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.
The impacts of SiN/Al 2 O 3 bi-layer passivation on the carrier transport characteristics in GaN-based metal-insulator-semiconductor high electron mobility transistors (MISHEMTs) were studied. Various mechanical stresses, as measured by micro-Ramam spectroscopy, were introduced on the GaN channel according to the different passivation systems. The SiN dielectric layer deposited by plasma enhanced chemical vapor deposition on top of the GaN capping layer resulted in compressive stress. On the other hand, the Al 2 O 3 passivation layer deposited by atomic layer deposition on SiN layer generated tensile stress, which compensated the compressive stress produced by the SiN layer. The correlation between the applied mechanical stress induced by the deposited dielectric layers and device performance of the GaN-based HEMT was also investigated. When a slight tensile stress was applied on the GaN channel through the bi-layer passivation, the carrier transfer characteristics were improved in terms of carrier concentration at the AlGaN/GaN interface, as well as carrier mobility and sheet resistance compared to the high compressive stress condition. These results show that the mechanical stress engineering via optimized passivation process is a promising technique for the improvement of the device performance in GaN-based MISHEMTs.
In the fabrication of InAlAs/InGaAs metamorphic high-electron-mobility transistor (mHEMT), the determination of whether etching has been completed to the desired gate recess depth is made by measuring whether the drain current through the channel layer has reached the target current. Non-uniformity of the etching rate occurs during wet etching with citric acid. In this study, the cause of that non-uniformity was investigated. We confirmed that an electrochemical potential caused by the electrolyte of the etching solution was induced between the ohmic electrode and the epitaxial layer of the recess region, resulting in a non-uniform etching rate. In particular, the case where the Au of an ohmic electrode is exposed by the monitor window for the measuring channel current was considered. The gate recess etch rate was changed by the presence, location and size of the photoresist openings on the ohmic electrodes.
Various GaN channel thicknesses (0.5, 2.0, 3.5 and 6.3 μm) grown by metal organic vapor chemical deposition (MOCVD) on sapphire substrate were prepared to investigate the effects of the channel thickness on the transistor characteristics. X-ray diffraction (XRD), pulsed ID(VD), as well as gate stress and DC measurements were employed in this study. The results have revealed that charge trapping in the AlGaN/GaN hetero-structure is reduced and transistor performance is improved as the GaN channel thickness is increased up to a certain value (TGaN_Channel = 3.5 μm); More specifically, as the GaN channel thickness is increased from 0.5 μm to 3.5 μm, the sheet resistance and carrier mobility values are changed from 475 to 400 Ω/□ and 780 to 1100 cm2/Vs, respectively. These results are attributed to the ameliorated crystalline quality when the GaN thickness increases as evidenced by the XRD data.
The proton radiation hardness has been investigated in GaN-based MIS-HEMTs with various gate insulating systems. Through the pulsed mode measurements and carrier mobility extraction, we have revealed that the Coulomb scattering generated by the trapped charges inside of the gate insulating layer is a key device performance degradation factor. We also have found out that SiN/Al2O3 bi-layer gate insulating system exhibits stronger immunity to the proton radiation compared to the SiN single-layer gate insulating system since the dielectric layer quality of ALD deposited Al2O3 is better than that of PECVD deposited SiN layer. Our systematic research emphasizes that to employ an excellent quality dielectric layer such as Al2O3 is essential factor for the improvement of the proton radiation hardness in GaN-based MIS-HEMTs.
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