Update 14_doping_and_devices_solutions.md

src/14_doping_and_devices_solutions.md

@@ -80,6 +80,8 @@ $$ I_s(T) \propto e^{-E_{gap}/k_BT}$$
 
 ### Subquestion 1
 
+![](figures/diagram_14.png)
+
 ### Subquestion 2
 This a "particle in a box" problem.
 $$-\frac{\hbar^2}{2m_e^{\ast}} \frac{\partial^2 \Psi_e(z)}{\partial z^2} = (E-U_0)\Psi_e $$