Design, modeling, fabrication and characterization of advanced high-voltage 4H-silicon carbide Schottky rectifiers
This thesis presents on the development of advanced 4H-SiC high-voltage Schottky rectifiers with improved performance when compared to conventional 4H-SiC Schottky rectifiers. Three types of 4H-SiC Junction Barrier Schottky (JBS) rectifiers, which utilizes adjacent pn junctions to shield the main Schottky contacts from high anode voltage during reverse blocking, have been explored. These rectifiers offer Schottky-like on-state and fast switching characteristics while their off-state characteristics have a low leakage current similar to that of the PiN junction rectifier.
Planar Junction Barrier Schottky (JBS) rectifiers with different design and p+ implantation process parameters were fabricated using a baseline process using Ti as the Schottky metal and the trade-offs between forward drop and leakage current density were determined. With the optimum design (S : ∼4μm), 4H-SiC JBS rectifier exhibits Schottky-like (V F<1.5V, Ron, sp∼3mΩ·cm2) forward characteristics and low leakage current (<1×10-5A/cm 2) with 1kV blocking capability.
A new rectifier structure, called Lateral Channel-JBS (LC-JBS) rectifier, which can more effectively shield the Schottky contact from the electric field both vertically and laterally during reverse blocking than conventional planer JBS rectifiers, has been invented and studied. Test LC-JBS rectifiers have been designed and fabricated using epi regrowth technique over selectively implanted regions in 4H-SiC, demonstrating a forward voltage drop less than 1.8V at 100A/cm2 and a breakdown voltage up to 1.5kV. With a Schottky opening (WS) between 4 and 5μm, the LC-JBS rectifier demonstrates PiN-like reverse characteristics with a leakage current density less than 1×10-7A/cm2 at 1100V and 50% reduction in zero-bias junction capacitance compared to that of a conventional Schottky rectifier, all achieved with a small (<0.4V) increase in the forward drop. Another rectifier structure, called Buried Channel-Junction Barrier Schottky (BC-JBS) rectifier, has also been experimentally demonstrated and it exhibits a performance intermediate to those of planar JBS and LC-JBS rectifiers. The LC-JBS rectifier offers a low reverse leakage current while the BC-JBS rectifier demonstrates a lower on-resistance and forward drop. Analytical models for both planar JBS and LC-JBS rectifiers have been developed to simulate their forward and reverse I-V characteristics.