Proposal and Demonstration of GaN-Based Normally-Off Vertical Field-Effect Transistor with a Design of Back Current Block Layer

Vertical field-effect transistor (VFET) structure has the advantage in improving both the breakdown voltage (BV) and on-resistance (RON) of semiconductor power devices when compared with the lateral devices. GaN-based normally-off VFET device is designed and demonstrated in this work and an additional back current block layer (B-CBL) is proposed and employed to further improve the device performances. By introducing the B-CBL design, the electric field distribution along the gate aperture is more uniform which leads to an obvious increase (~30%) of BV in the proposed device while the RON is kept nearly constant. Therefore, the figure of merit (FOM) value of the proposed VFET is improved apparently in comparison with that of the conventional GaN-based VFET devices.