Analysis of effects of interface-state charges on the electrical characteristics in GaAs/GaN heterojunctions

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 × 1014 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.