A normally OFF GaN CAVET and its thermal and trap analysis

Abstract

We propose and investigate an enhancement-mode (normally OFF) current-aperture vertical electron transistor (CAVET) with a novel structure. The novelty lies in the achievement of the desired normally OFF/enhancement-mode operation through polarization engineering by employing a hybrid current-blocking layer (HCBL) made of an isolation material and aluminum nitride (AlN). The AlN introduces a conduction barrier for the electron gas located at the AlGaN–GaN interface, effectively making the proposed device operate in an enhancement/normally OFF mode. The isolation portion of the HCBL suppresses the off-state leakage current and drastically improves the breakdown performance. Calibrated technology computer-aided design (TCAD) simulations show that the proposed polarization-engineered (PE)-CAVET structure displays normally OFF operation with a threshold voltage (VTH) of 2.2 V and a breakdown voltage twice that of the conventional GaN CAVET. A study of the thermal properties of the proposed structure reveals a significant improvement in the drain current due to the use of a heat sink, while the trap analysis shows that the leakage current in the CAVET structure can be suppressed by carefully choosing a proper acceptor trap concentration and energy level. On the other hand, donor traps degrade the performance of the CAVET, albeit not as severely as in the conventional device.