Researches On The Characteristics Of AlGaN/GaN MIS-HENT Power Switching Device

Ga N-based High Electron Mobility transistor(HEMT) as power switching device, attracted many researchers’ attentions for its outstanding performances in high power,high frequency and high off state breakdown voltage applications. Although HEMT had made important progress, but there were still some unsolved problems, current collapse is the most significant problem, which had constrained its further applications. On the other hand, the conventional devices with Schottky contact gate, was proved to have larger gate leakage current and lower breakdown voltage. Devices with MIS(Metal/insulator/Semiconductor) structure were suggested to be its substitute. Moreover, there were some problems in the fabrication technologies of HEMTs, such as Ohmic contact, which had rough surface and poor thermal stability, was expected to be improved. In this thesis, the studies on the fabrication technologies and characterizations for the Al Ga N/Ga N MIS-HEMT based on Al2O3 gate dielectric films deposited by Atomic-Layer-Deposited(ALD)were carried out. The major work and achievements are showed in the following.(1) By optimizing the materials of substrate and the structure of power switching device, especially optimizing the device gate dielectric preparation technology, we eventually successfully prepared Al Ga N/Ga N MIS-HEMT power switching device and conducted a series of electrical characteristics test. Al Ga N/Ga N MIS-HEMT Power switching device using Al2O3 as gate dielectric whose saturated output current had obvious enhancement, increased by 50 m A. The threshold voltage of Schottky gate HEMT was-2.95 V, which was bigger than the threshold voltage of the device for Al2O3 gate dielectric Al Ga N/Ga N MIS-HEMT devices(-7.5V). The peak transconductance of Schottky gate HEMT(8ms) ws slightly higher than Al2O3 gate dielectric Al Ga N/Ga N MIS-HEMT devices(7ms). This was because of Al2O3 gate dielectric, grid and two-dimensional electron gas channel capacity decreases. The gate leakage current of Al2O3 gate dielectric Al Ga N/Ga N MIS-HEMT devices was less than the gate leakage current of Schottky gate HEMT, which reduced two orders of magnitude.(2) The threshold hysteresis phenomenon of MIS-HEMTs resulted from the trap sta tes on the surface and/or in the bulk of dielectric oxide film affected the reliability of the device. CF4 plasma treatment can reduce the threshold voltage hysteresis phenomenon of the device. Subsequent annealing treatment can reduce the gate leakage. The leakage current was 1.16 m A before annealing@Vgs=10V, which reduced to 280 n A after annealing.the saturation current density of the device was 520 m A/mm@Vg=10V. The off state breakdown voltage increased from 50 V to 290 V due to annealing treatment.(3) A 2μm gate-length, 35 mm gate-width ALD-Al2O3 Al Ga N/Ga N MIS-HEMT has been demonstrated. The device exhibited a low specific on-resistance of 0.57 Ω?mm2, a large maximum saturate drain current of 12.5A and a minimal threshold hysteresis of 0.05 V. By improving the preparation process of buffer, the off state breakdown voltage of the device increased to 600 V.