We present SiO2/GaN interfaces with low interface state density and high breakdown electric field. The SiO2 films were deposited by plasma-enhanced atomic layer deposition (PEALD) using bis(diethylamino)silane and O2 plasma at 300°C on n-type GaN (0001) homoepitaxial layers. An interface state density of less than 1011 cm–2eV–1 at 0.3 eV below the conduction band edge was confirmed by a conductance method. The value is much lower than those of previously reported ALD-SiO2/GaN interfaces (1012-1013 cm–2eV–1). Low fixed charge density at the SiO2/GaN interface of 3.7×1011 cm–2 and a high dielectric breakdown field of ~10 MV/cm were obtained. Moreover, the interface state density and current–voltage characteristics were further improved by post-deposition annealing at 400°C in N2 ambient. Scanning transmission electron microscopy with energy dispersive X-ray analysis revealed existence of a GaOx interlayer between SiO2 and GaN. The unintentional interlayer could be one of reasons for improving interface properties at the ALD-SiO2/GaN.
Gamma-ray irradiations of up to 500 kGy on homoepitaxial n-type GaN layers were carried out, and the formation of electron traps was investigated by deep-level transient spectroscopy (DLTS) using Ni Schottky barrier diodes (SBDs). Before performing DLTS, current–voltage (I–V) and capacitance–voltage (C–V) measurements of the SBDs were performed and it was found that there was no change in the net donor concentration, ideality factor, and Schottky barrier height after irradiation. In the DLTS measurements, two new peaks, labeled G1 and G2, were observed after irradiation. The filling pulse width dependence of G1 revealed that the peak consists of two electron trap levels, labeled G1a (EC − 0.13 eV) and G1b (EC − 0.14 eV). Isothermal capacitance transient spectroscopy measurements of samples with different Schottky barrier heights showed that the G2 peak is a complex peak consisting of at least three electron traps, labeled G2a (EC − 0.80 eV), G2b (EC − 0.98 eV), and G2c (EC − 1.08 eV). The production rates (formation rates of traps by gamma-ray irradiation) for each trap were obtained. Finally, we investigated the annealing behavior of each trap and found that G1b and G2b decreased by the same amount with increasing annealing temperature, suggesting that the behavior originates from a recombination of vacancy–interstitial (Frenkel) pairs.
Atomic layer deposited Al2O3/GaN metal-oxide-semiconductor (MOS) diodes with and without post-metallization annealing (PMA) were irradiated with gamma-rays. Capacitance–voltage measurements were made before and after irradiation to investigate trap formation in Al2O3 films and interface states between Al2O3 and GaN. Negative flat-band voltage shifts were observed. The flat-band voltage shift depends on the Al2O3 thickness, showing different distributions of gamma-ray-induced positive charges for samples with and without PMA. The interface state density of the PMA sample slightly increased after irradiation, but was lower than that of the sample without PMA before irradiation.
Production rate (PR = trap concentration/incident fluence) of traps formed by energetic particles is important for predicting device degradation caused by radiation when developing radiation-resistant devices. We demonstrate a clear correlation between non-ionizing energy loss (NIEL) and PR of an electron trap at about 0.12–0.20 eV below the conduction band edge [ EC − (0.12–0.20) eV] for various types of energetic particles in gallium nitride (GaN). NIEL values in GaN for electrons, protons, and [Formula: see text]-rays were calculated using a screened-relativistic treatment, and NIEL values for gamma-rays were calculated by simulating slowed-down spectra due to shielding material. To obtain the PRs of the electron trap, 60Co gamma-rays with an average photon energy of 1.25 MeV and electron beams with energies from 137 keV to 2 MeV were irradiated onto n-type GaN Schottky barrier diodes. We measured the concentration of an electron trap at EC − (0.13–0.14) eV using deep-level transient spectroscopy. We also used the PRs of electron traps with similar energy levels of EC − (0.12–0.20) eV from previous studies on electrons, protons, and [Formula: see text]-rays irradiated on GaN. All the trap PRs were proportional to the NIEL in a range of eight orders of magnitude, which confirms that the energy levels formed by various energetic particles have the same origin of being generated by atomic displacements. The obtained relationship coefficient between the NIEL and PRs of the trap is useful for predicting the degradation of GaN-based devices due to traps formed by various kinds of radiation.
Deep-level transient spectroscopy (DLTS) using Schottky barrier diodes (SBDs) is widely used for quantitative analysis of deep levels. This study focuses on the dependence of Schottky barrier height on apparent time constants and concentrations of electron traps in n-type GaN. DLTS using SBDs with various barrier heights was carried out. Experimental data show that large reverse leakage currents due to low barrier heights resulted in underestimation of time constants and concentrations. Theoretical calculations considering the impact of leakage currents reproduced experimental results well. Based on the calculations, we suggest a minimum required barrier height where accurate time constants and concentrations can be evaluated.
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