Gallium Oxide based High Voltage Diode : Design, Fabrication, Characterization and Modelling

Abstract

High-efficiency power electronic devices intend to play a significant role in curbing global warming and enhancing energy conservation. Owing to its superior material properties, Gallium oxide (Ga2O3) has emerged as a new competitive candidate that promises to deliver performance beyond the capabilities of the current SiC or GaN technologies. For higher breakdown voltage (BV) or lower reverse leakage current, innovative designs should be introduced to lower the surface electric field to less than the material’s critical electric field. This thesis investigates various diode designs through simulation and fabrication to increase the breakdown voltage.

First, lateral SBDs are fabricated on Sn-doped optical float-zone (OFZ) grown β−Ga2O3 samples. The effect of trenches on BV is investigated. Modeling of temperature-dependent reverse leakage current is demonstrated using the thermionic emission (TE) model, Poole-Frenkel (PF) emission model, and Fowler-Nordheim (FN) tunneling mechanism. To increase the BV, vertical SBDs are fabricated on industry-standard β−Ga2O3 samples. The BV of 362 V is reported for this design.

Secondly, a computer-aided design technology tool, TCAD-Silvaco, is utilized to understand and simulate the device behavior of β−Ga2O3-based lateral and vertical diodes that incorporate the reduced surface field (RESURF) effect caused by Trench MOS Barrier Schottky (TMBS) structure, bipolar diode design utilizing p-type NiOx and field-plate structure. The carrier concentration in NiOx film is mapped to its deposition recipe. Etch-recipes of NiOx are optimized. The TCAD designs are then implemented through fabrication. For a vertical diode with the p-type NiOx as the field plate, the BV is measured as ≈ 500 V. For the bipolar vertical diodes, the BV of 1317 V, ON-resistance of 6-7 mΩ−cm2 and Baliga’s figure of merit (BFOM) of 1.16 GW/cm2 are reported. Large area multi-finger vertical diodes are designed in various dimensions of finger width, pitch, and total contact area. In these devices, the breakdown voltage is reported to be 1173 V with an absolute forward current of 100 mA at 4.5-6 V. For mesa-free large-area diodes, an ION of 1-1.5 A is reported at 5-8 V. The reverse recovery time is estimated to be below 100 ns for these diodes.

Finally, the implantation of Ga2O3 with ions of Sn and Si is simulated using SRIM. The SRIM data is analyzed systematically to deduce the selection of ion energies and the corresponding dose to design a desired dopant profile. These analyses are essential in designing transistors.

In summary, this thesis focuses on the steady design and implementation of high-voltage diodes. It encompasses a comprehensive study of the device behavior through established models and TCAD simulation. This work explores new prospects for achieving the capabilities of Ga2O3-based electronic devices.