The ultra-high voltage gate turn-off thyristor (GTO) device based on 4H-SiC, under the action of bidirectional carrier injection and conductivity modulation effects, can withstand high voltage while obtaining high pass current, meeting the requirements of ultra high power applications in terms of power density and reliability. PAM-XIAMEN can grow 4H-SiC epitaxial structure for GTO device fabrication. Take the following structure for example：
1. SiC GTO Epitaxial Structure
| Epi Layer | Thickness | Doping Concentration |
| P+ anode | 2.5um | 1×1019cm-3 |
| N+ base | 2um | 8×1017cm-3 |
| P- drift | 50um | 2×1014cm-3 |
| P+ buffer layer | ||
| N+ filed stop layer | ||
| N+ 4H-SiC substrate |
2. What Is A Gate Turn-off Thyristor?
Gate turn off thyristor is a type of thyristor with self turn-off capability and thyristor characteristics. If a forward voltage is applied to the anode and a forward trigger current is applied to the gate, the GTO will conduct. In the case of conduction, the gate is coupled with a sufficiently large reverse trigger pulse current, and the GTO switches from conduction to blocking. Although its performance is inferior to that of insulated gate bipolar transistors and power field-effect transistors, it has the advantages of high voltage resistance, large current capacity, and strong surge resistance of general thyristors. Therefore, GTO has gradually replaced ordinary thyristors and become the main switching device in large and medium capacity converter devices.
The structure of SiC gate assisted turn off thyristor can be divided into two types: symmetric and asymmetric. The symmetrical GTO has a high breakdown voltage in both forward and reverse directions, while the asymmetric GTO generally has a much higher forward breakdown voltage than the reverse breakdown voltage. The converter valve used in high-voltage DC transmission systems requires a higher breakdown voltage in both forward and reverse directions.
3. SiC Gate Turn-Off Thyristor Application
SiC GTO is very suitable for applications with fast current change rate (di/dt) switching at extremely high peak currents. Currently, it can achieve tens of thousands of reliable operations. Compared with voltage controlled power switching devices, SiC GTO has no gate oxygen and can be used under harsh high temperature conditions. The application of ultra-high voltage SiC GTO power switching devices (greater than 10 kV) in civil fields such as high-voltage flexible and direct current transmission, motor drive, and electric traction is very important for improving the performance of power transmission, propulsion, and traction systems.
In high-voltage power devices, gate turn off thyristor based on SiC have the features of strong current processing ability, high voltage level, low leakage current, and fast shutdown characteristics; Moreover, it has lower conduction resistance than SiC MOSFETs, lower conduction voltage drop, lower power consumption, and higher operating temperature than Si IGBT and SiC IGBT.
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