Anyone know lots about Tunnel Diodes? I have a poorly phrased question

[PsychonautQQ]

Can somebody help me understand why it is possible to have a 100% transmission rate through both potential boundaries created by a tunnel diode, while the transmission rate through only one of the walls can be very small??

 

[Simon Bridge]

The fact there are two barriers in the second example and only one in the first is what makes the difference - the wavefunctions do not interact with one barrier and then the other one - but the two barriers together make an entire system that informs the whole wavefunction in one go.

The peicewise analysis you may have met is just a mathematical convenience.