Gallium Nitride Normally-Off Vertical Field-Effect Transistor Featuring an Additional Back Current Blocking Layer Structure

A gallium nitride (GaN) semiconductor vertical field-effect transistor (VFET) has several attractive advantages such as high power density capability and small device size. Currently, some of the main issues hindering its development include the realization of normally off operation and the improvement of high breakdown voltage (BV) characteristics. In this work, a trenched-gate scheme is employed to realize the normally off VFET. Meanwhile, an additional back current blocking layer (BCBL) is proposed and inserted into the GaN normally off VFET to improve the device performance. The electrical characteristics of the proposed device (called BCBL-VFET) are investigated systematically and the structural parameters are optimized through theoretical calculations and TCAD simulations. We demonstrate that the BCBL-VFET exhibits a normally off operation with a large positive threshold voltage of 3.5 V and an obviously increased BV of 1800 V owing to the uniform electric field distribution achieved around the gate region. However, the device only shows a small degradation of on-resistance (RON). The proposed scheme provides a useful reference for engineers in device fabrication work and will be promising for the applications of power electronics.

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.