4H-SiC MPS Diode Epitaxial Wafer

The merged PiN Schottky (MPS) diode has the characteristics of low turn-on voltage, high conduction current, fast switching speed, low reverse leakage current, and high breakdown voltage, making it the most ideal power diode. Combining the excellent forward and switching characteristics of SBD diodes with the outstanding breakdown characteristics of PiN diodes. The excellent material properties of SiC, combined with the superior structural advantages of MPS diodes, make SiC MPS diodes the most promising type of power diode for development. The MPS structure is currently mainly composed of 4H-SiC material. PAM-XIAMEN can grow 4H-SiC epitaxial wafer for MPS diode fabrication, take the following epi-structure for reference:

1. 4H-SiC MPS Diode Epitaxial Structure

Epilayer	Material	Thickness	Doping Concentration
Drift layer	n- 4H-SiC epi	–	–
Substrate	n+ 4H-SiC substrate

 

2. Silicon Carbide Merged PIN Schottky Diode Structure and Working Principle

The basic structure of MPS diode is shown in Figure 1. In addition to the small-sized P+ region, there is also a large-sized P+ region used to improve the surge reliability of the device. The function of the small P+ region is exactly the same as that of the P+ region in JBS diodes, while the function of the large P+ region is to improve the conductivity of the device under high currents. At high current, the PN junction corresponding to the high P+ region will open and inject minority carriers into the drift region of the device; The resulting conductivity modulation effect will greatly reduce the resistance of the device.

Fig. 1 Schematic diagram of 4H-SiC MPS diode structure

From the perspective of device structural characteristics, MPS diodes and JBS diodes have no essential difference, and their structural features are the alternating arrangement of P+ regions and Schottky regions. The difference between the two devices lies in their operating modes: in JBS diodes, the P+ region only shields high electric fields when the device is reverse biased to reduce leakage at the Schottky junction, and does not work when the device is forward biased; In MPS schottky diodes, the P+ region plays the same role when the device is reverse biased, and also participates in conduction when the device is forward biased and the forward bias voltage is high, in order to improve the bipolar conductivity of the device.

The application scenarios of SiC Schottky MPS transistor include PFC, boost circuits, and high voltage, high-power motor drives.

3. P-type Ohmic Contact Process for SiC MPS Diodes

The P-type ohmic contact process is the most significant difference between MPS diode process and JBS diode process, and it is also the most critical step in the process. In the case of high current surges, the PN junction corresponding to the large P+ region of the MPS diode will open to enhance the device’s bipolar conductivity and improve its ability to withstand high current surges. Therefore, a good P+ region ohmic contact should provide a sufficiently small contact resistance to reduce the voltage drop of the device in bipolar operating mode.

Compared to the ohmic contact on N-type SiC, the ohmic contact on the large P+ region in the active region required for SiC MPS diode process is more difficult to achieve. The reason is that the P+ region is formed by ion implantation, with limited doping concentration, and the doping ions are not uniformly distributed within the semiconductor. Only in the range of 0.1-0.2 μ m very close to the surface can the doping concentration reach 1e18 cm^-3. There is also an issue with the activation rate of ions injected simultaneously. Under typical high-temperature annealing conditions, only about 20-65% of the injected ions can be activated, resulting in a lower effective doping concentration. So the P-type ohmic contact process of SiC MPS diodes requires special attention.

The commonly used metal materials for P-type SiC ohmic contacts include Pd, Ni, Pt, and Al. Al metal itself has a low work function, but multiple studies have reported that it can form good ohmic contacts on P-type SiC. Considering the low melting point of Al metal itself (~660 ℃), it is generally achieved by stacking or alloying with other metals to increase the melting point. Common combinations include Ti/Al, Ti/Ni/Al, Al/Ti/Al, etc.

Whether you need 4H-SiC epitaxial wafers for research or for industrial applications, please contact us email at [email protected] and [email protected].