Update 14_doping_and_devices_solutions.md

src/14_doping_and_devices_solutions.md

@@ -10,7 +10,7 @@ from math import pi
 ### Subquestion 1
 Law of mass action (general):
 $$ n_e n_h = \frac{1}{2} \left(\frac{k_BT}{\pi\hbar^2}\right)^3 
-(m_e^{\ast}m_h^{\ast})^{3/2}e^{-\beta E_{gap}$$
+(m_e^{\ast}m_h^{\ast})^{3/2}e^{-\beta E_{gap}}$$
 
 Charge balance condition:
 $$ D = N_D - N_A$ - n_e + n_h$