Authors: Zhe Jian
Source: Deep Blue (University of Michigan) (article, 2022-01-01)
Field: Materials Science — Electronic, Optical and Magnetic Materials

Ga2O3-Based Devices for High Power Switching Applications Ga2O3 is emerging as an attractive semiconductor for high power devices, which is promising to enable efficient high-power switches in the 2-20 kV voltage range. This dissertation is focused on understanding and resolving the fundamental issues severely limiting the performance of Ga2O3-based transistors by a combination of device design and developing novel fabrication processes. Thermal management is crucial for engineering the performance and reliability of the emerging Ga2O3 technology with potential applications in harsh environments. The effects of temperature on the electrical characteristics of Ga2O3 trench and regular Schottky barrier diodes (SBD) device structures were studied. The superior thermal stability of trench SBDs will be presented in this dissertation. High-quality dielectrics are important for enabling high-performance Ga2O3 field effect transistors (FETs). Especially, in the case of Ga2O3 for which shallow p-type doping does not seem to be feasible, developing a robust dielectric with large breakdown voltage and low interface trap density is crucial to take full advantage of Ga2O3 potential for high power switching applications. Two gate dielectrics including ALD-Al2O3 and MOCVD-AlSiO were investigated for β-Ga2O3 MOS capacitors (MOSCAP) and deep UV-assisted capacitance-voltage measurements were used to characterize the interfacial and bulk properties of dielectrics. These results will be presented and a comparison between these two dielectrics will be discussed. Rapid advancements have been reported on key device DC parameters such as threshold voltage, on-resistance, leakage current and breakdown voltage. However, there is still a lack of knowledge on the switching performance of Ga2O3-based power devices. A novel 3.5 kV Fin-FET structure was designed and tested using Silvaco TCAD device-circuit hybrid simulator. The impacts of electron mobility, substrate thickness and fin width/pitch size ratio on the switching performance will be presented which provide helpful insights for design and fabrication of Ga2O3 power FinFETs for low-waste power conversion applications. α-Ga2O3, which is a meta-stable phase, has the largest band gap (5.3 eV) compared to other polymorphs of Ga2O3. Furthermore, the corundum-structure of α-Ga2O3 makes it a promising wide bandgap semiconductor candidate because of the ability to produce heterostructures with its (Al, In, Ga)2O3 alloys which will enable bandgap engineering. In order to achieve α-Ga2O3- devices with different geometries, it is essential to develop high etch-rate etching conditions with low surface damage and smooth etch surface morphology. Inductively-coupled plasma technique was used to study the dry etching of α-Ga2O3. The effect of BCl3/Cl2/Ar gas ratio, bias and plasma powers and chamber pressure on etch rate, surface roughness and mask selectivity will be presented in this dissertation. Two main challenges of β-Ga2O3 are its relatively low electron mobility and unavailability of p-type doping. On the other hand, GaN, has a high electron mobility, high 2D charge (2DEG) density, moderate thermal conductivity, and p-type doping with Mg. Therefore, the integration of β-Ga2O3 with GaN can potentially enable the fabrication of novel GaN/Ga2O3 high-frequency and high-power devices combining the merits of both GaN and Ga2O3 in addition to novel optoelectronic devices. Heterogeneous integration of N-polar GaN and β-Ga2O3 substrates in nano-scale are proposed either via direct bonding or by adding an ALD-ZnO as the “glue” layer to enhance bonding uniformity. The impact of post-annealing temperature on the structural characteristics and electrical quality of bonded interface will be discussed. Computer science ; Power (physics) ; Electrical engineering ; Engineering ; Physics Ga2O3 and related materials ; GaN-based semiconductor devices and materials ; Advanced Photocatalysis Techniques