transistors - Saturation current in Ebers-Moll equations for BJT: what is it and how to measure it?

In Ebers-Moll Equations for common emitter BJT the inverse saturation current $I_s$ appears as a parameter. What is the saturation current $I_s$ exactly and how should I measure in a common emitter BJT (like the one in picture)?

---

More precisely there is an approximation of the model where the current $I_{ES}$ appear :

$$\displaystyle {I_{\text{E}}=I_{\text{ES}}(e^{\frac {V_{\text{BE}}}{V_{\text{T}}}}-1)\\I_{\text{C}}=\alpha _{F}I_{\text{E}}\\I_{\text{B}}=(1-\alpha _{F})I_{\text{E}}}$$ The first equation is simply the diode model for the junction BE and that current $I_{ES}$ should be the reverse saturation current of the base–emitter diode. So can I measure it by simply doing the following steps?

• Invert generator VBB (to get reverse bias of BE junction)


• Put ammeter in series with Rb and measure the current $I_{ES}$

If this is the case, can the junction CB be reverse or non reverse biased? Does it make any difference on $I_{ES}$?

(A secondary doubt is about the parameter $\alpha_F$, the common base forward short-circuit current gain: is it easily measurable or should it be read on the datasheet of the BJT model used?)

---

Nevertheless in the complete Ebers-Moll model there is $I_S$, which is simply defined as saturation current. Is it still the inverse saturation current of the BE junction? How to measure this current?