Abstract-Imaging Polarization in GaN Surfaces by Laser Terahertz Emission Microscopy

Yuji Sakai, Iwao Kawayama, Hidetoshi Nakanishi, and Masayoshi Tonouchi

https://www.osapublishing.org/abstract.cfm?uri=cleo_si-2017-SM4J.6&origin=search

Polarizations in GaN surfaces are visualized using terahertz emission microscopy. A non-radiative-inversion domain that is hardly distinguishable with photoluminescence imaging was clearly observed with this method.

© 2017 OSA

Abstract-Comparison between laser terahertz emission microscope and conventional methods for analysis of polycrystalline silicon solar cell

Hidetoshi Nakanishi^1,a), Akira Ito^1,b), Kazuhisa Takayama^2,c), Iwao Kawayama^2,d), Hironaru Murakami^2,e) and Masayoshi Tonouchi^2,f)
http://scitation.aip.org/content/aip/journal/adva/5/11/10.1063/1.4935913?TRACK=RSS
a) nakanisi@screen.co.jp, Tel:+81-75-931-7925(ext.8303427). 322 Furukawa-cho, Hazukashi, Fushimi-ku, Kyoto 612-8486, Japan
b) a.ito@screen.co.jp, Tel:+81-75-931-7925(ext.8306049)
c) takayama.k0123@gmail.com, Tel:+81-6-6879-7983
d) kawayama@ile.osaka-u.ac.jp, Tel:+81-6-6879-7983. 2-6 Yamadaoka, Suita, Osaka 565-0871, Japan
e) hiro@ile.osaka-u.ac.jp, Tel:+81-6-6879-7982
f) tonouchi@ile.osaka-u.ac.jp, Tel:+81-6-6879-7981.
AIP Advances 5, 117129 (2015); http://dx.doi.org/10.1063/1.4935913

A laser terahertz emission microscope (LTEM) can be used for noncontact inspection to detect the waveforms of photoinduced terahertz emissions from material devices. In this study, we experimentally compared the performance of LTEM with conventional analysis methods, e.g.,electroluminescence (EL), photoluminescence (PL), and laser beam induced current (LBIC), as an inspection method for solar cells. The results showed that LTEM was more sensitive to the characteristics of the depletion layer of the polycrystalline solar cell compared with EL, PL,and LBIC and that it could be used as a complementary tool to the conventional analysis methods for a solar cell

Abstract-Visualization of GaN surface potential using terahertz emission enhanced by local defects

Yuji Sakai

, Iwao Kawayama

, Hidetoshi Nakanishi

 & Masayoshi Tonouchi

• Scientific Reports 5, Article number: 13860 (2015)
• doi:10.1038/srep13860

http://www.nature.com/articles/srep13860

Wide-gap semiconductors have received significant attention for their advantages over existing semiconductors in energy-efficient power devices. To realize stable and reliable wide-gap semiconductor devices, the basic physical properties, such as the electric properties on the surface and at the interface, should be revealed. Here, we report visualization of terahertz (THz) emission from the surface of GaN, which is excited by ultraviolet femtosecond laser pulses. We found that the THz emission is enhanced by defects related to yellow luminescence, and this phenomenon is explained through the modification of band structures in the surface depletion layer owing to trapped electrons at defect sites. Our results demonstrate that the surface potential in a GaN surface could be detected by laser-induced THz emission. Moreover, this method enables feasible evaluation of the distribution of non-radiative defects, which are undetectable with photoluminescence, and it contributes to the realization normally-off GaN devices.