1. Advanced Drift Diffusion Device Simulator for 6H and 4H-SiC MOSFETs

2. MOSFET Device Simulation
MOSFET Device Structure
Semiconductor Equations
Poisson Equation:
Electron current continuity equation:
Hole current continuity equation:
Electron current equation:
Hole current equation:

3. Mobility Models Low field mobility: High field mobility: Oxide
Bulk
Electron Flow
Electron
Surface Phonon
Surface Roughness
Trap
Fixed Charge
Matthiessen's rule
mLF = Low Field Mobility mB = Bulk Mobility
mSP = Surface Phonon Mobility
mSR = Surface Roughness mobility
mC = Coulomb Scattering Mobility
Low field mobility:
High field mobility:
High Field Mobility:

4. Screened Coulomb Scattering Mobility
Screened Coulomb Potential:
Fermi’s Golden Rule:
2D Matrix Element:
Scattering Rate:
Screened Coulomb Scattering Mobility:

5. ID-VGS at Room Temperature
Circles : Simulated Points
Line: Experimental data

6. Occupied interface trap density
Negatively charged interface traps:
Dit = Interface traps density of states
f(E) is the probability density function.

7. Interface Trap Density of States
Neutrality Point
Figure . Interface trap density of states for 4H-SiC: Constant distribution in midgap and an exponential rise near the band edges.

8. Mobility Variation with Depth
VGS = 14V. Lots of Screening. Coulomb Mobility effect only very close to interface. Surface Roughness mobility dominates
VGS = 2V. Less Screening. Coulomb Mobility dominates

9. Current Density Variation with Depth
Peak of the current density is some distance away from the interface

10. Nit – VGS and Ninv – VGS at RmT
Fixed Oxide Charge Density ~ 1.45e12 cm-2

11. Screened Coulomb Scattering Mobility
Coulomb scattering decreases rapidly with increase in depth inside the semiconductor
Oxide charges located away from the interface have less effect on Coulomb scattering
Screening is directly proportional to the inversion layer charge density
Scattering rate is inversely proportional to electron temperature (energy)
Scattering rate is directly proportional to the density of oxide charges and occupied interface traps

12. Future Work
Implement oxide charging - interface trap charging model in simulator
Implement a robust surface roughness mobility model
High temperature high power simulations
Modeling of different Power MOSFET structures