back diode operation
Ebbers Moll model says that these 2 are equivalent..This means that while analysing their behaviour thru equations, the BJT can be replaced with this model
However , when go into the internal operation , the conept of a short and long base diode creeps in .
The 2 diodes in back to back give an effectively long base width and the width will be larger than the diffusion length of the holes .So effectively no current flows from the first diode to the second diode ..But for amplification , u need that current should flow from the emitter to collector ..
Also in BJT, u use a short base diode so that the current that recombines in base is less .