SiC p-n Junction and Schottky Barrier Diodes

This Datareview covers the state of diodes in SiC polytypes both made from p-n junctions and using Schottky barriers. After defining the necessary theoretical background to junction diodes the various device structures used and the performances obtained are detailed. A range of metals has been used to produce Schottky barriers on three of the SiC polytypes and the performances achieved in this type of device are listed. 

SiC p-n diodes clearly illustrate the advantages of wide bandgap semiconductors in general and SiC in particular. The elementary theory of p-n junctions yields the following expression for the reverse saturation current density, JR, for a p+-n junction [1]  

In wide bandgap materials, n, is very small and therefore the second term in the right hand part of Eqn (1) is dominant. In a-SiC at room temperature, the theoretical value of nj is as low as 1 carrier perm3 For an estimate, let us assume certain values for mn and mp, independent of an energy gap, since this assumption will not change the order of magnitude of the resulting number. Let us take mn = 0.3me and mp = 0.6me to be specific. Then we find  

FIGURE 1 Dependence of theoretical generation current on the energy gap (at room temperature) [2], 

Under forward bias, the diode current voltage characteristic is described by the following equation [2]  

---

SiC p-n junction and Schottky barrier diodes C SCHOTTKY BARRIER DIODES... 

LEDs are made from boron-doped 4H-SiC. Three colour displays have been demonstrated. SiC ultraviolet photodetectors made from p-n junction and Schottky barrier diodes can be used up to temperatures of 700 K and are expected to be radiation tolerant. These photodiodes are more sensitive than their silicon counterparts. 

In the following analysis, both p-z-n and junction barrier Schottky diodes will be evaluated for use in a 3-kV, 30A SiC bridge rectifier module. Four of these modules will replace the 10 Si diode bridge rectifiers and will reduce system volume and increase efficiency. To optimize the design of the module, we will evaluate the power density at the die level as a function of the number of paralleled diodes in each rectifier leg. A typical value of the heat-transfer coefficient of conventional, power components is 100 W/cm In the present analysis, we have a design limit of 200 W/cm and will determine the number of JBS and p-z -n diode needed to meet this goal. 

---