How to find the step and impulse response of a circuit with a diode
The step and impulse response are characteristical of linear systems. 

Thus, those responses can't be calculated for systems containing non-linear devices acting as such.

Of course, if those non-linear devices are continuously operating within their linear region (as most transistors and diodes sometimes do), then they can be assimilated to linear devices and their "effect" can be computed into a step or impulse response. 

But in no way a device that will be switching during normal continuous operation (rectifiers, etc) can be reduced to a linear model for the purpose of calculating the system response.