Research On Novel Structure Of AlGaN/GaN HFET Power Device

Power semiconductors are exerting a deep influence on human living through the fileds like power management, power transmission, machinery controlling, etc. Si power devices have been developing for over half a century, and their performance is approaching the physical limits. The increasing demand for higher performance is forcing researchers to try new semiconductors. Gallium Nitride(GaN) material are considered as excellent candidates for the next-generation power devices because it has the merits of wide band gap, high electron mobility,high critical electric field etc. AlGaN/GaN heterostructure with a high concentration of two-dimensional electron gas(2-DEG), endows the fast switching speeds and low conduction losses of AlGaN/GaN heterostructure field effect transistor(HFET), but it makes the conventional HFET for depletion mode that is not conducive to power switching applications. Therefore, the Enhancement-mode(E-mode) Al GaN/GaN HFET become technical difficulties of GaN-based power devices. In this dissertation, AlGaN/GaN HFET for power applications based on the domestic GaN-on-Si wafer are paid attention to, and the main results of this research are summarized as follows:(1) Based on the existing research results of AlGaN/GaN HFET device simulation in our lab, carried out the research of key processes for E-mode power devices. A recipe of high-quality Ohmic contact is optimized and a low contact resistance ohmic contact is obtained. A high efficiency, low damage and rate controlled recess etching process is developed and the most critical process for fabrication of E-mode AlGaN/GaN HFET is obtained.(2) Based on the novel gate recess etching process, the concept of partial-gate-recess for performance improvement of E-mode GaN power devices is proposed and experimentally demonstrated. A partial-gate-recess with carefully control the recess-depth was performed with an optimized recessed-barrier-thickness of ~1.5 nm that is thin enough to completely deplete the 2-DEG channel in the gate region. Meanwhile, the remaining barrier preserves the as-grown quantum-well of the heterostructure physically intact and thus effectively mitigates the lattice damage caused by gate recess. The fabricated E-mode Al2O3/AlGaN/GaN MIS-HFET deliver a threshold voltage(VTH) of +1.5 V. The maximum drain current density(Id,max) and transconductance(Gm,max) are 693mA/mm and 166mS/mm, respectively. The MIS-HFET with Lgd of 10 μm features an OFF-state breakdown voltage of 860 V at leakage current of 1 μA/mm. The corresponding specific on-resistance(Ron,sp) is as low as 1.18 m?·cm2 yielding a high power figure-of-merit of 626 MW/cm2.(3) The MIS-gated hybrid-anode-diode(MG-HAD) with a 20 nm Al2O3 high-k dielectric inserted between the schottky metal and the heterostructure to suppress the reverse leakage is proposed. The fabricated MG-HAD delivers reverse leakage current less than 10 μA/mm up to 1100 V yielding 5-order ON/OFF current ratio at 25 oC. The reverse leakage exhibiting a moderate temperature dependence is successfully suppressed less than 10 μA/mm up to 616 V at 150 oC.