3aA_MI-3High Precision Phase-Shifting Electron Holography of GaN Semiconductor Devices

Electron holography (EH) is widely used for quantitative observation of electric potential in semiconductor devices. We have so far developed high precision phase-shifting electron holography (PS-EH) that can detect weak phase of 0.01 rad level [1–3]. Here, we applied the PS-EH to measure accurate potential distribution of 2-dimensional electron gas (2DEG) layer formed at GaN/AlGaN semiconductor interface. We prepared a bulk sample having GaN/AlxGa1-xN (x = 0.25) interface grown on Si substrate. To make the uniform thin sample for PS-EH, we used a cryo-FIB technique, in which the TEM sample was prepared at 130 K to reduce FIB damage layer and sample distortion. Figures 1(a) and 1(b) show the TEM image and the typical hologram around the GaN/AlGaN interface, respectively. We reconstructed the phase image using 50 holograms whose interference fringes were shifted one after another. Figure 1(c) shows a 1-dimensional potential profile around the interface. The sharp potential change due to the 2DEG layer was successfully visualized within 15 nm from the interface. (a) TEM image, (b) hologram, and (c) 1D potential profile around GaN/Al0.25Ga0.75N interface. The author thanks Mr. Yasunori Goto and Mr. Tomoyoshi Kushida in Toyota Motor Corporation for supplying the GaN sample and valuable discussion. [1] K. Yamamoto et al., J. Electron Microsc. 49 (2000) 31. [2] H. Sasaki et al., J. Electron Microsc. 63 (2014) 235. [3] S. Anada, K. Yamamoto et al., J. Appl. Phys., 122 (2017) 225702.