems also exist for time-dependent breakdown. The buffer and drain-gate leakage currents were obtained by a simple method and the conventional breakdown characterization method was modified by using these two currents. The problems in the conventional breakdown characterization method are solved by using the modified method. Experiments indicate that the modified breakdown characterization method is crucial to investigate the breakdown mechanisms, especially when source-gate leakage current cannot be neglected compared with the buffer leakage current. [ABSTRACT FROM AUTHOR]