Add new file

src/14_doping_and_devices_solutions.md

+```python tags=["initialize"]
+from matplotlib import pyplot as plt 
+import numpy as np
+from math import pi
+```
+# Solutions for lecture 13 exercises
+
+## Exercise 1: Crossover between extrinsic and intrinsic regimes
+
+### Subquestion 1
+
+### Subquestion 2
+
+### Subquestion 3
+
+
+
+
+## Exercise 2: Donor ionization
+
+### Subquestion 1
+
+### Subquestion 2
+
+### Subquestion 3
+
+
+
+## Exercise 3: Performance of a diode
+
+### Subquestion 1
+
+### Subquestion 2
+
+### Subquestion 3
+
+
+
+
+## Exercise 4: Quantum well heterojunction in detail
+
+### Subquestion 1
+
+### Subquestion 2
+
+### Subquestion 3
+
+### Subquestion 4
+
+### Subquestion 5
+
+### Subquestion 6
+
+### Subquestion 7
+