Learning Forum

[susu]

Last time I asked how to calculate the two default values(well carrier capture rate and well carrier eascape rate) in the example Laser modulation bandwidth simulation , and I tried to calculate the two values according to the reference given in the example, but the results were not similar. The following are the specific values I used to calculate the two values,is there anything wrong? the reference is a 850nm diode laser, so i search the diffusion coefficence of GaAs,and plug the value into the formula.

And Last time you mentioned it could use CHARGE to estimate. Is there any examples of calculating these two values by using CHARGE? Thank you very much for your answer!

 

[kghaffari]

Hi, 

Thank you for reaching out. We will need to look into this further. I will check with the team and let you know if we need more information or have updates for you. As far as I know we don't have an example that demonstrates extracting these values with CHARGE.

Best,

Khash

[kghaffari]

Hi,

Thank you for your patience. I have updates regarding your question earlier. We may have a published example for extracting carrier capture and escape rates in future. However, in the meantime please find our recommendations below for extracting these two variables:

Capture Rate – In the referenced publication in this article (under References), refer to Fig. 1. The carrier capture rate is dominated by the carrier difusion over the left SCH for holes and right SCH for electrons (depending on the orientation of doping layers). The carrier diffusion 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 you need to know the mobility which is a material property. The equation for D is given in section A.

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 barrier can be included in tau-s. 1/tau_s can be set as “well carrier capture rate” in the same group of options.

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.

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 then needs to be added to diffusion time. This may be estimated either approximately, analytically, or by running CHARGE simulation and post-processing results.

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

Best,

Khash