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)?

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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?)

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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?