Combining Explicit trap distribution with Lombardi mobility in 2D MOSFET

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I am working on a 2D nMOSFET stationary study in COMSOL 6.3 (Build 420) using the Semiconductor Module. I am trying to combine two features that each work individually but fail when used together:

  1. Trap-Assisted Surface Recombination (boundary, Boundary 5) with Explicit trap distribution, Continuous Energy Level sub-node, Gaussian σ=0.1 eV, midgap centred
  2. Arora + Lombardi + Caughey-Thomas mobility model chain with continuation parameter cp

WHAT WORKS SEPARATELY: - Explicit trap distribution alone converges using a three-step sequence: trap-free solve at subthreshold → ramp Nt at fixed Vg → sweep Vg forward ✓ - Lombardi + Caughey-Thomas alone converges using the auto-generated Segregated solver ✓

THE PROBLEM: When combining both, the auto-generated Segregated solver computes this scale for the trap occupancy variable at the start of the solve:

Trap Occupancy (comp1.semi.tasr1.ctb1.ft): 2.3e+35

This is clearly wrong — ft is a dimensionless occupancy fraction bounded between 0 and 1, so its scale should be ~1. The incorrect scale of 2.3e+35 makes the Newton step sizes completely wrong and the solver diverges.

WHAT I HAVE TRIED: - Setting manual scale of ft = 1 in Dependent Variables node — this is reset when Show Default Solver regenerates the configuration - Fully Coupled solver instead of Segregated — also fails, same root cause - Lower/Upper bounds on ft (0 to 1) added to Segregated node — helps slightly but does not resolve the scaling issue - Various Nt/cp ramp orderings — the system converges up to Nt = 1×10¹² m⁻² but fails consistently at Nt = 1×10¹³ m⁻² with residual stalling at ~7×10²

SPECIFIC QUESTION: How can I permanently set the scale of comp1.semi.tasr1.ctb1.ft to ~1 in the auto-generated Segregated solver for Lombardi, so that it persists and is not reset by Show Default Solver? Is there a known approach for combining Explicit trap distribution with field-dependent mobility models in a 2D stationary semiconductor study?

I am attaching the log file showing the incorrect scale. Any suggestions welcome.



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