How to read some certain band diagrams? I have some problems on understanding some semiconductors band diagram.
For instance, I understand quite well something like this:

I understand it because it is quite simple: there are the energy levels (Conduction, Fermi, Intrinsic Fermi and Valence) at right and left, and the transition region between them. Quite fine.
But sometimes I see something different. For instance, for a Metal Oxide Semiconductor structure, I see something like this:

or this in case of a cascade of quantum wells:

So, what are all these strange shapes inside the green circles? In the first picture only at right the energy levels are specified, while the shape in the green circle is not specified: what physical quantity is it? In the second picture there is no specification.
 A: Both confusing diagrams show heterostructures (i.e. one device containing different materials), and the different materials can have very different properties.
In the first figure:

*

*At the left is a metal. By definition, a metal has no band gap. So only the Fermi Level is shown.

*In the middle (circled in green) is an insulator. The difference between an insulator and a semiconductor is kind of arbitrary. Both have a band gap, and the top and bottom of the circled parallelogram show the conduction band minimum ($E_c$) and valence band maximum ($E_v$), respectively, for the insulator. Note that the band gap is significantly larger than for the semiconductor at the right. There seems to be a voltage applied across the insulator (typical for how these devices are used), so $E_c$ and $E_v$ are not constant.

*At the right is a semiconductor, which you understand.

In the second figure, only $E_c$ is shown. The discontinuous jumps are where the material changes --- e,g, from GaAs to AlGaAs. The two materials have different band structures, so $E_c$ is discontinuous. The overall downward "slope" of $E_c$ is because some voltage is being put across the device.
