Market Opportunity for bulk GaN Power Device -Based on technology ‘s View
GaN-based wide band-gap semiconductors have attracted much attention due to their excellent properties, such as high breakdown electric field, high power switching efficiency and high thermal stability. Besides, the inherent polarization is built in AlGaN/GaN hetero-junction structure, and further promises higher sheet carrier density (ns) in the two dimensional electron gas (2DEG), as well as a diminution of on-state resistance (Ron) for power switching applications. In particular, the loss at high frequency (about 1MHz) was lower than Si device by a factor of 10. It’s means that high frequency operation is a strong probability for GaN device. In other words, the system size and weight can be reduced drastically by using GaN device because of smaller filter and less passives. Nevertheless, there is still lack of suitable substrates for GaN-based devices to develop fully their superiorities.
In recent decades, many studies of the growth of GaN-based epilayers on a variety of substrates, such as sapphire, SiC, bulk GaN, and Si, had been published. Among the aforementioned substrate materials, bulk GaN is regarded as a relatively promising substrate for use in GaN-based epitaxy due to homo-epitaxial growth. It was well-known that the largest obstacle for the development of GaN-on-GaN power device is the substrate. Typically, free-standing GaN substrate today are fabricated by hydride vapor phase epitaxy (HVPE) using MOCVD-grown GaN-on-sapphire template. However, the threading dislocation densities(TDDs) is still ranging from 3x106–1x107 cm-2. On the other hand, many papers pointed out that leakage would be easily occurred from channel to substrate through threading dislocations (TDs), accelerate degradation of GaN power device, and have a well-documented negative impact on laser diode lifetime. Consequently, TDDs below 104 cm-2, as are available in GaAs and should be available in true bulk GaN, are often regarded as being necessary for vertical GaN-on-GaN power devices.