We report on demonstrating high performance lateral β-Ga2O3 metal-oxide-semiconductor field-effect transistors (MOSFETs) with source-connected field plate (FP) on a thin (150 nm) and highly Si-doped (n = 1.5 × 1018 cm−3) β-Ga2O3 epitaxial channel layer grown by ozone molecular beam epitaxy (MBE) on Fe-doped semi-insulating (010) substrate. For a MOSFET with a gate-drain spacing (Lgd) of 25 μm, the three terminal off-state breakdown voltage (VBR) tested in Fluorinert ambient reaches 2321 V. To the best of our knowledge, this is the first report of lateral β-Ga2O3 MOSFET with high VBR of more than 2 kV and the highest VBR attained among all the Ga2O3 MOSFETs. The breakdown voltages with different Lgd from 5–25 μm ranged from 518–2321V, with a linear trend of increasing breakdown voltage for larger spacing lateral MOSFETs. Combining with high electrical performances and excellent material properties, source-connected FP lateral β-Ga2O3 MOSFET implies its great potential for next generation high-voltage and high-power switching devices applications above 2 kV.
Enhancement-mode (E-mode) Al 2 O 3 /AlGaN/GaN MISHEMTs were fabricated by shallow recess combined with CF 4 plasma treatment (SR/F) and deep recess (DR) to compare the effect of each process technique on the device performance. To prevent the device performance degradation induced by plasma damage during gate recess, the digital etch technique was employed. The fabricated E-mode devices have positively shifted threshold voltage, and exhibit lower transconductance (g m ) and saturation drain current than depletion-mode devices. Due to the CF 4 plasma damage during F-treatment, SR/F shows a sharp drop of g m curve and low saturation drain current. In contrast, DR presents broad g m and high saturation drain current. It is also revealed that the digital etch for gate recess exhibits an isotropic etch profile, consequently increasing the on-resistance. There is no remarkable difference between SR/F and DR in f T and f max , but DR has a better linearity over SR/F owing to the absence of plasma damage during F-treatment. This results reveal that the DR using digital etch is promising technique to obtain the high performance E-mode MISHEMTs compared to the F-treatment.
We report the electrical characteristics of GaN-based high electron mobility transistors (HEMTs) operated on various substrates/films. For the detailed investigation and comparison of the electrical properties of GaN-based HEMTs according to the substrates/films, GaN-based HEMTs were processed using 4-inch sapphire substrates and separated from their original substrates through the laser lift-off technique. The separated AlGaN/GaN films including processed GaN-based HEMTs were bonded to AlN substrate or plated with a 100 µm-thick Cu at the back-side of the devices since AlN substrate and Cu film exhibit higher thermal conductivity than the sapphire substrate. Compared to the sapphire substrate, DC and RF properties such as drain current, transconductance, cut-off frequency and maximum oscillation frequency were improved, when GaN-based HEMTs were operated on AlN substrate or Cu film. Our systematic study has revealed that the device property improvement results from the diminishment of the self-heating effect, increase in carrier mobility under the gated region, and amelioration of sheet resistance at the access region. C(V) and pulse-mode stress measurements have confirmed that the back-side processing for the device transfer from sapphire substrate onto AlN substrate or Cu film did not induce the critical defects close to the AlGaN/GaN hetero-interface.
Bullying in the workplace has long been regarded as an endemic problem in organizations and not just as an individual's exceptional or deviant behavior. Bullying in the workplace causes individuals to experience anger, fear, sadness, and guilt, and it increases counterproductive work behavior in an organization, which negatively affects both work and non-work performance. Given these contexts, we analyzed job attitudes, self-esteem, and perceptions of union support according to workplace bullying among 1,932 call-center counselors. To summarize the analysis results, first, when the occurrence of workplace bullying was high, it was expected that there would be a negative (-) relationship with job attitude. In addition, when the occurrence of workplace bullying is high, individual self-esteem is damaged, and it is expected that there will be a negative (-) relationship with job attitude, and the mediating role of self-esteem is proposed as a hypothesis. Lastly, if the awareness of union support is high, it can be expected that the union will be recognized as occupying the role of a supporter and that, even if exposed to workplace bullying, the negative relationship with job attitude can be alleviated. As a result of the analysis, the proposed hypothesis was supported, and the results were discussed in the research implications.
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