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Electron traps in AlGaN/GaN high electron mobility transistors were studied by combining theoretical and experimental methods. Energy levels about EC-0.9 eV due to irradiation are identified by deep-level transient spectroscopy (DLTS). Two electron traps, H1 (EC-0.63 eV) and H2 (EC-0.9 eV), were observed in the DLTS spectra. H1 was produced in device or material manufacturing, and H2 was caused by displacement damage. First, we reported that the signal peak of H2 can contribute from three defects labeled H2-1, H2-2, and H2-3 with energies EC-0.77 eV, EC-0.9 eV, and EC-0.98 eV, respectively. According to defect migration temperature and first principles calculation results, it is found that different configurations of di-nitrogen vacancy structures are the source of EC-0.77 eV and EC-0.9 eV signals. The defect of EC-0.98 eV is more stable at high temperatures, which may be related to gallium vacancy. [ABSTRACT FROM AUTHOR]

This article investigates the displacement damage on AlGaN/GaN high-electron-mobility transistors (HEMTs) using the 30-MeV fluorine ions. The electrical degradation and the defects in HEMTs were examined before and after irradiation. Three defect states are detected in a deep-level transient analysis system (DLTS), including a broad surface state peak ($N_{1}$) and two bulk defect peaks ($H_{1}$ and $H_{2}$). The energy levels of these two defects are $E_{\mathrm {C}} 0.63$ eV ($H_{2}$) and $E_{\mathrm {C}} 0.91$ eV ($H_{1}$), respectively. There is a linear relationship between the concentration of $H_{1}$ and the fluorine ion fluence. The radiation damage and electrical performance degradation of AlGaN/GaN HEMTs are simulated by combining with simulation software of different methods. The calculated results are in agreement with the experimental data. The performance degradation caused by heavy ion of the device is mainly caused by the $H_{1}$ defect. The effect of defects with shallow energy level is shielded by the Fermi-level pinning in deeper energy level. Moreover, the defect distribution of GaN in AlGaN/GaN heterojunction plays a major role. It is found that the method of combining experimental data with multiscale simulation is an effective way to predict the radiation damage of devices. [ABSTRACT FROM AUTHOR]

To explore the role of hydrogen in radiation degradation of AlGaN/GaN high-electron-mobility transistors (HEMTs), the performance degradation of the hydrogen untreated and pretreated devices is compared under the exposure of carbon ions. The energy of carbon ions is chosen as 7.6 MeV, and the maximum fluence reaches 4 × 1012 cm−2. By electrical character measuring, it is found that the positive shift of the threshold voltage and the decrease of the transconductance occur after to the irradiation. Hydrogen pretreatment accelerates the shift of threshold voltage and the decrease of the transconductance. The threshold voltage of the device is almost unchanged under 1-MeV electron irradiations. This means that the displacement damage leads to the shift of the threshold voltage. The height of Schottky barrier hardly changes in the hydrogen pretreated devices, showing that the ionization defects such as the formation of interface states under the gate are not the main cause of device degradation. Deep level transient spectrum (DLTS) results show that the irradiations cause the increase of gallium vacancies, and the hydrogen pretreatment inhibits its formation. According to the first principle calculation, the existence of hydrogen in GaN layer can reduce the formation energy of and the number of charges of the defects. It is speculated that hydrogen atoms participate in the evolution of radiation defects, which changes the types and number of defects in the devices. [ABSTRACT FROM AUTHOR]

The electrical degradation in AlGaN/GaN high-electron-mobility transistors (HEMTs) is examined under irradiation with 7.6-MeV carbon (C), 20-MeV oxygen (O), and 30-MeV fluorine (F) ions in situ. To characterize the radiation damage in the HEMTs, the ionizing dose Di, displacement dose Dd, and number of vacancies versus the chip depth in the devices have been calculated for heavy ions. As expected, in all three types of HEMTs, the output current decreases more than 30% and threshold voltage positive shifts after the irradiation fluence of 4 × 1012 ions/cm2. The performance degradation of AlGaN/GaN HEMTs is caused by radiation-induced charged defects. Based on calculation and experimental results, it is shown that the nonionizing energy loss (NIEL) method is not suitable for estimating the degradation of AlGaN/GaN HEMTs either considering gallium vacancy or considering both gallium vacancy and nitrogen vacancy. In the same displacement damage dose, the threshold voltage degradation rate depends on the type of incident particles and independent of the channel length. The damage caused by carbon ions is the smallest and the damage caused by fluoride ions is the largest. [ABSTRACT FROM AUTHOR]

This paper identifies the location of E C -0.9 eV trap caused by irradiation in AlGaN/GaN high electron mobility transistors (AlGaN/GaN-HEMTs). Helium ions at 40 keV and 400 keV were selected as the irradiation source. The 40 keV He ions only causes damage in the passivation and AlGaN layer, while the 400 keV He ions will cause damage mainly in GaN layer. The test results show that the threshold voltage of the device positive shift after 400 keV He ion irradiation. The carrier mobility and the Schottky barrier also show decreases. Deep level transient spectrum (DLTS) results show a defect with E C -0.9 eV in GaN layer after irradiation. While, the displacement damage in the passivation and AlGaN layer cause negative shift of the threshold voltage and the decrease of the carrier mobility. Combined with the DLTS and TCAD simulation, the location of defects with E C -0.9 eV caused by displacement damage is in the GaN layer. [ABSTRACT FROM AUTHOR]

Radiation defects in gallium nitride devices were analyzed by combining experiments with simulation methods. Various forms of native defects, impurities, and these hydrogenated defect complexes in GaN were studied with first-principles calculations employing hybrid functionals which exhibit a reference data base for experimental analysis. We consider hydrogen complexes made of the combinations of single point defects (V Ga , V N), di-vacancies (V Ga -V Ga , V N -V N , V Ga -V N) and impurities (C, O, Si). Formation energies were computed for configurations with different charge states after full geometry optimizations. From the calculated formation energies, thermodynamic transition levels were evaluated, which are related to the thermal activation energies observed in experimental techniques such as deep level transient spectroscopy (DLTS). Hydrogen interstitial atoms were identified by the combination of DLTS and first-principles calculations. The transition level measured by DLTS was E C -0.5 eV, which is consistent with the calculation value. The signal of E C -0.9 eV peak in DLTS may be consisting of [V Ga ]-3/-2 and [V N -V N ]+1/+2. According to the degradation of the electrical performance of the AlGaN/GaN high electron mobility transistors and the calculation results, the hydrogen passivation may be caused by [V Ga ]-3, [V Ga -V Ga ]-2 and [V Ga -V N ]-1. [ABSTRACT FROM AUTHOR]