Abstract-Strong emission of terahertz radiation from nanostructured Ge surfaces

Chul Kang¹, Jung Woo Leem², Inhee Maeng¹, Tae Heon Kim³, Jong Seok Lee³,Jae Su Yu^2,a) and Chul-Sik Kee^1,b)
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a) E-mail: jsyu@khu.ac.kr
b) E-mail: cskee@gist.ac.kr
Appl. Phys. Lett. 106, 261106 (2015); http://dx.doi.org/10.1063/1.4923372

Indirect band gap semiconductors are not efficient emitters of terahertz radiation. Here, we report strong emission of terahertz radiation from germanium wafers with nanostructured surfaces. The amplitude of THz radiation from an array of nano-bullets (nano-cones) is more than five (three) times larger than that from a bare-Ge wafer. The power of the terahertz radiation from a Ge wafer with an array of nano-bullets is comparable to that from n-GaAs wafers, which have been widely used as a terahertz source. We find that the THz radiation from Ge wafers with the nano-bullets is even more powerful than that from n-GaAs for frequencies below 0.6 THz. Our results suggest that introducing properly designed nanostructures on indirect band gap semiconductor wafers is a simple and cheap method to improve the terahertz emission efficiency of the wafers significantly.