exercise 2

src/14_doping_and_devices.md

@@ -238,6 +238,14 @@ Let us now work out what happens when the semiconductor is at the border between
 
 ### Exercise 2: Donor ionization
 
+Previously we have assumed that all dopants are ionized.
+Let us examine when this is a good assumption.
+For that we consider a doped semiconductor in the extrinsic regime.
+
+1. Assume that all dopants are ionized, determine the position of the Fermi level.
+2. Write down the concentration of dopants that are not ionized.
+3. Determine at what donor concentration one cannot assume anymore that all donors are ionized in germanium at room temperature.
+
 ### Exercise 3: Performance of a diode
 
 ### Exercise 4: Quantum well heterojunction in detail