─ 6 ─of as-deposited electrodes. Almost no conduction occurs with this electrode. This result indicates that both GaN/Ni interfac-es are rectifying interconnections. The line connecting hollow circles is the prole of electrodes after annealing at 673 K for 3.6 ks without voltage application. The conductivity at high voltage is improved, whereas it is still poor at low voltages. Such a non-linear electric conduction prole indicates that a high Schottky barrier is still existing at the GaN/Ni interface and suppressing the conduction at low voltages. The line con-necting black squares is the prole of electrodes after anneal-ing at 673 K for 3.6 ks applying voltage. Although the prole is still non-linear, it shows that the conduction at low voltages is improved by the annealing applying voltage. Fig. 8 shows a TEM bright eld image and corresponding selected-area electron diffraction pattern taken from a cross-section of a GaN/Ni interface after annealing at 673 K for 3.6 ks applying voltage. From the bright eld image shown in Fig. 8(a), Ni is directly connected to GaN. This result indi-cates that no Ga-Ni intermetallic compound is formed by any of possible interfacial reactions. The diffraction pattern shown in Fig. 8(b) supports the consideration. Fig. 8(b) consists of arrayed spots corresponding to [1-21-0] zone-axis of GaN sin-Fig. 6 Preparation and settings of the electrodes formed on the GaN single crystal substrate. (a) The layout and dimensions of the electrodes, (b) the connection of electrodes for voltage application during heat treatment.Fig. 7 Differences in I-V characteristics among three GaN/Ni electrodes with or without heat treatment and voltage application.-2-1012-0.06-0.04-0.0200.020.040.06Current, I [mA]Voltage, V [V] as deposited annealed (673 K, 3.6 ks) annealed & voltage applied (673 K, 3.6 ks, 30 V)Fig. 8 Bright field image of GaN/Ni interface cross-section after annealing at 673 K for 3.6 ks with voltage application.
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