Generation and recombination rates

The recombination mechanisms that nextnano++ takes into account for the right-hand-side of (2.2.20) are

• Shockley-Read-Hall (SRH) recombination

• Auger recombination

• Radiative recombination

• “fixed (applied)”

The equations and parameters used for the three recombination mechanisms on the top are explained here: recombination_model{ }.

The last one “fixed (applied)” is the contribution defined from structure{region{generation{}}} and optics{ photogeneration{ } }. These typically represent generation instead of recombination and used for the simulation of the devices under irradiation such as solar cells or CCDs. (For example, see nextnano++ tutorial GaAs solar cell.)

According to the specification in the section classical{ }, nextnano++ can calculate optoelectronic characteristics of the arbitrary structure by means of the so-called semi-classical model.

In this model, various quantities are calculated from the spontaneous emission rate, which is calculated at each position $\mathbf{x}$ for the photons with each energy $E$ based on the energy-resolved carrier densities $n(\mathbf{x},E)$ and $p(\mathbf{x},E)$ obtained in the forgoing simulation.

Spontaneous emission rate

(2.2.23)$$R_{\mathrm{rad}}^{spon}(\mathbf{x},E)=C(\mathbf{x})\int d{E}_{\text{h}}\int d{E}_{\text{e}}n(\mathbf{x},E_{\text{e}})p(\mathbf{x},E_{\text{h}})\delta (E_{\text{e}}-E_{\text{h}}-E).$$

Here $C(x)$ [${\mathrm{cm}}^3{\mathrm{s}}^{-1}$] is the (material-dependent) radiative recombination parameter which is proportional to the one specified in the database (Radiative recombination)

Then the other optical characteristics like stimulated emission rate, absorption/gain spectrum, and the imaginary part of the dielectric constant are calculated according to this $R_{\mathrm{rad}}^{spon}(\mathbf{x},E)$.

Generation by the irradiation (fixed(applied))

There is another radiative recombination rate output on recombination.dat called “fixed(applied)”, which should be always negative. This is the contribution of the generation specified from structure{region{generation{}}} and optics{ photogeneration{ } }. When we do not specify either of them, this recombination rate is always 0.

(2.2.24)$$\begin{array}{r}\begin{array}{rlr}{R}_{\text{fixed}}(\mathbf{x})=& -(G(\mathbf{x})& \text{ specified from structure{ }})\\ & -(\int dEG(E,\mathbf{x})\text{ calculated according to the configuration in classical{ }}).\end{array}\end{array}$$

This is mostly used for the analysis of the absorbing devices such as solar cells or CCDs.

---

Last update: 04/12/2024