| Summary: | 碩士 === 國立臺灣大學 === 電子工程學研究所 === 104 === In this thesis, we focus on the fabrication of normally-off AlGaN/GaN high electron mobility transistor (HEMT). First of all, we discusse the effect of fluoride-based plasma treatment and gate recess process on the shift of threshold voltages of the device. Then, the device is fabricated with the combination of fluoride-based plasma treatment and recess-gate structure. A thermal annealing process is used to repair the surface after dry etch. The device shows positively threshold voltage shift of 2 V.
To reduce the gate leakage current and ensure that device can be biased at higher gate voltage, Al2O3 is used as gate dielectric and the gate current is decreased about four order of magnitudes. Interface trap emerges after ion bombardment, which reduces the gate-control-ability and makes threshold voltage shift toward negative seriously. In order to reduce interface traps, KOH diluent is used to passivate the surface and we focus on the fabrication of gate recess MOSHEMT.
To fabricate normally-off devices, AlGaN barrier is fully-removed with very low etching rate that can precisely control the recess depth. Device with high performance shows threshold voltage of 1V and maximum drain current of 285 mA/mm. The C-V and pulse I-V measurement are used to analyze interface traps. And we compare the difference between two-dimensional electron gas (2DEG) channel devices and inversion channel devices.
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