| Summary: | 碩士 === 國立中央大學 === 電機工程學系 === 102 === This thesis focus on the enhancement of off-state breakdown voltage of AlGaN/GaN Metal-Insulator-Semiconductor Field Effect Transistors (MIS-FETs) by using MOCVD grown different epitaxy structures on Si.
With increasing GaN buffer layer up to 4.6 μm thick, the fabricated AlGaN/GaN MIS-FETs off-state breakdown voltage is up to 960 V at LGD = 20 μm, while the 2.5 μm GaN thick buffer layer has 795 V device breakdown voltage. However, with increasing buffer layer thickness, the edge crack extends to 1.5 cm, which means only 65% area of 6-inch silicon substrate is available. For the purpose of enhance wafer area efficiency, several ways were surveyed to improve devices characteristics without extend buffer layers thickness. The first selection is 5% Al-content AlGaN as buffer layer. 5% AlGaN has off-state breakdown 705 V while GaN buffer layer equips 795 V, which was because dislocation densities serious affect off-state leakage path and breakdown voltage, growth condition of 5% AlGaN need to be optimized.
From previous results, that is the dislocation densities seriously affect device off-state characteristics, the growth of AlN interlayer experiment was designed for enhancing epitaxial quality. Which improved the devices breakdown voltage from 795 V to 926 V, about 16% breakdown voltage enhancement. Furthermore, off-state I-V curve of the devices fitted the theory of Space Charge Limited Current, which advanced understanding of the cause of the devices off-state leakage current formation.
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