feat: Band-to-band tunneling and impact ionization [FXC-2838]

[marc-flex]

• Add docs
• Modify CHANGELOG

Greptile Overview

Updated On: 2025-09-29 14:36:05 UTC

Summary

This PR adds the Hurkx model for direct band-to-band tunneling (HurkxDirectBandToBandTunneling) to the TCAD components. The implementation follows the established patterns in the codebase and includes proper physics equations, parameter validation, and comprehensive integration.

Key additions:

• New HurkxDirectBandToBandTunneling class with well-documented physics equation and parameters
• Proper integration into the RecombinationModelType union type
• Complete API exports and documentation updates
• Basic instantiation test to ensure the class can be constructed
• Clear changelog entry following project conventions

Confidence Score: 4/5

• This PR is safe to merge with only minor stylistic considerations
• Score reflects a well-implemented feature following established patterns, but with a minor suggestion about parameter defaults that could improve usability
• Minor attention to generation_recombination.py for the sigma parameter default value consideration

Important Files Changed

File Analysis

Filename	Score	Overview
tidy3d/components/tcad/generation_recombination.py	4/5	Added new HurkxDirectBandToBandTunneling model class with proper documentation and physics equation; minor suggestion on parameter defaults
tidy3d/components/tcad/types.py	5/5	Properly integrated new HurkxDirectBandToBandTunneling into RecombinationModelType union
tests/test_components/test_heat_charge.py	5/5	Added basic instantiation test for HurkxDirectBandToBandTunneling with valid parameters

Sequence Diagram

sequenceDiagram
    participant User
    participant API as Tidy3D API
    participant HurkxBTBT as HurkxDirectBandToBandTunneling
    participant RecombModel as RecombinationModelType
    participant Simulation as ChargeSimulation

    User->>API: Import tidy3d
    API-->>User: Module loaded with HurkxDirectBandToBandTunneling
    
    User->>HurkxBTBT: Create instance with parameters (A, B, E_0, sigma)
    HurkxBTBT->>HurkxBTBT: Validate parameters (A > 0, E_0 > 0, sigma required)
    HurkxBTBT-->>User: HurkxDirectBandToBandTunneling instance
    
    User->>RecombModel: Add to RecombinationModelType union
    RecombModel-->>User: Model type validated
    
    User->>Simulation: Use in charge simulation setup
    Simulation->>HurkxBTBT: Calculate R_BTBT = A * (np - ni²)/((n+ni)(p+ni)) * (|E|/E₀)^σ * exp(-B/|E| * (Eg/Eg300)^1.5)
    HurkxBTBT-->>Simulation: Band-to-band tunneling recombination rate
    Simulation-->>User: Simulation ready with Hurkx BTBT model

Loading

[greptile-apps]

_{6 files reviewed, 1 comment}

_{Edit Code Review Agent Settings | Greptile}

[github-actions]

Diff Coverage

Diff: origin/develop...HEAD, staged and unstaged changes

• tidy3d/components/tcad/generation_recombination.py (100%)

Summary

• Total: 14 lines
• Missing: 0 lines
• Coverage: 100%

[damiano-flex]

I noted a couple of improvements in the docs. But other than that, it looks great!