物理工学コースからのおしらせ

講師：Filip Tuomisto氏（Department of Applied Physics, Aalto University, Finland）

演題：Semiconductors, devices and interfaces: what can we tell with positrons?

日時：4月26日（木）15：00～

場所：工学研究院　総合研究棟　W701室

Charge localization (trapping) phenomena in semiconducting and insulating crystalline solids are central to the function of all present and future electronic devices. Whether we discuss micro-processors, fast power switches, light-emitting devices (LEDs) or photovoltaics, the fundamental challenges are the same: how, where and why are the charge carriers (i) generated in or injected into the device, (ii) transferred through the relevant parts device and eventually collected in some other part, and (iii) trapped while, before or after being transferred. Positron annihilation spectroscopy is a well-established method for studying point defects, in particular vacancies, in semiconductors and insulators [1]. Theory predicts a certain kind of sensitivity also to interfaces between semiconducting materials [2].
I will first give a brief introduction to state-of-the-art positron annihilation experiments and how to efficiently employ theoretical calculations in interpreting the results for vacancy-type defects. Then I will discuss three recent examples of experiments, where positrons are used for analyzing small impurity atoms in GaN [3], alloy disorder in InGaN alloys [4], and interface traps in GaN/AlGaN high electron mobility transistors (HEMTs) [5].
References
[1] F. Tuomisto and I. Makkonen, Rev. Mod. Phys. 85, 1583 (2013).
[2] I. Makkonen et al., Phys. Rev. B 82, 041307(R) (2010).
[3] F. Tuomisto et al., Phys. Rev. Lett. 119, 196404 (2017).
[4] V. Prozheeva et al., Appl. Phys. Lett. 110, 132104 (2017).
[5] V. Prozheeva et al., in preparation.


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