What Is The Impact Of Lattice Mismatch-induced Strain On The Tunneling Current Density And Peak-to-valley Current Ratio In An Esaki Tunnel Diode, Specifically When The Diode Is Fabricated On A Relaxed SiGe Buffer Layer With A 20% Ge Composition, And How Can I Incorporate This Effect Into My Simulation Using A Non-equilibrium Green's Function Formalism?

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The impact of lattice mismatch-induced strain on an Esaki tunnel diode fabricated on a relaxed SiGe buffer layer with 20% Ge composition can be understood through its effects on material properties and device performance. Here's a structured summary of the analysis and the approach to incorporate these effects into a simulation using the non-equilibrium Green's function (NEGF) formalism:

Impact of Strain on Device Performance

  1. Band Structure Modification:

    • Strain alters the bandgap and effective masses of electrons and holes. Compressive strain in SiGe reduces the bandgap and modifies carrier effective masses, enhancing tunneling probability.

  2. Tunneling Current Density:

    • The change in effective mass due to strain affects the transmission coefficient, directly influencing the tunneling current. Reduced effective mass increases tunneling probability, potentially raising current density.

  3. Peak-to-Valley Current Ratio (PVCR):

    • Strain modifies band alignment and density of states, which can sharpen or blunt the I-V characteristics, affecting PVCR. The exact impact depends on how strain influences the band structure and tunneling efficiency.

Incorporating Strain Effects into NEGF Simulation

  1. Strain Calculation:

    • Determine strain values using elasticity theory, considering lattice constants of Si and SiGe (20% Ge).

  2. Strained Band Parameters:

    • Use deformation potential theory to compute changes in bandgap, effective masses, and band alignment due to strain.

  3. NEGF Model Updates:

    • Incorporate strained band parameters into the NEGF simulation by adjusting tight-binding parameters or dispersion relations.

  4. Potential Profile Adjustment:

    • Account for strain-induced electric fields (e.g., piezoelectric effects) in the potential profile used in the NEGF calculation.

  5. Simulation Execution:

    • Run the NEGF simulation with updated material parameters and potential profiles to compute tunneling current density and PVCR.

  6. Result Analysis:

    • Compare results with and without strain to quantify performance changes. Focus on transmission coefficient and current-voltage characteristics.

Considerations

  • Material Parameters: Ensure accurate deformation potential constants for SiGe (20% Ge) and consider strain uniformity across layers.
  • Secondary Effects: While focusing on band structure and effective mass, note dielectric constant and electron-phonon interactions as potential influences.
  • Implementation: Verify if the NEGF implementation can handle strained materials, modifying the code if necessary.

By systematically addressing each aspect, the simulation will provide insights into how lattice mismatch-induced strain influences the tunnel diode's performance, guiding design optimizations for enhanced device characteristics.