PhD/Training positions

Jun 8, 2017

Seminar June 14, 2017, 2:30 pm, GeePs

Professor Tonouchi will give a seminar on "Laser terahertz emission microscope and its application to the evaluation of solar cells and GaN wafers", at GeePs, Salle du Conseil, Building G, on Wednesday 14 June, at 2:30 pm.

Posted by: admmdmi

One can observe terahertz (THz) radiation from various kinds of materials, when excited with a femtosecond laser, owing to ultrafast current modulation. THz waves reflect various kinds of properties such as local electric field, particularly ultrafast transient phenomena, in their waveforms. The observation of the THz waveforms enables us to explore ultrafast nature of electronic materials and devices as a THz emission spectroscopy.

When one excites the THz emission from a certain substance with the femtosecond optical pulses and visualizes the emission image by scanning the laser beam on it, the resolution of the image is limited by the laser beam diameter rather than THz wavelength. Thus construction of a laser-THz emission microscope (LTEM) would provide a new tool for materials / device science and applications [1].

We proposed and have been developing LTEM since 1997. In this talk, we will report the basics of LTEM, dynamic pump-and-probe LTEM (DTEM) [2], near field LTEM, and some examples focusing on the evaluation of solar cells [3,4] including deep inside imaging of carrier dynamics in a TUNDEM cell (unpublished), and GaN wafers [5,6]. The molecular desorption study from atomic layer materials is also an interesting application [7,8].

 [1] H. Murakami, et al., “Scanning laser THz imaging system,” Journal of Physics D: Applied Physics 47, 374007 (2014).

[2] H. Murakami, et al., “Study of photoexcited-carrier dynamics in GaAs photoconductive switches using dynamic terahertz emission microscopy,” Photonics Research 4, A9 (2016).

[3] H. Nakanishi, et al., “Comparison between laser terahertz emission microscope and conventional methods for analysis of polycrystalline silicon solar cell,” AIP Advances 5, 117129 (2015).

[4] T. Mochizuki, et al., “Probing the surface potential of oxidized silicon by assessing terahertz emission,” Appl. Phys. Lett. 110, 163502 (2017)

[5] Y. Sakai, et al., “Visualization of GaN surface potential using terahertz emission enhanced by local defects,” Scientific Reports 5, 13860 (2015).

[6] Y. Sakai, et al., “Polarization imaging of imperfect m-plane GaN surfaces,” Appl. Phys. Lett. Photonics 2, 041304 (2017).

[7] Y. Sano, et al. “Imaging molecular adsorption and desorption dynamics on graphene using terahertz emission spectroscopy,” Scientific Reports 4, 6046 (2014).

[8] F. R. Bagsican, et al. “Adsorption energy of oxygen molecules on graphene and two-dimensional tungsten disulfide,” Scientific Reports 7, 1774 (2017).