September 11, 2024 at 6:04 pm

Kyle

Ansys Employee

Here is some additional advice on calculating the carrier capture/escape rates:

**Capture rate:**

Refer to Fig. 1 in the reference on the documentation page for this example. The carrier capture rate is dominated by the carrier diffusion time over the left SCH for holes and right SCH for electrons (depending on the orientation of doping layers). The carrier diffusion time tau_s is given at the end of section C. But reading sections A and B is advised. The input variables are Ls (length of one side of SCH if it is symmetric) and diffusion constants for electrons and holes Dn, Dp. To calculate Dn, Dp the user needs to know the mobility which is a material property. The equation for D is given in section A.

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In TWLM, Ls can be set as "total barrier thickness" in SCH group of options. The total means that all the barriers that are in between quantum wells can be added to SCH thickness Ls and diffusion over those barriers can be included in tau_s. 1/tau_s can be set as "well carrier capture rate" in the same group of options.

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**Escape rate:**

The formula for escape time tau_e is given in section G. In TWLM, 1/tau_e can be set as "well carrier capture rate". Lw can be set as "total well thickness". Total means the sum of thicknesses of all wells if there are more than one.

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The method above may be insufficient for GRINSCH structures (Graded Index SCH). Due to material alloy grading in space there are strong electric fields. The drift time than needs to be added to diffusion time. This may be estimated either approximately analytically or by running CHARGE simulation and post-processing results.

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As a sanity check, the calculate rates should be approximately on the same order as our default values in TWLM.