(556d) 30 a Forward Current with 240 V Reverse Breakdown Ga2O3 Field-Plated Schottky Rectifiers

There has been a significant amount of interest for β-Ga₂O₃ in the power electronics field due to its outstanding electrical properties, such as ultra-wide bandgap (4.5-4.9 eV) and high critical breakdown field (6-9 MV/cm). Schottky rectifiers fabricated on β-Ga₂O₃ have shown promise in improving the efficiency of inductive motor and power supplies due to their fast switch speeds and low forward voltage drop in comparison with Silicon based p-n diodes. To engineer high current devices, large device areas must be utilized; however, the fabrication of large-area high-breakdown voltage devices is currently limited by the defect density in the drift region, for which the crystal quality is expected to improve. In order to accomplish this, multiple diodes with desirable breakdown voltages can be interconnected to obtain high forward currents which replicate real world application of this technology. In this work, we report on the first β-Ga₂O₃ Schottkydiode array with more than 30 A of absolute forward current with a 240 V reverse breakdown voltage.

The starting material for device fabrication was a Sn doped β-Ga₂O₃ single crystal (001 surface orientation) with 20 μm Si doped β-Ga₂O₃ epitaxial layer grown by halide vapor phase epitaxy (HVPE). A Ti/Au backside ohmic contact was deposited followed with a rapid thermal anneal at 550°C under N₂ ambient. 40 nm of Al₂O₃ and 360 nm of SiN_x were deposited on top of the drift layer using atomic layer deposition (ALD) and plasma enhanced chemical vapor deposition (PECVD), respectively. Dielectric openings of different sizes (0.40.4 mm² to 11 mm²) were opened with buffered oxide etchant (BOE) followed by deposition of 500 µm Ni/Au contacts using E-beam evaporation. The on-off ratio for individual devices is within the range of 10⁶ to 10⁸ which is consistent with previous reported values for β-Ga₂O₃ devices with Ni/Au Schottky contacts. The Schottky barrier height and ideality factor are 1.01 eV and 1.01, respectively. The reverse recovery time was measured to be 32 ns with an I_rr of 55 mA. Capacitance-voltage measurements show that the carrier concentration is in the range of 1.62 - 1.85 10¹⁶ cm^-3 for the drift region. In order to interconnect devices with low leakage current (< 50 nA), 200 nm of SiN_x were deposited on the sample surface to passivate all devices. Subsequently, 21 devices were opened using BOE, followed by the deposition of a thick Ni/Ti/Au metal stack. 33 A of absolute forward current was achieved at a forward bias of 4.25 V with a 240 V reverse breakdown voltage. These values yield a figure of merit (V_B²/R_ON) of 4.8 MW/cm². The calculated on-off ratio for the array is in range of 10⁵-10¹⁰ at a fixed 4 V of forward bias. For power electronic applications, this work is another breakthrough toward β-Ga₂O₃’s application in high-current and high-breakdown voltage rectifiers.