Experimental Study Of Terahertz Wave Switch Based On The Photoelectric Effect

With the rapid development of terahertz sources and detectors, the application of terahertz technology capabilities of the functional devices has been widely concerned. In this paper, the terahertz transmission characteristics based on the photoconductive effect has been studied experimentally. A scheme of terahertz switch was proposed based on semiconductor material of high-resistivity silicon.The photoconductive effect generated in the semiconductor material under the laser irradiation directly affects the terahertz absorption characteristics. In this article, the process of concentration variation of the photo-excited carriers, and the mechanism of the minority carrier lifetime were analyzed. Terahertz transmission characteristics is compared by experiments using the different semiconductor materials with different minority carrier lifetime. A preliminary terahertz switch scheme based on high-resistivity silicon was determined by considering the tradeoff between the response rate and the amplitude modulation depth. In addition, several solutions were explored to reduce the minority carrier lifetime of high-resistivity silicon. The minority carrier lifetime dropped to around 0.7μs successfully by the means of heat-treatment process, which can easily diffuse transition metals into the silicon bulk and introduce deep-level recombination center into the band gap.Finally, by research on the photoconductive effect of the high-resistivity silicon and the terahertz functional elements, this paper presents an architecture of a high-power high-speed optical systems constructed to meet the requirements of high-speed switching. Experimental results measured by BWO system show that the photoconductive terahertz switch performs well. The response rate of the structure can exceed 1 MHz, and the amplitude modulation depth is about 25%.