Comprehensive Design and Simulation of E-Mode β-Ga₂O₃ Current-Aperture Vertical Electron Transistors

Due to its ultra-wide bandgap, high critical electric field, and large Baliga's figure of merit (BFOM), beta-phase gallium oxide (β-Ga₂O₃) has attracted significant research attention for high-power, high-voltage, and high-frequency applications. Compared with lateral devices such as high electron mobility transistors (HEMTs), vertical devices have tremendous advantages in power electronics, including higher voltage and current handling capability, immunity to surface-related issues, simpler cooling requirement, smaller chip area, and easiness in scalability. Recently, β-Ga₂O₃ based current aperture vertical electron transistors (CAVETs) have been demonstrated. However, the device performance is still far from the β-Ga₂O₃ material limit, and several major challenges need to be addressed and, such as low breakdown voltage, high off-state leakage, small gate voltage swing, and difficulty in realizing enhancement mode (E-mode).<br/>In this work, we perform the first comprehensive design and modeling of β-Ga₂O₃ CAVETs and explore their performance limit using TCAD SILVACO simulation. The simulated CAVETs structure consisted of an n⁺-Ga₂O₃ substrate, an 8 um Ga₂O₃ drift layer, a 0.8 um Ga₂O₃ aperture layer containing an aperture with the length of 20 um, two current blocking layers (CBLs) located at both sides of the aperture formed by nitrogen implantation, a 0.15 um Ga₂O₃ channel layer, two n⁺-Ga₂O₃ contact regions for the source and drain, and a 50 nm Al₂O₃ layer as gate dielectric. The length of gate, gate to source, and gate to drain is 40 um, 10 um, and 9 um, respectively. For the mobility simulation of Ga₂O₃, field-dependent saturation velocity mobility model and thermal dependent mobility model were introduced. For the breakdown simulation of the devices, lattice heating model and impact ionization model were incorporated. Furthermore, the incomplete ionization model was used for both donors and accepters in Ga₂O₃, which is critical for the accurate simulation of the CBL region. The device model was calibrated with experimental results such as transfer curves and breakdown characteristics. It was found that the threshold voltage (V_TH) of the devices was sensitive to and increased with the doping concentration in the channel layer. When the doping concentration in the channel layer was lower than 5×10¹⁷ cm^-3, the device changed from the depletion mode to the enhancement mode. Under zero bias, electric fields were concentrated between the gate and the CBL with a low breakdown voltage (BV) of 260 V, which is caused by insufficient gate control over the channel. Several gate structures will be investigated for the optimal BV-R_ON performance, including p-Gate, deep-recessed gate and p-type recessed gate. These results can provide critical references for the future development of high-performance vertical β-Ga₂O₃ power electronics.