1. Why Wide Bandgap Semiconductor?

• Wide Bandgap Semiconductors (GaN and SiC) differ significantly from conventional silicon (Si) since they have a larger bandgap and breakdown field than Si. The properties allow GaN and SiC devices to operate at high power and temperatures (Table I). 
   
• Among the three materials of Si, SiC, and GaN, GaN shows the highest Baliga’s Figure-Of-Merit (BFOM) values, which is a performance index of power semiconductor devices operating at high frequencies. 

2. Why GaN HEMT?

• GaN High Electron Mobility Transistor (GaN HEMT) benefits from AlGaN/GaN heterostructure and epitaxial polarization effect leading to a lateral two-dimensional electron gas (2DEG) near the interface with high concentration and mobility. It is noted that the 2DEG concentration in the un-doped heterostructural quantum well is typically as high as 1x10¹³ cm^-2. 

• Simultaneous high electron concentration and mobility in the channel contribute to low RDSon and therefore low conduction loss in the HEMT operation at much higher switching frequencies than Si-based MOSFETs, IGBT…etc, which are formed primarily based on p-n junctions. 
   
• Owing to the above outstanding characteristics of GaN semiconductors, GaN modules or system products can therefore be designed with higher conversion efficiency but lower cost and smaller size or weight than those constructed by conventional Si-based power devices.

3. Why GaN on Si Substrates?

• Compared to SiC and Sapphire substrates, GaN on Si substrates presents advantages of competitive cost and potential to be applied on large-dimensional sizes such as 8” and 12” Si wafers. Through optimizing epitaxial buffer layers to overcome issues of defects and wafer bowing induced by large differences in lattice constant and thermal expansion coefficient, GaN-on-Si epitaxial technology is developed for device application. 
   
• Compatible wafer fabrication process and common Si substrates make the GaN-on-Si technology easily integrated into current Si circuits. Highly compact System-on-Chip (SoC) platforms can be performed. Not only cost and circuit size can be reduced but also performance is greatly enhanced.