Electrical properties of p + -GaAs/n-GaN and n + -GaAs/n-GaN junctions fabricated by surface-activated bonding are investigated by measuring their capacitance-voltage (C-V) and current-voltage (I-V) characteristics. The difference between their flat-band voltages (0.17 eV), which are extracted from C-V measurements, disagrees with the ideal value (1.52 V), suggesting that the Fermi level should be pinned at the bonding interface. The C-V characteristics of the two junctions are calculated by assuming that the Fermi level is pinned at the interface. The measured C-V characteristics quantitatively agree with modeled ones obtained by assuming that the interface state density and conduction band discontinuity are 1.5 ' 10 14 cm %2 eV %1 and 0.63 eV, respectively. The effective heights of barriers at interfaces, which we estimate by analyzing dependences of I-V characteristics on the ambient temperature, are >10-20 meV for the two junctions at room temperature. This suggests that the transport of carriers is dominated by tunneling through interface states.

Hard x-ray photoelectron spectroscopy measurements are performed on ≈10-nm-thick GaAs film/Si substrate junctions fabricated by the surface activated bonding and selective wet etching. The chemical shifts of Ga-O and As-O signals in Ga 2p 3/2 and As 2p 3/2 core spectra indicate that oxides are formed in a part of GaAs films neighboring GaAs/Si interfaces due to the surface activation process. Analyses of Ga-O and As-O signals show that the thickness of such buried oxides is decreased due to a post-bonding annealing at temperatures up to 400 ℃. This means that the electrical properties of bonding interfaces, which are in the meta-stable states, are improved by the annealing. The thickness of oxides is different from that of amorphous-like transition layers at the GaAs/Si interfaces observed by transmission electron microscopy.

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