Investigation of Al2O3/GaN interface properties by sub-bandgap photo-assisted capacitance-voltage technique

Abstract

Interfaces in Al2O3/n-GaN capacitors fabricated on free-standing GaN substrates were investigated using sub-bandgap photo-assisted capacitance-voltage measurements. After post-metallization annealing (PMA) at 300 °C, the metal-oxide-semiconductor (MOS) devices exhibited excellent capacitance-voltage (C-V) characteristics without frequency dispersion under dark conditions and a quite low interface state density (Dit) of ∼7×1010 cm-2 eV-1 for energies less than ∼1.2 eV from the conduction band edge. Despite the outstanding characteristics under dark conditions, it was found that sub-bandgap irradiation also resulted in shifts of the C-V curves toward the negative bias direction, which indicates the existence of donor-type interface traps. As a result, the Al2O3/n-GaN Dit distribution does not show the generally reported U-shape: for energies less than ∼1.2 eV from the conduction band edge, a Dit of ∼7×1010 cm-2 eV-1 was observed, although Dit rapidly increased to ∼2-4×1012 cm-2 eV-1 near the valence band edge. These interface states near the valence band edge are positively charged due to trapped holes when the states are located above the Fermi level.

Wide-range-adjusted threshold voltages for E-mode AlGaN/GaN HEMT with a p-SnO cap gate

“…Furthermore, the interface state between p-SnO and (Al)GaN is another factor affecting the device performance. According to the reports of (Al)GaN MOS-HEMT, the polarity, energy level positions, and concentrations of interface traps may cause the instability of V th [40,41]. Therefore, we assumed two defect levels (E 1 = E c − 0.5 eV, E 2 = E v + 0.5 eV) and two defect densities (1 × 10 13 and 1 × 10 11 cm −2 ) at the p-SnO/AlGaN interface.…”

Interface formation of Al2O3 on n‐GaN(0001): Photoelectron spectroscopy studies

“…Physical vapor deposition (PVD) is successfully used for the growth of the aluminum oxide 39–41 on other substrates, and it seems like an interesting choice for an alternative to ALD‐Al 2 O 3 . Al 2 O 3 /n‐GaN system is widely studied by many groups, 3,42–48 mostly focusing on near interface trap density and electrical properties. So far, a few reports have been published on the properties of the Al 2 O 3 /n‐GaN interface formed by ALD 12,18,49 but none by PVD.…”

Separate evaluation of interface and oxide hole traps in SiO2/GaN MOS structures with below- and above-gap light excitation

“…So far, traps in Al 2 O 3 /GaN MOS structures have been extensively studied using the photo-assisted C-V method. [24][25][26] An earlier study indicated that a low average interface state density (D it ) of 7 × 10 10 cm −2 eV −1 can be achieved within the entire bandgap of GaN through postmetallization annealing (PMA) of Al 2 O 3 /GaN structures at 800 °C in nitrogen (N 2 ) gas. 24) However, at this temperature condition, grain boundaries form in the Al 2 O 3 layer due to its partial crystallization, leading to a high gate leakage current.…”

“…17) With a reduced PMA temperature of 300 °C, D it values as low as 7 × 10 10 cm −2 eV −1 were successfully achieved for energies less than 1.2 eV from the conduction band edge (E C ), while higher D it values of (2-4) ×10 12 cm −2 eV −1 were detected near the valence band edge (E V ). 25) Despite these important findings in Al 2 O 3 /GaN structures, reports on SiO 2 /GaN structures remain limited. To gain insight into the hole traps in SiO 2 /GaN systems, systematic photo-assisted C-V measurements should be conducted on a set of samples processed under various conditions.…”

“…Figure 3(a) shows the hysteresis of sample PECVD-O 2 800 as a function of illumination time. When the photon energy was 1.72 eV or less, the amount of hysteresis saturated after an illumination time of 2 h. In contrast, when the photon energy was increased to 1.88 eV, the saturation behavior was not observed even within an illumination time of 3 h. Therefore, in this study, we evaluated the trap distribution by illuminating the light within the energy range of 1.39-1.72 eV for 2 h. From the wellconverged hysteresis values obtained under these conditions, we derived the energy distribution of D it using the following formula: 25,28)…”