Engineering Dielectric and Field Plate for High Field and Thermal Management in High-Power Vertical β-Ga₂O₃ Schottky Diodes

The ultra-wide bandgap (UWBG) semiconductor, β-Ga₂O₃, has gained great interest for high-power electronics due to its large bandgap of (4.8eV), high breakdown field (8 MV/cm), and the availability of native substrates. These advantageous properties also make them attractive candidates for extreme environment applications that necessitate operation under high electric field, high temperature, and harsh radiation. However, a key requirement for robust high-power devices is to have ability to manage extreme heat and high field effects to prevent accelerated thermal or electrical failure. This is particularly challenging for β-Ga₂O₃devices due to the low inherent thermal conductivity of β-Ga₂O₃(11 -24 W/m K), which is an order of magnitude lower than other (U)WBG semiconductors. To circumvent this limitation, efficient β-Ga₂O₃device design strategies need to be developed that can address both high field and thermal effects in high-power applications. However, to date, most vertical β-Ga₂O₃ device reports have focused on maximizing the device performance by managing high field effects, without incorporating thermal considerations. Although thermal management of β-Ga₂O₃ devices have been investigated, the existing reports predominantly focused on lateral device structures, keeping vertical β-Ga₂O₃ power switches largely unexplored. Hence, an electro-thermal co-design of vertical β-Ga₂O₃ Schottky barrier diodes (SBDs) is fundamentally required since vertical devices are the preferred choices of multi-kV power switches compared to the lateral counterparts.<br/>Towards this goal, we explored vertical β-Ga₂O₃ SBD by engineering device design and field management strategies that can address both high field and thermal management. For field plates, we investigated a stack of high-permittivity (κ) dielectric (BaTiO₃ or TiO₂)/AlN where the top high-κ dielectric will maximize field reduction and bottom AlN will enhance heat transport at β-Ga₂O₃ interface. The AlN is utilized as insulator due to its poor electrical conductivity but excellent thermal conductivity (up to ~340 Wm^-1K^-1), high critical breakdown field (15.4 MVcm^-1), and higher conduction band offset (ΔE_C =0.6 to 1.34 eV) with β-Ga₂O₃ compared to BaTiO₃ (ΔE_C~0.08 eV), which can enable enhanced heat transport, high field sustainability, and reduced leakage at the field-plate interfaces.<br/>Here, we performed Silvaco TCAD modeling to obtain Joule heat power profile in vertical β-Ga₂O₃ SBDs of 10 µm drift layer (doping 1x10¹⁶ cm^-3) with field-plate (FP) formed using BaTiO₃ (250 nm, κ=150) versus stacked BaTiO₃ (150 nm)/AlN (100 nm). For the BaTiO₃ FP SBD, a concentrated Joule heat hotspot was found to appear at Schottky contact edge near field plate. However, the peak Joule heat power was reduced by 80% with BaTiO₃/AlN FP due to the enhanced transport by AlN at interface. Moreover, at reverse bias, the peak field of BaTiO₃/AlN FP SBD appeared in AlN which has higher breakdown field than β-Ga₂O₃. Thus, the complementary properties of two UWBG materials can improve both high field and thermal management of vertical β-Ga₂O₃ SBDs.<br/>We also explored a combined edge termination with deep mesa etch and BaTiO₃/AlN FP. The deep etch was reported to improve high-voltage performance of vertical β-Ga₂O₃ SBDs by terminating high field at anode edges [1]. We obtained that the deep etch can also further decrease the concentrated thermal hot spot at Schottky edges, with a monotonic reduction of Joule heat power by 14%, 26%, 36%, and 44% observed for etch depths of 1, 2, 3, and 4 µm compared to the planer SBD.<br/>To gain insights about the thermal boundary conductance (TBC), we are investigating TBC across AlN/β-Ga₂O₃ and BaTiO₃/β-Ga₂O₃ interfaces using the Landauer approach. We also fabricated AlN/β-Ga₂O₃ and TiO₂/β-Ga₂O₃ structures on HVPE-grown 10 µm β-Ga₂O₃wafers for electrical and thermal characterization, which will be reported at the conference.<br/><br/><b>Ref: </b>[1] S. Dhara, Appl. Phys. Lett. 121, 203501 (2022)