Taku Horii

Extremely Low On-Resistance and High Breakdown Voltage Observed in Vertical GaN Schottky Barrier Diodes with High-Mobility Drift Layers on Low-Dislocation-Density GaN Substrates

Vertical GaN Schottky barrier diodes (SBDs) were fabricated on freestanding GaN substrates with low dislocation density. High quality n-GaN drift-layer with an electron mobility of 930 cm2 V-1 s-1 was obtained by optimizing the growth conditions by reducing the intensity of yellow luminescence using conventional photoluminescence measurements. The specific on-resistance (RonA) and the breakdown voltage (VB) of the SBDs were 0.71 mΩ cm2 and over 1100 V, respectively. The figure of merit (VB2/RonA) was 1.7 GW/cm2, which is the highest value among previously reported SBDs for both GaN and SiC.

Novel Designed SiC Devices for High Power and High Efficiency Systems

Two types of 4H-silicon carbide (SiC) MOSFETs are proposed in this paper. One is the novel designed V-groove trench MOSFET that utilizes the 4H-SiC (0-33-8) face for the channel region. The MOS interface using this face shows the extremely low interface state density (Dit) of 3 × 1011 cm2 eV-1, which causes the high channel mobility of 80 cm2 V-1 s-1 results in very low channel resistance. The buried p+ regions located close to the trench bottom can effectively alleviate the electric field crowding without the significant sacrifice of the increase of the resistance. The low specific ON-state resistance of 3.5 mQ cm2 with sufficiently high blocking voltage of 1700 V is obtained. The other is the double implanted MOSFET with the carefully designed junction termination extension and field-limiting rings for the edge termination region, and the additional doping into the junction FET region. With a high-quality and high-uniformity epitaxial layer, 6 mm × 6 mm devices are fabricated. The well balanced specific ON-state resistance of 14.2 mQ cm2 and the blocking voltage of 3850 V are obtained for 3300 V application.

Ti/Al/Si Ohmic Contacts for both n-Type and p-Type 4H-SiC

An ohmic contact process by using tri-layer materials for a source contact of a silicon carbide (SiC) metal oxide semiconductor field effect transistor (MOSFET) is proposed. The authors validate its extremely low contact resistance for both n-type and p-type SiC by a simple process. The characteristics of Ti/Al/Si ohmic contacts were measured by using the transfer length method (TLM). We examined the dependence of the contact resistance on the thickness of each layer of Ti/Al/Si. Then, it is found that Ti/Al/Si contacts with an appropriate thickness show excellent ohmic properties for both n-type and p-type SiC. N-type specific contact resistance (ρn) of 3.7 × 10-6 Ω cm2 and p-type specific contact resistance (ρp) of 1.7 × 10-4 Ω cm2 are obtained with Ti (20 nm) /Al (30 nm) /Si (30 nm).

High-Breakdown-Voltage GaN Vertical Schottky Barrier Diodes with Field Plate Structure

Gallium nitride (GaN) vertical Schottky barrier diodes (SBDs) with a SiNx field plate (FP) structure on low-dislocation-density GaN substrates have been designed and fabricated. We have successfully achieved the SBD breakdown voltage (Vb) of 680V with the FP structure, in contrast to that of 400V without the FP structure. There was no difference in the forward current-voltage characteristics with a specific on-resistance (Ron) of 1.1mcm2. The figure of merit V2b/Ron of the SBD with the FP structure was 420MWcm-2. The FP structure and the high quality drift layers grown on the GaN substrates with low dislocation densities have greatly contributed to the obtained results.

150 A SiC V-groove trench gate MOSFET with 6 × 6 mm2 chip size on a 150 mm C-face in-house epitaxial wafer

We report the successful demonstration of large current and high-speed switching properties of SiC V-groove trench gate MOSFETs (VMOSFETs). A drain current of 150 A (at V DS = 2 V and V GS = 18 V) and breakdown voltage of 960 V were achieved from a packaged 6 × 6 mm2 single chip. Moreover, short switching times of t r = 81 ns and t f = 32 ns were also obtained. To fabricate such VMOSFETs with high yield, highly uniform in-house epitaxial growth technology on a 150-mm-diameter wafer is also one of the keys, owing to its characteristic dependence on drift layer carrier concentration.