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.

Abstract-Characteristics of terahertz pulses from antireflective GaAs surfaces with nanopillars

Chul Kang¹, Jung Woo Leem², Joong Wook Lee³, Jae Su Yu², and Chul-Sik Kee^1,4

¹Ultra-Intense Laser Laboratory, Advanced Photonics Research Institute, GIST, Gwangju 500-712, South Korea
²Department of Electronics and Radio Engineering, Institute for Laser Engineering, Kyung Hee University, Gyeonggi-do 446-701, South Korea
³Department of Physics, Chonnam National University, Gwangju 500-757, South Korea
⁴Center for Subwavelength Optics, Seoul 151-747, South Korea 

http://jap.aip.org/resource/1/japiau/v113/i20/p203102_s1?isAuthorized=no

We investigated the characteristics of terahertz pulses generated from antireflective GaAs surfaces with nanopillars under femtosecond laser excitation. Although the antireflective nanostructures contribute to the enhancement of free photocarrier excitation in GaAs, they could reduce the transient photocurrent density and advance the start time of the photocurrent decay. Thus, the relative amplitudes of the high-frequency spectral components of terahertz pulses increased, whereas the energies of the pulses decreased. However, we showed that thinly distributed nanopillar structures could generate a short terahertz pulse without a reduction in the pulse energy.

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